U.S. patent application number 11/149861 was filed with the patent office on 2005-10-13 for retractable optical fiber assembly.
Invention is credited to Pons, Sean M..
Application Number | 20050226588 11/149861 |
Document ID | / |
Family ID | 32908034 |
Filed Date | 2005-10-13 |
United States Patent
Application |
20050226588 |
Kind Code |
A1 |
Pons, Sean M. |
October 13, 2005 |
Retractable optical fiber assembly
Abstract
A retractable optical fiber assembly includes a housing, a spool
rotatably disposed within the housing and an optical waveguide
reeled onto the spool. The optical waveguide has a central length
of unjacketed optical fiber and shorter end lengths of jacketed
optical fiber terminating in optical connectors. The optical
waveguide is reeled onto the spool such that the end lengths of
jacketed optical fiber are extracted off the spool and retracted
onto the spool in the same direction. The spool is biased in a
first rotational direction relative to the housing by a torsion
spring that exerts a retracting force on the jacketed optical
fiber. A mechanical stop is also provided to prevent rotation of
the spool in a second rotational direction opposite the first
rotational direction. In an exemplary embodiment, the assembly is a
test fiber box for use with optical test equipment to test an
optical network.
Inventors: |
Pons, Sean M.; (Valdese,
NC) |
Correspondence
Address: |
CORNING CABLE SYSTEMS LLC
P O BOX 489
HICKORY
NC
28603
US
|
Family ID: |
32908034 |
Appl. No.: |
11/149861 |
Filed: |
June 10, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11149861 |
Jun 10, 2005 |
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10376929 |
Feb 28, 2003 |
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6915058 |
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Current U.S.
Class: |
385/135 |
Current CPC
Class: |
G02B 6/4457 20130101;
G01M 11/3109 20130101 |
Class at
Publication: |
385/135 |
International
Class: |
G02B 006/00 |
Claims
That which is claimed:
1. A retractable optical fiber assembly comprising: a housing; a
spool rotatably disposed within the housing; and an optical
waveguide reeled onto the spool, the optical waveguide comprising a
predetermined length of unjacketed optical fiber and a
predetermined length of jacketed optical fiber wound radially
outwardly of the unjacketed optical fiber.
2. The retractable optical fiber assembly of claim 1 wherein the
housing surrounds the spool and includes an exit port through which
the jacketed optical fiber is extracted and retracted.
3. The retractable optical fiber assembly of claim 1 wherein the
unjacketed optical fiber forms a central length of the optical
waveguide and the jacketed optical fiber forms the opposite end
lengths of the optical conductor.
4. The retractable optical fiber assembly of claim 3 further
comprising an optical connector terminated to each of the end
lengths of the optical waveguide.
5. The retractable optical fiber assembly of claim 3 wherein a
curved channel is formed on an exterior face of the spool and
wherein the central length of the optical waveguide is positioned
within the channel, the channel reversing the direction of travel
of the central length of the optical waveguide relative to the
spool.
6. The retractable optical fiber assembly of claim 1 wherein the
optical waveguide comprises a continuous optical fiber having a
central length of unjacketed optical fiber and a pair of end
lengths of jacketed optical fiber.
7. The retractable optical fiber assembly of claim 1 further
comprising torsion spring means operably positioned between the
housing and the spool, the jacketed optical fiber being biased on
the spool by a retracting force exerted by the torsion spring
means.
8. The retractable optical fiber assembly of claim 7 further
comprising a mechanical stop for preventing rotation of the
spool.
9. The retractable optical fiber assembly of claim 8 wherein the
mechanical stop is releasable for extracting the jacketed optical
fiber from the housing and for retracting the jacketed optical
fiber into the housing.
10. The retractable optical fiber assembly of claim 1 wherein the
housing defines an exit port through which the jacketed optical
fiber is extracted and retracted and wherein the retractable
optical fiber assembly further comprises a cover movably mounted on
the housing to open and close the exit port.
11. The retractable optical fiber assembly of claim 10 wherein the
optical waveguide is completely enclosed within the housing when
the cover is in a closed position and wherein the jacketed optical
fiber is accessible when the cover is in an open position.
12. The retractable optical fiber assembly of claim 1 wherein
mandrel channels are located on an exterior face of the spool, the
mandrel channels comprising means for reducing the amplitude of
higher-order modes propagating in a cladding region of a multimode
optical fiber.
13. The retractable optical fiber assembly of claim 1 wherein the
jacketed optical fiber is strain relieved to the spool.
14. The retractable optical fiber assembly of claim 1 wherein the
spool is rotatably disposed in a cylindrical cavity formed in the
housing.
15. A retractable optical fiber assembly comprising: a housing
defining an interior cavity and an exit port; a spool rotatably
disposed on the housing within the interior cavity; and an optical
waveguide reeled onto the spool, the optical waveguide having a
central portion comprising a predetermined length of unjacketed
optical fiber and a pair of end portions comprising predetermined
lengths of jacketed optical fiber wound radially outwardly of the
unjacketed optical fiber; and wherein the end portions of jacketed
optical fiber are extracted off the spool and retracted onto the
spool through the exit port.
16. The assembly of claim 15 wherein both end portions of jacketed
optical fiber are wound on the spool in the same direction.
17. The assembly of claim 15 further comprising means for exerting
a biasing force for retracting the end portions of jacketed optical
fiber onto the spool and a mechanical stop for preventing rotation
of the spool, the mechanical stop being releasable to permit the
end portions of jacketed optical fiber to be extracted off the
spool against the biasing force.
18. A test fiber box for testing an optical network, the test fiber
box comprising: an optical waveguide reeled onto a rotatable spool,
a central portion of the optical waveguide comprising an unjacketed
optical fiber and a pair of end portions of the optical waveguide
comprising jacketed optical fiber having an optical connector
terminated to the free end thereof, rotation of the spool in a
first direction extracting the jacketed optical fiber and
connectors off the spool for connection between optical test
equipment and the optical network, rotation of the spool in a
second direction opposite to the first direction retracting the
jacketed optical fiber onto the spool for storage within the test
fiber box.
19. The test fiber box of claim 18 further comprising a housing
defining an interior cavity, the spool rotatably disposed within
the interior cavity and biased in the second direction relative to
the housing.
20. The test fiber box of claim 18 wherein the jacketed optical
fiber is strain relieved to the spool so that the unjacketed
optical fiber is not extracted off the spool when the spool is
rotated in the first direction.
21. The test fiber box of claim 18 wherein the spool has a curved
channel formed on an exterior face and wherein the unjacketed
optical fiber is positioned within the channel so that the
direction of travel of one end of the unjacketed optical fiber is
reversed.
22. The test fiber box of claim 21 wherein the channel has a radius
of curvature at least equal to the minimum bend radius of the
unjacketed optical fiber.
23. The test fiber box of claim 22 wherein the optical waveguide
comprises a single mode optical fiber.
24. The test fiber box of claim 18 wherein the optical waveguide
comprises a multimode optical fiber and wherein an exterior face of
the spool has mandrel wrap channels comprising means for reducing
the amplitude of higher-order modes propagating in a cladding
region of the multimode optical fiber.
25. The test fiber box of claim 18 wherein the optical waveguide
has a length of not more than about 1000 meters.
Description
FIELD OF THE INVENTION
[0001] The invention relates to a retractable optical fiber
assembly. More particularly, the invention relates to a retractable
optical fiber assembly that can be used in conjunction with optical
test equipment to test, qualify, evaluate, demonstrate, emulate,
calibrate, or benchmark an optical system, optical network or
optical equipment. In an exemplary embodiment, the invention is a
test fiber box for use with an optical time domain reflectometer
(OTDR) for testing of an optical network.
BACKGROUND OF THE INVENTION
[0002] A test fiber box, also commonly referred to as a "launch
cord," "launch cable," "break-out box," "dead zone box" or "pulse
suppressor" is typically utilized in conjunction with optical test
equipment to test, qualify and evaluate the transmission
characteristics of optical systems, optical networks or optical
equipment. Examples of transmission characteristics include loss,
length, time delay and reflectance. Test fiber boxes are primarily
intended to increase the length of optical waveguide between
optical test equipment, such as an optical time domain
reflectometer (OTDR), and a component of an optical network for
purposes of testing and analysis. Test fiber boxes are also used
for product demonstration and training purposes, system emulation,
and for equipment calibration and benchmarking. In certain
circumstances, test fiber boxes have also been employed in
conjunction with an optical power meter and optical light source,
or related test equipment, as a jumper for loss testing. However,
the use of a conventional test fiber box as a jumper is considered
impractical due to weight, bulk, and cost considerations.
[0003] One conventional test fiber box includes a length of optical
waveguide suitable for use with an OTDR to test the optical time
domain reflectometry characteristics of an optical network. The
length of optical waveguide necessary for OTDR testing typically
ranges from about 50 meters to about 5 kilometers, and the optical
waveguide typically consists of a central length of unjacketed
optical fiber and shorter end lengths of jacketed optical fiber.
The central length of unjacketed optical fiber is substantially
longer than the end lengths of jacketed optical fiber. The optical
waveguide can be continuous, or the end lengths of jacketed optical
fiber can be fused to the central length of unjacketed optical
fiber. Regardless, the optical waveguide is stored in a rigid
enclosure with the central length of unjacketed optical fiber being
inaccessible to the user and the end lengths of jacketed optical
fiber being accessible to the user. The unjacketed optical fiber is
typically stored in a separate compartment and the end lengths of
jacketed optical fiber are typically wrapped together around two or
more retaining posts to form loops of jacketed optical fiber within
the enclosure. The jacketed optical fiber can be unwrapped to
connect the optical test equipment (i.e., OTDR) to the optical
network. The dimensions of the enclosure are typically about 9
inches.times.8 inches.times.3.5 inches for a length of optical
waveguide between about 50 meters and about 5 kilometers.
[0004] The size and weight of conventional test fiber boxes,
however, presents several problems. The test fiber box is generally
too large to fit comfortably inside an OTDR transit case and must
be transported separately, resulting in possible loss or
misplacement of the test fiber box. If dropped or inadvertently
moved, the weight of the test fiber box can cause damage to the
OTDR, to the connector adapter in the optical network, or to the
components of the test fiber box itself. Furthermore, field
installers and technicians naturally tend to prefer smaller,
lightweight test equipment, if only to reduce the bulk of their
portable tools. Another problem with existing test fiber boxes is
that the jacketed optical fiber and the optical connectors on the
ends of the jacketed optical fiber are difficult to manage. The end
lengths of jacketed optical fiber can easily become entangled as
they are repeatedly unwrapped and rewrapped, thereby causing stress
and damage to the optical waveguide (e.g., glass fiber) and jacket.
In addition, the test fiber box may include a protective lid, which
may be inadvertently closed and thereby damage the jacketed optical
fiber or connectors. Furthermore, protective caps (e.g., dust caps)
for the optical connectors are easily misplaced, thereby subjecting
the connectors to possible damage from dust, dirt or debris.
[0005] Although existing test fiber boxes provide for storage of
the optical waveguide and connectors, that is not their primary
purpose. Fiber optic storage reels are available to store excess
lengths of optical waveguide in optical network enclosures, such as
splice trays, distribution boxes, cross-connect cabinets, and
splice closures. However, fiber optic storage reels are primarily
intended for storing relatively short lengths of slack optical
waveguide. Fiber optic storage reels are also available in which
the optical waveguide is coiled on the reel in such a manner that
the ends of the optical waveguide can be unwound from the reel at
the same time and in the same direction. One such fiber optic
storage reel includes an S-shaped or teardrop-shaped channel that
receives the optical waveguide and reverses the direction of travel
of one end, while maintaining the minimum bend radius of the
optical waveguide. However, test fiber boxes typically employ
relatively long lengths of unjacketed optical fiber to provide
sufficient delay time for test signals to propagate. The known
fiber optic storage reels do not provide adequate means for
protecting and storing the long length of optical waveguide
necessary for a test fiber box within a manageable size
assembly.
BRIEF DESCRIPTION OF THE DRAWINGS
[0006] FIG. 1 is a perspective view illustrating an exemplary
manner in which a retractable optical fiber assembly constructed in
accordance with the invention may be used to connect optical test
equipment, such as an optical time domain reflectometer (OTDR), to
an optical network.
[0007] FIG. 2 is a perspective view of the retractable optical
fiber assembly of FIG. 1 shown with the optical waveguide retracted
onto the spool and stored within the housing.
[0008] FIG. 3 is an exploded perspective view showing the internal
components of the retractable optical fiber assembly of FIG. 1.
[0009] FIG. 4 is an enlarged perspective view illustrating an
exemplary manner in which the central length of unjacketed optical
fiber may be configured on the spool to reverse the direction of
one end of the optical waveguide, while maintaining the minimum
bend radius.
[0010] FIG. 5 is another perspective view of the spool shown with
the central length of unjacketed optical fiber of the optical
waveguide exploded from the spool.
[0011] FIG. 6 is a partial cross-section of a portion of the spool
and the housing of the retractable optical fiber assembly of FIG. 1
showing the mechanical stop engaged for preventing rotation of the
spool.
[0012] FIG. 7 is a partial cross-section of the portion of the
spool and the housing shown in FIG. 6 illustrating the manner in
which the mechanical stop is released to permit rotation of the
spool and allow extraction or retraction of the end lengths of
jacketed optical fiber.
[0013] FIG. 8 is a perspective view of the retractable optical
fiber assembly of FIG. 1 illustrating an exemplary manner in which
the end lengths of jacketed optical fiber may be grasped to extract
the jacketed optical fiber and connectors to connect the optical
waveguide between optical test equipment and an optical
network.
[0014] FIG. 9 is an enlarged detail view of a portion of the spool
of the retractable optical fiber assembly of FIG. 1 illustrating an
exemplary manner in which the end lengths of jacketed optical fiber
may be strain relieved to the spool.
DETAILED DESCRIPTION OF THE EMBODIMENTS
[0015] A retractable optical fiber assembly 10 in accordance with
the invention is especially suited for connecting optical test
equipment 14 to an optical network 12 so that the optical network
can be tested, evaluated, qualified, demonstrated, calibrated,
monitored or otherwise analyzed. In the exemplary embodiments shown
and described herein, the retractable optical fiber assembly 10 is
an improved test fiber box suitable for use in conjunction with
optical test equipment 14, such as an optical time domain
reflectometer (OTDR), to test the optical network 12. The test
fiber box 10 contains a predetermined length of optical waveguide
20 suitable for performing the required testing in conjunction with
the OTDR 14. In particular, the test fiber box 10 functions in the
same manner as a conventional "test fiber box," "launch cord,"
"launch cable," "break-out box," "dead zone box" or "pulse
suppressor" to provide from about 50 meters to about 5 kilometers
length of optical waveguide to enhance the optical transmission
readings on the OTDR 14. The test fiber box 10 not only provides
for compact, retractable storage of the relatively long optical
waveguide 20, but also completely encloses and protects the optical
waveguide 20 when it is not in use. The compact nature of the test
fiber box 10 is especially suitable for use in relatively tight
quarters, such as cramped wiring closets containing optical
distribution panels, optical cross connect panels or other
components commonly employed in optical networks.
[0016] The optical waveguide 20 used in the test fiber box 10
comprises a continuous length of optical fiber that is reeled onto
a rotatable spool 40 and disposed within an enclosure, or housing
30. The optical waveguide 20 can be extracted off the spool 40 or
retracted onto the spool 40 by rotating the spool 40 in opposite
directions relative to the housing 30. Preferably, the optical
waveguide 20 is a single, continuous optical fiber. However,
optical waveguide 20 may be formed by fusing multiple fiber
portions together, as will be described. Furthermore, either single
mode optical fiber or multimode optical fiber may be employed in
test fiber box 10, depending of course upon the test and the
optical network with which the test fiber box 10 will be used. In
the exemplary embodiment shown and described herein, the optical
waveguide 20 comprises a central length of unjacketed optical fiber
21 and shorter end lengths of jacketed optical fiber 22 on the
opposite ends 25 of the unjacketed optical fiber 21. The central
length 21 is unjacketed to reduce the bulk of the optical waveguide
20 that must be stored within the housing 30, and thereby reduce
the necessary diameter and/or width of the spool 40 and the housing
30. The central length of unjacketed optical fiber 21 accounts for
the majority of the length of optical waveguide 20 contained within
the test fiber box 10. The end lengths of jacketed optical fiber 22
make up the portion of the optical waveguide 20 that will be
extracted from the housing 30 when the test fiber box 10 is
connected between the optical test equipment (i.e., OTDR) 14 and,
for example, the adapter of a fiber optic connector in the optical
network 12. In an exemplary embodiment, the test fiber box 10
contains about 1000 meters of optical waveguide 20 and the length
of each end length of jacketed optical fiber 22 is only about 1
meter to about 3 meters in length.
[0017] In the preferred embodiment using a continuous optical
waveguide 20, the end lengths of jacketed optical fiber 22 can be
formed by inserting each end 25 of the optical waveguide 20 into a
fanout tubing having the desired length. Each end length of
jacketed optical fiber 22 preferably comprises optical waveguide
20, an outer jacket 23 of conventional construction and a plurality
of strength members 24, for example KEVLAR.RTM. reinforced aramid
fiber available from E.I. du Pont de Nemours and Company,
positioned between the optical waveguide 20 and the outer jacket
23. In other embodiments, separate end lengths of jacketed optical
fiber 22 may be fused or otherwise spliced to the ends 25 of the
central length of unjacketed optical fiber 21 to form the optical
waveguide 20. Optical connectors 26 are terminated at the free ends
of both end lengths of jacketed optical fiber 22 so that the
optical waveguide 20 can be connected between the optical test
equipment 14 and the optical network 12. Any number of conventional
optical connectors 26, including but not limited to SC, ST and FC
type connectors, can be terminated to the end lengths of jacketed
optical fiber 22. The choice of optical connectors 26 will be
dependent upon the optical network and the type of optical test
equipment 14 with which the test fiber box 10 is to be used. In the
exemplary embodiments shown and described herein, the optical
waveguide 20 is wound, or reeled, onto a generally cylindrical
spool 40 disposed within and capable of rotating relative to the
housing 30.
[0018] Spool 40 may be formed in any manner, but is preferably
molded from a conventional thermoplastic material, for example
LEXAN.RTM. polycarbonate resin sheet material available from
General Electric Company. The spool 40 comprises two circular outer
flanges 41 located in conventional fashion on opposite ends of a
cylindrical central hub 40a. The optical waveguide 20 is wound
around the central hub 40a and onto the spool 40 such that the two
end lengths of jacketed optical fiber 22 extend outwardly from the
spool 40, as will be described in greater detail hereinafter.
Preferably, the optical waveguide 20 is reeled onto the spool 40 in
such manner that the end lengths of jacketed optical fiber 22
extend outwardly from the spool 40 side-by-side in the same
direction (FIG. 3). Thus, both end lengths of the jacketed optical
fiber 22 can be extracted off the spool 40 and the optical
connectors 26 can be connected to the optical test equipment 14 and
the optical network 12.
[0019] FIGS. 4 and 5 illustrate an exemplary manner in which the
central length of unjacketed optical fiber 21 may be configured on
the spool 40 to reverse the direction of one end 25 of the optical
waveguide 20, while maintaining the minimum bend radius of the
optical waveguide 20. As a result, both end lengths of jacketed
optical fiber 22 will extend outwardly from the spool 40 in the
same direction and may be extracted off the spool 40 and retracted
onto the spool 40 in a preferred manner. When the test fiber box 10
is assembled using this technique, the central length of unjacketed
optical fiber 21 cannot be bent or curved beyond a radius of
curvature that is small enough to introduce significant losses
and/or attenuations in the signal transmitted though the optical
waveguide 20. A curved fiber routing channel 43 provided on an
exterior face 42 of one of the spool flanges 41 insures that the
radius of curvature of the central length of unjacketed optical
fiber 21 will not be less than the minimum radius of curvature of
the optical waveguide 20 at which losses or attenuation due to
excessive bending could be introduced, typically about 1.5 inches.
The minimum radius of the channel 43 is equal to or greater than
the minimum bend radius of the optical waveguide 20 with which the
spool 40 is to be used, and the width of the channel 43 is slightly
greater than the diameter of the central length of unjacketed
optical fiber 21. When the central length of unjacketed optical
fiber 21 is positioned within channel 43, the opposite ends of the
optical waveguide 20 will extend outwardly from the spool 40 in the
same direction towards an exit port 36 provided in the housing 30
so that the end lengths of jacketed optical fiber 22 and optical
connectors 26 can be extracted off the spool 40 and retracted onto
the spool 40.
[0020] Channel 43 preferably comprises an S-shaped or
teardrop-shaped profile, commonly referred to as a "ying-yang,"
because the direction of travel of the optical fiber is reversed as
the profile is traversed. The "ying-yang" configuration is
especially desirable because it avoids crossover of the optical
fiber, which may result in twisting and subsequent deterioration or
breakage of the optical fiber. The channel 43 with the "ying-yang"
configuration also permits the central length of unjacketed optical
fiber 21 to transition smoothly from the exterior face 42 of the
spool flange 41 to the area surrounding the central hub 40a between
the spool flanges 41. A slot 45 extends inwardly from the outer
edge of the spool flange 41 and intersects the channel 43. The
radial extent of slot 45 is sufficient so that the optical
waveguide 20 will not be crimped or kinked in the transition
between the channel 43 on the exterior face 42 and the area between
the flanges 41. In this manner, the same spool 40 can be used for
optical waveguides 20 having significantly different lengths and
intended for use with different optical test equipment 14 and/or
optical networks 12. Annular shims may also be inserted around the
central hub 40a when a spool 40 is used for shorter length optical
waveguides 20 as an additional means of preventing damage to the
optical waveguide fiber 20 due to crimping or kinking at the
location of the slot 45. After the end of the central length of
unjacketed optical fiber 21 has traversed the channel 43 and exited
through the slot 45, the spool 40 is rotated in a conventional
manner to reel the remaining length of unjacketed optical fiber 21
onto the spool 40.
[0021] Mandrel wrap channels 44 are located on opposite sides of
the channel 43 on the exterior face 42. Each of the mandrel wrap
channels 44 intersects the channel 43 near the center of the spool
flange 41, and one of the mandrel wrap channels 44 extends around a
hole extending through the central hub 40a of the spool 40. The
mandrel wrap channels 44 are used when the optical waveguide 20
comprises multimode optical fiber, but are not necessary when the
optical waveguide 20 comprises only single mode optical fiber.
Mandrel wrap channels 44 comprise means for reducing the amplitude
of higher-order modes propagating in the cladding area of multimode
optical fibers in accordance with EIA/TIA/ANSI loss testing
recommendations. The two channels 44 are intended for use with
multimode optical fibers having different standard core sizes. For
example, one of the channels 44 may be configured to receive 50
micron multimode optical fiber, while the other channel 44 is
configured for use with 62.5 micron multimode optical fiber. A
multimode optical fiber is first routed into the fiber channel 43,
and then routed into the appropriately sized mandrel wrap channel
44 at its intersection with the channel 43. Typically five turns of
the multimode optical fiber in the corresponding mandrel wrap
channel 44 are sufficient to reduce the amplitude of higher-order
modes propagating in the cladding area of the multimode optical
fiber in accordance with EIA/TIA/ANSI loss testing
recommendations.
[0022] Once the central length of an unjacketed single mode or
multimode optical fiber 21 is routed in the appropriate channel(s)
43 (44) on the exterior face 42 of the spool flange 41, both end
lengths of jacketed optical fiber 22 are attached to the spool 40.
As best shown in FIG. 9, a pair of tie-down holes 46 are located
adjacent the outer edge of each spool flange 41 of the spool 40.
The tie-down holes 46 are used to strain relieve the end lengths of
jacketed optical fiber 22 to the spool 40. As shown, the strength
members 24 extending beyond the jacket 23 on each end length of
jacketed optical fiber 22 are threaded through the tie-down holes
46 and tied off. The two end lengths of jacketed optical fiber 22
may be tied off using the same tie-down holes 46, or may be tied
off to tie-down holes 46 at different locations on the same spool
flange 41. Preferably, however, the end lengths of jacketed optical
fiber 22 are tied off using tie-down holes 46 on different spool
flanges 41. More preferably, the locations of the tie-down holes 46
on the different spool flanges 41 are aligned opposite one another
so that the two end lengths of jacketed optical fiber 22 remain
side-by-side and parallel when extracted off the spool 40 and
retracted onto the spool 40. When the end lengths of jacketed
optical fiber 22 are secured to the spool 40 in this manner, the
tensile forces applied to the optical waveguide 20 to cause
rotation of the spool 40 (and thereby extract the jacketed optical
fiber 22 off the spool 40) will be transmitted through the jacket
23 and/or the strength members 24 to the spool 40. Similarly when
the spool 40 is rotated in the opposite direction (to retract the
jacketed optical fiber 22 onto the spool 40, as will be described),
the tensile forces applied to the optical waveguide 20 will be
transferred from the spool 40 through the jacket 23 and/or strength
members 24. In this manner the optical waveguide 20, and in
particular the central length of unjacketed optical fiber 21, will
be isolated from the tensile forces applied during extraction and
retraction of the end lengths of jacketed optical fiber 22.
[0023] The end lengths of jacketed optical fiber 22 surround the
central length of unjacketed optical fiber 21 when the optical
waveguide 20 is reeled on the spool 40 so that the central length
of unjacketed optical fiber 21 is not exposed to the environment
outside the housing 30. The portion of the unjacketed optical fiber
21 disposed in fiber routing channel 43, and in one or both of the
mandrel wrap channels 44 for multimode fiber, will be separately
covered by a protective cover 55 (FIG. 3) that is secured to the
exterior face 42 of the spool flange 41. Thus, the unjacketed
optical fiber 21 disposed in channel 43, and possibly in mandrel
wrap channels 44, will be encapsulated between the cover 55 and the
exterior face 42 of spool flange 41. Cover 55 may be fabricated
from any suitable lightweight, substantially rigid material, such
as MYLAR.RTM. available from E.I. du Pont de Nemours and Company.
The spool 40 is positioned within the housing 30 where optical
waveguide 20, when reeled, will be completely enclosed and
protected from dust, dirt and other potentially damaging
environmental conditions. Only the end lengths of jacketed optical
fiber 22 and the optical connectors 26 can be extracted from the
housing 30. Since the jacket 23 and/or the strength members 24 are
physically attached to the spool 40, a short portion of the end
lengths of jacketed optical fiber 22 will remain within the housing
30 even when the maximum length of jacketed optical cable 22 is
extracted from the housing 30. As shown, the housing 30 is
substantially cylindrical so that with the generally cylindrical
spool 40 disposed within the housing 30, the complete retractable
optical fiber assembly (i.e., test fiber box) 10 will occupy a
relatively small volume. The test fiber box 10 will therefore be
compact for transport and suitable for use in cramped spaces.
[0024] As shown herein, the housing 30 is fabricated in two mating
sections consisting of a housing base 31 and a housing cover 32. As
best seen in FIG. 3, the housing base 31 defines a generally
cylindrical interior cavity 35, which is dimensioned to receive the
spool 40 with the optical waveguide 20 reeled on the spool 40. The
cavity 35 is formed by an annular housing wall 33, extending
upwardly from the floor of the housing base 31. A recessed ledge 34
formed at the top of the housing wall 33 allows the housing cover
32 to rest along the top of the housing base 31 to enclose the
interior cavity 35. The housing cover 32 is mounted on the top of
the housing base 31 after the spool 40 with the optical waveguide
20 reeled on the spool 40 is positioned within the interior cavity
35. Both the housing base 31 and the housing cover 32 may be formed
of a rigid metal or a durable plastic. Alternatively, one of the
housing components may be made of metal and the other made of
plastic. Other materials may also be used to fabricate the housing
base 31 and housing cover 32, such as a resin/fiber composite
(e.g., glass epoxy) or a polycarbonate sheet molding compound
(e.g., LEXAN.RTM.). In another embodiment, the housing 30 could
comprise top and bottom plates spaced apart by a cylindrical shell.
Although the compact size might be compromised, the housing 30 need
not be cylindrical, and could instead be rectangular, hexagonal,
octagonal, or some other non-cylindrical geometric configuration.
The interior cavity 35, in which the spool 40 is disposed, likewise
does not need to be cylindrical, as long as there is enough space
within the interior cavity 35 to permit the spool 40 to rotate
freely to extract the optical waveguide from the housing 30 and to
retract the optical waveguide 20 into the housing 30. For example,
if the housing 30 was rectangular, the circular spool 40 could rest
in a rectangular interior cavity 35.
[0025] The optical waveguide 20 is extracted from and retracted
into the interior cavity 35 of the housing 30 through an exit port
36 provided in the housing wall 33. The generally circular housing
wall 33 defines an inner tangential groove 39 communicating between
the interior cavity 35 and the exterior of the test fiber box 10.
Tangential groove 39 is large enough for the pair of end lengths of
jacketed optical fiber 22 to pass through, but not large enough to
permit the optical connectors 26 to pass. An outer tangential
groove 60 adjacent the inner tangential groove 39 is large enough
to receive at least the rear portions of the optical connectors 26
therein when the optical waveguide 20 is fully retracted into the
housing 30. A separator pin 38 extends laterally through the
tangential groove 39 to prevent the end lengths of jacketed optical
fiber 22 from twisting as they are extracted from or retracted into
the housing 30 so that the optical fiber will not be damaged. A
removable exit port cover 58 may be attached, for example with
screws, to the housing base 31 to close off the tangential groove
39 and tangential groove 60. As shown, a protective cap 37 is also
provided to close the open end of exit port 36 (i.e., tangential
groove 60). The cap 37 is movably attached to the housing 30
adjacent the open end of tangential groove 60. For example, the cap
37 may be pinned at an edge, and preferably at an outer edge, by
one or more smooth, cylindrical pins 37a. Accordingly, the cap 37
can be rotated between an open position, in which the end lengths
of jacketed optical fiber 22 can be extracted or retracted, and a
closed position, in which the optical waveguide 20 is completely
retracted within the housing 30 and the optical connectors 26 are
protected by the closed cap 37 from environmental damage.
[0026] As best shown in FIG. 8, a protruding retaining member 39,
such as a partially recessed spring-loaded ball, is provided on the
outermost end of the exit port 36. The retaining member 39 engages
the underside of the cap 37 to retain the cap 37 in the closed
position (FIG. 2), but still permits the cap 37 to be moved to the
open position (FIG. 8) to extract the end lengths of jacketed
optical fiber 22 and the optical connectors 26. The cap 37
preferably has a thin wall and a generally rectangular interior
cavity that will provide space for the front portions of the
optical connectors 26 when the optical waveguide 20 is entirely
retracted within the housing 30. When the cap 37 is in the closed
position, the optical connectors 26 are completely enclosed within
the tangential groove 60 and the cap 37 so that separate connector
dust caps, which can be easily lost, are not needed. The front
portions of the optical connectors 26 will, however, extend
slightly beyond the outer end of the tangential groove 60 so that
the optical connectors 26 can be readily grasped to extract the end
lengths of jacketed optical fiber 22 and the optical connectors 26
from the housing 30 after the cap 37 is rotated to the open
position.
[0027] As shown in the exemplary embodiments shown and described
herein, the spool 40 and the optical waveguide 20 reeled on the
spool 40 are not entirely free to rotate relative to the housing
30, but the spool 40 is biased in a first direction relative to the
housing 30 so that the optical waveguide 20 is automatically
retracted into the housing 30. As best shown in FIG. 3, a spiral
coiled spring or helical torsion spring 47, similar to a clock
spring, is disposed between the spool 40 and a tubular mounting
sleeve 56 secured to the housing 30. The mounting sleeve 56 is
secured, for example by screws, to both the housing cover 32 and
the housing base 31. The torsion spring 47 encircles the mounting
sleeve 56 and the mounting sleeve 56 extends through the central
hub 40a of the spool 40 concentric with the axis of rotation of the
spool 40. The torsion spring 47 may be separated from the housing
base 31 by a spring washer 57 having a smooth upper surface.
Although not shown, at least a portion of the torsion spring 47 is
seated within the central hub 40a of the spool 40 and the outer end
of the torsion spring 47 is attached to the spool 40 in a known
manner, for example by inserting the outer end of the torsion
spring 47 into a vertical slot formed on the interior of the
central hub 40a. The inner end of the torsion spring 47 is attached
to the mounting sleeve 56, for example by inserting the inner end
of the torsion spring 47 into a vertical slot 59 formed in the
mounting sleeve 56. As a result, the inner end of the torsion
spring 47 is fixed relative to the housing 30. With the opposite
ends of the torsion spring 47 thus attached, rotation of the spool
40 in a first direction compresses the torsion spring 47, while
rotation of the spool 40 in a second direction, opposite to the
first direction, relaxes the torsion spring 47. Thus, extraction of
the end lengths of jacketed optical fiber 22 and the accompanying
rotation of the spool 40 causes the torsion spring 47 to compress.
The compressed torsion spring 47 exerts a returning force on the
spool 40 that biases it in the second direction, thereby tending to
retract the end lengths of jacketed optical fiber 22 into the
housing 30.
[0028] The test fiber box 10 further comprises a mechanical stop 48
disposed between the peripheral edges of the spool flanges 41 and
the housing wall 33. Although residing primarily in the interior
cavity 35 of the housing 30, the mechanical stop 48 comprises an
actuator button 52 protruding through an opening 61 formed through
the housing wall 33. The mechanical stop further comprises a stop
arm 49 that pivots about a stud 53 protruding laterally through the
stop arm 49 from at least one of the housing base 31 and housing
cover 32. The action of mechanical stop 48 is illustrated in FIGS.
6 and 7. A linear coil spring 50 is disposed between the end of the
stop arm 49 opposite the actuator button 52 and the housing wall
33. Linear spring 50 acts as an extension member that biases the
stop arm 49 counterclockwise about the stud 53, as shown in FIG. 6.
When depressed, the actuator button 52 rotates the stop arm 49
clockwise about the stud 53 against the linear spring 50. FIG. 6
illustrates the mechanical stop 48 in an engaged position which
prevents rotation of the spool 40, and thus, extraction of the
optical waveguide 20 reeled on the spool 40 from the housing 30 or
retraction of the optical waveguide 20 reeled on the spool 40 into
the housing 30. In the engaged position, stop ridges 54
frictionally engage the peripheral edges of the spool flanges 41 to
prevent rotation of the spool 40. As previously mentioned, the
mechanical stop 48 is biased in the engaged position so that unless
the actuator button 52 is depressed and the stop arm 49 rotates
clockwise, the spool 40 will not rotate relative to the housing
30.
[0029] FIG. 7 illustrates the released position that results when
the actuator button 52 is depressed from the exterior of the
housing 30. In the released position, the spool 40 is free to
rotate relative to the housing 30 for either extraction or
retraction of the end lengths of jacketed optical fiber 22 and the
optical connectors 26. With the mechanical stop 48 in the released
position (FIG. 7) and the end lengths of jacketed optical fiber 22
extracted though the exit port 36, the torsion spring 47 is
compressed (i.e., coiled beyond the static position) so that a
restoring force is stored in the torsion spring 47. When the end
lengths of jacketed optical fiber 22 are released, the spool 40
rotates relative to the housing 30 to relieve the restoring force
in torsion spring 47 unless the actuator button 52 is released and
the mechanical stop 48 is in the engaged position. Of course, the
actuator button 52 would be released and the mechanical stop 48
engaged when the optical waveguide 20 is connected between optical
test equipment 14 and an optical network 12. After the optical
connectors 26 are disconnected from the optical network 12 and the
optical test equipment 14, the actuator button 52 is then depressed
to release the mechanical stop 48, thereby permitting rotation of
the spool 40 (which is biased by the torsion spring 47 in the
second direction) and retraction of the end lengths of jacketed
optical fiber 22 under the influence of torsion spring 47. Since
the end lengths of jacketed optical fiber 22 are of approximately
equal length, both end lengths 22 and their respective optical
connectors 26 will be retracted into the housing 30 in unison, and
the connectors 26 will be received within the exit port 36 so that
the cap 37 can be closed to protect the ends of the optical
connectors 26.
[0030] It should be understood that neither the torsion spring 47
nor the mechanical stop 48 are essential, even though they may be
desirable. For instance, a simple crank can be provided on the side
the housing 30 of the test fiber box 10 to allow a user to retract
the end lengths of jacketed optical fiber 22 back into the housing.
Other embodiments could employ a functionally equivalent torsion
spring having a different configuration, or a functionally
equivalent mechanical stop having a different configuration. For
example, a mechanical stop could be configured on the side of the
housing 30 that engages ratchet surfaces provided on the side of
the spool 40. Other embodiments could also employ multiple spools
of optical waveguide so that the same test fiber box could be
attached between multiple sets of optical test equipment and/or
multiple optical networks. Alternatively more than one optical
waveguide could be reeled onto the same spool so that more than one
pair of end lengths of jacketed optical fiber could be withdrawn at
the same time.
[0031] Although the retractable optical fiber assembly shown and
described herein is especially suited for use in connecting optical
test or monitoring equipment to an optical network, it should be
understood that it need not be so limited. The retractable optical
fiber assembly could also be employed as a readily accessible
jumper if needed. Therefore, the exemplary embodiments and the
alternatives discussed herein are merely representative in nature
and should be considered to be limiting in any manner. Accordingly,
the invention is not limited to the representative embodiments and
instead should be understood and defined as broadly as possible by
the appended claims.
* * * * *