Note: Descriptions are shown in the official language in which they were submitted.
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This invention relates to access nodes in fiber optic
links and networks. It Finds particular application in local area
networks.
In one example of local area network, a fiber extends
around a loop or ring. Light is transmitted from a central office
around the loop from a modulated light emitting source. Depending on
the activity around the loop, light is received back from the loop at
a photodetector in the central office.
That activity may take the form of a variety of passive
or active fiber optic devices which are inserted into the line at a
number of discrete positions depending on the particular functional
requirement at each position.
The functional requirements are for example a fiber
optic tap at which optical signals can be both diverted from and
inserted into the fiber optic channel, or a subsidiary loop providing
an extension to tune network, or a wavelength division multiplexer or
demultiplexer for inserting or extracting light of a particular
wavelength into or from the loop fiber, or finally, an active module
such as a repeater to boost the signal within the loop fiber. Most
known structural implementations of these functional requirements are
characterized by a metal or plastics package including a container
part through the wall of which extend one or more optical fibers in
sealed feed through arrangements. Typically the package has a cover
which is screwed, glued or soldered to the container part into which
optical and electro-optical elements are fixed.
These known device packages cannot easily be modified in
order to substitute functions. A modular arrangement is now proposed
which enables functional changes at an optical fiber access node to
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be made relatively quickly.
According to one aspect of the invention there is
provided an optical fiber access node comprising a housing, an input
fiber terminating at the housing for directing light transmitted
thereby into the housing, an output fiber terminating at the housing
for receiving light from within the housing and transmitting it away
from the housing, and a fiber optic module retractable insertable
into the housing to a lock position, the module having an element
with an input port and an output port wherein, in said lock position,
the input port is located to receive light from the input fiber and
the output port is located to direct light into the output fiber.
The element can be a bypass fiber or a fiber having an
integral tap or extension loop. The element can alternatively be a
wavelength division multiplexing or demultiplexing device. In
another alternative, the element can be an active device with an
electrical control means extending thereto. Such an active device
can incorporate one or both of a light emitting device and a
photodetector together with a control circuit therefore.
A module can have an outer surface thereof adapted to
closely abut an inner surface of the housing in the lock position of
the module. Abutting surfaces can have a cooperating projection and
recess therein to ensure accurate positioning of the module within
the housing.
Preferably the axes of the input and output fiber are
aligned at their terminations with the housing.
Each of the fibers can adhere to a graded index lens
mounted within a wall of the housing. The module can have a recess
or projection in a front surface thereof to enable the module to be
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manually gripped. The fiber optic element can be cast in a plastics
matrix.
Alternatively the element can be set into a V groove or
grooves in a base plate of the module and a top plate thereof can
overlie the element, the module further comprising means for biasing
the top plate towards the bottom plate to clamp the element.
The fiber optic element can have multiple parts.
The fiber ends exposed at walls of the housing can be
polished flat. The input and output fibers can be pigtail fiber
lengths of high radius core up to 100 microns diameter.
The housing can have a flange extending around a front
edge thereof to enable the housing, following insertion into an
aperture within a wall, to be fixed to the wall. The module too can
have a flange positioned to abut and seal against the housing flange
so as to cover space between the module and housing and thereby
prevent entry of dirt and contaminants.
An embodiment of the invention will now be described by
way of example with reference to the accompanying drawings, in
which:-
Figure 1 is an exploded view of an optical fiber access
node particularly adapted for a wall mounting;
Figure 2 is a plan view of a tapping module for use in
the Figure 1 access node;
Figure 3 is a plan view of an extension module for use
in the Figure 1 access node;
Figure 4 is an exploded perspective view of a
multiplexer module for the access node of Figure 1;
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Figure 5 is a perspective view of an active module For
use in the access node of Figure 1;
Figure 6 is a perspective view of an alternative type of
housing for an access node according to the invention; and
Figure 7 is a perspective view of another form of access
node according to the invention.
Referring in detail to the drawings, Figure 1 shows a
fiber optic access node having an input fiber 10, an output fiber 12,
a receptacle or housing 14 at which the fibers terminate, and an
insertable module 15.
Fibers 10 and 12 are 50 micron core diameter fibers
which extend through the wall of the molded plastics housing 14. The
housing 14 is defined by a box 16 having a depth "d" of 10
centimeters, width "w" of 6 centimeters and height "h" of 2
centimeters. The box 16 has a surrounding faceplate or flange 15
having screw apertures 17 by means of which the box can be screwed to
a wall. The fibers are mounted within annular flanges 18 integral
with the box 16 so that central axes of the fibers are aligned. The
fibers are fixed in position by a mass 19 of epoxy resin. The input
and output fibers 12 and 14 have end surfaces which extend flush with
the inner side surfaces of the box 16. During manufacture of the
access node, the fibers 12 and 14, which can be pigtail fibers, are
fixed at the correct anchoring positions shown by inserting a dummy
module (not shown) into the box 16, pushing the fibers 12 and 14
against the dummy module, and then applying the mass 19 of adhesive.
Shown in spaced relationship to the housing 14 is a
Fiber optic module 15 containing an element 18. The module 15 can be
inserted into the housing in the direction of arrow 20, the leading
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part of the parallelopiped module dimensioned to fit snugly into the
housing 14~ The fiber optic element has input and output zones,
respectively 22 and I which in use, align with the exposed surfaces
of the input and output fiber 10 and 13. To ensure accurate
alignment, the side surfaces of the module and the inner side
surfaces of the box 16 are formed with cooperating pips 26 and pits
28.
the module has a flange 27 at its front edge. On a back
surface of the flange 27 is a gasket 29. When the module is inserted
into the housing 14, the gasket seals over the space between the
inner wall of the box 16 and the outer surface 31 of the module. The
module has a recessed handle 25 enabling it to be readily gripped to
pull it from the housing 14. As an alternative to a recessed handle,
the module can have a protruding handle or can alternatively be made
of a slightly greater depth than the receptacle so that a part of the
module juts above the entrance to the receptacle.
In the embodiment shown in Figure 1, the element 18 is
simply a bypass fiber which has polished end surfaces 22 and 24
extending flush with the outer side surfaces of a molded plastic
support 31. The module is made by mounting a fiber within a vertical
elongate chamber, injection molding plastics around the mounted
; fiber, allowing the plastics to solidify and then cutting the molding
into lengths corresponding to width "w" of the box 16. The cut
surfaces corresponding to the side surfaces of the module shown in
Figure 1 are then polished.
The access node is inserted easily into a loop fiber
(not shown) by cleaving the loop fiber and fusion splicing the distal
ends of the input and output pigtail fibers 10 and 12 to the cleaved
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ends of the loop fiber.
As indicated previously the advantage of the modular
access node is that modules 15 can be substituted when the service
given at a particular access node is to be changed. The module shown
in Figure 1 is the simplest module, a bypass. A more complex module
is shown in plan view in Figure 2, the module having a fiber length
30 extending between the module side surfaces as in the Figure 1
module but with a tapping fiber 32 extending out of the module 15
from a front surface 38. In use when the module 15 is inserted into
the housing 14, light can be tapped from the loop fiber to a piece of
station equipment 34. Alternatively light can be generated or
modulated at the station 34 and transmitted back into the loop fiber.
The module can be made in a manner similar to the module of Figure 1.
Thus a number of tapping zones can be formed on a single host fiber
by twisting the tapping fibers around -the host fiber and heating the
several twist zones to promote fusion. Such an optical fiber tap is
known as a fused coupler. Ideally several such taps are formed along
a single host fiber which is then encapsulated in plastics and cut
into separate one tap lengths corresponding to the desired width of
the modules.
Referring to Figure 3 the module here is made using a
single fiber 36 but instead of it passing directly between the side
surfaces of the module, the module is made with a loop of the fiber
extending out of the front wall 38 of the plastics molding 28. The
loop is then cleaved to enable a piece of station equipment 40 or
perhaps a test set to be inserted into the extension loop.
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Referring to Figure 4, there is shown a wavelength
division demultiplexer module. The module has two molded plates 42
and 44. A lower rigid plastics plate 42 has a series of V grooves 46
dimensioned and sited to receive the various parts of a wavelength
division demultiplexer, a wavelength dependent filter 48, an input
fiber 49, a pair of graded index lenses 50, and output fiber taps 51
and 52. The upper plate 44 is made of resilient plastics and has
recesses 54 for location of the demultiplexer elements. The two
plates 42 and 44 are fixed together by screw and nut assemblies (not
shown) extending through holes 47. In operation of the multiplexer,
light incident on the filter 48 from input fiber 49 has components at
different wavelengths I and I The incident light
directed at the filter at an angle at which light at wavelength
I passes through the filter 48 and into output fiber 51
while light at wavelength I is reflected from the filter 48
and is directed by the graded index lens into the output fiber 52.
Other assemblies of demultiplexer elements are known and
can be packaged in a module similar to that shown in Figure 4. This
demultiplexer module is used, for example, when several optical
channels are to be demultiplexed from a single loop fiber signal,
each channel being transmitted at a distinct wavelength. Although
only the demultiplexer is shown in Figure 4, it will be understood
that a multiplexer has an identical configuration but in the latter
case, fibers 51 and 52 are input fibers and fiber 49 is an output
fiber.
Referring to Figure 5 there is shown in perspective view
another module of the two-plate type shown in Figure 4. Clamped
between the plates in an array of locating grooves or recesses are a
light emitting diode 56, a PIN photo diode 58 and between these two
devices and electrically connected to them by leads is an integrated
circuit 60. The integrated circuit interfaces with a plug 64
insertable into an aperture defined by the two plates 42 and 44, the
plug having leads 62 for connection to equipment necessary to power
the light emitting diode and the PIN photo diode.
The various components of the Figure 5 module can be
individually mounted between the plates or can be encapsulated in a
plastics matrix with leads 62 extending from one face, a laser output
facet exposed at another face and a photodetector input surface
exposed at a third face.
As an alternative to wide core input and output fibers
used in the previous embodiments, Figure 6 shows a module having
input and output fibers 66 and 68 respectively, of 50 micron core and
120 micron outer diameter. The fibers have ends fixed by masses 70
of an epoxy resin to graded index lenses 72 and 74. These lenses are
mounted to the housing or receptacle in the same way as the wide core
fiber illustrated in Figure 1. The lens 72 operates to expand the
beam originating from the input fiber 66 for passage through a
relatively large diameter bypass within the module (not shown), the
expanded light then being focused by the lens 74 onto the core of
the output fiber 68.
The embodiments of Figure 1 to 5 have a single input and
a single output fiber terminating at the housing 14. In many optical
fiber loop installations, a ribbon fiber is used. As shown in the
Figure 7 access node, the receptacle or housing 78 is of relatively
shallow depth and ribbon fibers 80 and 82 terminate along opposed
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sides. The module I a rectangular hollow, internally reflecting
star coupler, is inserted downwardly into the receptacle or tray, an
input aperture 86 of the star coupler being aligned with the input
fiber ribbon 80 and its outlet apertures being aligned with the
output fiber ribbon go. Cooperating pips and pits (not shown) on
abutting surfaces lock the module in position. The module is
withdrawn by tugging on a handle 88.
In all of the embodiments shown above, the input and
output fibers are axially aligned at their terminations with the
receptacle. It will be understood that the fibers can approach the
module at angles to one another. A corresponding reorientation of
the element or elements within the module may be necessary but this
is readily achievable using a flexible fiber.
In addition, the fibers terminate at opposed faces of a
rectangular receptacle. In fact, another fiber can terminate at a
reverse face of the receptacle, the corresponding module also having
en, additional port. Indeed, so long as the module can be readily
extracted from the receptacle and is securely retained in the
receptacle during normal operation, the module and receptacle housing
can be of other shapes with a plurality of input and/or output
fibers.
