U.S. patent application number 15/362077 was filed with the patent office on 2017-06-15 for high density multi-fiber ferrule for optical fiber connector.
The applicant listed for this patent is NANOPRECISION PRODUCTS, INC.. Invention is credited to Michael K. BARNOSKI, Gregory L. KLOTZ, Shuhe LI, Robert Ryan VALLANCE.
Application Number | 20170168246 15/362077 |
Document ID | / |
Family ID | 47295127 |
Filed Date | 2017-06-15 |
United States Patent
Application |
20170168246 |
Kind Code |
A1 |
LI; Shuhe ; et al. |
June 15, 2017 |
HIGH DENSITY MULTI-FIBER FERRULE FOR OPTICAL FIBER CONNECTOR
Abstract
A ferrule for a high density optical fiber connector, supporting
a first set of optical fibers of a first fiber cable and a second
set of optical fibers of a second fiber cable. The ferrule supports
the first and second sets of optical fibers in at least one plane.
In one embodiment, the first set of optical fibers are supported in
a first row of open grooves, and the second set of optical fibers
are supported in a second row of open grooves. The optical fibers
in the first row are staggered with respect to the optical fibers
of the second row. The ferrule comprises two halves, each having an
open structure that has a row of open grooves precisely formed
thereon in a plane. In another embodiment, the ferrule supports the
first and second sets of optical fibers in a single row, in an
alternating interleaving manner.
Inventors: |
LI; Shuhe; (Pasadena,
CA) ; VALLANCE; Robert Ryan; (Newbury Park, CA)
; BARNOSKI; Michael K.; (Pacific Palisades, CA) ;
KLOTZ; Gregory L.; (La Verne, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
NANOPRECISION PRODUCTS, INC. |
El Segundo |
CA |
US |
|
|
Family ID: |
47295127 |
Appl. No.: |
15/362077 |
Filed: |
November 28, 2016 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
13650099 |
Oct 11, 2012 |
9507099 |
|
|
15362077 |
|
|
|
|
61620945 |
Apr 5, 2012 |
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G02B 6/3887 20130101;
G02B 6/3862 20130101; G02B 6/3885 20130101; G02B 6/3839 20130101;
G02B 6/36 20130101; G02B 6/3882 20130101 |
International
Class: |
G02B 6/38 20060101
G02B006/38 |
Claims
1. A ferrule for supporting optical fibers in an optical fiber
connector, comprising a body structured with open grooves to
support a first set of optical fibers and a second set of optical
fibers, and with partitions to separate adjacent optical fibers in
the open grooves, wherein the optical fibers are bare with cladding
exposed, wherein the body of the ferrule comprises a first part and
a second part opposing each other and maintained in mating
relationship to support the first and second sets of optical
fibers, and wherein the first set of optical fibers are staggered
with respect to the second set of optical fibers at opposing
surfaces of the first part and the second part, wherein the
partitions define walls of adjacent open grooves, such that each
open groove receives an optical fiber without the optical fiber
protruding above the groove.
2. (canceled)
3. The ferrule as in claim 1, wherein the first part and the second
part of the ferrule correspond to a first ferrule halve and a
second ferrule halve, respectively, wherein the first ferrule halve
has a plurality of a first open grooves supporting the first set of
optical fibers and the second ferrule halve has a plurality of
second open grooves supporting the second set of optical fibers,
wherein the first open groove and the second groove are defined on
the opposing surfaces of the first part and the second part.
4. The ferrule as in claim 3, further comprising a collar clamping
on the first and second ferrule halves to maintain the first and
second ferrule halves in mating configuration.
5. The ferrule as in claim 1, wherein the ferrule is structured to
support the first set of optical fibers in a first row of open
grooves in a first plane and the second set of optical fibers in a
second row of open grooves in a second plane different from the
first plane.
6. The ferrule as in claim 5, wherein the ferrule comprises a first
set of open grooves supporting the first set of optical fibers, and
a second set of open grooves supporting the second set of optical
fibers.
7. The ferrule as in claim 6, wherein the ferrule is structured
such that the first set of optical fibers in the first plane are
staggered with respect to the second set of optical fibers in the
second plane.
8. The ferrule as in claim 6, wherein the ferrule comprises a first
ferrule halve and a second ferrule halve, wherein the first ferrule
halve comprises the first set of open grooves supporting the first
set of optical fibers, and the second ferrule halve comprises the
second set of open grooves supporting the second set of optical
fibers.
9. The ferrule as in claim 8, wherein the first set of open grooves
are defined on a first surface of the first ferrule halve, and the
second set of open grooves are defined on a second surface of the
second ferrule halve, wherein the first surface and the second
surface are mated when the first ferrule halve and the second
ferrule halve are assembled to form the ferrule.
10. The ferrule as in claim 9, wherein the ferrule is structured
such that the first set of optical fibers in the first plane are
staggered with respect to the second set of optical fibers in the
second plane.
11. The ferrule as in claim 6, wherein the partitions comprise
first partitions at the first surface and second partitions at the
second surface, and wherein the ferrule is structured such that
adjacent optical fibers in the first set of open grooves are
separated by the first partitions at the first surface, and
adjacent optical fibers in the second set of open grooves are
separated by the second partitions at the second surface, wherein
when the first surface and the second surface are mated, the first
partition face the second set of open grooves and the second
partitions face the first set of open grooves.
12. The ferrule as in claim 11, wherein the first partitions
include first flat portions at the first surface, and the second
partitions include second flat portions at the second surface,
wherein when the first surface and the second surface are mated,
the first flat portions cover the second set of open grooves and
the second flat portions cover the first set of open grooves.
13. The ferrule as in claim 1, wherein the optical fibers each has
a diameter D, wherein immediate adjacent terminating end sections
of the first set of optical fibers have a centerline spacing of 2D,
and the immediate adjacent terminating end sections of the second
set of optical fibers have a centerline spacing of 2D.
14. The ferrule as in claim 13, wherein the terminating end
sections of the first and second sets of optical fibers are
staggered such that the terminating end sections of immediate
adjacent optical fibers of the first and second sets of optical
fibers have a centerline spacing of D.
15. A ferrule for supporting optical fibers in an optical fiber
connector, comprising a body that comprises a first set of open
grooves in a first plane to support a first set of optical fibers,
and a second set of open grooves in a second plane different from
the first plane to support a second set of optical fibers, wherein
the first set of optical fibers are of a first fiber cable and the
second set of optical fibers are of a second fiber cable, wherein
the first fiber cable is separate from the second fiber cable,
wherein each open groove receives an optical fiber without the
optical fiber protruding above the open groove, and wherein the
first set of open grooves are defined on a first surface at a
perimeter of the body of the ferrule, and the second set of open
grooves are defined on a second surface at the perimeter of the
body of the ferrule.
16. The ferrule as in claim 15, further comprising a frame covering
the first and second surfaces.
17. A ferrule for supporting optical fibers in an optical fiber
connector, comprising a body structured with at least an open
groove to support a first set of optical fibers and a second set of
optical fibers, wherein the first set of optical fibers are of a
first fiber cable and the second set of optical fibers are of a
second fiber cable, wherein the first fiber cable is separate from
the second fiber cable, wherein the optical fibers are bare with
cladding exposed, wherein the first set of optical fibers are
staggered with respect to the second set of optical fibers, and
wherein the ferrule is structured such that the first set of
optical fibers are staggered with respect to the second set of
optical fibers with longitudinal axis of the first and second sets
of optical fibers in a single plane.
18. The ferrule as in claim 17, wherein the ferrule is structured
such that the first set of optical fibers are interleaved with
respect to the second set of optical fibers in the single plane,
wherein the first and second sets of optical fibers are arranged
side-by-side, with the optical fibers of the first set of optical
fibers alternating with the optical fibers of the second set of
optical fibers.
19. The ferrule as in claim 18, wherein the ferrule is structured
such that the alternating optical fibers are arranged to be
touching side-by-side.
20. The ferrule as in claim 19, wherein the ferrule comprises a
first ferrule halve and a second ferrule halve, wherein the first
ferrule halve and the second ferrule halve together define a wide
flat opening sized to receive the first and second sets of optical
fibers arranged side-by-side.
21. The ferrule as in claim 20, wherein a first wide flat section
is defined on a first surface of the first ferrule halve, and a
second wide flat section second set of open grooves are defined on
a second surface of the second ferrule halve, wherein the first
wide flat section and the second wide flat section together define
the wide flat opening in the ferrule to accommodate the first and
second sets of optical fibers.
22. The ferrule as in claim 5, wherein the ferrule is structured
such that the first plane and the second plane are separate
parallel planes.
23. The ferrule as in claim 1, wherein the first set of optical
fibers are of a first fiber cable and the second set of optical
fibers are of a second fiber cable, wherein the first fiber cable
is separate from the second fiber cable.
24. An optical fiber connector, comprising: the ferrule as claimed
in claim 1; and a housing supporting the ferrule.
Description
PRIORITY CLAIM
[0001] This application is a continuation of U.S. patent
application Ser. No. 13/650,099 filed on Oct. 11, 2012, which
claims the priority of U.S. Provisional Patent Application No.
61/620,945 filed on Apr. 5, 2012, which is fully incorporated by
reference as if fully set forth herein. All publications noted
below are fully incorporated by reference as if fully set forth
herein.
BACKGROUND OF THE INVENTION
[0002] Field of the Invention
[0003] The present invention relates to optical fiber connectors,
in particular ferrules in optical fiber connectors.
[0004] Description of Related Art
[0005] There are many advantages of transmitting light signal via
optical fiber waveguides and the use thereof is diverse. Single or
multiple fiber waveguides may be used simply for transmitting
visible light to a remote location. Complex telephony and data
communication systems may transmit multiple specific optical
signals. These devices couple fibers in an end-to-end relationship,
with the coupling being one source of light loss. Precision
alignment of two polished ends of fibers is needed to ensure that
overall optical loss in a fiber link is equal or less than the
specified optical connector loss budget for a system. For
single-mode telecommunication-grade fiber, this typically
corresponds to connector fiber alignment tolerances that are less
than 1000 nm. This means that in both parallel fiber and single
fiber links, operating at multi-gigabit rates, the components
applied to align the fibers must be assembled and fabricated with
sub-micron precision.
[0006] In an optical fiber connection, an optical fiber connector
terminates the end of a cable that contains one or multiple fibers,
and enables quicker connection and disconnection than splicing. The
connectors mechanically couple and align the cores of fibers so
that light can pass end-to-end. Better connectors lose very little
light due to reflection or misalignment of the fibers. Connectors,
in both parallel/multiple fiber and single fiber links, operating
at multi-gigabit rates must be assembled with subcomponents
fabricated with sub micron precision. As if producing parts with
such precision levels were not challenging enough, for the
resulting end product to be economical it must be done in a fully
automated, very high-speed process.
[0007] Current optical fiber connectors have not changed in basic
design for many years. The basic connector unit is a connector
assembly. FIG. 1 illustrates an example of an optical fiber
connector 400 for a cable 410 containing optical fibers 412, which
is commercialized by US Conec Ltd. The connector includes an
assembly of components consisting of a ferrule 402, a ferrule
housing 404, a cable jacket or boot 406, alignment guide pins 408,
and other hardware provided within or outside the housing (e.g.,
cable strain relief, crimp, biasing spring, spacer, etc.). The
ferrule 402 and the terminating end faces of the fibers 412 are
polished. The ferrule 402 in the optical fiber connector 400 is
spring-loaded to provide an axial bias to press together the
polished end faces of the fibers in two connectors in an end-to-end
configuration. In most cases, the intent is to establish physical
contact between coupled fibers to prevent loss of light. Physical
contact avoids a trapped layer of air between two fibers, which
increases connector insertion loss and reflection loss. An adaptor,
not shown, is required to securely couple the ferrules of two
connectors (the ferrule housing 404 of each connector is plugged
into the adaptor).
[0008] The optical fiber connector illustrated in FIG. 1
manufactured by US Conec Ltd. is purportedly in accordance with the
structure disclosed in U.S. Pat. No. 5,214,730, which is assigned
to Nippon Telegraph and Telephone Corporation. As illustrated in
the '730 patent, the optical fiber connector receives a optical
fiber ribbon cable having a plurality of individual optical fibers
and maintains the individual optical fibers in a predetermined
relationship. The optical fiber connector can be mated with another
optical fiber connector (e.g., using an adaptor) so as to align the
plurality of individual optical fibers of one optical fiber
connector with the plurality of optical fibers of the other optical
fiber connector.
[0009] The ferrule 402 from US Conec Ltd. is generally in the form
of a plastic block having a series of over-sized through-holes that
provide sufficient clearance for inserting the terminating ends of
optical fibers 412 and alignment pins 408 into the block. The
ferrule 402 is formed by molding of a plastic polymer that is often
reinforced by glass particles. To insert the terminating ends of
the multiple optical fibers 412 through the holes in the ferrule
block 402, the protective jacket and buffer (resin) layers of the
optic fiber are stripped off to expose the cladding layer near the
terminating ends, and the cladding layer is coated with a layer of
epoxy. The terminating ends of the optical fibers are then threaded
into the over-sized holes in the ferrule. The ends of the optical
fibers 412 are securely held in the ferrule 402 upon curing of the
epoxy. Similarly, the alignment pins 408 are retained with epoxy
after inserting into the oversized holes in the ferrule 402
provided for the pins.
[0010] The above described ferrule has several significant
drawbacks. The injection molded structure inherently does not hold
tolerance well. The polymer is not rigid and deforms when loads
(forces or moments) are applied to the fiber cable or connector
housing. Polymers are also susceptible to creep and thermal
expansion/contraction over longer periods of time. The clearance in
the over-sized holes in the ferrule further affects tolerance of
end-to-end alignment of fibers. The epoxy shrinks upon curing,
which leads to bending of the plastic ferrule. Further, epoxy
creeps over time, leading to pistoning or retracting of the optical
fiber ends (which are pushed against the ends of adjoining fibers)
within the holes in the ferrule under the applied axial bias of the
spring-load in the connector. This compromises the integrity of the
surface contact interface of opposing fiber end faces. These and
other deficiencies result in poor resultant tolerance that is more
to be desired for modern day optical fiber applications.
[0011] Currently, it is generally accepted that fiber connectors
cost too much to manufacture and the reliability and loss
characteristics are more to be desired. The tolerance of the fiber
connectors must improve, and the cost of producing fiber connectors
must decrease if fiber optics is to be the communication media of
choice for short haul and very short reach applications. The
relatively widespread and ever increasing utilization of optical
fibers in communication systems, data processing and other signal
transmission systems has created a demand for satisfactory and
efficient means of inter-joining fiber terminals.
[0012] Further, with increasing demand for high capacity optical
fiber transmissions, multiple strands of optical fibers are bundled
in a cable (e.g., 410 in FIG. 1) and many cables each having
multiple optical fibers are routed through an optical fiber
network. Heretofore, multi-fiber connectors such as that shown in
FIG. 1 have optical fibers terminating in a row in a single plane.
The optical fibers terminating in a connector are part of and
extend from a single optical fiber cable. The optical fibers 412
are individually received in separate holes in the ferrule block
402, wherein adjacent optical fibers from the same fiber bundle or
cable are separated within the ferrule block 402. Consequently, the
number of holes provided in the ferrule 412 limits the density of
inter-joining fiber terminals per fiber connector 400. As one can
appreciate, for a larger number of inter-joining fiber terminals at
a coupling location in the network, a larger optical fiber
connector having a larger footprint and/or a larger number of fiber
connectors 400 are required. Larger connection and additional fiber
connectors 400 at a coupling location result in bulk that takes up
more space at the connection location, which could be
disproportionate to the size of the optical fiber cable 410.
Furthermore, termination and cabling costs increase when multiple
connectors are necessary.
[0013] Heretofore, U.S. Conec Ltd. supplies molded ferrules that
support an array of optical fibers. Ferrules are available with up
to 6 rows of 12 fibers for a total 72 fibers of a single fiber
cable. However, such ferrules possess the same deficiencies noted
for molded ferrules that support a linear array of fibers noted
above. It becomes more difficult to hold the required tolerances
for molded ferrules. In fact, the 72-fiber ferrule is only
available for multi-mode fiber due to poor tolerances. Further, the
arrays of holes in ferrule blocks are not conducive to forming by
stamping processes.
[0014] It is therefore desirable to develop a new high density
optical fiber connector design, and in particular a new high
density ferrule design, which can accommodate a significantly
higher density of optical fibers, which results in low insertion
loss and low return loss, which provides ease of use and high
reliability with low environmental sensitivity, and which can be
fabricated at low cost.
SUMMARY OF THE INVENTION
[0015] The present invention provides a ferrule for an optical
fiber connector, which overcomes many of the drawbacks of the prior
art ferrules and connectors. The ferrule in accordance with the
present invention provides an optical fiber connector, which can
accommodate a significantly higher density of optical fibers, which
results in low insertion loss and low return loss, which provides
ease of use and high reliability with low environmental
sensitivity, and which can be fabricated at low cost. In accordance
with the present invention, the density of terminating optical
fibers in a fiber connector may be significantly increased (e.g.,
doubled) for a given width or footprint of the ferrule. In one
aspect, the inventive ferrule supports optical fibers extending
from one or more optical fiber cable (e.g., ribbon shaped or
rounded cables). In one embodiment, the ferrule is structured for
accommodating multiple optical fibers bundled in separate optical
fiber cables.
[0016] In accordance with the present invention, the ferrule is
provided with fiber grooves and alignment pin grooves that are open
channels, as compared to through-holes in a ferrule block (e.g., a
molded ferrule block). This avoids the need to insert optical
fibers and alignment pins in holes with additional clearance as was
practiced in the prior art. By providing open channels for the
fibers and alignment pins, no clearance needs to be provided for
the fibers and alignment pin. By not having any clearance between
the grooves in the ferrule and the fibers and alignment pins which
would otherwise lead to movements between the parts, the alignment
pins and the fibers can be more accurately located relative to each
other. The spacing of the fibers and pins can be better maintained
under changes in environmental conditions, for example, as the
ferrule can accommodate more dimensional variations without
affecting specified alignment tolerances. The optical fiber
connector thus formed results in low insertion loss and low return
loss. The ferrule configuration also allows ease of attaching
terminating fiber ends to the ferrules, compared to threading epoxy
coated fibers through holes in prior art ferrules. Without using
epoxy, the reliability of the optical fiber connector is not
affected by any aging/creeping of epoxy material. By selecting
appropriate materials for the ferrule, the performance of the
optical fiber connector is less sensitive to thermal variations.
The open structure of the ferrule lends itself to mass production
processes such as stamping and extrusion, which are low cost, high
throughput processes.
[0017] In one embodiment of the present invention, a first set of
terminating optical fibers (e.g., of a first fiber cable) are
supported in a first row of open fiber grooves, and a second set of
terminating optical fibers (e.g., of a second fiber cable) are
supported in a second row of open fiber grooves, with the first row
parallel to the second row. In one embodiment, the optical fibers
in the first row are staggered with respect to the optical fibers
of the second row.
[0018] In one embodiment, the ferrule comprises two halves, each
having an open structure that has a row of open grooves precisely
formed thereon in a plane. The two ferrule halves are stacked, with
the rows of grooves parallel to each other. Each row of grooves in
a ferrule halve accommodates the optical fibers of an optical fiber
cable. In one embodiment, the grooves are configured to be open
fiber clamping grooves, which can securely clamp the optical fibers
without the need for epoxy or a complementary precision part. In
one embodiment, at least a section of the longitudinal opening of
the groove is provided with opposing lips to provide a clamping
effect. The width of the longitudinal opening defined between the
lips along at least a section of the grooves is narrower than the
diameter of the optical fibers to create a tight fit (e.g., an
interference fit) with respect to the fibers, which allows the end
section of an optical fiber to be inserted laterally into the
longitudinal opening of groove, but which snuggly retains the
optical fiber in the groove. The grooves and the width of the
longitudinal groove openings are shaped and sized to retain the
fibers without any clearance to allow for movement of the fiber
relative to the groove.
[0019] In another embodiment of the present invention, the ferrule
is configured to align the terminating optical fibers in a row in a
plane, whereby the axis of adjacent optical fibers are spaced at a
distance substantially corresponding to the diameter of the optical
fibers. In one embodiment, the terminating optical fibers are
arranged side-by-side in a row within a plane in the ferrule, with
adjacent optical fibers touching each other. In one embodiment, in
the row of terminating optical fibers, optical fibers of two
different optical fiber cables are alternately arranged in a
staggered and interleaved manner. In one embodiment, the ferrule is
provided with at least a single wide opening that receives and
accommodates the optical fibers in the side-by-side touching
configuration. There may be more than one opening, each receiving
and accommodating a set of optical fibers in a row within a plane.
In another embodiment, the terminating optical fibers are arranged
in more than one row within a ferrule/connector.
[0020] In another aspect of the present invention, the inventive
ferrules are precision formed by high throughput processes, such as
stamping and extrusion.
[0021] In one embodiment, the ferrule body is made of a metal
material, which may be chosen to have high stiffness (e.g.,
stainless steel), chemical inertness (e.g., titanium), high
temperature stability (nickel alloy), low thermal expansion (e.g.,
Invar), or to match thermal expansion to other materials (e.g.,
Kovar for matching glass).
[0022] The ferrule in accordance with the present invention
overcomes many of the deficiencies of the prior art, resulting in a
high density optical fiber connector that results in low insertion
loss and low return loss, which provides ease of use and high
reliability with low environmental sensitivity, and which can be
fabricated at low cost.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] For a fuller understanding of the nature and advantages of
the invention, as well as the preferred mode of use, reference
should be made to the following detailed description read in
conjunction with the accompanying drawings. In the following
drawings, like reference numerals designate like or similar parts
throughout the drawings.
[0024] FIG. 1 illustrates a prior art optical fiber connector.
[0025] FIG. 2 illustrates a perspective view of a high density
optical fiber connector in accordance with one embodiment of the
present invention.
[0026] FIG. 3 is an end view of the optical fiber connector in FIG.
2.
[0027] FIG. 4 is an exploded view of the optical fiber connector in
FIG. 2.
[0028] FIG. 5 is a top view of the optical fiber connector in FIG.
2.
[0029] FIG. 6 is a side view of the optical fiber connector in FIG.
2.
[0030] FIG. 7 is a sectional view of a portion of the lower ferrule
halve, in accordance with another embodiment of the present
invention.
[0031] FIG. 8 illustrates a perspective view of a high density
optical fiber connector in accordance with a further embodiment of
the present invention.
[0032] FIG. 9 is a top view of the optical fiber connector in FIG.
8.
[0033] FIG. 10 is a side view of the optical fiber connector in
FIG. 8.
[0034] FIG. 11 is an end view of the optical fiber connector in
FIG. 8.
[0035] FIG. 12 is an exploded view of the optical fiber connector
in FIG. 8.
[0036] FIG. 13 is an end view of a high density optical fiber
connector, in accordance with another embodiment of the present
invention with respect to FIG. 8.
[0037] FIG. 14 illustrates a perspective view of a high density
optical fiber connector in accordance with yet another embodiment
of the present invention.
[0038] FIG. 15 is an exploded view of the optical fiber connector
in FIG. 14.
[0039] FIG. 16 is an end view of the optical fiber connector in
FIG. 14.
[0040] FIG. 17 is a top view of the optical fiber connector in FIG.
14.
[0041] FIG. 18 is a side view of the optical fiber connector in
FIG. 14.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0042] This invention is described below in reference to various
embodiments with reference to the figures. While this invention is
described in terms of the best mode for achieving this invention's
objectives, it will be appreciated by those skilled in the art that
variations may be accomplished in view of these teachings without
deviating from the spirit or scope of the invention.
[0043] The present invention provides a ferrule for an optical
fiber connector, which overcomes many of the drawbacks of the prior
art ferrules and connectors. The ferrule in accordance with the
present invention provides an optical fiber connector having an
optical fiber ferrule, which can accommodate a significantly higher
density of optical fibers, which results in low insertion loss and
low return loss, which provides ease of use and high reliability
with low environmental sensitivity, and which can be fabricated at
low cost. In accordance with the present invention, the density of
terminating optical fibers in a fiber connector may be
significantly increased (e.g., doubled) for a given width or
footprint of the ferrule. The inventive ferrule supports optical
fibers extending from one or more than one optical fiber cable
(e.g., ribbon shaped or rounded cables). The ferrule is structured
for accommodating multiple optical fibers bundled in the same or
separate optical fiber cables. In one embodiment of the present
invention, a second set of terminating optical fibers of a first
fiber cable are arranged in a first row of open grooves, and a
first set of terminating optical fibers of a second fiber cable are
arranged in a second row of open grooves, with the first row
parallel to the second row. In one embodiment, the optical fibers
in the first row are staggered with respect to the optical fibers
of the second row. One embodiment of the present invention is
illustrated in FIGS. 2-6.
[0044] FIG. 2 illustrates a perspective view of an optical fiber
connector 10 having an assembly of components including a ferrule
12 in accordance with one embodiment of the present invention. The
connector 10 further includes a ferrule housing 14 (shown in dotted
lines), a cable boot 16 (shown in dotted lines), and alignment
guide pins 18. FIG. 2 is a simplified illustration of the optical
fiber connector 10. Other than the ferrule 12 that is structured in
accordance with the present invention, the other components of the
optical fiber assembly 10 may further include those found in the
optical fiber assembly shown in FIG. 1 (i.e., the ferrule in
accordance with the present invention may be made backward
compatible to be used in MTO/MPO optical fiber connectors as
offered by US Conec Ltd.). FIGS. 3-6 are various views of the
optical fiber connector 10, with the ferrule housing 14 and cable
boot 16 omitted from view.
[0045] In the illustrated embodiment, the ferrule 12 comprises two
ferrule halves 12a and 12b. The ferrule halves 12a and 12b are
identical in structure in the illustrated embodiment. This
facilitates inventory of identical components. However, the ferrule
halves need not be identical, as long as they are capable of being
mated together to support the optical fibers 20a and 20b.
[0046] Referring also to FIG. 4, each ferrule halves (12a, 12b) has
a generally T-shaped structure, including a head section (36a, 36b)
and a tail section (26a, 26b). The head sections (36a, 36b) each
has an open structure that has a row of open grooves (24a, 24b)
precisely formed thereon in a plane. The two ferrule halves 12a and
12b are stacked, with the head sections (36a, 36b) mated together,
and the rows of grooves 24a and 24b are parallel to each other.
Each row of open grooves (24a, 24b) of a ferrule halve (12a, 12b)
accommodates the optical fibers of a separate optical fiber cable
(22a, 22b).
[0047] In the illustrated embodiment, twelve optical fibers 20a are
held within a jacket 27a to form a first optical ribbon fiber cable
22a, and twelve optical fibers 20b are held within a jacket 27b to
form a second optical ribbon fiber cable 22b (see also FIG. 2). The
terminating optical fibers 20a of the first optical fiber cable 22a
are received in a first row of longitudinal open grooves 24a in the
head section 36a of the first ferrule halve 12a, and the
terminating optical fibers 20b of a second fiber cable 22b are
received in a second row of longitudinal open grooves 24b in the
head section 36b of the second ferrule halve 12b, with the first
row parallel to the second row. The grooves (24a, 24b) receive the
terminating end sections of the optical fibers (20a, 20b) in their
bare form with cladding exposed, without protective buffer and
jacket layers.
[0048] The configuration of the rows of grooves is more clearly
seen from the end view of the ferrule 12 in FIG. 3. In the
illustrated embodiment, each groove has a substantially U-shaped
cross-section with substantially parallel sides. The head sections
36a and 36b of the ferrule halves 12a and 12b are mated with the
grooved surfaces facing towards each other. The grooves 24a and 24b
are staggered, such that optical fibers 20a in the first row are
staggered with respect to the optical fibers 20b in the second row.
In particular, the longitudinal openings of the grooves 24a in the
head section 36a of the first ferrule halve 12a each faces a
longitudinal flat portion 13b (or partition) that separates
adjacent grooves 24b defined in the head section 36b of the second
ferrule halve 12b, and the longitudinal openings of the grooves 24b
in the head section 36b of the second ferrule halve 12b each faces
a longitudinal flat portion 13a that separates adjacent grooves 24a
defined in the head section 36a of the first ferrule halve 12a. The
depth of the grooves is sized to completely receive the optical
fibers. In the illustrated embodiment, the depth of the grooves is
at least D (e.g., 125 .mu.m), the diameter of the bare section of
the optical fibers, with cladding exposed, without protective
buffer and jacket layers, as referenced throughout herein. Each
flat portion (13a, 13b) substantially covers the corresponding
opposing groove opening. In the illustrated embodiment, each
portion (13a, 13b) completely covers the corresponding opposing
groove opening.
[0049] The lateral centerline spacing S of adjacent grooves of a
ferrule halve is equivalent to the width of a groove plus the width
of a separating flat portion (13a, 13b). In the illustrated
embodiment, the width of a flat portion (13a, 13b) is substantially
similar to the width of the U-shaped grooves, which substantially
corresponds to the diameter D of bare sections of optical fibers.
Accordingly for the embodiment illustrated in FIG. 3, the lateral
(in the direction along the plane of the interface between the two
ferrule halves) centerline spacing between adjacent grooves 24a and
24b are substantially equivalent to diameter D of a bare optical
fiber (20a and 20b), and the lateral centerline spacing S is
substantially equivalent to 2D.
[0050] The flat portions (13a, 13b) of one head section (36a, 36b)
serve to cap the openings in the grooves (24a, 24b) of the other
head section. With the depth of the grooves being substantially D,
each flat portion (13a, 13b) and its corresponding opposing groove
together define a space that precisely positions the optical fibers
(20a, 20b).
[0051] The width of the longitudinal opening defined between the
walls along at least a section of the grooves is slightly narrower
than the diameter of the bare optical fibers to create a tight fit
(e.g., an interference fit of 1 .mu.m) with respect to the bare
fibers (bare sections with cladding exposed, without protective
buffer and jacket layers), which allows the end section of an
optical fiber to be inserted laterally into the longitudinal
opening of groove, but which snuggly retains the optical fiber in
the groove. The grooves and the width of the longitudinal groove
openings are shaped and sized to retain the fibers without any
clearance to allow for movement of the fiber relative to the
groove. The grooves may have a rounded bottom to conform to the
external shape of the optical fiber, or a flat bottom or a v-groove
(thus resulting in spaces between the fiber and the wall of the
groove). The rounded bottom is preferable since it increases the
contact area with the fiber and provides more uniform elastic
stress within the fiber. The use of a groove with an interference
fit contrasts with that of the molded ferrule as shown in FIG. 1,
which has a hole that is toleranced to be larger than the diameter
of the optical fiber. Consequently, the oversized hole does not
govern the position of the optical fiber.
[0052] The tail sections (26a, 26b) of the ferrule halves 12a and
12b are thinner than the head sections (36a, 36b). The facing sides
of the tail sections (26a, 26b) together define a recess 28
there-between, which is sized to receive and clamp the jackets 27a
and 27b between the ferrule halves 22a and 22b when they are mated
together in the configuration illustrated in FIG. 2. The jackets
27a and 27b of the fiber ribbon 22a and 22b are fitted within the
recess 28, which provides additional room to accommodate the
thickness of the jackets (27a, 27b) and the protective buffer and
jacket layers on the fibers 20 within the jackets (27a, 27b). The
outsides of the ends of the tail sections (26a, 26b) are thinned,
to fit into a collar 52, thereby clamping the jackets (27a, 27b).
The collar 52 and the tail sections (26a, 26b) together provide
strain relief on the fiber cables (22a, 22b). The alignment pins 18
are supported by the through-holes defined by the open grooves
(54a, 54b) at the head sections (36a, 36b) and holes 29 provided at
the stubs 55 on the collar 52. The collar 52 maintains the head
sections (36a, 36b) of the ferrule halves (12a, 12b) in a mating
configuration. The collar 52 may be deemed a component part of the
ferrule 12.
[0053] It is noted that the collar 52 may be omitted, and the head
sections of the ferrule halves can be maintained in a mating
configuration by laser welding, for example.
[0054] Given that the optical fibers (20a, 20b) are completely
retained in the grooves (24a, 24b), the optical fibers (20a, 20b)
are positioned with precision in the ferrule halves (12a, 12b) by
the grooves (24a, 24b). The position and orientation of the optical
fibers (20a, 20b) is set by the location and parallelism of the
grooves (24a, 24b). Accordingly, the relative locations (e.g.,
spacing) of the optical fibers (20a, 20b) in the ferrule halves
(12a, 12b) are precisely maintained within the ferrule, e.g., for
alignment to fibers in an opposing optical fiber connector (which
has a female structure to receive the alignment pins 18). No
complementary ferrule would be required to securely and precisely
position the fibers within the optical fiber connector. Even though
complementary ferrule halves do not serve any alignment function or
effective support to position the fibers 20b in the ferrule halve
12b, and vice versa, however, by providing two ferrule halves 12a
and 12b each having the above groove clamping structure, the
ferrule halves 12a and 12b together form a ferrule 12 that
accommodates a high fiber density.
[0055] In another aspect of the present invention, the fiber
grooves of the above-disclosed embodiment are precision formed by
high throughput processes, such as stamping and extrusion.
[0056] In one embodiment, the ferrule body is made of a metal
material, which may be chosen to have good thermal dimensional
stability (e.g., Invar).
[0057] One can appreciate instead of ribbon cables, the optical
fibers may be bundled in the form of rounded fiber cables, without
departing from the scope and spirit of the present invention.
[0058] In another embodiment of the present invention, the ferrule
comprises ferrule halves that have an open structure with precision
groove clamping features formed thereon, which can securely hold
optical fibers without the need for epoxy or a complementary
precision part. FIG. 7 illustrates a section of the grooves 24b in
the head section 36b of the ferrule halve 12b. The ferrule halve
12a can have a similar groove structure.
[0059] The grooves 24b are structured to securely retain the fibers
20b (bare sections with cladding exposed, without protective buffer
and jacket layers) by an opening that clamps the fibers 20b, e.g.,
by interference fit (or press fit). The interference fit assures
that the fibers 20b are clamped in place and consequently the
position and orientation of the fibers is set by the location and
parallelism of the grooves 24. The use of an interference fit
contrasts with that of the molded ferrule as shown in FIG. 1, which
has a hole that is toleranced to be larger than the diameter of the
optical fiber. Consequently, the oversized hole does not govern the
position of the optical fiber.
[0060] In the embodiment illustrated in FIG. 7, the width W of the
longitudinal opening 23 of the grooves 24b is made slightly
narrower than the diameter of the optical fibers 20b. In
particular, the opening 23 is defined by lips 25 formed at the
opposing longitudinal edges of the longitudinal opening 23. The
width W of the longitudinal openings 23 is slightly under-sized to
allow the terminating end section of the optical fibers to be
inserted laterally into the longitudinal openings 23 of the grooves
with an interference fit. The magnitude of interference can be set
by the manufacturing process so that loading the fiber into the
groove causes only elastic deformation or minor plastic deformation
in the lip. The grooves should not be plastically deformed;
otherwise it will affect the accuracy of the fiber locations.
[0061] Specifically, to attach the fibers 20b to the head section
36b of the ferrule 12b, the terminating end section of the fibers
20b are pressed lengthwise into the grooves 24b through the
longitudinal openings 23 with a snap action (i.e., not in the axial
direction of the grooves), with the tip of the fibers 20b slightly
protruding beyond the end face of the head section 36b. Further,
the width W of the longitudinal openings 23 and the grooves 24b are
sized and shaped to snuggly retain the section of optical fibers
20b in the grooves 24b without providing any clearance for axial
and lateral movements of the end face of the fibers relative to the
grooves to ensure tight tolerance for optical coupling between end
faces of two adjoining fibers. No epoxy would be required for
retaining the bare fiber sections in the grooves given the
interference along the mating surfaces between the fibers 20b and
the grooves 24b.
[0062] The embodiment shown in FIG. 7 illustrates the
cross-sectional shape of the open grooves 24 generally conforming
to the body of the fibers 20b. The fiber 20b is securely "clamped"
within the groove 24b, with the lips 25 pressing on the top of the
fiber 20b against the bottom and other parts of the groove 24b. In
the illustrated embodiment, the wall of the fiber 20b is shown to
press against the entire wall of the groove 24b, except near the
opening 23. This provides a substantially uniform pressure on
substantially the entire circumference of the fiber, which has less
effect on the optical signals transmitted through the fiber 20b due
to stress-induced changes in fiber or core indices of refraction.
However, it is well within the scope and spirit of the present
invention to structure the grooves in the ferrule with different
cross-sections that would still provide adequate interference fit
to securely retain the fibers 20b in the grooves 24b. For example,
the grooves may have a flat or curved bottom, curved sidewalls, or
flat sidewalls perpendicular or at a slight divergent angle to the
flat bottom (e.g., a v-bottom), and inwardly directing lips to
define the longitudinal opening of the groove. These groove
configurations would result in certain spaces between the curved
fiber walls and the flat or curved sidewalls of the groove, but the
clamping action by the lips 25 and/or vertical walls of the grooves
against the fiber nonetheless would not provide any clearance to
allow for movement of the fibers within the groove. The empty
spaces may be filled with an additional material such as epoxy for
encapsulation purpose, to prevent the entrapment of particles,
especially during mechanical polishing of the ferrule end face.
[0063] Given that the fiber 20b is completely retained in the
groove 24b, and the profile of the groove such as lips 25 and the
bottom of the groove dictate the location of the fiber 20b within
the groove, the fiber 20b is positioned with precision in the
ferrule by the groove. Accordingly, the relative locations (e.g.,
spacing) of the fibers 20b in the ferrule halve 12b are precisely
maintained within the ferrule, e.g., for alignment to fibers in an
opposing optical fiber connector (which has a female structure to
receive the alignment pins 18).
[0064] Similar groove structure can be provided in the head section
36a of the ferrule halve 12a based on the same considerations.
Except for the structure of the groove, the structures of the other
sections of the ferrule halves 12a and 12b and the other components
of the connector 10 remain similar to the embodiment shown in FIG.
2.
[0065] As an example and not limitation, in one embodiment, for
optical fibers 20b made of silica and having a diameter of 125
.mu.m, in a ferrule made of kovar (54% Fe, 29% Ni, 17% Co)
material, the length of the grooves 24b may be 1 to 3 mm, the
diameter or width (i.e., the maximum lateral dimension D) of the
grooves 24b is 0.124 mm, and the width W of the longitudinal
openings 23 is 105 .mu.m. The sidewalls of the groove 23 tilt
inward towards the opening 23 at an angle .theta. of about 5 to 20
degrees with respect to the vertical tangent to the fiber 20b. The
interference provided is about 1 .mu.m, appropriate for the silica
and kovar material. The silica glass is very high strength in
compression, so it will withstand high contact pressures from the
interference fit.
[0066] For a ferrule having the groove clamping structure in
accordance with FIG. 7, no complementary ferrule would be required
to securely and precisely position the fibers within the optical
fiber connector. Even though complementary ferrule halves do not
serve any alignment function or effective support to position the
fibers 20b in the ferrule halve 12b, and vice versa, however, by
providing two ferrule halves 12a and 12b each having the above
groove clamping structure, the ferrule halves 12a and 12b together
form a ferrule 12 that accommodates a high fiber density.
[0067] It can be appreciated from the foregoing that open channels
or grooves can be more easily and precisely formed, compared to
forming through-holes in a plastic ferrule block practiced in the
prior art, such as the connector shown in FIG. 1. In one
embodiment, the grooves are initially formed (e.g., by precision
stamping), followed by narrowing of the openings of the grooves,
for example, by stamping or punching the top surface of the ferrule
body to push the material at the two opposing edges of the opening
into the opening in the groove to form a lip, or laser machining to
melt the material at the corners of the opening to flow into the
opening of the groove to form a lip. In another embodiment, the
clamping grooves may be precision formed by extrusion. Further
information on the high throughput forming of the clamping grooves
shown in FIG. 7 has been disclosed in U.S. patent application Ser.
No. 13/440,970, filed Apr. 5, 2012, which was commonly assigned to
the assignee of the present invention. This application is fully
incorporated by reference as if fully set forth herein.
[0068] A precision stamping process and apparatus has been
disclosed in U.S. Pat. No. 7,343,770, which was commonly assigned
to the assignee of the present invention. This patent is fully
incorporated by reference as if fully set forth herein. The process
and stamping apparatus disclosed therein may be adapted to
precision stamping the ferrules of the present invention.
[0069] FIGS. 8-12 illustrate a high density optical fiber connector
in accordance with another embodiment of the present invention.
With the exception of the ferrule, the general structure of the
optical fiber connector 110 in this embodiment is similar to the
structure of the optical fiber connector 10 in the embodiment of
FIGS. 2-6. The optical fiber connector 110 includes a ferrule 112
comprising two ferrule halves 112a and 112b, a collar 52, a ferrule
housing and a cable boot (similar to those shown in FIG. 2 but are
omitted from view for simplicity). The structure of the collar 52
is similar to that shown in FIG. 2. The general structure of the
ferrule halves 112a and 112b are similar to the T-shaped structure
of the ferrule halves 12a and 12b in FIG. 2, except for the fiber
grooves.
[0070] In this embodiment, the ferrule 112 is configured to align
the terminating optical fibers (20a, 20b) of ribbon cables (22a,
22b) in a row in a plane, whereby the axis of adjacent optical
fibers (20a, 20b) are spaced at a distance substantially
corresponding to the diameter D of the bare optical fibers (without
buffer and protective layers, with the cladding exposed). As
illustrated in FIG. 11, the terminating optical fibers (20a, 20b)
are arranged side-by-side in a row within a plane in the ferrule,
with adjacent optical fibers touching each other. The optical
fibers 20a and 20b alternately extend from the different optical
fiber cables 22a and 22b. In the row of terminating optical fibers,
optical fibers 20a alternate with optical fibers 20b in a staggered
and interleaved manner. In the illustrated embodiment, the ferrule
112 is provided with at least a single wide flat opening 124 that
receives and accommodates the row of optical fibers (20a, 20b) in
the side-by-side touching configuration. The wide flat opening 124
is defined by the head sections (136a, 136b) of the complementary
ferrule halves 112a and 112b. As more clearly seen in FIG. 11, each
head sections (136a, 136b) has a wide flat section (150a, 150b)
with a curved lip (152a, 152b) (which combination of structures may
be deemed to be an open groove). When the head section 136a of the
ferrule halve 112a is mated to the head section 136b of the ferrule
halve 112b, the wide flat section 150a is parallel to the flat
section 150b, which together defines a space between the flat
sections (150a, 150b) within the lips (152a, 152b) to accommodate
the row of optical fibers (20a, 20b) in a tight side-by-side
configuration. The single flat opening 124 provides a simple
structure to precisely align the optical fibers (20a, 20b) in the
optical connector 110, by relying on the inherently precise
dimension of the optical fibers to provide the needed spatial
spacing in the row of optical fibers. Given the flat structure of
the flat sections (150a, 150b), the ferrule halves can be more
easily precision formed (e.g. by stamping) with tight tolerance.
The collar 52 maintains the head sections (136a, 136b) of the
ferrule halves (112a, 112b) in a mating configuration. The collar
52 may be deemed a component of the ferrule 112.
[0071] In the embodiment shown in FIG. 11, the holes for the
alignment pins 18 are defined by a combination of a circular
cylindrical open groove provided on one ferrule halve and a square
cylindrical open groove provided on the other ferrule halve. In the
illustrated embodiment, the ferrule halve 112a is provided with the
circular cylindrical groove 154, and the ferrule halve 112b is
provided with the square cylindrical groove 156. However, it is
within the scope and spirit of the present invention to provide a
circular cylindrical groove and a square cylindrical groove on each
ferrule halve, so as to provide ferrule halves that are symmetrical
and/or identical. The circular cylindrical groove 154 can be
precisely formed (e.g., by precision stamping), and the depth of
the square cylindrical groove 156 can be precisely formed without
requiring precision forming the walls of the square cylindrical
groove. Variations in lateral dimension of the square groove 156 do
not affect pin alignment. When the head sections (136a, 136b) are
mated together, the combination of the precisely defined circular
cylindrical walls and the precise depth of the square cylindrical
wall accurately and precisely position the alignment pins 18.
Similar pin alignment support structure may be provided as in the
earlier embodiments of FIGS. 2-6.
[0072] FIG. 13 illustrates an alternate embodiment of an optical
fiber connector 110', in which the holes for alignment pins 18 are
defined by the combination of circular cylindrical open grooves
provided on the head sections (136a', 136b') of the half ferrules
(112a', 112b'). Comparing to FIG. 11, the remaining structures of
the optical fiber connector 110' remain similar to the embodiment
shown in FIGS. 8-12.
[0073] There may be more than one flat opening 124, each receiving
and accommodating a set of optical fibers supported in a row within
a plane. In another embodiment, the terminating optical fibers are
supported in more than one row/layer within a ferrule/connector
(not shown), by splitting a ferrule halve into two or more
layers.
[0074] In an alternate embodiment (not shown), the ferrule halves
may be made more symmetrical, wherein each ferrule halve is
structured with a head section having a similar slight U-shaped
wide trough defined by a wide flat section flanked by a curved lip
at each edge. When the ferrule halves are mated, the U-shaped wide
troughs of the ferrule halves together define an enclosed space
that accommodates a row of staggered/alternating optical fibers
(20a, 20b) in a tight side-by-side configuration. The support holes
of the alignment pins may also be made symmetrical in this
embodiment (e.g., with symmetrical open grooves), or may remain
asymmetrical as shown in FIG. 11.
[0075] FIGS. 14-18 illustrate a high density optical fiber
connector in accordance with a further embodiment of the present
invention. In this embodiment, the optical fiber connector 210
includes a single piece ferrule 212, a frame 252, a ferrule housing
and a cable boot (similar to those shown in FIG. 2 but are omitted
from view for simplicity). In this embodiment, the ferrule 112 is
configured to align the terminating optical fibers (20a, 20b) of
ribbon cables (22a, 22b) in two rows of open grooves (224a, 224b)
in two parallel planes. The optical fibers 20a and 20b alternately
extend from the different optical fiber cables 22a and 22b. As
illustrated in FIG. 16, the terminating optical fibers 20a of the
first fiber cable 22a are supported in open grooves 224a provided
on the top surface at the perimeter of the ferrule 212, and the
terminating optical fibers 20b of the second fiber cable 22b are
supported in open grooves 224b provided on the bottom surface at
the perimeter of the ferrule 212. The grooves (224a, 224b) can take
the same structure as grooves 24 on the surfaces of ferrule halves
(12a, 12b) in the embodiment of FIG. 3, or the grooves 24b in the
embodiments of FIG. 7.
[0076] Each open groove (224a, 224b) completely receives the
corresponding optical fiber (20a, 20b). The frame 252 has inside
flat sections (250a, 250b) facing the grooves (224a, 224b) when the
ferrule 212 is inserted into the frame 252. The flat sections
(250a, 250b) completely cover the grooves (224a, 224b). Given that
the optical fibers (20a, 20b) are completely retained in the
grooves (224a, 224b), the optical fibers (20a, 20b) are positioned
with precision in the ferrule halves (12a, 12b) by the grooves
(224a, 224b). The position and orientation of the optical fibers
(20a, 20b) is set by the location and parallelism of the grooves
(224a, 224b). Accordingly, the relative locations (e.g., spacing)
of the optical fibers (20a, 20b) in the ferrule halves (12a, 12b)
are precisely maintained within the ferrule, e.g., for alignment to
fibers in an opposing optical fiber connector (which has a female
structure to receive the alignment pins 18). No complementary
ferrule or frame would be required to securely and precisely
position the fibers within the optical fiber connector 210. Even
though the frame 252 does not serve any alignment function or
effective support to accurately position the fibers (20a, 20b) in
the ferrule 212, however, the frame 252 serves to cover the grooves
(224a, 224b) to prevent accidental dislodgment of the optical
fibers.
[0077] The jackets (27a, 27b) of the fiber cables (22a, 22b) are
inserted through openings in the strain relief anchor 256, and are
supported on the extension 258. The extension 258 has a stub 260
extending into a central opening 262 in the ferrule 212. Alignment
pins 18 are inserted into the space or holes 264 provided in the
ferrule 212, extending into holes 266 provided in the strain relief
anchor 256. The holes 264 are defined by a split 268 provided at
each edge of the ferrule 212. The thickness of the material of at
least one prong 270 defining the split is made thinner, to
facilitate flexing of the prong 270. A flexure is formed, which
defines a compliant structure that clamps the alignment pins to
accurately and precisely locate the alignment pins for alignment to
another complementary optical fiber connector. The compliant
clamping structure makes it possible for the alignment pins to be
inserted into the holes 264 with no clearance needed, thus not
requiring epoxy to fill any clearance between the holes and the
alignment pins.
[0078] While the frame 252 is shown to surround the perimeter of
the ferrule 212 in the illustrated embodiment, a frame may be
structured to cover the grooves (224a, 224b) without surrounding
the perimeter of the ferrule 212. For example, a frame may be
structured to be a partial ring (e.g., C-shaped) in the end view of
FIG. 16 instead of a complete ring (not shown). Alternatively, the
frame 252 may be omitted, and the anchor 256 may be provided with
two extending flat fingers covering the grooves (224a, 224b) on the
top and bottom surface of the ferrule 212 (not shown).
[0079] The compliant alignment pin clamping structure is the
subject matter of a separate U.S. patent application concurrently
filed herewith (attorney docket no. 1125/239). Such application is
incorporated by reference as if fully set forth herein.
[0080] As were in the case of the previous embodiments, the ferrule
212, frame 252 and/or the anchor 256 may be made of metal and
formed by high-throughput stamping and/or extrusion processes. In
one embodiment, the ferrule body is made of a metal material, which
may be chosen to have high stiffness (e.g., stainless steel),
chemical inertness (e.g., titanium), high temperature stability
(nickel alloy), low thermal expansion (e.g., Invar), or to match
thermal expansion to other materials (e.g., Kovar for matching
glass).
[0081] It is well within the scope and spirit of the present
invention, to provide a ferrule structure that combines the fiber
support structure of embodiment of FIGS. 8-13 with the multiple
level fiber support structure of embodiment of FIGS. 14-18, to
further improve the density of fibers on the ferrule without
significantly increasing the footprint or form factor of the
ferrule/optical fiber connector. For example, instead of providing
grooves (224a, 224b) on the ferrule 212 in the embodiment of FIGS.
14-18, the grooves (224a, 224b) can be replaced with wide flat
sections that mate with complementary features on a frame to form
two wide flat openings, in each of which two sets of fibers can be
retained in an interleaved, tight, side-by-side configuration
similar to the embodiment of FIGS. 8-13. This would form a ferrule
and optical fiber connector that accommodate 4.times.12=48
fibers.
[0082] While the above described embodiments referred to two
separate fiber bundles (e.g., 2 fiber cables of 12 fibers each), it
is clear that the inventive high density ferrule structure is also
applicable to a single fiber bundle, e.g., 24 fibers of a single
bundle supported by two separate row of open grooves (e.g.,
staggered) or in a single row in an interleaved fashion.
[0083] The ferrule in accordance with the present invention
overcomes many of the deficiencies of the prior art. The density of
optical fibers accommodated in an optical connector is
significantly increased (e.g., doubled for a given width or
footprint of the ferrule), without significant increase in
thickness of the ferrule. By not having any clearance between the
grooves in the ferrule and the fibers and alignment pins which
would otherwise lead to movements between the parts, the alignment
pins and the fibers can be more accurately located relative to each
other. The spacing of the fibers and pins can be better maintained
under changes in environmental conditions, for example, as the
ferrule can accommodate more dimensional variations without
affecting specified alignment tolerances. The optical fiber
connector thus formed results in low insertion loss and low return
loss. The open groove ferrule configuration also allows ease of
attaching terminating fiber ends to the ferrules, compared to
threading epoxy coated fibers through holes in prior art ferrules.
Without using epoxy, the reliability of the optical fiber connector
is not affected by any aging/creeping of epoxy material. By
selecting appropriate materials for the ferrule, the performance of
the optical fiber connector is less sensitive to thermal
variations. The open structure of the ferrule lends itself to mass
production processes such as stamping and extrusion, which are low
cost, high throughput processes.
[0084] While the invention has been particularly shown and
described with reference to the preferred embodiments, it will be
understood by those skilled in the art that various changes in form
and detail may be made without departing from the spirit, scope,
and teaching of the invention. Accordingly, the disclosed invention
is to be considered merely as illustrative and limited in scope
only as specified in the appended claims.
* * * * *