Note: Descriptions are shown in the official language in which they were submitted.
CA 02444843 2012-12-04
D-SHAPED WAVEGUIDE AND OPTICAL COUPLER USING THE WAVEGUIDE
Technical Field
This invention relates to optical waveguides and couplers, and more
particularly to
optical waveguides and couplers, having a large outer diameter and
substantially D-shaped.
Background Art
It is known that optical fibers having non-circular cross-sectional outer
shapes, such
as a D-shaped fiber, are used for various purposes, such as coupling light (or
the evanescent
field) into and/or out of the fiber and/or for mechanically determining,
orienting or aligning
the polarization states of a fiber. Some uses of such D-shaped fiber is
discussed in US
Patents 4,386,822; 4,054,366; 4,669,814; 4,387,954; 4,589,725; 4,054,366;
3,887,264;
3,823,997. However, in such cases, the fiber is either highly lossy or very
difficult to
manufacture and/or very difficult to use because they are very delicate and
fragile. In
particular, when a portion of a cladding of an optical fiber is removed to
create a D-shaped
fiber portion, it is very fragile due to the very small diameter of the
cladding, e.g., about 125
microns.
Summary of the Invention
Objects of the present invention include provision of an optical waveguide
that
permits access to the evanescent field and is easy to use and manufacture.
According to the present invention, an optical waveguide includes an outer
cladding
having at least one inner core disposed therein, which propagates light in
substantially a few
- 1 -
CA 02444843 2003-10-16
WO 02/075404
PCT/US02/09111
spatial modes. A portion of the optical waveguide has a generally D-shaped
cross-section
and a transverse outer waveguide dimension that is greater than about 0.3 mm.
The present invention provides a significant improvement over prior art
optical
fibers by providing a glass (or silica-based) optical waveguide having a D.-
shape and a large
outer dimension which allows for access to the evanescent field and/or
attachment or
alignment of the waveguide without the problems associated with D-shaped
optical fiber.
The invention provides a flat surface for access to the evanescent field for
optical coupling
into or out of the waveguide, and/or for attachment or alignment purposes. The
waveguide
may resemble a short "block" or a longer "cane" type, depending on the
application and
dimensions used.
The large outer diameter of the D-shaped waveguide, has inherent mechanical
rigidity which improves packaging options and reduces bend losses. Also, the
large outer
diameter allows the waveguide to resist damage from handling which typical
bare optical
fibers would exhibit. Also, the D-shaped waveguide may be made in long lengths
(on the
order of many inches, feet, or meters) then cut to size as needed for the
desired application.
Also, the large D-shaped waveguide size allows the waveguide to be further
ground,
polished etched or machined while retaining its mechanical strength. Also, the
waveguide
has a large end surface area to attach an optical fiber pigtail to the
waveguide or for
attaching multiple optical fibers to multiple cores in the waveguide. Further,
because the
waveguide has a large outer diameter compared to that of a standard optical
fiber (e.g.,
about 125 microns), the waveguide does not need to be coated with a buffer (or
jacket) and
then stripped to form the D-shape or to write gratings therein, thereby
requiring less steps
than that needed for conventional optical optical fibers, and preserving the
structural
integrity and optical properties of the waveguide. Thus, the present invention
is easily
manufacturable and easy to handle.
Further, the invention provides some advantages for grating writing into the
waveguide in the D-shaped section due to the flat surface, such as lower
power, better
optical absorption by the core, and/or easier alignment. In addition, the
invention allows for
the creation of multi-core devices and couplers.
One or more gratings may be embedded (or imprinted) in the D-shaped waveguide.
Also, one or more gratings or a plurality of cores or concentric or ring
cores, may be located
within the waveguide cladding, thereby allowing for multiple waveguiding paths
within the
waveguide.
- 2 -
CA 02444843 2003-10-16
WO 02/075404
PCT/US02/09111
The foregoing and other objects, features and advantages of the present
invention
will become more apparent in light of the following detailed description of
exemplary
embodiments thereof.
Brief Description of the Drawings
Fig. 1 is a perspective view of a large diameter D-shaped optical waveguide,
in
accordance with the present invention.
Fig. 2 is a cross-section of a large diameter D-shaped optical waveguide, in
accordance with the present invention.
Fig. 3 is a top view of a large diameter D-shaped waveguide, in accordance
with the
present invention.
Fig. 4 is a side view of a large diameter D-shaped waveguide, in accordance
with the
present invention.
Fig. 5 is a side view of a large diameter D-shaped waveguide having a free
space
optical input, in accordance with the present invention.
Fig. 6 is a perspective view of a large diameter D-shaped single pigtail ended
optical
waveguide, in accordance with the present invention.
Fig. 7 is a top view of a large diameter D-shaped single pigtail ended
waveguide, in
accordance with the present invention.
Fig. 8 is a side view of a large diameter D-shaped single pigtail ended
waveguide, in
accordance with the present invention.
Fig. 9 is an end cross-section view of a large diameter D-shaped optical
waveguide
having a single optical cores, in accordance with the present invention.
Fig. 10 is an end cross-section view of a large diameter D-shaped optical
waveguide
having an optical core and an inner cladding, in accordance with the present
invention.
Fig. 11 is an end cross-section view of a large diameter D-shaped optical
waveguide
having an optical core and an inner cladding which is partially removed, in
accordance with
the present invention.
Fig. 12 is an end cross-section view of a large diameter D-shaped optical
waveguide
having an optical core and an inner cladding, in accordance with the present
invention.
Fig. 13 is a perspective view of a large diameter D-shaped optical waveguide
having
an optical core and an inner cladding, in accordance with the present
invention.
- 3 -
CA 02444843 2003-10-16
WO 02/075404
PCT/US02/09111
Fig. 14 is an end cross-section view of a large diameter D-shaped optical
waveguide
having a substantially D-shaped geometry, in accordance with the present
invention.
Fig. 15 is an end view of a large diameter D-shaped optical waveguide having a
plurality of concentric optical cores, in accordance with the present
invention.
Fig. 16 is an end cross-section view of a large diameter D-shaped optical
waveguide
having a plurality of optical cores, in accordance with the present invention.
Fig. 17 is an end view of a large diameter D-shaped optical waveguide having
an
elliptical core, in accordance with the present invention.
Fig. 18 is a side view of two large diameter D-shaped optical waveguides, in
accordance with the present invention.
Fig. 19 is a side view of a four port coupler formed from the two large
diameter D-
shaped optical waveguides of Fig. 18, in accordance with the present
invention.
Fig. 20 is an end cross-section view of two coupled large diameter D-shaped
optical
waveguides having a plurality of optical cores, in accordance with the present
invention.
Fig. 21 is an end cross-section view of an alternative embodiment of two
coupled
large diameter D-shaped optical waveguides having a plurality of optical
cores, in
accordance with the present invention.
Fig. 22 is an end cross-section view of an alternative embodiment of two
coupled
large diameter D-shaped optical waveguides having a plurality of optical
cores, in
accordance with the present invention.
Fig. 23 is a top view of an optical coupler formed from the two large diameter
D-
shaped optical waveguides, in accordance with the present invention.
Fig. 24 is an end cross-section view of a large diameter D-shaped optical
waveguide
having a grating writing beam incident on it, in accordance with the present
invention.
Fig. 25 is a perspective view of a large diameter D-shaped optical waveguide
disposed on a planar waveguide, in accordance with the present invention.
Fig. 26 is a side view of Fig. 25, in accordance with the present invention.
Fig. 27 is a side view of a tube fused to an optical fiber, in accordance with
the
present invention.
Fig. 28, is a side view of a large diameter D-shaped optical waveguide having
a
grating therein, in accordance with the present invention.
Fig. 29, is a side view of a large diameter D-shaped optical waveguide having
a
blazed grating therein, in accordance with the present invention.
- 4 -
CA 02444843 2012-12-04
Fig. 30, is a side view of a large diameter D-shaped optical waveguide having
an
alternative blazed grating therein, in accordance with the present invention.
Fig. 31, is a side view of a large diameter D-shaped optical waveguide having
a
plurality of gratings therein, in accordance with the present invention.
Fig. 32 is a side view of an optical coupler formed from the two large
diameter
D-shaped optical waveguides, in accordance with the present invention.
Best Mode for Carrying Out the Invention
Referring to Figs. 1-4, a large diameter D-shaped optical waveguide device 9,
has a
circular waveguide portion 11, a D-shaped waveguide portion 10, and has at
least one core
12 surrounded by a cladding 14. The waveguide device 9 comprises silica glass
(Si02) based
material having the appropriate dopants, as is known, to allow light 15 to
propagate in either
direction along the core 12 and/or within the waveguide device 9. The core 12
has an outer
dimension dl and the waveguide device 9 has an outer dimension d2.
The cladding 14 has an outer dimension d2 of at least about 0.3 mm and the
core 12
has an outer dimension dl such that it propagates only a few spatial modes
(e.g., less than
about 6). For example for single spatial mode propagation, the core 12 has a
substantially
circular transverse cross-sectional shape with a diameter dl less than about
12.5 microns,
depending on the wavelength of light. One standard telecommunications nominal
core
diameter is 9 microns (and outer waveguide diameter of 125 microns). The
invention will
also work with larger or non-circular cores that propagate a few (less than
about 6) spatial
modes, in one or more transverse directions. Further, the optical waveguide
device 9 may be
a birefringent, polarization maintaining, polarizing, multi-core, or multi-
cladding optical
waveguide (discussed more hereinafter). Also, the core 12 of the waveguide
device 9 need
not be located in the center (left-to-right) of the waveguide device 9 but may
be located
anywhere in the waveguide device 9 that provides the functions described
herein.
Also, other materials for the optical waveguide device 9 may be used if
desired. For
example, the waveguide 10 may be made of any glass material, e.g., silica,
phosphate glass,
or other glasses, or made of solely plastic. For high temperature
applications, an optical
waveguide made of a glass material is desirable. Also, the waveguide 10 may
resemble a
short "block" type or a longer "cane" type geometry, depending on the length
of the
waveguide and outer dimension of the waveguide.
- 5 -
CA 02444843 2012-12-04
Incoming light 15 may be launched into the waveguide 10 and/or the core 12 by
splicing a suitable standard optical fiber 22 (having a cladding 26 and a core
25) to one or
both axial ends 28 of either the circular portion 11 of the waveguide or D-
shaped portion 10
of the waveguide (discussed herein after) using any known or yet to be
discovered
techniques for splicing fibers or coupling light from an optical fiber into a
larger waveguide,
that provides acceptable optical losses for the application. Referring to Fig.
5, instead of
using an optical fiber, incident light 34 may be directly incident on the core
or be focussed
into the core 12 by a lens 32, which focuses input light 30. Figs. 6-8, show
the case where
the optical fiber 22 is attached (or pigtailed) to only one end of the
circular waveguide
portion 11.
The large diameter (or cane) circular waveguide portion 11 has a length Li and
a
diameter d2 and provides an optical interface to allow easy axial coupling (or
pigtailing) of
the optical fiber 22 to the D-shaped waveguide portion 10. The circular
portion 11 is only
required if the distance d4 of the large diameter D-shaped waveguide portion
10 does not
allow enough space for the fiber 22 to be attached, provided a fiber is used
for carrying the
light into or out of the waveguide device 9.
The D-shaped portion 10 has a flat surface 100 and a rounded outer surface
104, and
has a length 12 and the outer transverse waveguide dimension d2 which are
determined by
the application and the desired rigidity of the device.
The D-shaped portion 10 is used to couple light into or out of the core 12 or
couple
with the evanescent field of the light in the cladding 14 (discussed more
hereinafter). The D-
shaped portion 10 may also or alternatively be used to orient the waveguide
along a
predetermined polarization axis. The flat surface 100 may be spaced any
predetermined
distance d4 from the center of the core 12. However, for coupling the
evanescent field, the
distance d4 should be no more than about 3 average core diameters.
Referring to Fig. 15, the waveguide may have multiple concentric cores 68,70
or a
ring or annulus core 72 (or inner claddings). In that case, the dimension dl
for calculating
the minimum dimension for the core would be the core having the smallest outer
dimension.
As used herein, the term "waveguiding region" refers to the core and any
additional cores or
inner claddings or outer cores that serve to guide the light in the waveguide.
For example, Figs. 9 and 10 illustrates the flat surface 100 passing through
only the
outer cladding 14 of the D-shaped waveguide 10. Alternatively, the flat
surface 100 may
pass through both an inner cladding 102 and the outer cladding 14 as shown in
Figs. 12 and
- 6 -
CA 02444843 2003-10-16
WO 02/075404
PCT/US02/09111
14. The flat surface 100 may even pass through the core 12, inner cladding 102
and outer
cladding 14 as shown in Fig. 12.
Figs. 10¨ 14 illustrate a D-shaped waveguide 10 having an inner core 12, an
inner
cladding 102 disposed around the core, and an outer cladding 14 disposed
around the inner
cladding. In Fig. 10, the waveguide 10 is formed to efficiently allow light to
propagate
along its length with minimal losses from the inner cladding 102. To this end,
the
waveguide 10 has various refractive indices through its cross section. For
example, in one
embodiment, the outer cladding 14 has the lowest refractive index, the core 12
has the
highest refractive index and the inner cladding 102 has a refractive index
higher than the
outer cladding 14, but lower than the refractive index of the core. Other
configurations are
possible, including matched indices and depressed inner clad designs, wherein
the index of
refraction of the inner cladding is less than the index of refraction of the
outer cladding,
which are contemplated within the scope of the present invention.
While the D-shaped waveguides 10 described hereinbefore includes a flat
surface
100 and a rounded outer cladding 14, the present invention contemplates other
shapes for
the rounded outer cladding portion 104. For instance, Fig. 14 illustrates a D-
shaped
waveguide 10 wherein the outer cladding 14 has sections 108 of the outer
perimeter 104
that are flat, such as a polygonal shape, or partially rounded as shown by the
lines 106,
provided the shape is not a planar waveguide (rectangular) shape.
Referring to Fig. 16, alternatively, two or more cores 60,62,63,65 may be
located
within the waveguide 10. The core 12 (Figs. 1-4) may be positioned axially
anywhere
within the waveguide 10 and need not be centered along the center line of the
waveguide
10. Also, cores (Fig. 5) may be located close to each other (to be
substantially touching or
optically coupling to each other) as shown by the cores 63,65, and/or
separated by any
desired distance within the waveguide 10, as shown by cores 60,62. For
multiple cores with
different diameters, each of the cores should meet the requirements described
herein for the
core 12.
Referring to Fig. 17, alternatively, the core 12 may have an asymmetrical end
cross-
sectional shape such as elliptical shape 64 or a rectangular shape 66. For
asymmetrical end
cross-sectional shapes, the smaller dimension dl would be used for determining
the
maximum core dimension. In that case, the core may propagate only one mode in
the
direction of the dimension dl and propagate a few modes in the other
direction. Also, the
- 7 -
CA 02444843 2012-12-04
end cross-sectional shape of the core 12 may have other shapes such as a
square, clam-shell,
octagonal, multi-sided, or any other desired shapes.
Referring to Fig. 28, the waveguide 10 may have a Bragg grating 16 impressed
(or
embedded or imprinted) therein. The Bragg grating 16, as is known, is a
periodic or
aperiodic variation in the effective refractive index and/or effective optical
absorption
coefficient of an optical waveguide, such as that described in US Patent No.
4,725,110 and
4,807,950, entitled "Method for Impressing Gratings Within Fiber Optics", to
Glenn et al;
and US Patent No. 5,388,173, entitled "Method and Apparatus for Forming
Aperiodic
Gratings in Optical Fibers", to Glenn. The grating 16 may be in the core 12
and/or in the
cladding 14 (see Fig. 30). Any wavelength-tunable grating or reflective
element embedded,
etched, imprinted, or otherwise formed in the waveguide 10 may be used if
desired. The
waveguide 10 may be photosensitive if a grating 16 are to be written into the
waveguide 10.
As used herein, the term "grating" means any of such reflective elements.
Further, the
reflective element (or grating) 16 may be used in reflection and/or
transmission of light.
The grating 16 has a grating length Lg, which is determined based on the
application
and may be any desired length. A typical grating 16 has a grating length Lg in
the range of
about 3 - 40 mm. Other sizes or ranges may be used if desired. The length Lg
of the grating
16 may be shorter than or substantially the same length as the length L of the
waveguide 10.
If a grating 16 is in the waveguide 10, light 34 is incident on the grating 16
which
reflects a portion thereof as indicated by a line 36 having a predetermined
wavelength band
of light, and passes the remaining wavelengths of the incident light 34
(within a
predetermined wavelength range), as indicated by a line 38 (as is known).
Referring to Fig. 29, a blazed grating 40 may be disposed in the waveguide 10
having a blaze angle with respect to the longitudinal axis of the waveguide
10, such as is
described in US Patents 5,042,897, "Optical Waveguide Embedded Light
Redirecting Bragg
Grating Arrangement", issued Aug. 27, 1991; and 5,061,032 "Optical Waveguide
Embedded
Light Redirecting And Focusing Bragg Grating Arrangement" issued Oct. 29,
1991, both to
Meltz et al. As is known a blazed grating 40 reflects a predetermined
wavelength band of
incident light 42 out of the waveguide as indicated by a line 44. Also, the
blazed grating 40
couples incident light 26 at this predetermined wavelength into the waveguide
as indicated
by a line 48.
- 8 -
CA 02444843 2012-12-04
Referring to Fig. 30, alternatively, a blazed grating 41 may reside partially
or
completely in the inner cladding 102, and performs the same basic function as
that described
with Fig. 28; however, it may have less back-reflection, such as is described
in copending
US Patent Application, published as 2003/0185509A1 on Oct 2, 2003, filed
contemporaneously herewith and in I. Riant, et al, "New and efficient
technique for
suppressing the peaks induced by discrete cladding mode coupling in fiber
slanted Bragg
grating spectrum", Optical Fiber Communication Conference 2000, pgs. 118/TuH3-
1 to
120/TuH3-3.
Referring to Fig. 31, for any of the embodiments described herein, instead of
a single
grating within the waveguide 10, two or more gratings 50,52 may be embedded in
the
waveguide 10. The gratings 50,52 may have the same reflection wavelengths
and/or profiles
or different wavelengths and/or profiles. The multiple gratings 50,52 may be
used
individually in a known Fabry Perot arrangement.
Further, one or more fiber lasers, such as that described in US Patent Nos.
5,305,335,
"Single Longitudinal Mode Pumped Optical Waveguide Laser Arrangement" may be
in the
D-shaped waveguide 10. In that case, the gratings 50,52 form a cavity and the
waveguide 10
at least between the gratings 50,52 (and may also include the gratings 50,52,
and/or the
waveguide 10 outside the gratings, if desired) at least a portion of which is
doped with a rare
earth dopant, e.g., erbium and/or ytterbium, etc.
Another type of fiber laser that may be used is a distributed feedback (DFB)
fiber
laser, such as that described in V.C. Lauridsen, et al, "Design ofDFB Fibre
Lasers",
Electronic Letters, Oct. 15, 1998, Vol.34, No. 21, pp 2028-2030; P. Varming,
et al, "Erbium
Doped Fiber DGB Laser With Permanent rc/2 Phase-Shift Induced by UV Post-
Processing",
100C'95, Tech. Digest, Vol. 5, PDI-3, 1995; US Patent No. 5,771,251, "Optical
Fibre
Distributed Feedback Laser", to Kringlebotn et al; or US Patent No. 5,511,083,
"Polarized
Fiber Laser Source", to D'Amato et al. In that case, a grating 84 is written
in a rare-earth
doped core and configured to have a phase shift of 'A/2 (where 'A is the
lasing wavelength) at
a predetermined location 56 near the center of the grating 16 which provides a
well defined
resonance condition that may be continuously tuned in single longitudinal mode
operation
without mode hopping, as is known. Alternatively, instead of a single grating,
the two
gratings 50,52 (Fig. 3) may be placed close enough to form a cavity having a
length of (N +
- 9 -
CA 02444843 2003-10-16
WO 02/075404 PCT/US02/09111
1/2)A., where N is an integer (including 0) and the gratings 50,52 are in rare-
earth doped fiber.
The gratings 50,52 may have the same reflection wavelengths and/or profiles or
different
wavelengths and/or profiles.
Alternatively, the DFB laser 84 may be located between the pair of gratings
50,52
where the core 12 is doped with a rare-earth dopant at least a portion of the
distance
between the gratings 50,52. Such configuration is referred to as an
"interactive fiber laser",
such as is described in US Patent 6,018,534, "Fiber Bragg Grating DFB-DBR
Interactive
Laser and related Fiber Laser Sources", to J.J. Pan et al. Other single or
multiple fiber laser
configurations configurations may be disposed in the waveguide 10 if desired,
such as those
described in US Patent 5,910,962, entitled "Multi-wavelength Fiber Laser
Source for Fiber
Optic Networks" to Pan, et al, or US Patent 5,892,781, entitled "High Output
Fiber
Amplifier/Lasers for Fiber Optic Networks", to Pan et al.
We have found that an outer diameter d2 of greater than about 300 microns (0.3
mm) provides acceptable results (without buckling or degrading) for handling,
grinding,
polishing, attaching, grating writing, which is much superior over prior art D-
shaped fiber.
The longer the desired length of the D-shaped section, the larger the outer
diameter d2 will
need to be to provide acceptable performance and rigidity.
The large diameter D-shaped optical waveguide 10 may be formed by obtaining
the
circular waveguide 11 (described hereinafter) and then, a portion of the
cladding 14 and/or
core 12 (or inner cladding 102 if applicable) is removed to form the surface
100. The
surface 100 may be formed by micro machining, grinding, polishing, etching or
otherwise
formed in waveguide 10 using known techniques. The face of the surface 100 may
be
further polished or fire polished or otherwise treated to enhance the optical
characteristics.
The D-shaped waveguide portion 10 may be made using fiber drawing techniques
(discussed hereinafter) now known or later developed that provide the
resultant desired
dimensions for the core and the cladding. In that case, the external surface
of the waveguide
will likely be optically flat, thereby allowing Bragg gratings to be written
through the
cladding similar to that which is done for conventional optical fiber.
Alternatively, the D-
shaped section may be made by obtaining a circular cane waveguide having the
desired
outer dimension and then polishing the outer surface and fire polishing if
necessary to
provide the desired flatness. The circular waveguide may be obtained (as
discussed
hereinafter, by drawing the cane waveguide, or by collapsing and fusing a tube
to an optical
fiber. In the event that the surface 100 is not optically flat the grating 16
may be written into
-10-
CA 02444843 2003-10-16
WO 02/075404 PCT/US02/09111
the waveguide 10 using an optically flat window and index matching fluid
between the
window and the surface 100, such as is discussed in US Patent 6,298,184,
"Forming a Tube-
Encased Fiber Grating", to Putnam.
Referring to Fig. 24, the invention may also provide some advantages for
grating
writing into the waveguide in the D-shaped section. For example, there may be
less light
scatter of the grating writing beams 58 during grating writing due to the flat
surface 100 as
opposed to writing a grating in a curved surface waveguide which causes a high
amount of
scatter. Further, if the core 12 is placed close to the surface, e.g., for an
evanescent-wave
coupler, there may likely be more optical power absorption into the core 12 of
the grating
writing beams 58 as there is less glass between the core 12 and the writing
beams 58. Also,
the flat surface 100 may be used for accurate grating writing alignment.
Because the waveguide 10 has a large outer diameter compared to that of a
standard
optical fiber (e.g., 125 microns), the waveguide 10 does not need to be coated
with a buffer
(or jacket) and then stripped to write the gratings, thereby requiring less
steps than that
needed for conventional optical fiber gratings, and preserving the structural
integrity and
optical properties of the waveguide.
-11-
CA 02444843 2003-10-16
WO 02/075404 PCT/US02/09111
Referring to Figs. 25 and 26, the D-shaped waveguide 10 may be used to couple
light into or out of a planar waveguide 80. The D-shaped waveguide 10 may have
an angle
polished end face 82 which reflects input light 86 from the fiber 22 to a
waveguiding
portion 88 of the planar waveguide 80. Alternatively, instead of the angled
end face 82, the
waveguide 10 may have a blazed grating 90, similar to that discussed
hereinbefore with
Figs. 29,30. The planar waveguide 80 has a corresponding blazed grating 87 or
angled
reflective surface 85 therein, or other optical directing device or feature to
allow the light 86
to pass bidirectionally between the core 12 of the waveguide 10 and the
waveguiding
portion 88. The surface 100 of the waveguide 10 is optically coupled to the
upper surface 92
of the planar waveguide 80 using known techniques, e.g., epoxy, fusion, glue,
glass solder,
etc.
As discussed herein, the D-shaped portion 10 may be used for waveguide
orientation
or alignment. In particular, referring to Fig. 17, when an elliptical core 66
(or other
polarization maintaining geometry) is used, the surface 100 may be used to
align the desired
polarization axis of the waveguide 10 with those of a connecting waveguide.
Referring to
Figs. 26, 29, and 30, this may also be done for alignment of a blazed grating
in the
waveguide 10 with another waveguide.
Referring to Fig. 23, a pair of D-shaped waveguides 110,112 having cores
111,113,
disposed therein respectively, may be used to form a 2x2 optical coupler. In
that case, a flat
coupling surface (or section) of a first D-shaped waveguide 110 is placed
across and in
contact with a flat coupling surface (or section) of a second D-shaped
waveguide 112. The
cores 111,113 intersect and light therefrom will couple between the two
waveguides
110,112 at a coupling region 116. The length of the coupling region may be
determined by
setting the angle 114 between the two waveguides 110,112. The portions of the
waveguides
110,112 that are not in contact with each other may be circular waveguide
portions
discussed hereinbefore, to minimize losses outside the coupling area.
Referring to Fig. 32, an alternative coupler embodiment has a first D-shaped
waveguide device 120 (similar to the device 9 of Fig. 1), and a second
waveguide device
122, each having respective waveguiding regions 121,123, and input/output
fibers 124,126
for coupling light 128 between the two fibers. The coupling efficiency may be
determined
by setting the gap G between the two devices. If the gap G is zero, maximum
coupling
efficiency exists.
- 12 -
CA 02444843 2012-12-04
Referring to Figs. 18-22, another type of coupler can be made by using two
circular
large diameter waveguides 200,202, as discussed hereinbefore, each having
respective
waveguiding sections 201,203 and cladding sections 205,207 and each end having
fiber
pigtails indicated by lines 206. Then, heating and bending ends away from each
other as
indicated by the lines 204. Next, a section of each cladding 209,211 is
removed, e.g., by
polishing, grinding, etching, machining, or other technique, leaving a pair of
flat surfaces
(the D-shape surfaces) 213,215, sufficient to expose the evanescent fields of
each of the
waveguides (based on the amount of coupling desired). These surfaces are
optically coupled
together using known techniques, e.g., optical epoxy, glue, fusion, of other
known
techniques to form a coupler 220 of Fig. 19. The coupler 20 will couple
optical signals
between the two waveguides 200,202 over a coupling length Lc. Alternatively, a
grating 222
may be disposed at a desired location along the coupling length Lc which may
be used to
provide various wavelength specific coupling to or from each of the four ports
of the device
220, such as is described in copending US Patent Application, published as US
2002/014226A1 on Oct 10, 2002. A similar coupler in fiber is described in US
Patent Nos.
5,459,801, and 5,459,807 entitled" Coupler Used to Fabricate Add-Drop Devices,
Dispersion Compensators, Amplifiers, Oscillators, Superluminescent Devices,
and
Communications Systems"; and 5,457,758 "Add Drop Device of a Wavelength
Division
Multiple, Fiber Optic Transmission System", all to Snitzer.
Referring to Figs. 20-22, instead of coupling together two waveguides each
having a
single core (or waveguiding section), the D-shaped waveguides may each have
multiple
cores, as discussed in Fig. 16, to create various different core coupling
arrangements as
shown in Figs. 20-22. For example, in Fig. 20, a first D-shaped waveguide 230
may have
two cores 231,232 and a second D-shaped waveguide 236 may have two cores
237,238,
where the coupling between the cores 232, 237 will be different that the
coupling between
the cores 231,238. Alternatively, in Fig. 21, a first D-shaped waveguide 240
may have two
cores 241,242 and a second D-shaped waveguide 246 may have two cores 247,248,
where
the coupling between the cores 242, 247 will be substantially the same if the
distances are
the same. Alternatively, in Fig. 22, any number of cores may be used in each
of the D-
shaped waveguides 250,252. Also, the number of cores in each D-shaped
waveguide need
not be the same.
The waveguide 10 may be made using fiber drawing techniques now known or later
- 13 -
CA 02444843 2012-12-04
developed that provide the resultant desired dimensions for the core and the
outer diameter
discussed hereinbefore. Because the waveguide 10 has a large outer diameter
(greater than
0.3 mm) compared to that of a standard optical fiber (e.g., 125 microns), the
waveguide 10
may not need to be coated with a buffer (or jacket) and then stripped to
perform subsequent
machining operations, thereby requiring less steps than that needed for known
fiber based
optical coupling configurations. Also, the large outer diameter d2 of the
waveguide 10
allows the waveguide to be ground, etched or machined while retaining the
mechanical
strength of the waveguide 10.
The present invention is easily manufactured and easy to handle. Also, the
waveguide 10 may be made in long lengths (on the order of many inches, feet,
or meters)
then cut to size as needed for the desired application.
Alternatively, the D-shaped optical waveguide 10 may be formed directly by
drawing the waveguide from a D-shaped preform, as described in commonly owned
U.S.
Patent Application, published as US 2002/0172459A1 on Nov. 21, 2002. An inner
preform
may be formed using known methods such as multiple chemical vapor deposition
(MCVD),
outside vapor-phase deposition (OVD) or vapor-phase axial deposition (VAD)
processes to
form the core, inner cladding and a portion of the outer cladding having the
desired
composition of material and dopants. One method of manufacturing the preform
is described
in U.S. Patent No. 4,217,027 entitled, 'Optical Fiber Fabrication and
Resulting Product". A
glass tube may then be collapsed onto the inner preform to provide the desired
outer
diameter of the outer cladding 14 of the preform. After the cylindrical
preform is formed,
the preform is ground, machined or otherwise formed into the desired D-shape.
The preform
is then heated and drawn using known techniques to form the D-shaped waveguide
10
having the desired dimensions as described hereinbefore. During the heating
and drawing
process, the preform is heated to a predetermined temperature to draw the
waveguide, but
sufficiently cool so that the waveguide maintains the D-shape. The advantage
of drawing
the D-shaped waveguide is that the flat surface 100 is fired smooth and flat.
Referring to Fig. 27, alternatively, instead of drawing the D-shaped or
circular
waveguides as described herein above, any of the large diameter optical
waveguide
structures described herein may be formed by a glass collapsing and fusing
technology
shown and described in commonly owned United States Patent, published as US
6,519,388,
- 14 -
CA 02444843 2012-12-04
filed December 6, 1999, as discussed below in more detail. By way of example,
the large
diameter optical waveguide structures may be formed by taking the optical
fiber 22 and
inserting it into an alignment tube 20 having an inner diameter slightly
larger than that of the
outer diameter of the optical fibers, which is then collapsed on the optical
fiber 22. When
this technique is used, there is need to splice the separate fiber 22 onto the
larger diameter
waveguides 11 or 10.
One or more tubes may be collapsed around the fiber to form the desired outer
diameter. For example, if more than one tube is to be used, a large diameter
optical
waveguide having an outer diameter of 3 millimeters may be formed by
collapsing a first
glass tube having a 1 millimeter outer diameter and a bore onto an optical
fiber having a
diameter of 125 microns arranged therein, then further collapsing a second
glass tube having
a 3 millimeter outer diameter and a corresponding bore onto the first glass
tube arranged
therein.
The tube 20 is made of a glass material, such as natural or synthetic quartz,
fused
silica, silica (Si02), Pyrex by Coming (borosilicate), or Vycort by Coming
(about 95%
silica and 5% other constituents such as Boron Oxide), or other glasses. The
tube should be
made of a material such that the tube 20 (or the inner diameter surface of a
bore hole in the
tube 20) can be fused to (i.e., create a molecular bond with, or melt together
with) the outer
surface (or cladding) of the optical fiber 10 such that the interface surface
between the inner
diameter of the tube 20 and the outer diameter of the fiber 10 become
substantially
eliminated (i.e., the inner diameter of the tube 20 cannot be distinguished
from the cladding
of the fiber 10).
The axial ends of the tube 20 where the fiber 10 exits the tube 20 may have an
inner
region 24 which is inwardly tapered (or flared) away from the fiber 10 to
provide strain
relief for the fiber 10 or for other reasons. In that case, an area 28 between
the tube 20 and
the fiber 10 may be filled with a strain relief filler material, e.g.,
polyimide, silicone, or other
materials. Alternatively, instead of having the inner tapered region 24, one
or both of the
axial ends of the tube 20 where the fiber 10 exits the tube 20 may have an
outer tapered (or
fluted, conical, or nipple) section, shown as dashed lines 27, which has an
outer geometry
that decreases down to the fiber 10 (discussed more hereinafter with Fig. 12).
The fluted
sections 27 may provide enhanced pull strength at and near the interface where
the
-15-
CA 02444843 2012-12-04
fiber 10 exits the tube 20, e.g., 6 lbf or more, when the fiber 10 is pulled
along its
longitudinal axis.
Where the fiber 10 exits the tube 20, the fiber 10 may have an external
protective
buffer (or jacket) layer 21 to protect the outer surface of the fiber 22 from
damage. The
buffer 21 may be made of polyimide, silicone, Teflon
(polytetraflouroethylene), carbon,
gold, and/or nickel, and have a thickness of about 25 microns. Other
thicknesses and buffer
materials for the buffer layer 21 may be used. If the inner tapered region 24
is used and is
large enough, the buffer layer 21 may be inserted into the region 24 to
provide a transition
from the bare fiber to a buffered fiber. Alternatively, if the axial end of
the tube 20 has the
external taper 27, the buffer 21 would begin where the fiber exits the tapered
27 portion of
the tube 20. If the buffer 21 starts after the fiber exit point, the exposed
bare portion of the
fiber 22 may be recoated with an additional buffer layer (not shown) which
covers any bare
fiber outside of the tube 20 and may also overlap with the buffer 21 and/or
some of the
tapered region 27 or other geometrically shaped axial end of the tube 20.
Other techniques may be used for collapsing and fusing the tubes to the fiber,
such as
is discussed in US Patent No. 5,745,626, entitled "Method For And
Encapsulation Of An
Optical Fiber", to Duck et al., and/or US Patent No. 4,915,467, entitled
"Method of Making
Fiber Coupler Having Integral Precision Connection Wells", to Berkey, or other
techniques.
Alternatively, other techniques may be used to fuse the fiber to the tube,
such as using a high
temperature glass solder, e.g., a silica solder (powder, liquid or solid), or
a liquid silica
compound, such that the fiber, the tube and the solder/compound all become
fused to each
other, or using laser welding/fusing or other fusing techniques.
The dimensions and geometries for any of the embodiments described herein are
merely for illustrative purposes and, as such, any other dimensions may be
used if desired,
depending on the application, size, performance, manufacturing requirements,
or other
factors, in view of the teachings herein.
It should be understood that, unless stated otherwise herein, any of the
features,
characteristics, alternatives or modifications described regarding a
particular embodiment
herein may also be applied, used, or incorporated with any other embodiment
described
herein. Also, the drawings herein are not drawn to scale.
- 16 -
CA 02444843 2012-12-04
Although the invention has been described and illustrated with respect to
exemplary
embodiments thereof, the foregoing and various other additions and omissions
may be made
therein and thereto.
-17-
