Note: Descriptions are shown in the official language in which they were submitted.
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10-166CA . Patent
Optical Coupling System
Field of the Invention
The present invention relates to an optical coupling system, particularly a
connection
system providing a reliable and uniform joint between optical elements.
Background of the Invention
The most common optical connection is between an optical fibre end and a
collimating lens, such as a graded index (GRIN) lens. A common coupler system
to comprises a sleeve in which a fibre end within a supporting ferrule is
joined to a lens by
attaching the sides of the ferrule and the lens to the interior bore of the
sleeve.
Manufacturing tolerances of, for instance, the lens diameter, the ferrule
diameter, or the
dimension and position of the bore within the ferrule, introduce variations
which make this
type of coupler difficult to use to achieve accurate alignment. The sleeve
must have a large
enough internal diameter to accommodate a ferrule or lens at its largest
tolerance. As a
result, smaller elements may unintentionally become tilted within the sleeve.
The fibre end
within the ferrule is not always concentric. If the ferrule internal diameter
is too large for
the fibre, or the ferrule bore is not perfectly centered, it becomes necessary
to adjust, or tune,
the alignment of the fibre to the lens. Similarly, for a fibre in a non-
centered port of the
2o ferrule, alignment adjustment is also necessary to achieve the correct port
coupling with the
lens. Alignment adjustment is limited and difficult within the confines of the
coupling
sleeve. Temperature changes in the environment also cause different elements
in the sleeve
coupler to respond differently, further affecting the quality of the coupling.
In many
instances, it is preferred to have the fibre aligned at a port on the lens
that is disposed
adjacent to, rather than aligned with, the optical axis of the lens. This is
difficult, requiring
specialized ferrules and little ability to tune the alignment, within a sleeve
coupler.
Another common practice is to couple an optical fibre to a lens, such as a
graded-
index (GRIN) lens, by placing the optical fibre into a ferrule or fibre tube
and joining an end
3o face of the tube directly to a face of the lens by applying a layer of
epoxy between them. A
direct ferrule to lens epoxy connection facilitates alignment of the coupled
elements and
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provides a uniform joint. The end faces of the lens and ferrule can be formed
to planar
surfaces reliably to prevent unwanted tilt angle at the coupling. Positioning
the fibre
adjacent to the optical axis of the lens is possible without the confining
sleeve coupler. Also,
relatively easy alignment tuning is possible to compensate for eccentric fibre
positioning
within the ferrule. However, index matching epoxy is not completely
transparent or uniform
to transmission. Transmission of light though the epoxy layer results in some
loss.
A third coupling system disclosed in application No 09/028,880 filed February
24,
1998, commonly owned with the present invention comprises a stand off spacer
element
1 o having a central transmission aperture. The stand off spacer permits
accurate control of
spacing between optical elements, and the angle of the coupling by coupling
the faces of the
stand off element to the coupling end faces of the optical elements. Adhesive
is only
applied to the stand off element, and the transmission aperture remains free
of adhesive.
However, in many instances, the spacing between elements is. not only
unnecessary, but
causes poor coupling due to the change in focal length and the air gap between
elements. A
direct connection between the optical elements which would permit tuning and
be free of
adhesive distortions would be preferred.
It is desired to provide a coupling system, which provides a reliable means
for direct
coupling between optical elements. It is further desired to provide a coupling
system, which
is unimpeded by transmission through an adhesive layer. It is also desired to
provide a
coupling system, which can accurately provide adjustment to the alignment of
the coupling.
Summary of the Invention
The present invention has found that the planar coupling end faces of the
optical
elements can be contoured to have an annular groove providing a barner between
a
transmission window, where no adhesive disrupts the optical coupling and a
peripheral
securing surface for providing an adhesive join between the elements. Surface
tension
3o maintains the adhesive between the peripheral securing surface and the end
face of the other
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element. The barrier provided by the groove prevents adhesive from migrating
and
obscuring the transmission window.
Accordingly, the present invention comprises an optical element for direct
adhesive
coupling to an additional optical element comprising:
a transmission area for transmitting an optical signal;
a coupling end face adapted for mating contact with a coupling end face of the
second optical element;
the coupling end face including a continuous groove spaced from an outside
1 o edge of the coupling end face defining a peripheral securing surface for
receiving adhesive,
the groove surrounding a transmission window through which a transmitted
signal is
coupled into the additional optical element in use.
A further preferred embodiment of the present invention comprises an optical
coupling
t 5 comprising:
a first optical element for transmitting an optical signal having a coupling
end face;
a second optical element for transmitting a signal having a coupling end face
for
joining to the coupling end face of the first optical element;
the coupling end faces of the first and second optical elements being
substantially
2o planar surfaces adapted to meet in close fitting relationship;
the coupling end face of the first optical element including a continuous
groove
spaced from an outside edge of the coupling end face defining a peripheral
securing surface
for receiving adhesive, the groove surrounding a transmission window through
which a
transmitted signal is coupled;
25 an adhesive join between the peripheral securing surface and the coupling
end face
of the second optical element.
A preferred method according to the present invention of coupling a first
optical element to
a second optical element for optical signal transmission through the coupling
comprises the
3o steps of:
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providing a first optical element having a transmission area for transmitting
an
optical signal and a coupling end face, the coupling end face of the first
optical element
including a continuous groove spaced from an outside edge of the coupling end
face
defining a peripheral securing surface for receiving adhesive, the groove
surrounding a
transmission window at the transmission area of the coupling end face of the
first optical
element;
providing a second optical element having a transmission area for transmitting
an
optical signal and a coupling end face for mating with the coupling end face
of the first
optical element;
1 o adhesively securing the peripheral securing surface of the first optical
element to the
coupling end face of the second optical element; and
providing tuning adjustment for aligning the transmission window of the
coupling
end face of the first optical element with the transmission area of the second
optical element.
The direct coupling of planar ferrule and lens surfaces of the present
invention
provides the advantages of alignment and tuning control. Other optical
elements such as
multiple lenses, or lenses and filters etc., may also advantageously be
coupled in accordance
with the invention to provide reliable coupling with an unimpeded transmission
area. If the
surface contact means used is adhesive, such as epoxy, metal solder, glass
solder, molten
2o glass, pressure activated adhesive or the like, between the planar surfaces
of the optical
elements, it is relatively easy to maintain the transmission window free of
adhesive for
unimpeded transmission. It is also possible to adjust the position of the
elements
to tune different alignment configurations.
2s It is an advantage of the present invention that aligned, direct coupling
can be
effected without loss due to transmission through adhesive.
It is a still further advantage that optical elements can be coupled in a
substantially
sealed environment.
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Further advantages will be apparent to those skilled in the art with reference
to the
detailed description of preferred embodiments and the accompanying drawings,
which
illustrate preferred embodiments of the invention by example only, in which:
Brief Description of Figures
Figure 1 is a side view of a direct coupling in accordance with the present
invention;
Figure 2 is an isometric view of the end faces of the optical elements of Fig.
1;
Figure 3 is a cross sectional view taken along line III - III of Fig. 2;
1 o Figure 4 is an isometric view of an alternative end face of the coupling
in accordance
with the invention;
Figure 5 is an isometric view of a further alternative end face of the
coupling in
accordance with the invention;
Figure 6 is an isometric view of an alternative end face of a housing for
supporting a
rod lens for a coupling in accordance with the invention;
Figure 7 is a cross sectional view of a prior art sleeve coupling system;
Figure 8 is a side view of a further prior art epoxy coupling system.; and,
Figure 9 is a side view of a prior art coupling using a stand off element.
Like numerals are used throughout to designate like elements.
Detailed Description of Preferred Embodiments
Figure 1 shows a preferred embodiment of the coupling generally at 10. A
ferrule 12 supporting fibre end 14 has a planar coupling face 15. A lens 16,
such as a
graded-index lens commonly used in this configuration, also has a planar
coupling face 17.
The ferrule 12 and lens 16 are joined in direct surface contact by an adhesive
layer 32.
Seen clearly in Fig. 2, the coupling end face 15 of the ferrule 12 includes an
arnlular groove
18. The groove 18 provides a barrier to the flow of adhesive separating a
transmission
3o window 20 from a peripheral securing surface 22 since the adhesive, through
surface tension
(capillary action), tends to flow along the securing surface 22 rather than
enter or cross the
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groove. Both the transmission window 20 and the peripheral securing surface 22
comprise
coplanar surfaces adapted to closely join a planar coupling end face 17 of the
lens 16. The
fibre 14 is polished to be coplanar with the end face 15 of the ferrule 12
generally at a six
degree angle from perpendicular to the longitudinal axis. The annular groove
18 can be in
either the ferrule or lens coupling end face 15 or 17. Alternatively, a sleeve-
like housing
similar to a ferrule can be provided to receive a rod lens, the housing having
a grooved end
face in accordance with the invention, for adhesively securing a coupling as
shown in Fig. 6.
A rod lens 16 is mounted within a housing. The end face 21 of the housing 19
is similarly
formed with a groove 18.
to
Fig. 3 shows the groove 18 which forms a well between the peripheral securing
surface 22 and the transmission window 20 to form a barrier to adhesive, such
as index
matching epoxy. The pressure between the planar coupling end faces 15, 17
prevents
adhesive from flowing onto the transmission window 20. As a result, coupling
is
accomplished without obstructing or hindering the quality of the optical
transmission with
epoxy between the optical elements. Of course the groove 18 could be any
continuous
shape separating a generally central transmission window 20 from a peripheral
securing
surface 22 to provide sufficient passage for the beam transmission. One or
more fibres 14
launch light into the lens 16. The actual beam width, even of a number of
adjacent fibres, is
2o very small. The transmission window 20 should be dimensioned to provide
sufficient
flexibility for tuning alignment. The peripheral securing surface should be of
sufficient area
to provide a secure adhesive join.
Fig. 4 illustrates an alternative embodiment of the invention including a vent
24 in
the peripheral securing surface 22, through which air can exit under pressure
as the coupling
faces 15, 17 are joined.
Fig. S illustrates a further alternative embodiment of the invention including
a
second annular groove 26 to provide an additional flow barrier between the
securing surface
22 and the transmission window 20. This embodiment may also include the vent
24
communicating with both grooves 18, 26.
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In production, a groove may be formed on al coupling end face of a ferrule,
lens or
housing. An accurate planar surface can then be ground on the formed end face.
Alternatively, a groove can be ground or cut into the end face of a finished
optical element.
The shape and depth of the groove are not critical. An adequate depth and
volume of the
groove 18 will prevent overflow. An accurate coupling end face for mating with
an
additional optical element is important.
The surface securing means is not limited to adhesive. Adhesive for securing
the
1 o coupling end faces 15, 17 may be understood to include: epoxy, metal
solder, glass solder,
liquid glass, glue, etc. An appropriate surface securing means is selected
depending on the
material used. The securing surfaces of cooperating end faces peripheral to
the transmission
window 20 may be metalized to receive a metal solder joint. By eliminating
additional
coupling elements, such as spacers, sleeves or cages, thermal expansion within
the coupling
no longer presents a significant problem.
Multiple optical elements can be joined in accordance with the present
invention to
provide reliable and unobstructed coupling through the entire assembly. To
couple to a
filter or filter substrate, it is preferable to grind a groove in a coupling
face of a graded-index
lens or lens housing. Thus through the complete assembly, clear transmission
is possible
unobstructed by epoxy at each joint.
Fig. 7 illustrates a prior art coupling incorporating a sleeve 30 in which a
fibre 14
within a ferrule 12 and a lens 16 are joined. Epoxy 32 between the sides of
the ferrule 12
and the lens 16 secures the optical elements to the inner wall of the sleeve
30. Substantially
no alignment tuning is possible within the sleeve.
Fig. 8 illustrates a further prior art coupling in which a coupling face of a
ferrule 12
supporting a fibre end 14 is joined directly to a coupling face of a lens 16
with an epoxy
layer 32. Epoxy is directly in the transmission path.
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Fig. 9 illustrates a third prior art coupling configuration using a stand off
element 40
between optical elements. This provides a transmission window free of
adhesive, however
the space between the optical elements has an adverse effect on coupling
efficiency.
The preceding examples are for illustration only, and are not intended to be
limiting.
Numerous other embodiments will be apparent to persons of skill in the art,
without
departing from the spirit and scope of the invention as defined in the
appended claims.
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