End-butt optical fiber coupler

An optical waveguide coupler having intersecting deep and shallow grooves in a planar solid substrate, in which the deep groove accommodates an alignment fiber for fine vertical alignment of an optical fiber with another optical fiber or with an optical component such as a switch, modulator, multiplexer or source of light. The shallow groove accommodates the optical fiber. The alignment fiber may be tapered or have any configuration such that its manipulation causes the alignment fiber to contact the underside of the optical fiber for raising or lowering the optical fiber. There may be a plurality of shallow and deep grooves for coupling more than one optical fiber.

BACKGROUND OF THE INVENTION 
This invention relates generally to couplers for optical fibers and more 
particularly to couplers for precisely aligning optical fibers in the 
vertical direction with other single-mode or multimode optical fibers or 
with optical components. 
Optical communication has been seriously pursued especially since 
light-transmitting dielectric fibers or optical fibers were drastically 
improved in terms of propagation loss and mechanical strength. Optical 
fibers are usually made of various dielectric materials, such as silica or 
quartz, and have core diameters which range in size from a few microns to 
hundreds of microns. 
One of the most important problems in optical communications is the 
connection or coupling between fibers, and also between fibers and various 
optical components. The coupling of the latter combinations is especially 
difficult due to geometric mismatch between fibers and other optical 
components. Coupling is more difficult in a single-mode fiber system than 
in a multimode fiber system because of the smaller core dimensions of 
single-mode fibers. For example, in the coupling between a single-mode 
fiber and a channel-waveguide, a mismatch of one micron may reduce 
coupling efficiency by as much as 50 percent. Conventional techniques for 
precise optical coupling are expensive; have one or more grooves in only 
one direction and include cumbersome means, such as a plurality of screws, 
for aligning optical fibers so that coupling to within micron tolerances 
is impractical; and in some devices, only one fiber may be aligned at a 
time. 
SUMMARY OF THE INVENTION 
It is the general purpose and object of the present invention to precisely 
couple optical fibers with other optical fibers or with other optical 
components. This and other objects of the present invention are 
accomplished by a two-dimensional, intersecting groove pattern excised 
(whenever used herein, this term will be understood as including processes 
such as preferential etching) from the surface of a substrate wherein a 
groove in one direction is deeper than an intersecting groove, and an 
alignment fiber rests in the deep groove. The shallow groove accommodates 
an optical fiber. The deep groove accommodates the alignment fiber so that 
the alignment fiber can contact the underside of the optical fiber. The 
alignment fiber may be tapered or have an eccentric cross-section so that 
sliding or rotating it, respectively, precisely raises or lowers the 
optical fiber to a desired level. Alternatively, a multiplicity of deep 
grooves having slightly different depths may accommodate alignment fibers 
of uniform diameter so that successively removing an appropriate number of 
alignment fibers from beneath an optical fiber aligns the optical fiber. 
The present invention provides such advantages as very fine alignment of 
optical fibers, both single-mode and multimode, to within a tolerance of 
less than one micron, convenience of operation, inexpensive construction, 
and simultaneous alignments of a plurality of optical fibers. 
Other objects and advantages of the invention will become apparent from the 
following detailed description of the invention when considered in 
conjunction with the accompanying drawing wherein:

DETAILED DESCRIPTION OF THE INVENTION 
Referring now to the drawings, wherein like reference characters designate 
like or corresponding parts throughout the several views, FIG. 1 
illustrates an embodiment of the present invention wherein a groove 
pattern, including a shallow groove 10 and an intersecting deep groove 12, 
is excised from the surface of a planar solid substrate material 14, such 
as silicon or gallium arsenide, and the deep groove accommodates an 
alignment fiber 16 preferably made from a dielectric material such as 
fused silica. It is preferable that the grooves 10 and 12 be V-shaped, as 
is the case when a crystal such as silicon or GaAs is preferentially 
etched; however, the grooves may be any convenient shape. Although FIG. 1 
illustrates the grooves in approximately two orthogonal directions, the 
present invention is not limited to this particular groove pattern: that 
is, the angle between two intersecting directions may be other than 
90.degree.; the grooves may be excised in more than two intersecting 
directions; and the number of shallow and deep grooves may vary to suit a 
particular application. 
As shown in FIG. 2, an optical fiber 18 rests in the shallow groove 10. The 
depth and width of the deep groove 12 are such that the alignment fiber 16 
lies beneath the optical fiber 18 and can contact the underside of the 
optical fiber. 
The alignment fiber 16 may be of any configuration, the manipulation of 
which precisely raises or lowers the optical fiber to a desired level. For 
example, the alignment fiber 16 may have a circular cross-section that 
tapers along the longitudinal axis of the alignment fiber at a convenient 
rate of one micron per suitable length, as for example, one or two 
centimeters. Thus, sliding the alignment fiber 16 a distance of one or two 
centimeters or any suitable length raises or lowers the optical fiber 18 
by an amount of one micron or a fraction or multiple thereof for precisely 
aligning the core 20 with the core 22 of another optical fiber 24. For 
aligning the optical fiber 18 with an optical component 26 having a 
channel waveguide 28, it is preferable to flip the component 180.degree. 
so that the channel waveguide is located just above the upper horizontal 
surface of the substrate 14, as shown in FIG. 3. In this case the base of 
the core 20 of the optical fiber 18 should be even with or just below the 
upper horizontal surface of the substrate 14 so that the optical fiber may 
be raised for precisely aligning the core with the channel waveguide 28. 
Alternatively, the alignment fiber 16 may have an eccentric cross-section 
with or without a taper so that rotating and/or sliding the fiber in its 
groove 12 for a given distance raises or lowers the optical fiber 18 by a 
desired amount. 
The alignment fiber 16 must not necessarily have a round cross-section but 
may, for example, be in the shape of a shim. 
FIG. 4 shows another embodiment of the present invention having a 
multiplicity of deep grooves 12 of varying depths. Each deep groove 12 
accomodates an alignment fiber 16 of uniform diameter. A shallow groove 
(not shown) supports an optical fiber 18 above the alignment fibers 16. 
Removal of the alignment fibers 16 beginning from the groove 12 of least 
depth lowers the optical fiber 18 to a suitable level for proper alignment 
of the core 20 with the core of another optical fiber or with an optical 
component, as for example, a channel waveguide 28 shown in FIG. 4. 
The shallow groove 10 in each embodiment of the present invention is mainly 
for the lateral alignment of the optical fiber 18. The possibility of 
slippage by the optical fiber 18 along the lateral direction as the 
optical fiber is vertically adjusted by the alignment fiber 16 is minimal, 
because the friction between the optical and alignment fibers is 
negligible, since the fibers have essentially a point contact, and also 
because the optical fiber tends to straighten up by itself. In order to 
completely eliminate any possibility of lateral displacement, another 
grooved substrate (not shown) may be placed on top of the optical fiber 18 
for pressing the optical fiber into place. 
Obviously many more modifications and variations of the present invention 
are possible in light of the above teachings. It is therefore to be 
understood that within the scope of the appended claims the invention may 
be practiced otherwise than as specifically described.