Uptapered single-mode optical fiber package for optoelectronic components

A package for an optoelectronic device, such as a laser, having a photo-active element optically coupled to an uptapered single-mode optical fiber which connects said optoelectronic array to an external device includes a housing having a solderable substrate to which the device is secured, a graded index lens also secured to said substrate at a distance calculated to provide a known magnification of light beam emanating from said laser and an uptapered single-mode optical fiber mechanically positioned and actively aligned to said mangified light beam to achieve optimal optical coupling to said optoelectronic device. The package includes a plurality of reference marks and surfaces such that the laser, the lens and the uptapered end of a single-mode optical fiber may be positioned for precise optical coupling using an active alignment for final adjustments. The reference surfaces include a pedestal for the laser and a plurality of stops for the lens integrally formed with the substrate. The package also includes a fiber tube and flange for mechanically positioning the uptapered fiber. The precisely calculated spacing based on the spacing of said photo-active element, the magnification of said lens, and the fiber positioning is achieved by mechanical means.

BACKGROUND OF THE INVENTION 
This invention relates to packaging of optoelectronic components which 
generate or process signals that pass through optical fibers. In 
particular, it addresses the critical need for providing stable, low-cost 
alignment of single-mode optical fibers to a single packaged device, such 
as a semiconductor laser. 
An optoelectronic package is a container or housing that provides 
protection and support for both active and passive components contained 
within it. These components and their interconnection represent an 
optical-electrical circuit and define the function of the package. The 
package also includes a means of connecting the internal components with 
the external environment, usually as electrical feed-through and optical 
fiber. Our invention is concerned with the optical fiber and how it is 
connected to the components within the package. 
To make an optical connection between an optical fiber and an 
optoelectronic component within a package, it is necessary to position or 
align the optical fiber in a way that allows efficient coupling between 
the optical fiber and the optoelectronic component. The precision needed 
for the alignment depends on the size of the light-emitting or light 
receiving elements, the type of optical fiber, and any type of focusing or 
defocusing elements which may be present. Optical fiber transmits light 
through its inner core, which is much smaller than the diameter of the 
optical fiber. There are two classes of optical fiber presently used in 
packaging semiconductor devices: single-mode and multi-mode, with typical 
core diameters of about 10 microns and 50 microns, respectively. Many 
telecommunication applications use single-mode optical fiber because of 
the superior bandwidth arising from its reduction of mode partition noise. 
The prior art for packaging semiconductor lasers is predominantly concerned 
with the easy task of aligning large cored multi-mode optical fiber. 
Multi-mode optical fiber is of little value for telecommunications because 
it suffers from mode-partition noise when used for high speed 
transmissions over a distance. 
Laser packaging with single-mode optical fiber has been done with optical 
fibers which have their ends either cleaved or tapered and lensed. A 
cleaved optical fiber has an optically flat end, while a tapered and 
lensed optical fiber is drawn down to a point in a fashion that aids light 
entering the fiber. Packages incorporating cleaved optical fibers require 
a separate lens, as does the package of this invention, while packages 
incorporating lensed optical fibers do not. 
Packages utilizing cleaved or tapered and lensed optical fibers suffer from 
stability problems associated with lateral movement of the optical fiber 
with respect to the laser. For this reason, the alignment of the optical 
fiber with the laser for such packages is usually done with expensive 
piezo-crystal micromanipulators having submicron sensitivity. The optical 
fiber is fastened with expensive laser welding techniques or special 
solders. 
As explained by Rideout, et al, "Improved LED and laser packaging using 
up-tapered single mode fibers," CLEO '89, Baltimore, Md., Apr. 25, 1989, 
the improved lateral tolerances arise from first magnifying the emitting 
spot image of the laser. The larger spot is then projected congruently 
onto the corresponding uptapered optical fiber. The lateral and angular 
sensitivities are: 
##EQU1## 
where the symbols mean: W.sub.o =spot radius of the optical fiber; 
.lambda.=wavelength 
.theta.=angular misalignment 
x=lateral misalignment 
The equations show that the spot radius of the light beam in the optical 
fiber determines these sensitivities. Since the spot radius is in the 
denominator of the lateral decoupling expression above, the benefit of 
decreased lateral sensitivity occurs with increased spot size. Conversely, 
the angular sensitivity becomes more detrimental since the spot radius is 
in the numerator of the angular misalignment expression above. 
When performing optical fiber alignments, the lateral alignment is more 
difficult to achieve than the angular alignment. Thus, the net effect of 
using a lens to magnify the spot radius of the light beam for coupling it 
to a larger diameter uptapered optical fiber is beneficial. 
It is worth noting that even though the thick section of the uptapered 
optical fiber does not qualify as a single-mode optical fiber diameter, it 
is short enough in length that it maintains only the single-mode. Thus, it 
is possible to obtain the advantage of the ease of alignment of a thick 
multi-mode optical fiber, while not losing the data transmission advantage 
of a thin single-mode optical fiber. 
SUMMARY OF THE INVENTION 
The principle object of the present invention is to provide an 
optoelectronic component package in which a single-mode optical fiber is 
easily and efficiently optically coupled to an active semicondutor laser. 
A second object of the present invention is to provide such a package for 
an optical connection that permits long distance, high speed transmissions 
of telecommunications data and information for the semicondutor element. 
Still a further object of the present invention is to provide such a 
package having a predictable, reproducible location of the optical fibers 
for maximum coupling efficiency, allowing for assembly line mass 
production of packaged optoelectronic components, since manufacturing is 
simplified, thereby reducing the costs of such packages. 
In one aspect of the invention, a package for an optoelectronic device 
having an active element optically coupled to a single-mode optical fiber 
connecting said optoelectronic device to an external device includes a 
housing to enclose the necessary components to convert electrical signals 
to optical signals. A substrate carrier within said housing has a 
solderable surface and a plurality of reference means for precise 
positioning of elements within said package. An optoelectronic 
semiconductor laser device having an active element is positioned with 
respect to one of said reference means and secured to said carrier 
substrate. A graded index lens, having a numerical aperature sufficient to 
access optically said active element and having a curvature on one end 
closest to said optoelectronic device, is positioned with reference to a 
second of said reference means and secured to said substrate a fixed 
distance from said optoelectronic active element to yield a desired 
magnification of light beams emanating from said active element. An 
uptapered single-mode optical fiber extends from a third one of said 
reference means within said housing to the exterior of said housing 
through a port thereof, said optical fibers being precisely positioned by 
a fiber tube flange secured to a side wall adjacent said port of said 
housing, the uptapered end of said optical fiber being mechanically 
aligned, with respect to the third of said reference means, for optical 
coupling through said lens to said photo-active spot of said 
optoelectronic device, while the opposite end of said single-mode optical 
fiber is outside said housing.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
This invention pertains to packages for optoelectronic devices which 
provide stable alignment, using a mechanical method for quick and 
efficient optical coupling of an uptapered single-mode optical fiber to 
the photo-active spot of the semi-conductor element. The package controls 
the uptapered fiber optical tolerances, allowing a relaxation of the 
optical fiber positional tolerance. 
The package of this invention uses a lens, with a sufficient numerical 
aperature and magnification, in conjunction with uptapered single-mode 
optical fiber. The alignment technique takes advantage of the relaxed 
mechanical tolerance and the magnification provided by the lens and the 
larger cored uptapered fiber optics. Such optical connections then permit 
independent transfer of telecommunications data and information for the 
semiconductor element. 
Specifically, this invention provides a new package for optically coupling 
an uptapered single-mode optical fiber to a single packaged optoelectronic 
device using a single lens mechanically aligned with the semiconductor 
element in order to magnify the spot image of the photo-active element to 
expand the size of the emitted light beam. This image is then coupled to 
an uptapered optical fiber. This magnification greatly facilitates 
mechanical alignment and coupling of the semiconductor laser to the 
associated optical fiber by relaxing mechanical tolerances associated with 
the position of the ray of light coming from the laser. 
Uptapered optical fibers are used because the effect of magnification 
increases the size of the beams or spot. These beams are best collected on 
the thick end of the uptapered fiber, where the size of the optical fiber 
best matches the size of the beams. For example, a typical uptapered 
optical fiber may have a core that is ten times larger on its thick end 
than the single-mode optical fiber that it tapers down to. This optical 
fiber is used with a lens that magnifies the spot size of the beam 
tenfold. This effect facilitates the alignment when assembling an 
optoelectronic package. 
Mechanical alignment is also possible with these packages because the 
location of the semiconductor beam can be known with high precision 
relative to the package. This is because the semiconductor photo-active 
element is usually patterned on the semiconductor with photolithography to 
a high level of precision, about one micron, and the lens projects a 
precise image of this pattern towards the fiber. If a lens with known 
magnification is first positioned rigidly in a specified location, then 
the location of the projected beam is know. Alignment to this beam 
automatically aligns the uptapered optical fiber held in a fixture 
engineered with the geometry set by the known magnification determined by 
the lens. 
FIG. 1 illustrates a generalized package for an optoelectronic component 
and a method for assembling the package, according to this invention. 
Package 10, shown partially cutaway in FIG. 1, comprises a housing 12, 
which completely encloses the necessary components that convert input 
electrical signals to optical signals. Preferably, housing 12 is made of 
brass and has a removable top for access to the interior. A carrier 14 
having a surface that is readily solderable, such as gold-plated copper or 
brass, is used to support the components. A pedestal 16 is secured to a 
first major surface of carrier 14 adjacent to a first end wall 15 of 
housing 12, for mounting and positioning a semiconductor laser 22 having a 
photo-active spot 23. Two lateral stops 18 and two axial stops 20 are also 
secured in a central location to the same major surface of carrier 14 for 
positioning a lens 24, which is hard soldered prior to the optical fiber 
alignment. Preferably carrier 14, pedestal 16 and stops 18, 20 are 
integrally formed as a one-piece element. A thermoelectric cooler 26 is 
secured to the second major surface of carrier 14. A second end wall 28 
has a circular opening (not shown in FIG. 1) to permit the insertion of 
the thick end of uptapered optical fiber 30, which is enclosed in a fiber 
tube 32 and rigidly held perpendicular to end wall 28 by a large flange 
34. The lens 24 focuses the light from the photoactive spot 23 of laser 22 
onto uptapered optical fiber 30. 
A plurality of mechanical features, and registration features and/or 
reference marks are incorporated into housing 12 and carrier 14 so that 
the total package 10 mechanically controls the uptapered-fiber optical 
tolerances, thus allowing a relaxation of the uptapered optical fiber 
positional tolerance. The uptapered-fiber optical tolerances controlled by 
package 10 are, the semiconductor position, the lens-to-semiconductor 
distance; the stability of lens attachment; and the tight angular control 
of the uptapered fiber. 
A one-piece carrier 14 holds the laser 22 and the lens 24. This controls 
the stability of the lens-to-semiconductor positional tolerance. 
Semiconductor 22 and lens 24 move in unison, despite shifts in other 
package parts caused by vibrations or thermal variations. The lens 24 is 
hard soldered prior to doing the optical fiber alignment to provide 
mechanical stability. For this optical element, lens 24, stability is more 
important than exact positioning. Some misalignment of the lens 24 can be 
compensated for during alignment of the uptapered optical fiber 30. 
The height of pedestal 16 controls the height of laser 22 (y-axis). The 
forward edge 36 of pedestal 16 serves as the forward reference mark for 
laser 22 (z-axis). A lateral reference mark 38 on pedestal 16 is aligned 
with an active region reference mark 40 on laser 22 (x-axis) to control 
the lateral position of laser 22. Axial stops 20 control the 
lens-to-semiconductor distance, while lateral stops 18 control the 
horizontal alignment of the lens 24 to the photo-active spot 23 of laser 
22. The relative positioning of the laser 22 and the lens 24 is usually 
set to a positional accuracy of about one-half mil. This can be done 
off-line under a stereomicroscope, making use of the reference marks 36, 
38, 40. 
The position of the lens 24 sets the magnification of the light-emitting 
area (photo-active spot 23) of laser 22. The magnification is set to best 
match the projected emitting area size with the core of the uptapered 
optical fiber 30. The proper magnification position is set by the axial 
and lateral stops 18, 20, which are registration features on the carrier 
14. 
The uptapered optical fiber 30, protected by a fiber tube holder 32, is 
mounted and aligned externally to the package 10. The uptapered end of 
optical fiber 30 extends inside the package to a fiber tip reference mark 
42 on carrier 14, which is a known distance from axial lens stops 20. The 
package cover (not shown in the figures) is in place, so that the interior 
of the package is protected from damage. After fiber positioning, using 
reference marks 42, 20 the uptapered optical fiber 30 is actively aligned, 
requiring only crude low cost micro-meters and is secured in position with 
simple means such as epoxy or screws (not shown in FIG. 1). Active 
alignment means the fiber is aligned to maximize the light beam entering 
the fiber while the laser is operating. The uptapered optical fiber 30 and 
the fiber tube holder 32 are easily removed and replaced for packages that 
have suffered fiber damage, because interior parts need not be disturbed. 
The uptapered optical fiber is held perpendicular to the package by a 
large fiber flange 34 on the fiber tube holder 32. This controls the 
angular uptapered optical fiber optical tolerance. It also improves 
stability because an uptapered optical fiber is more sensitive to angular 
misalignment than a conventional tapered and lensed or cleaved fiber. 
A long focal distance between the lens 24 and the uptapered end of optical 
fiber 30 allows space to introduce optical elements such as filters and 
opto-isolators. In this space the light beam is nearly collimated, greatly 
simplifying the optical designs incorporating these elements. 
The carrier 14 supporting the lens 24 and semiconductor 22 could be part of 
a circuit board, multi-chip module, or semiconductor waferboard carrying 
other optical and electronic components. 
The lens 24 could be either a GRIN type, convex, plano-convex, or 
combination of several lenses. The only requirement is that it provide the 
necessary magnification to match light spot sizes with the uptapered end 
of optical fiber 30. 
Internal optical elements, such as opto-isolators or filters, can be 
located in the space between the lens 24 and the fiber 30 in any 
combination. Optical coatings could also be placed on the lens 24 to 
provide some of the function of these optical elements. 
The registration or reference marks 18, 20, 36, 38, 42 on the carrier can 
be either mechanical stops, slots, pins, visual lines, steps or the like. 
The only requirement is that they be part of the carrier 14 and provide 
half mil or better accuracy for the lens 24 and the semiconductor 22 
positions. 
FIG. 1 shows the uptapered-fiber laser package with the lid removed so that 
the components are visible. This package incorporates an externally 
aligned uptapered fiber 30, which is aligned and epoxied onto the outside 
of the package housing 12 at room temperature. This is the only active 
alignment, and can be performed without piezoelectric staging because of 
the relaxed lateral alignment tolerances. An AR-coated GRIN lens images 
the laser spot onto the uptapered fiber. This lens is soldered in place 
with high temperature solder for maximum stability. 
FIGS. 2a, 2b, 2c, 3 and 4 illustrate details of the preferred embodiment of 
the uptapered single-mode optical fiber package according to the 
invention, as built and tested by the inventors. In these figures, the 
same reference numbers are used for corresponding parts as were used in 
FIG. 1. Some elements not part of the invention are shown in the figures 
and mentioned in the specification without further elaboration. 
FIGS. 2a, 2b and 2c are top, side and end views of the preferred embodiment 
of package 10, illustrating its assembly. The following items are specific 
to this embodiment. A graduated index (GRIN) lens is used for lens 24. A 
thermo-electric temperature control (TEC) 26 is present. This package is 
designed for epi-down semiconductor mounting. The carrier 14 does not 
extend the full length of the housing 12, so the fiber tip reference mark 
42 is on the base of the housing. A precision fiber tube 32 having an 
epoxy fill tube 60 for securing the optical fiber 30 after alignment holds 
the uptapered end of the optical fiber. Fiber tube flange 34 surrounding 
fiber tube 32 is fastened with epoxy to the outside of the at epoxy joint 
62 to complete the alignment. 
A screw mounting slot 50 is present. An SMA connector socket 54, a high 
frequency microline 56 connected thereto, and seven d.c. in-line pin outs 
to provide high speed electrical signals complete the package. The package 
housing 12, the fiber tube 32, and the cover (not shown) are preferably, 
made of brass. Carrier 14 is preferably made of nickel and gold-plated 
copper. Package 10 in this embodiment is a high speed laser package having 
the uptapered fiber optical tolerance controls built into the package. 
The lasers used in this package are 1.3 .mu.m Vapor-Phase-Regrowth Burled 
Heterostructure (VPR-BH) lasers which have a demonstrated maximum 
bandwidth of 22 GHz and typical bandwidths of 15 GHz. Previously developed 
microstrip techniques are used to preserve the high frequency integrity of 
the package to 25 GHz..sup.5 Measurements of the variation in output power 
with slight changes in axial position of the uptapered indicate that back 
reflections which might introduce noise are less than -45 dB. 
Excellent packaged coupling efficiencies of approximately 30% are obtained, 
which compare favorably to the maximum of 35% obtained on the laboratory 
bench, and 22% which are obtained using standard tapered-and-lensed fibers 
with a 12 .mu.m radius tip and a 30.degree. included angle. 
The lens 24 used is a SELFOC GRIN lens (model PCH 1.8-0.22). The uptapered 
fiber 30 used was made at GTE Laboratories Incorporated. It has an 
uptapered core size of 90.mu. and a single mode fiber core size 9.mu.. The 
fiber has a cut and polished tip to reduce light scattering loss. 
The features of the package that control the uptapered-fiber optical 
tolerances are shown in Table I. Based on measurements of the package, the 
mechanical optical tolerances are shown in Table I. The use of a one piece 
carrier 14 eliminates tolerance "stack-up" arising if separate pedestal, 
lateral, and axial stops were bonded to the carrier. 
TABLE I 
______________________________________ 
Package Optical Control Tolerances 
Control Point Tolerance 
______________________________________ 
fiber tip reference 5.0 mils 
fiber tube flange 0.5.degree. of arc 
axial stops 0.5 mils 
lateral stops 0.5 mils 
pedestal height 0.5 mils 
active region reference 
0.1 mils* 
lateral reference 0.5 mils 
forward reference mark 0.5 mils 
______________________________________ 
*this item is normally defined with photolithography 
This embodiment uses epi-down lasers. This eliminates the positional 
tolerance associated with the thickness of the wafer because the light 
emitting area is essentially at the pedestal/semiconductor interface. A 
reference mark 40 on the laser 22 enables its correct positioning on the 
pedestal 16 during assembly since the active region 23 in the 
semiconductor 22 is on the reverse side and not visible. 
The GRIN lens 24 straddles a slot that determines its height above the 
carrier and its lateral position. The back edge of the lens registers with 
a raised edge on the carrier 14 that defines the axial stop 20. 
Table I compares observed tolerances for the uptapered fiber package with 
those of a typical lensed-and-tapered fiber package. These tolerances 
represent the measured misalignment which reduces the coupled power by 
about 25%..sup.2 The most important implications of this table for package 
design are: (1) the relaxed tolerance in the uptapered fiber position 
(lateral and transverse) is responsible for the increased yield, 
stability, and ease of assembly, (2) Critical tolerances (angular 
alignment and magnification) are met by built-in alignment marks and stops 
in the one-piece carrier, fiber flange, and housing, as schematically 
shown in FIG. 1. The fiber flange was designed to automatically align the 
uptapered fiber parallel to the beam within 0.5.degree.. 
TABLE I 
______________________________________ 
Tolerances for Components Within Package 
Approximate Uptapered Fiber 
Tapered and Lensed 
Tolerances Package Fiber Package 
______________________________________ 
Fiber position: 
axial (parallel to fiber) 
125 .mu.m* 4 .mu.m 
lateral (.parallel. to laser) 
25 .mu.m 0.5 .mu.m 
transverse (.perp. to laser) 
25 .mu.m 0.5 .mu.m 
Fiber angle 0.5.degree. 12.degree. 
GRIN lens 13 .mu.m Not Applicable 
Semiconductor laser 
13 .mu.m Not Applicable 
______________________________________ 
*component held to within tolerance by selfalignment to package hardware. 
FIGS. 3 and 4 are enlarged top views of the embodiment of FIG. 2a, showing 
further details of the package features which mechanically control the 
fiber optic tolerances. Referring now to these figures, two optical path 
distances, L1 (FIG. 4) and L2, (FIG. 3) should be maintained to achieve 
the correct magnification in the package 10. L1 is the distance between 
laser 22 and lens 24 while L2 is the distance between lens 24 and 
uptapered-fiber 50. Distance L1 was 15.5 mils. A magnification of 10 was 
used to optically match the semiconductor spot size 23 with the uptapered 
core. Distance L1 can be checked with a low power (30.times.) 
stereomicroscope. Distance L2 is controlled by setting the fiber tip at 
the fiber tip reference mark. L2 is 0.475 inches. 
For stability, the GRIN lens 24 is soldered to the carrier 16 with a 
reasonably hard 52/48 In/Sn 118.degree. C. solder. The solder should be 
reflowed, and the lens position adjusted along its slot if L1 is found 
incorrect when checked. 
Following active alignment, a bead of epoxy is applied to both the fiber 
tube flange 34 and the tube 32 epoxy fill hole 60. Our package allows its 
cover to be in place during the alignment. 
The fiber tube flange 34 controls the fiber angle at 90.degree.. The 
package normally does not require angular alignment. Only translational 
alignment is needed. 
Our uptapered fiber 30 requires an angular alignment of one half degree of 
arc. If the tolerances listed in Table I are maintained, and the L1 
position is checked and adjusted properly, the package will achieve this. 
If these tolerances are not strictly held, good alignments are still 
possible, but the active alignment process must include angular alignment 
of the fiber 30 rather than just lateral alignment. This is done by 
varying the angle of the fiber tube 32 slightly about the horizontal and 
vertical axes. Epoxy may still be used to join 62 the flange to the 
package. 
The completed package offers both temperature and optical power monitoring 
of the semiconductor 22. Temperature regulation is provided by the 
thermoelectric cooler 26 as controlled by the thermistor 30. Optical power 
monitoring is provided by the rear facet detector 72 that measures the 
lost light emitting from the rear of the laser 22. 
High frequency capability is provided by several features. A 50 ohm 
impedance microstrip line transmits the high speed signal between the 
laser and an SMA microwave connector 54. A short wirebond between the 
semiconductor 22 and microstrip 56 minimizes parasitic capacitances and 
inductances. In FIG. 2a, the microstrip line 56 opposite the SMA connector 
54 provides for only mechanical positioning and serves no electrical 
function. 
A second embodiment (not shown) is the same as the first embodiment except 
that the semiconductor laser 22 is mounted epi-up. This means that the 
light emitting region 23 is now near the top surface of the semiconductor 
die. The pedestal height 17 must be reduced to off-set the thickness of 
the semiconductor 22 and bring the light-emitting spot 23 back to the axis 
of the lens 24. 
This embodiment offers two advantages over the first embodiment: 
The active region 23 features in the semiconductor are directly visible, 
allowing more precise alignment to the lateral reference mark 38 on the 
pedestal 16. 
It allows for epi-up bonding of semiconductor material reducing diebonding 
yield loss present with some diebonding solders and laser structures. 
The comparative disadvantage of this design is that the wafer thickness now 
becomes a controlling optical tolerance requiring an additional wafer 
thinning processing step or alternatively a set of calibrated carriers 
with different known pedestal heights. 
It is possible to vary the design of package 10 while preserving elements 
of our invention. Variations could be both internal or external to the 
package housing. The material comprising the package housing 12 may be 
metal, ceramic or plastic. 
EXTERNAL VARIATIONS 
The diameter of the uptapered-fiber 30 may be increased requiring a greater 
magnification from the lens 24. The greater magnification is achieved by 
using a different lens or lens position. This variation, of increasing the 
magnification, results in further reduction of the lateral positional 
tolerance. 
The length of the thick section of the uptapered-fiber 30 may be altered. A 
shorter length section would make a more compact package. 
The fiber 30 may be held by a variety of different shaped holders but it 
always needs to be held rigidly. It is likely that it would always require 
some kind of flange type attachment 34 such as the one in FIG. 1 to 
maintain stability. 
Some commercial fibers are supplied with flange shaped connectors on the 
end and it is likely that uptapers will be supplied this way once the 
uptapers become commercially available. If this happens, the uptapered 
package may be designed to accommodate the commercial flange rather than 
have a special package flange. 
The mode of fastening the fiber may be varied. Different types of epoxies, 
polyesters, solders or welds may be used. In some circumstances it may be 
possible to screw, crimp, or even use an amalgam to attach the fiber 
holder to the package. 
INTERNAL VARIATION 
The package is made more compact by using stronger, shorter focal length 
lenses. In this case, the end of the uptapered-fiber is placed closer to 
the lens. 
In conclusion, we have realized the first laser package to incorporate an 
uptapered fiber pigtail. Because of the relaxed alignment tolerances 
afforded by the uptapered, external alignment and attachment of the fiber 
can be implemented. The result is an easy-to-assemble, rugged package that 
is suitable for all local loop applications, and readily lends itself to 
automated packaging techniques.