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Dense Multi-Port Optical Component Solutions
Using Impact Mount Technology (IMT)
Michel Rondeau, Shin-Lo Chia
Valdor Fiber Optics Inc., 2621 Barrington Court,
Hayward, CA 94545
Tel:
(510) 293-1212, Fax: (510) 293-9777 email: michel@valdor.com
Davis
H. Hartman
11451
East Desert Troon Lane, Scottsdale, AZ 85255
Tel: (480) 513-2585, Fax: (480) 513-0608,
email: dhhii@ieee.org
Abstract: Impact mount technology (IMT) is a method of
manufacturing low cost fiber assemblies.
We describe a progeny of IMT, called HeptoPort,
which represents a major manufacturing breakthrough for scalable low cost
self-aligned, multi-port optical component design. Assembly technique and physical
architecture are described.
Ó2000 Optical Society of America
OCIS codes:
(060.2340) Fiber Optics Components, (220.1140) Alignment
1.
Introduction – System Context
Currently, in the telecom industry, technology is far ahead
of the marketplace. Of the three
design drivers, cost, performance, and reliability, cost heavily
dominates the list. Market
dynamics are pressuring manufacturers to produce fiber optic components
at very low cost; but they cannot support the economy of scale that
traditionally accompanies high volume manufacturing.
There is,
however, still demand for performance and reliability at the right
price. Important performance
issues such as wavelength and port scalability, loss uniformity, and
modularity can only be achieved through manufacturing innovation, whereby
tight process control parameters produce the desired results. The emerging importance of
manufacturing innovation to component and module performance represents a
paradigm shift for the optical communications industry [[i]]. Impact Mount Technology (IMT), and its
progeny, HeptoPort™, typifies this paradigm
shift. Multiple ADMs, DWDM selectors, isolators, interleavers,
and many other functions can be incorporated in a single component, sharing
the cost of expensive elements such as filters, lenses, etc.
2.
Impact Mount Technology (IMT)
Figure 1 - (a) Schematic
depiction of the IMT process. The metal
ferrule is compression fit directly onto the glass surface of the optical
fiber. (b) Photograph of a Kovar ferrule impact mounted with an on 8° APC bare
fiber.
IMT is a radial compression fit of a ductile metal around
a cylindrical glass surface. The need to metallize
optical fiber is obviated by Impact Mount Technology (IMT).
Figure 1 illustrates a single fiber ferrule IMT
process. Attachment of metal
ferrules to the fiber(s) occurs in one fast mechanical action. This action, called the impact, occurs
between the stripped fiber and ferrule, using a precision impact mount
die. The Impact Mount connectors/ferrules are made from various metal
alloys, the most common types being stainless steel and copper-nickel
alloy. The main body of the connector can be all metal or constructed
with glass-reinforced polymer.
For a single fiber operation, the result is a hermetic
mechanical fit of the fiber to the inside of the ferrule. The process satisfies Telcordia GR-488 environmental exposure
requirements. Fibers with IMT
ferrules maintain helium leak rates of 2.7x10-11 atm.-cc/s over 2000 thermal cycles of ‑40oC
to 100oC. Pull-test
results on the fiber pigtails exceeded the 1kg requirement and the fiber
piston movement was typically less than 80nm. The ferrule is attached to the package
via laser welding or solder processing.
The IMT process is well
suited for machine automation. It
is used in production of fiber pigtails for telecommunications
applications [[ii]]. The fiber pigtail preparation may also
be readily integrated with automated alignment and attachment stations
when using IMT to attach the ferrule onto the fibers.
3.
HeptoPort Technology
Experience with IMT has led to a new concept for affixing
and terminating multiple fibers, with extraordinary self-alignment
features. The mechanical
compression in IMT is so uniform that it can be used to affix fiber
bundles in hexagonal close-packed arrangements within a ferrule. The circular symmetry inherent to
hexagonal close-packed fiber bundles lends itself naturally to the IMT
method. IMT guides, in one
instantaneous action, arrays of stripped optical fibers to their natural
hexagonal close-packed arrangement, like marbles falling into a box. The alignment of the positions of the
centers of the surrounding “planetary” fibers, relative to the center
“sun” fiber, is determined entirely by the uncertainties in fiber outside
diameter, circularity, and core/cladding concentricity. These uncertainties are less than 0.6
microns, worst case, for the seven-fiber HeptoPort™
configuration.
Figure 2 shows a scanning
tunneling electron microscope photograph of the end face of an IMT
ferrule mounted with seven ports.
The ductile metal has surrounded the fiber bundle, and all seven
fibers are in contact with each other.
They have found their naturally preferred positions in the
hexagonal close-packed configuration.
Figure 2
- STEM photograph of a HeptoPort
structure, showing self-alignment of the seven fibers.
Figure 3 –
Diagram of the HeptoPort™ architecture, including
seven-fiber IMT multi-port I/O, expanded beam optics, and processing
element. Different processing
elements can be incorporated into this architecture, resulting in
different functions, without requiring retooling.
The HeptoPort concept is embodied in a physical
architecture, shown in Figure 3.
This architecture suggests a new genre of multi-port applications
in the optical communications industry.
The technology and its associated architecture are called HeptoPort.
Utilizing IMT and expanded beam optics as an integral part of the
physical structure, it is possible to produce a variety of external
functionalities by implementing different processing elements in the HeptoPort body.
Two examples of this concept are WDM add-drop multiplexers and
isolators.
4.
Applications
 A
typical bill of materials for an opto product
consists of 60 to 70% opto/package-related
items (Figure 4). Most of this
cost is consumed in solving the difficult optical alignment issues, and
then qualifying the products using the chosen solution. HeptoPort™
gives the designer a means to reduce alignment and packaging costs
directly. Additionally, these
costs can be amortized over a number of independent units. This is accomplished by sharing multiple
ports over a single ferrule, which is as easy to align as a single
unit. An added benefit to this
approach comes with the compact design of the ferrules. Fiber pitch using HeptoPort™
alignment is 125 microns; twice as small as the MT array configuration
offers. For example, using HeptoPort™ multi-port solutions, arrays of hexagonal
close-packed arrays of single mode fibers could be aligned to VCSEL
arrays patterned in the same array configuration. The result would be seven, 10, or even
37 fiber/VCSEL devices aligned using methods not too different than those
employed for single fibers.
Using HeptoPort technology,
arrays of like-functions can be integrated onto the same physical
structure. Implementing the HeptoPort architecture for integrating multiple
components dramatically reduces cost.
For a 2x1 add/drop multiplexer the number of thin film
filters and GRIN lenses is halved.
Thus, there is reduction in module component bill-of-materials
(BOM) cost of 50%. The reduced
degrees of freedom and component alignment variances also allows for
lower assembly costs. The
multiplexer footprint area is halved.
This configuration also improves channel isolation by ‑10dB,
and allows for bi-directional multiplexer operation.
Two examples of the concept
are ADMs and isolators. In each case, the critical processing
element (filter, in the case of ADMs, and
quarter wave plate, for isolators) is shared among a number of
functionally independent, but coexisting units. Since an ADM is a three-port device,
two units can be implemented in a single 2‑mm HeptoPort
ferrule. For isolators, which are
two port devices, up to seven can be shared, with directionality being an
application-dependent design parameter.
Clearly, many other passive optical functions using HeptoPort can be imagined. Because multiple fiber arrays are
self-aligned, and because circular symmetry is preserved, alignment of
arrays of fibers to active electro-optics, such as VCSEL arrays, is
greatly alleviated.
Table 1 shows histogram data
on port reflection and throughput loss, for a representative sample of
ten three-fold OADM units, integrated onto the HeptoPort
seven-fiber structure. As shown,
both reflect-port and pass-port loss are not only low, but consistent
across the tri-fold units in each HeptoPort
structure, and from one tri-fold unit to the next.
Table 1
5.
Summary
IMT and HeptoPort represent a
paradigm shift in optoelectronic packaging. Offering unparalleled self-alignment
features with significant cost reduction for the module designer, HeptoPort opens an entirely new set of physical
design options for the optical networking industry.
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