Page 354 - Optical Communications Essentials

Manufacturing Issues

344 Chapter Twenty

complete, a ferrule is loaded automatically and attached to the prepared fiber.
Before attachment, a metered amount of thermally curable epoxy is dispensed
into the ferrule. The fiber is inserted into the ferrule, and the assembly is
heated to cure the epoxy. After the ferrule attachment process is complete, pig-
tails are unloaded into an empty cassette as a fiber pigtail. The entire process
is controlled by a personal computer. The system software provides all operator
controls, including multilevel user access, error logging, process statistics, and
diagnostics. The throughput capability is 120 fibers per hour.

20.4. Packaging
The term packaging refers to the encapsulation of a device in a form that takes
into account optical power coupling, thermal management, mechanical support,
and hermetic sealing for environmental protection. In addition there are the
standard concerns related to electrical connections. These concerns are the
same as for ordinary microelectronics packages and are relevant only for active
devices, since passive components do not have electrical connections.

20.4.1. Optical connection
The optical connection is the most critical aspect of a photonics package. Since
light must be coupled efficiently into very small fiber cores, the optical connec-
tions require extremely precise alignment. They are especially sensitive to axial
misalignments, as noted in Sec. 8.3. In some cases alignments need to be held
to a fraction of a micrometer in order to have an acceptable component. To
make matters more complicated, passive devices often have multiple couplings,
all of which need to be precision-aligned simultaneously.
Micropositioning machines are available commercially that allow six-axis align-
ments to a resolution precision of 0.1 nm. Such systems usually can be software-
controlled to allow their use for both development techniques and manufacturing
procedures. Typically included with such machines is a video magnification
system with illumination.

20.4.2. Thermal management
Management of thermal effects is an important factor for both active and passive
devices. Thermal gradients within or across a device can lead to misalignments of
components within a device package, which may cause a reduction in optical
power coupling efficiency. In addition, heat generated within active components
needs to be dissipated in order to avoid degradation of the device. In most cases
this is done by means of a thermoelectric (TE) cooler. Typically the TE cooler is
soldered to the package base, which later will be mounted on an external heat sink.
A TE cooler (which also is known as a Peltier cooler, since its function is based
on the Peltier effect) is a semiconductor-based electronic component that func-
tions as a small heat pump. When a low voltage is applied to a TE module, heat

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