Full text of DOI:10.1557/mrs2001.73

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MEMS devices offer a number of advan-
tages to optical designers. These devices
have proven to be surprisingly robust and
long-lived, especially ones whose parts
flex without microscopic wear points. Re-
search in this area has been extremely
active over the last decade, producing mi-
croscopic versions of most macromachines.
The size scale at which these machines
work well makes them a particularly good
match to optics problems where the de-
vices, structures, and relevant wavelengths
range in size from one to several hundred
micrometers. Using integrated-circuit (IC)
batch-processing techniques, MEMS de-
vices are economical to produce because
many can be made simultaneously. In ad-
dition, designers and manufacturers can
exploit the extensive capabilities of the
IC fabrication industry and profitably use
previous-generation equipment. In an era
in which an IC factory costs a billion dol-
lars and is obsolete in less than five years,
the ability to reuse the equipment for a
new class of cutting-edge products is very
appealing. IC fabrication techniques also
allow designers to integrate microme-
chanical, analog, and digital microelectronic
devices on the same chip, producing multi-
functional integrated systems.
MEMS for Light-Wave
Networks
C. Randy Giles, David Bishop,
and Vladimir Aksyuk
Introduction
Why MEMS Devices For
Light-Wave Systems?
As demonstrated in this issue, the
emerging field of microelectromechanical
systems (MEMS) is beginning to impact
almost every area of science and technol-
ogy. MEMS have the potential to revolu-
tionize light-wave systems. Microdevices
such as optical switches, variable attenua-
tors, active equalizers, add/drop multi-
plexers (ADMs), optical cross-connects
(OXCs), gain tilt equalizers, data trans-
mitters, and many others are beginning to
find ubiquitous application in advanced
light-wave systems. This article shows
examples of these devices and briefly
describes how they function.
Shown in Figure 1 is a plot of the system
capacity of light-wave systems as a func-
tion of time. As can be seen, driven by the
explosive growth of the Internet, the rate
of progress surpasses even that of Moore’s
law, the prediction that transistors will
double in speed about every 18 months.
For light-wave systems, the doubling time
for system capacity is 6–9 months. There-
fore, light-wave systems architects must
quadruple system capacity every year, but
may only increase costs by a factor of 2.
For equipment vendors, staying on this
trend is quite a feat. MEMS have the po-
tential to make it possible.
Where in a Light-Wave Network
will MEMS Devices be Applied?
Work at Bell Laboratories, Lucent Tech-
nologies, on optical MEMS has focused
Figure 1. A plot of the evolution of
light-wave system capacity as a
function of time.
Figure 2. Schematic diagram of a light-wave network with MEMS applications shown as
red dots.
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MEMS for Light-Wave Networks
on a number of devices such as optical
modulators, variable attenuators, switches,
add/drop multiplexers, active equalizers,
and optical cross-connects. Figure 2 shows
an overview of places in light-wave net-
works where applications for MEMS com-
ponents are implemented. Each red dot is
a place where MEMS can be the solution
of choice.1–4
Figure 3 is a micrograph of a 1 ꢀ 2
(1 port in, 2 ports out) MEMS optical switch.
The mirror is connected to a “see-saw”
that either reflects the light from the opti-
cal fiber on the left to the fiber at right
angles to it or moves out of the way to
allow the light to go straight through into
the other fiber. Figure 4 shows a micro-
mirror for use in a variable attenuator.
Light from a fiber at right angles to the
mirror is reflected to an output fiber, and
the coupling between the two can be
adjusted by applying a voltage to the elec-
trode to the left of the large mirror. Fig-
ure 5 is an array of micromirrors for use in
an add/drop multiplexer. In operation, each
wavelength of light in an optical fiber gets
spatially demultiplexed by a grating and
lands on its own mirror, to be correctly
routed to either the output port or the
drop port. Shown in Figure 6 is a two-axis
Figure 7. The first large MEMS-based
optical cross-connect (OXC).
micromirror for use in an all-optical cross-
connect. The mirror is doubly gimbaled so
that light can be routed in two directions
to allow complex switching functions to
be accomplished, leading to MEMS-based
optical cross-connects with a petabit ca-
pacity (1000 terabits). Figure 7 shows the
first MEMS-based large OXC (optical cross-
connect). Such switches have very large
port counts, low losses, fast switching
speeds, and are relatively low-cost.
Figure 5. An array of micromirrors for
use in an add/drop multiplexer.
Summary
With MEMS devices such as these now
being deployed in active light-wave net-
works, the new capabilities presented by
MEMS-based optical devices makes them
well-situated for future commercial growth.
Figure 3. A 1 ꢀ 2 (1 port in, 2 ports out)
MEMS optical switch.
References
1. C.R. Giles, B. Barber, V. Aksyuk, R. Ruel, L.
Stulz, and D. Bishop, Photon. Technol. Lett. 1998.
2. R. Giles, V. Aksyuk, B. Barber, A. Dentai, E.
Burrow, C. Burrus, L. Stulz, J. Hoffman, B.
Moyer, and D. Bishop, “Highly Efficient Light-
Actuated Micromechanical Photonic Switch for
Enhanced Functionality at Remote Nodes,”
presented at the Optical Fiber Conference, San
Jose, CA, 1998.
3. A.G. Dentai, E.C. Burrow, C.R. Giles, C.A.
Burrus, and J.C. Centanni, Electron. Lett. 33
(8) (1997) p. 718.
4. J.E. Ford, V. Aksyuk, D.J. Bishop, and J.A.
Walker, J. Lightwave Technol. 17 (1999) p. 904. ꢀ
Figure 4. A micromirror for use in a
variable attenuator.
Figure 6. A two-axis micromirror for use
in an all-optical cross-connect.
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