Page 163 - An Introduction to Microelectromechanical Systems Engineering

142 MEM Structures and Systems in Photonic Applications

continue to seek customers for their products. The difficult economic environ-
ment has necessitated that the surviving companies develop products that are cost
competitive, especially against similar products made using alternative traditional
technologies, while passing the stringent Telcordia™ standards of reliability (see
Chapter 8). MEMS has become widely accepted as the fabrication technology of
choice for a number of functions, in particular for dynamic attenuation of the light
intensity inside the fiber, known as variable optical attenuators (VOAs); beam steer-
ing of light among an array of fibers, also known as optical switching or cross con-
nects; and, to a lesser extent, as components within tunable lasers. It is important to
note that while the primary market that drove the development of such devices was
fiber-optic telecommunication, there remain other applications, albeit in smaller
markets, that can benefit from these innovations (e.g., imaging, microscopy, and
spectroscopy).
We examine in this section four different types of MEMS-based photonic
devices whose sole function is to manipulate or generate light. We begin first
with two distinct embodiments of a tunable laser product, one from Iolon, Inc.,
of San Jose, California, and the other from Santur Corporation of Fremont,
California. Next, we describe a wavelength locker from Digital Optics Corporation
of Charlotte, North Carolina. We then follow with an optical switch from Ser-
calo Microtechnology, Ltd., of Liechtenstein; then a beam steering mirror, or
three-dimensional (3-D) optical switch, from Integrated Micromachines, Inc., of
Irwindale, California; and finally a VOA from Lightconnect, Inc., of Newark,
California.

Tunable Lasers
Lasers are at the core of fiber-optical communication where information is impressed
upon streams of light inside a fiber. The advent of wavelength-division multiplexing
(WDM) in the last decade offered a tremendous increase in information bandwidth
by multiplexing multiple wavelengths into a single fiber. But as the number of wave-
length channels increased to 100 and beyond, wavelength agility and the ability to
switch between channels without human intervention has become of great impor-
tance. This is where tunable lasers promise to play a significant role [4].
Tunable lasers as bench-top test instruments have achieved a great degree of
technical maturity in the recent past. Companies such as New Focus, Inc., of San
Jose, California, and Agilent Technologies of Palo Alto, California, have offered
such products for many years. But the innovation brought forth by MEMS technol-
ogy aims to miniaturize these instruments from bench-top dimensions to fit in the
palm of a hand. This miniaturization is necessary because equipment space inside
central offices is very limited—a central office houses racks of electronic and optical
equipment for processing and routing of data and voice. The use of tunable lasers in
telecommunications has been primarily in the wavelength range of 1,528 nm to
1,565 nm (known as the C-Band) and 1,570 nm to 1,610 nm (known as the L-Band).
The International Telecommunication Union (ITU) of Geneva, Switzerland, has
specified the use to be on a grid of discrete channels throughout the C- and L-Bands
at optical frequencies spaced 50 GHz (~ 0.4 nm) apart [5]. This grid specification
brings forth the need for a wavelength “locker” to prevent a laser from drifting from
its assigned wavelength on the ITU grid.