Major Areas of Opportunity - Implications of Emerging Micro-and Nanotechnologies - page 51

sible. With history as a guide, there is little doubt that the development of photo-
nic crystal materials will have a major impact on optical applications.
Microelectromechanical Systems (MEMS)
MEMS are structures, devices, or systems having some parts on the scale of
micrometers that are produced by any of several techniques collectively termed
“micromachining.” They are generally called microsystems in Europe and, some-
times, micromechatronics in Japan. In broad terms, there are four classes of
MEMS. The first involves micromachined structures that have no moving parts.
Included here are channels and nozzles for fluids and guides for optical and RF
signals. The second class of MEMS is sensors that transduce some aspect of the
world into electronic data. Many MEMS sensors have been commercialized,
notably pressure sensors, microphones, accelerometers, and angular rate sensors.
The third class of MEMS includes mostly actuators, essentially the inverse of
sensors, because they transduce information into some physical, chemical, or
biological effect. They are now being made into products, primarily for commu-
nications. The last class of MEMS includes systems that involve both sensors and
actuators. Microfluidic systems already on the market, data storage systems that
promise terabit per square centimeter densities, and micro-energy systems now
under development are in this class.
Optical MEMS. Optical MEMS, sometimes called MOEMS, involve light in the
visible, infrared, or ultraviolet spectral regions. There is a natural aspect to the
interaction of light with MEMS, because the dimensions of MEMS, even though
small by ordinary standards, are large compared to the wavelength of optical
radiation. Hence, micro-optical systems can manipulate light in a diffraction-
limit regime. Further, light exerts negligible pressure on MEMS components, so
that only small forces are required for moving and holding mirrors and other
optical structures. Optical MEMS are poised to have a dramatic impact on the
optical networks that are the backbone of the Internet. In fact, they could be an
enabling element for the “all-optical” network that would eliminate the need to
convert from optical to electronic and back to optical at switching nodes. Micro-
mirrors will reflect signals from an incoming optical fiber, whatever their wave-
length, to the proper outgoing fiber. There is still electronics involved in reading
the headers on the incoming optical signals and powering the MEMS devices;
this network is not based on all-optical nonlinearities, which are generally too
weak for practical use. Other approaches to optical switching include micro-
fluidics and attenuated total internal reflection, both of which are alternative
MEMS techniques, and electrooptic switches based on either inorganic (e.g.,
LiNbO 3 ) or polymer organic electro-optic materials. Given the wide range of
requirements and applications—from high-speed modulation to individual wave-