Major Areas of Opportunity - Implications of Emerging Micro-and Nanotechnologies - page 53

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pixels from the digital mirror device sold by Texas Instruments (more detail on
the fabrication of this device is given in Chapter 4). A micrograph of part of an
array of thermoresistive pixels from a Honeywell uncooled infrared imager is
also shown (lower right).
The source is a VCSEL in which the cavity length, and hence the output
wavelength, can be tuned by moving a micromirror on a cantilever with a volt-
age-determined electrostatic force. 81 VCSELs are becoming the source of choice
for optical fiber networks, and the tunability of such devices is useful for wave-
length agility.
Micromirrors have been made in many different configurations individually
and in arrays. The round mirrors in Figure 3-6 were developed by Lucent Tech-
nologies for switching signals from one optical fiber to another. 82 They are 500
micrometers in diameter and can be tilted controllably in two directions. Such
mirrors have been made into arrays for switching optical pulses between 1,024
incoming fibers to the same number of exit fibers. The system containing the
MEMS mirror array, termed a lambda router, is capable of passing all the current
Internet and telephone traffic in the world.
Alternative MEMS optical switches based on switchable gratings and on
fluidic devices (bubbles) are also under development. Small as well as large
companies are involved in developing MEMS for network switching. In 2000,
four start-up companies making optical MEMS mirrors were sold for a total of
almost $6 billion in stock; in the spring of 2002, their value was much less. The
decline in the stock market and in the pace of telecommunications infrastructure
development has delayed the introduction of MEMS switches into the long-haul
communications grid, but they are now beginning to be used. MEMS mirror
arrays are proving important not only for the communication of information but
also for its display. A digital mirror device (DMD) 83 is the display engine for
conference room projectors and, soon, for digitally fed movie theaters and home
entertainment centers. The micromirrors in the DMD flip

tilted position in the inset. The drawing on the left shows two of the 16- µ

10 degrees to pass the
incident light to the screen or into a beam dump. The device consists of three
layers, the lower being electronic, the middle having the mechanics, and the top
being the optical mirror. The torsional hinges supporting the mirrors are 5

±

×
0.1 micrometers, and they last for over 10 billion cycles. Each of the mirrors is 16
mm on a side. DMDs now on the market contain millions of mirrors. Of all the
systems ever produced by humankind, these devices have the most moving parts.
It has been reported that 100,000 of these devices have been sold in the past few
years, so there are over 50 billion MEMS mirrors already in use for this single
optical MEMS display technology (see Chapter 4 for a discussion of the manu-
facturing challenges that had to be surmounted).
The last type of optical MEMS is detectors, which are generally found in
arrays to form imagers. They are particularly important for the imaging of objects
in the infrared (IR) region, where the heat from people and ordinary objects is

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