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16 1 From Optical MEMS to Micromechanical Photonics

Lens
DMD chip
110 inch

Screen
Lens
Light
source
Color
filter
Lens
Fig. 1.18. Optical layout of a projector using a DMD [1.5]. Courtesy of Larry J.
Hornbeck, Texas Instruments, USA c 1993 IEEE
Spring

Fixed
Gimbal frame
ring

Hinged
sidewall
Electrodes
100 mm
Assembly arm
Fig. 1.19. Surface-micromachined beam-steering micromirror [1.7] c 2003 IEEE

communication. Optical MEMS has become a household word thanks to
the enormous interest in fiber-optic switchingtechnology. Micromirror-based
all-optical switches are thought to be the only actual solution to wavelength
division multiplexing(WDM) because they are independent of wavelength.
Miniaturized optical switches can be changed to select different optical paths
by adjustingthe mirror tilt (without optic to electric transformation).
The micromirrors were fabricated based on the surface micromachiningof
polysilicon thin films (Fig. 1.19) in the first stage [1.6, 1.7]. Miniaturization
methods enable the creation of arrays of tiny, high-capacity optical switches,
such as those for switching256 input light beams to 256 output fibers devel-
oped at Lucent Technologies [1.7]. An optical switch of 1152 × 1152 optical
cross-connects was fabricated by Nortel. Free-space switchingwith a MEMS
micromirror array between two stacked planar lightwave circuits (PLCs) is
used to construct a wavelength-selective switch [1.39].
Recently, bulk micromachiningof crystalline silicon has been revived
(Fig. 1.20) [1.40, 1.41] because the conventional mirror surface (polysilicon)
fabricated by surface micromachiningis thin (1 µm) and deformable due to
the presence of both residual stress and a metal film coating[1.42]. The use of