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12 1 From Optical MEMS to Micromechanical Photonics

Characteristics of MEMS
– Viscosity >> inertia Æ Surface effect increase
2
– Response time [L ] Æ Quick response
2
– Reynolds number [L ] Æ Laminated flow
5
– Moving energy [L ] Æ Low energy
– Effect on environment Æ Environmentally friendly
Technologies of MEMS
– Fabrication: micromachining
– Drive force: electric, optic
– Material: silicon, compound

Optical MEMS
– Sensors
– Switches
– m-TAS

Fig. 1.12. General characteristics of scaling laws: the merits of miniaturization

generating electrostatic force is easier to fabricate in a limited space than the
inductance coil that generates the magnetic field for actuation. Actually, to
drive thick and heavy MEMS [1.25], electromagnetic force is used because the
electrostatic drivingforce is too weak.
We deal mostly with micrometer-sized devices. In the micrometer regime,
conventional macrotheories concerningelectrical, mechanical, fluidic, optical,
and thermal devices require corrections. Specific properties of the thin film
material differ from those of bulk. Shape change due to thermal stress or fast
movement occurs in the micromirror fabricated by surface micromachining,
which degrades the optical quality of the laser beam.

1.3.2 Light Processing by Micromechanics
Since light can be controlled by applying relatively low energy, the electro-
static microstructures such as moving mirrors or moving gratings have been
fabricated on the same wafer. Applications of movingmirrors in micro posi-
tioning have begun to appear recently, and many kinds of digital light switches
have been demonstrated. These include a DMD [1.5], an optical scanner [1.33],
a tunable IR filter [1.25], and a comb-drive nickel micromirror [1.34]. A nickel
micromirror driven by a comb-drive actuator was fabricated by nickel surface
micromachining. The micromirror was 19 µm high and 50 µm wide and the
facet reflectivity was estimated to be 63%. A microstrip antenna was fab-
ricated on a fused quartz structure that could be rotated to adjust spatial
scanningof the emitted microwave beam [1.35].