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20 1 From Optical MEMS to Micromechanical Photonics

Optiacal fibre 2.4 mm
Pin hole

Scanning mirror

Focal point
100 mm
Tissue
Fig. 1.25. Microconfocal optical scanning microscope fabricated for minimally in-
vasive medical diagnosis and treatment (m-COSM). Reprinted from [1.53] with per-
mission by M. Esashi, Tohoku University, Japan

1.3.3 Kinetic Energy of Light

Light is conventionally applied in optical data storage such as CDs and DVDs,
in an optoelectronic information apparatus such as displays and printers, in
optical communication devices such as optical fibers and LDs, and in optical
measurements usingvarious kinds of sensors. In these applications, we have
utilized the electromagnetic aspect of light. On the other hand, in optical
MEMS and in micromechanical photonics applications, the kinetic energy
aspect of light becomes important.
Poweringof miniaturized equipments or systems by a light beam has re-
cently been rediscovered, and many kinds of transduction from light energy to
kinetic energy have been developed. The photoelectric effect was used to make
a photostrictional actuator driven by light-induced conformational change of a
polymer, semiconductor or ceramic. The photothermal effect was used to make
a tiny resonator [1.14], a micropump, a microgripper [1.54] and a waveguide
switch [1.55]. A photoformed gripper, designed for handling micro-objects in
a narrow space, is actuated by the volume change of fluid upon applying laser
power. This photothermal energy will be useful as a driving force of minia-
turized systems because of its high power density and good energy transfer
efficiency. A photoelectrochemical effect was studied for the development of a
storage battery [1.56].
A photovoltaic microdevice to cover the surface of a miniaturized sys-
tem was developed for amorphous silicon thin films triple-stacked and series-
connected to obtain a high voltage of 200 V [1.57]. A microdevice to transfer
energy via light to a microwave by combiningpiezoelectric force and an an-
tenna has been reported [1.58].

1.3.4 Micromechanical Control by Optical Pressure
Ashkin et al. demonstrated optical trappingin 1970. A great deal of the-
oretical and experimental knowledge and technology in this field has been