Page 37 -

26 1 From Optical MEMS to Micromechanical Photonics
distributed feedback laser diode (DFB LD) with a wavelength of 1.3 µm, a
photodiode (PD) and a polyimide waveguide on a silicon substrate.
Figure 1.34a shows the velocity measurement principle. The DFB LD in
Fig. 1.34b illuminates the human skin and the lights scattered by the flowing
blood and by the stationary tissue interfere on the PD. The beat frequency
between the two depends on the average velocity of the blood flow. This
integrated flow sensor can be positioned directly on a finger and permits real-
time monitoringof the blood flow.

1.5 Future Outlook of Optical MEMS
and Micromechanical Photonics

One advantage of the optical method in microdevices is that it is not af-
fected by electromagnetic interference. This is particularly critical for highly
integrated devices. Other advantages are its remote control and friction-free
characteristics, which are of great value in optical tweezers and optical rotors.
An earlier disadvantage was that the optical technique required lenses and
fiber systems to guide the light to a PD or a moving mechanism, but recent
micromachiningtechnology has made it easy to eliminate these lenses and
fiber systems, leadingto the easy integration of optics, mechanics and elec-
tronics. In this section we present current and potential applications of the
optical MEMS and micromechanical photonics.
Various kinds of optical MEMS/micromechanical photonics devices have
been fabricated on Si substrates, polymers, and III–V compounds. They in-
clude a micrograting/micromirror with a rotating stage for optical inter-
connects, a micromirror scanner for displays and printers, a micromirror
switch/tunable LD for wavelength division multiplexing (WDM) systems, in-
formation and communication apparatus, and sophisticated positioningsys-
tems at submicrometer and nanometer levels. Other applications may be in
medical instruments such as micropumps for disposable drugdelivery sys-
tems [1.52], medical microsystems for minimally invasive diagnosis and treat-
ment [1.53] and µ-TAS [1.48].
Researchers have been usingvarious types of controlling/drivingmethods:
for example, optical, electrostatic, electromagnetic, and piezoelectric methods,
as shown in Table 1.2. Optical force is classified into optical pressure, photo-
electric, photothermal, and photo-electrochemical effects. Table 1.2 shows al-
ready proposed or commercialized optical MEMS/micromechanical photonics
devices and systems classified accordingto the drivingmethod and materials
used. Refer to the fabrication method and reference number given after each
device/system. In the table, we can see not only conventional sensors and
actuators but also the recently developed tunable LDs, optical switches, scan-
ners, mirrors, optical heads, near-field probes, control devices with nanometer
precision, and medical microsystems [1.73] for diagnosis and treatment.