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1.5 Future Outlook of Optical MEMS and Micromechanical Photonics 29
The reduction of friction force and the adoption of contact sticking-free
mechanisms are important in microscale operation. Therefore, microstructures
without contact, for example, a micromirror suspended by two torsion hinges
[1.5], a cantilever [1.17], a deformable membrane [1.16], and a flyingslider
[1.69] are preferably used to prevent friction and sticking.
Figure 1.35 shows the direction of development in these technical fields.
The horizontal axis shows miniaturization (size) and the vertical axis shows
the number of functions that characterize the optical MEMS/micromechanical
photonics devices. To evaluate the number of functions, we first considered
how optics, mechanics, and electronics are combined (1) simple assembly,
(2) hybrid, and (3) monolithic. Second, in how many directions can the de-
vice/system move (1) 1D, (2) 2D, and (3) 3D. Finally, what kind of functions
does the device/system have: measurement, feedback control, recognition, and
remote power supply. We gave a point for each function. The maximum num-
ber of points becomes 3 + 3 + 5 = 11. Many kinds of proposed optical MEMS
and micromechanical photonics devices are seen, and the fabrication of mole-
cular devices is the final goal in the figure.
It is apparent from the figure that there are two development directions ow-
ingto miniaturization. First, as the device/system size decreases, the number
of functions decreases, for example, from an MDF (exchanger: main distribut-
ingframe) to an optical disk system to optical interconnection to an actuator
and to a sensor. It is a natural direction and has led to the commercializa-
tion of many products (white circles), as seen in the figure. Second, as the
device/system size decreases the number of functions increases, for example,
from a sensor to an optical resonator to an electrostatic motor to an opti-
cal motor and to a molecular device. It is an ideal and a research-oriented

11
In commercial
Under development
Molecular device
9 MDF Optical disk Rotor / Mixer
Number of function 7 5 Fiber connector DMD m-TAS Motor Alignment
Pump
Scanner Bow tie
Switch
probe
Tunable LD
IR sensor
Blood flow sensor
Surface actuator
Acutuator Resonator Encoder
Diagnosis
3 Pressure sensor
probe
Accelerometer
1
1.0 m 1.0 mm 1.0 mm
Optical MEMS size
Fig. 1.35. Proposed and commercialized devices/systems fabricated using optical
MEMS and micromechanical photonics. The horizontal axis is device/system size
and the vertical axis is the number of functions