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18 1 From Optical MEMS to Micromechanical Photonics

Optical disk

Micro-Fresnel
lenses
LD

45
458 mirrors
Z Rotary beamsplitter
Y
X Integrated PD
Si FS-MOB
Fig. 1.22. A free-space optical pickup head integrated by surface micromachining
[1.20]. Courtesy of Ming Wu, University of California, USA

The compatibility principle is based on spherical aberration correction and
objective NA control for each disk. Optical MEMS technologies are applied
to control NA (aperture) depending on the wavelength [1.45], to integrate op-
tical components (Fig. 1.22) [1.20], and to track the optical disk groove [1.9].
Rotable microstages are implemented by a suspended polysilicon plate fabri-
cated by micromachining.
In order to realize an ultrahigh-density optical disk, a tiny-aperture
probe is needed. However, the optical transmittance decreases rapidly as the
aperture diameter decreases below 100 nm. To increase the transmittance, a
bow–tie probe with an actuator driven by electrostatic force was successfully
fabricated (Fig. 1.23) [1.46]. The on-chip actuator provides not only a narrow
gap to enhance the intensity of the near field but also precision alignment of
the optical components.

µ-TAS/bio MEMS
Chip-scale technologies are diversifying into the field of microfluidics, such
as a sample analysis system for physiological monitoring, sample preparation
and screening, and a biomedical treatment application for a new surgical tool
and drugdelivery [1.47].
A micrototal analysis system (µ-TAS) [1.48] is expected to reduce inspec-
tion time or the amount of reagent needed. The system shown in Fig. 1.24
comprises inlets for the sample and reagent loading, microchannels with a
mixingchamber and an analysis chamber, and outlets for sample wastes.
In a microchannel, mixingis performed mainly by diffusion owingto the
small Reynolds number. To promote a diffusion effect by interweavingtwo
fluids, mixingdevices such as micronozzle arrays to increase the contact area,