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1.3 Miniaturized Systems with Microoptics and Micromechanics 17
Base layer Torsion spring
Silicon oxide
Mirror
substrate Tilt mirror

Pivot
Electrode Trench
substrate

Terraced electrode AuSn solder
Fig. 1.20. Single-crystalline mirror actuated by electrostatic force applied via ter-
raced electrodes. Reprinted from [1.40] with permission by T. Yamamoto, NTT,
Japan

(a) Blue optical disk DVD/CD (b) Blue optical disk/DVD CD

Collimated Divergent Collimated Divergent
Wavelength Wavelength
beam beam beam beam
selective selective
aperture aperture

405 nm LD 660 nm/785 nm LD 405 nm/660 nm LD 785 nm LD
Fig. 1.21. Blue ray/DVD/CD compatible optical head technology. The compati-
bility principle is based on spherical aberration correction and objective NA control
for each disk [1.45]. Courtesy of R. Katayama, NEC, Japan

silicon-on-insulator (SOI) substrates together with deep reactive ion etching
(DRIE) is now an established technology for fabricating high-performance
optical switches because of the flatness of the mirror [1.43].

Optical Heads

Various optical disk systems with a Blue ray/digital versatile disk (DVD)/
compact disc (CD) compatible optical head, a free-space integrated optical
head, and an electrostatic torsion mirror for trackinghave been investigated
for the advanced DVD [1.44]. Flyingoptical heads with various small-aperture
probes are proposed for next-generation near-field recording.
Three kinds of light wavelength λ and objective lens NA are used
for the optical heads of a Blue ray, a DVD and a CD: (λ, NA) =
(405 nm, 0.8), (650 nm, 0.6), and (785 nm, 0.5), respectively. Compatibility of
heads with different wavelengths and different NAs, is needed (Fig. 1.21) [1.45].