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1.4 Integrated Systems with LDs and Micromechanics 23

Laser diode
(LD1)

Laser diode (LD2)
GaAs Microcantilever

Fig. 1.29. Photograph of central part of a resonant sensor

Mirror

Photodiode
0.6 mm
U-shaped LD

Microlens
Gap

Scale Pitch L
Fig. 1.30. Schematic drawing of an optical encoder consisting of a photodiode (PD),
a U-shaped laser diode (LD), and microlenses [1.68]

A microcantilever (MC), LD, and a photodiode (PD) have been fabricated on
the surface of a GaAs substrate, as shown in Fig. 1.29. Possible applications are
resonant frequency detection sensors such as accelerometers, and mechanical
filters such as those for synchronizingsignal detection, which are described in
Sect. 2.4.2 [1.17].

1.4.3 Optical Encoder
Elimination of bulky optical components, includinga beamsplitter, a reflection
mirror, a photodiode, and a collimatinglens, will lead to adjustment-free,
cost-effective small optical devices. An optical encoder consistingof a PD, a
U-shaped LD, and microlenses, as shown in Figs. 1.30 and 1.31, was proposed.
It has been evaluated to measure the relative displacement between a scale
grating and the encoder itself with a resolution of 0.01 µm [1.68].
When the encoder moves a distance x relative to the grating, the phase
shift of the light refracted at the grating of pitch Λ is + 2πx/Λ for one etched