Page 174 - Optical Communications Essentials

Active Optical Components

164 Chapter Ten

Figure 10.1. A simple example of a MEMS
actuation method. The top shows an off posi-
tion, and the bottom shows an on position.

Figure 10.2. The use of MEMS technology to
make a tunable VCSEL.

a slight variation on the VCSEL structure illustrated in Fig. 6.12. In the con-
figuration shown in Fig. 10.2, the top curved external mirror membrane can be
moved up or down. This action changes the length of the lasing cavity and hence
changes the wavelength of the light emitted by the laser.
Initially MEMS devices were based on standard silicon technology, which is a
very stiff material. Since some type of electric force typically is used to bend or
deflect one of the MEMS layers to produce the desired mechanical motion, stiffer
materials require higher voltages to achieve a given mechanical deflection. To
reduce these required forces, recently MEMS devices started being made with
highly compliant polymeric materials that are as much as 6 orders of magnitude
less stiff than silicon. This class of components is referred to as compliant
MEMS, or CMEMS. This technology employs a soft, rubberlike material called

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