Page 257 - Introduction to Information Optics

24: 4. Switching with Optics

Thickness = t

Fig. 4.32. A comb drive with interdigitated fingers.

substrate. In addition, there may be lateral instability depending on how the
actuator is supported. If lateral stiffness is insufficient, the upper actuator will
be attracted sideways and fingers may stick to the fixed ones.

4.4.3. MEMS OPTICAL SWITCHES

Optical switches based on MEMS have several advantages. They can form
very large arrays in a very compact volume with low signal attenuation. They
also have high contrast and low cross talk, and are wavelength and polariz-
ation independent. Quite a few MEMS switching schemes have been proposed
and demonstrated. We will discuss two examples of these switches.

4.4.3.1. Deformable Diffraction Gratings
Deformable diffraction gratings are an array of microelectromechanical
switching devices that manipulate light by diffraction [40]. Figure 4.33 shows
a cross section of one pixel for a switched and nonswitched state. Electrostati-
cally deflectable microbridges are made from silicon nitride that is deposited
in tension over a silicon dioxide sacrificial spacer. The bridges are overcoated
with aluminum for high reflection. The air gaps are formed by using an
isotropic wet etch to selectively remove the sacrificial spacer.