Page 261 - Introduction to Information Optics

246 4. Switching with Optics

Index-matching
fluid

Trench Waveguides

(b)

Fig. 4.35. MEMS switches without moving parts, (a) Unswitched beam passes straight through
the trench, (b) Switched beam bounced into the new waveguide by total internal reflection.

waveguides. InkJet technology uses small heaters near the index-matching fluid
to create a bubble at that spot. When the heaters are not turned on, the
trenches are filled with the index-matching fluid. The beam passes unimpeded
straight across the trench and continues into the solid waveguide (Fig. 4.35a).
When the optical signal needs to be rerouted, a bubble is created by the heater.
The gas bubble occupies the trench near the waveguide. In this case, total
internal reflection occurs since light comes at a sufficiently oblique angle from
a higher index medium (waveguide) to a lower index medium (gas bubble in
the trench). The beam reflects off the surface of the bubble, and moves in a new
direction into a different waveguide (Fig. 4.3 5b).
This type of switche has several interesting features. Cross talk in this tech
nology is very low compared with traditional planar waveguide technology.