Page 223 - Introduction to Information Optics

208 4. Switching with Optics

::::FT.ln
Time
I in

Fig. 4.6. Set-rest operation in an optically bistable system.

controlled by the control intensity I c. The required amount of change in d for
switching depends on the linewidth of the transmission peak.
The control signal should be at a different wavelength or polarization, or
different incident angle from the data signal, such that it can be separated from
the data signal at the output.

4.2.3. NONLINEAR DIRECTIONAL COUPLER

A nonlinear directional coupler is an intensity-dependent routing switch.
Figure 4.7 shows the structure of a directional coupler. It consists of two
waveguides placed closely to one another for a finite distance. These wave-
guides are coupled together through their overlapped evanescent fields. They

z =0

P»Pc

B P«Pc

Fig. 4.7. Nonlinear directional coupler.