Page 221 - Introduction to Information Optics

206 4. Switching with Optics

D

•lout

Fig. 4.3. A nonlinear FabryPerot etalon.

Obviously T is a function of <5. Figure 4.4 plots T versus d for R i — R 2 — R.
The maximum transmittance is unity and the minimum transmittance ap-
proaches zero as R approaches unity. Therefore, the switching operation can
be realized by changing n. If the etalon is initially set at the maximum T, change
in d will switch Tto a low value.

4.2.2. i. Self-switching
When a nonlinear medium is placed in the etalon, the phase delay becomes

S = (2n/Wn 0 + n 2I)D, (4.8)
where / is the total intensity in the etalon. In this case, the transmittance in Eq.
(4.7) is a function of total intensity. On the other hand, the total intensity is
related to the input intensity

(4.9)
= I. mT/B t

0 2rrm 2(m+l)rc 5

Fig. 4.4. Transmittance of a Fabry -Perot etalon as a function of 6 for R, = R 2 = R.