Page 498 - Introduction to Information Optics

9.2. Parallel Optical Logic and Architectures

elector
array

Fig. 9.6. Free-space programmable logic array based on a crossbar switch [7. 11].

can be expressed as

(9,2)

Thus, the AND operation can be implemented by inverting the input first, then
performing the OR operation, and finally inverting the ORed outputs. The
final sum of product is obtained by performing the OR operation on all the
product terms. Therefore, a sum of products can be achieved by a NOT-OR-
NOT-OR sequence. Correspondingly, an optical programmable logic array
can be constructed based on a crossbar interconnection network, as shown in
Fig. 9.6 [7,11]. The switch SLM can be dynamically programmed to imple-
ment various operations. In this architecture, a LCLV is used for NOT
operation, and all the products are collected in the detector using a cylindrical
lens. A control unit constructed with free-space holographically interconnected
1-nanosecond-latency optoelectronic NOR gates is presented in [59]. Figure
9.7 shows a crossover interconnected OR-NOR gate array for a serial adder
[58].
Recently, a logic array processing module using an electron-trapping (ET)
device has been proposed (Fig. 9.8) [23]. The ET device has the advantages of
high resolution, nanosecond response time, and high sensitivity. The ET device
fabricated can be made from Eu- and Sm-doped CaS. Both ground and excited
states of the impurities exist within the bandgap of the wide-bandgap host
material. Short-wavelength visible light, such as blue, excites electrons from the
ground state of Eu which are then transferred over to Sm. The electrons can
remain in the ground state of Sm for a long time. But subsequent exposure to
infrared light excites the trapped electrons to the excited state of Sm. Then the
electrons transfer to the excited state of Eu and emit red light while returning