All-optical NAND logic gate using organic materials

Conventional electronic logic circuits in today's computers impose extreme limitations on computational speed, complexity, compactness. In highly dense electronic logic circuits the connections simply cannot handle electric signals swiftly and reliably. On the other hand, optical interconnections and optical integrated circuits are sought to provide answers to future computing and compactness demands. Optical devices are immune from electromagnetic interference and free from electrical short circuits. They have low-loss transmission and provide large bandwidth (i.e. multiplexing capability), and are manufacturable in compact sizes, are lightweight and inexpensive. Recently, we demonstrated an all-optical NAND logic gate having nanosecond response time by waveguiding two collinear nanosecond white light caused by focusing a pulsed Nd:YAG laser at 1064 nm along with a cw He-Ne laser at 632.8 nm through a polydiacetylene derivative of 2-methyl-4- nitroaniline (PDAMNA) thin film. The physics involved in the process was explained based on Z-scan studies of the same polymer using He-Ne laser. These studies show an induced absorption by an excited state, resulting in a reverse saturable absorption (RSA) in the system. The RSA figure of merit in PDAMNA was estimated. The size and sign of the real and imaginary parts of the third order nonlinearity were evaluated. These studies also demonstrate for the first time to our knowledge, that reverse saturable absorption in an optical system can be used to build similar logic gates.