High contrast ratio all-optical 4 x 2 encoder based on two-dimensional photonic crystals

Optical encoders are circuits that are used in the design of optical processors. To reduce the size of optical devices, it is necessary to design small-scale logic circuits. In this study an all-optical 4 x 2 encoder based on 2D photonic crystals, was designed and simulated. The simple structure of this optical encoder makes it possible to build it in optical integrated circuits. Owing to its low dimensional structure and the use of simple defect paths, the delay time of the encoder will be reduced and so, the data bit rate will be increased. The obtained transmission delay time for the proposed encoder is less than 0.1 ps. Another characteristic of the proposed optical encoder is that the output optical power in "0" logic state is very low, which increases the contrast ratio as compared to the previous works. The contrast ratio CR = 16.5 dB was obtained for the proposed encoder.