Numerical modeling of logic gate in optical communication

Abstract

The thesis comprehensively reviews the propagation of soliton pulse as a signal for communication. A theoretical model for the transmission of ultrashort soliton pulse is developed by numerical solution of Nonlinear Schrodinger Equation, NLSE by using Matlab programming. This study is able to demonstrate that soliton pulse can be generated as signal bit 1 and 0 as computational elementary signal. The signal produced is in the region of time domain, hence the system is compatible for the generation in the Time Domain Multiplexing (TDM) system. Linear and nonlinear directional couplers were used in fiber optics communications. The soliton pulse is based on the secant-hyperbolic model. Results show that the soliton pulse can maintain its power even after travelling for 100 km. The soliton pulse reduces its power when the Group Velocity Dispersion (GVD) parameter, β2 is increased in the negative dispersion domain. The phase change of soliton pulse form 0 to π has shown an increase in the normalized power. However the soliton pulse exhibit chaotic behavior after a rapid increase of power at a phase of 0.8. Three models have been developed; the model of soliton code generator, soliton phase modulator, and bisoliton propagation. Two soliton input was generated inside fiber coupler and the code generator will encode its signal within the altered time difference of ±0.25t. The signal would move in the fiber coupler and the phase modulator controls the phase of the bisoliton generation from 0 to 2π. The result is the formation of optical logic AND and OR gate at the phase difference of 0.4π and 1.1π with normalized power of ~6 and parameter offset ε=0.25.