Nonlinear optics of coupled systems are new and actively developing field in modern physics. Such optical set-ups are useful not only for purely scientific research, but also for practical applications, such as multiplexers, optical couplers and supercontinuum sources. In following work we show full chain of development of nonlinear coupled systems. We derive Multimode Nonlinear Schrodinger Equations (MM-GNLSE) in a rigorous way. Next, we implement and discuss numerical implementation of MM-GNLSE via Split-Step Fourier method (SSFM). Next, we present and discuss in details designing, development and production of three-core Photonic Crystal Fibre (PCF). Finally, we present results of measuring linear and nonlinear properties of prototype fibre.