Finite difference time domain (FDTD) analysis was used to design a photonic integrated circuitry (PIC) based on a Silicon-on-Insulator (SOI) structure. Light coupling efficiency from a single mode photonic crystal waveguide (PCW) into a single mode fibre (SMF) through adiabatic tapered waveguide and microrings based on resonance acting as spot-size converters (SSCs), is demonstrated. Optimisation of each component and their integration into a single optical chip is presented. SSCs are optimised in order to reduce back reflection and increase coupling efficiency between all devices constituting the optical chip. Significant reduction of back-reflections, insertion losses and the Fabry-Perrot noise are obtained by optimising each component and when mode and impedance matching conditions are achieved. The transmission characteristics of each component are investigated and low propagation losses in the PIC are reported.