Photonic crystal waveguides (PhCWGs), designed by removing one or more slabs from a perfectly periodic structures, are possibly future optoelectronic circuit elements that promising a good ability to confine light in a direction and allowing it to propagate in other direction. One of the problem in their application is the coupling from a PhCWG to a completely different structure. This difficulty arrives from sudden change in structure’s geometry. In this thesis, to over come this difficulty we used a transition region between two photonic crystal structures that have completely different geometrical parameters. According to our simulation results we find that by using transition region, coupling can be achieved almost without any loss.