In this paper we theoretically analysed the influence of the number of QWs in the active region and the cladding layer width on the confinement factor, near field patterns and far field patterns. A comparison between the conventional step separate confinement heterostructure (SCH) and a graded-index separate structure (GRIN-SCH) is done regarding these parameters. We found that in the case of single quantum well structure the step cavity gives the highest values of the confinement factor. As the number of wells (N) in the active region is increased the superiority of one structure or the other depends on the cladding layer width and the value of N, but for values of N higher than six, the confinement factor is always higher in the structure with a GRIN cavity, independent of the cladding layer width. In general the far field patterns in GRIN structure have lower values of the full width half-maximum (FWHM). The cutoff condition for a mono mode optical cavity is also calculated in both structures.