one of the methods consists in dividing a light wavefront emerging from a narrow slit, by passing it through two slits closely spaced side by side. The two parts of the same wavefront travel through different paths and reunite on a screen to produce fringe pattern. This is known as interference due to division of wavefront. This method is useful only with narrow sources. Young's double slit, fresnel biprism emplow this technique.
alternately the amplitude of a light wave is divided into two parts namely reflected and transmitted components by partial reflection at a surface. The two parts travel through different paths and reunite to produce interference fringes. This is known as interference due to division of amplitude.