A THEORETICAL INVESTIGATION ON PROPAGATION CHARACTERISTICS AND COUPLING EFFICIENCIES OF A COUPLING SYSTEM

In a butt-joint coupling system, a fiber is coupled to a slab waveguide by a fiber ended micro-lens (FEML), so that the electromagnetic field emerging from the FEML is completely different from the fiber mode. The conventional method for calculations of the coupling efficiency, such as the overlap integral method, is not valid. In this paper, a Monte Carlo model for the coupling system is proposed, based not only on the principles of reflection and refraction at media interface plane, but also on the diffractions of micro lens. This model incorporates the geometrical surface of both the fiber end-face micro-lens and slab waveguide, the relative position of the fiber and slab waveguide, and also takes into consideration both the aberration and diffraction effects. The propagation characteristics and coupling efficiencies of the system are simulated. The losses caused by misalignment of the system are also discussed.