Enhancement of the coupling efficiency in optical fibers using two-beam interference

Summary form only given. Coupling light into a waveguide or a fiber is based typically on using a lens with a small f-number to focus the input beam into the waveguide. Such a coupling scheme becomes increasingly complex and lossy for single-mode fibers (Hallard, 1990). We show that this problem can be overcome by launching the central fringe generated by the interference pattern of two Gaussian beams. In an earlier publication, we have demonstrated that using interference schemes, it is possible to enhance the coupling efficiency in a quasi-phase matched second-harmonic generation process by as much as 67% in 4 /spl mu/m waveguides (Benaich et al, Appl. Phys. Lett., vol. 75, p. 3261, 1999). To better understand the limits of optical coupling efficiency into fibers, we have undertaken both theoretical and experimental investigations.