2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/225193We consider mode coupling in multimode optical fibers using either two Bragg gratings or a Bragg grating and a long-period grating. We show that the magnitude of the band edge curvature can be controlled leading to a flat, quartic band-edge or to two band edges at distinct, nonequivalent $k$-values, allowing precise control of slow light propagation.6 pages, 3 figuresOpticstext