Intermodal coupling by periodic microbending in dual-core fibres: comparison of experiment and theory

Grating coupling (caused by periodic microbending) between the quasi-even and quasi-odd normal modes of dual-core fibers is treated. and an accurate design formula is derived for the coupling coefficient. An analytical form for the intrinsic coupling coefficient of two dissimilar cores is also given. Good agreement is found between theory and experimental data on fibers perturbed either by acoustic flexural waves or fixed mechanical gratings. The paper provides useful design rules for dual-core fiber devices