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We proposed a novel optical coupling technique based on two parallel singlemode-multimode- singlemode (SMS) fiber structures. This technique utilizes one SMS structure to excite multiple cladding modes within an output singlemode fiber. The excited multiple cladding modes will be coupled to the input SMF in the second SMS structure by placing the two SMS fiber structures in parallel and in close contact each other. The coupled cladding modes will be re-coupled to a guided core mode by the second SMS fiber structure. Theoretical analysis for such technique was provided and experimentally we have achieved a pass band spectral response with an extinction ratio higher than 20 dB and a maximum coupling efficiency of 5.9%.
Wu, Q., Ma, Y. Yuan, J., Semenova, Y, Wang, P.: Evanescent field coupling between two paralled close contact SMS fiber structures. Optics Express, Vol.20, 3, 2012, pg. 3098-3109. doi:10.1364/OE.20.003098