10 May 2012 Narrow band forward coupling using Bragg reflectors
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In this work, we revisit the operation principles of Bragg reflectors assisted directional couplers. We show that an efficient narrow band forward coupling operation can be achieved by an appropriate engineering of the Bragg grating waveguides dispersion properties. Our theoretical analysis reveals the existence of a minimum Bragg grating coupling strength for co-directional phase matching. This threshold coupling condition is an essentially new aspect of Bragg grating asymmetric directional couplers as compared to conventional co-directional couplers and Bragg reflectors. The threshold condition is analytically determined, and a coupled mode theory four-wave model is successfully applied to describe the behavior of the investigated device. It is shown that the optimal operation is achieved with only one Bragg grating distributed along one of the two waveguides. A numerical validation of the results of coupled mode theory is performed for the case of shallow-etched Silicon on Insulator (SOI) ridge waveguides with Bragg grating assisted coupling. The selectivity is a factor of 5.5 higher than that obtained in the conventional approach of asymmetric directional couplers where III-V waveguides with different alloy compositions are coupled vertically. The proposed design is shown to be compatible with existing micronano- fabrication technology.
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A. Lupu, K. Muhieddine, E. Cassan, and J.-M. Lourtioz "Narrow band forward coupling using Bragg reflectors", Proc. SPIE 8431, Silicon Photonics and Photonic Integrated Circuits III, 84310I (10 May 2012); doi: 10.1117/12.922023; https://doi.org/10.1117/12.922023


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