Abstract
Counter-directional coupling between subwavelength-diameter silica wire and single-line-defect two-dimensional photonic crystal slab waveguide is studied numerically using parallel three-dimensional finite-different time-domain method. By modifying silica wire properties or engineering photonic crystal waveguide dispersion band, the coupling central wavelength can be moved to the slow light region and the coupling efficiency improves simultaneously. One design gives 82% peak power transmission from silica wire to photonic crystal waveguide over an interacting distance of 50 lattice constants. The group velocity is estimated as 1/35 of light speed in vacuum.
Highlights
There have been extensive studies of slow light in twodimensional photonic crystal slab waveguide (PCSW) [1,2,3]
We show that the coupling efficiency can be improved greatly when the coupling central wavelength is moved to the slow light region
We have studied the counter-directional coupling between SiO2-Wr and PCSW using P3D FDTD simulations and coupled mode analysis
Summary
There have been extensive studies of slow light in twodimensional photonic crystal slab waveguide (PCSW) [1,2,3]. SiO2-Wr can be placed on the side of PCSW0 [7] This side coupling risks generating unwanted photonic crystal surface modes [10] and lowering the coupling efficiency. Another issue is that the photonic crystal lattice between the line-defect and the silica wire is limited to only a few row of air holes in order to achieve sufficient side coupling, This might weaken the in-plane light confinement of PCSW0 and lead to larger propagation loss. This discrepancy may result from numerical errors in P3D FDTD and PWE methods Another reason is that the actual dispersion curves for both SiO2-Wr and PCSW0 are slightly modified for the weakly-coupled system compared to their unperturbed counterparts
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