Abstract
We design, fabricate and experimentally demonstrate a highly efficient adiabatic mode converter for coupling light into a silicon slot waveguide with a slot width as large as 320 nm. This strip-to-slot mode converter is optimized to provide a measured insertion loss as low as 0.08 dB. Our mode converter provides 0.1 dB lower loss compared to a conventional V-shape mode converter. This mode converter is used to couple light into and out of a 320 nm slot photonic crystal waveguide, and it is experimentally shown to improve the coupling efficiency up to 3.5 dB compared to the V-shape mode converter, over the slow-light wavelength region.
Highlights
In slot photonic crystal waveguides (PCWs) [1], the strong optical confinement in the slot filled with a low index material, such as air or organic polymers [2,3,4], is combined with the enhanced light-matter interaction provided by a slow-light structure [5, 6] for improving the device performance and miniaturizing device size
The rail width (Rw) of the slot waveguide section is optimized to 225nm, yielding an optimized mode converter length of 30μm
In addition to coupling light between a strip waveguide and a 320nm-wide slot waveguide, our adiabatic mode converter is used to couple light into and out of a 320nm-wide EO-polymer refilled slot PCW
Summary
In slot photonic crystal waveguides (PCWs) [1], the strong optical confinement in the slot filled with a low index material, such as air or organic polymers [2,3,4], is combined with the enhanced light-matter interaction provided by a slow-light structure [5, 6] for improving the device performance and miniaturizing device size. The non-zero width of the fabricated tip due to lithography limitation leads to a discontinuity at the center of the mode profile, causing the total insertion loss to be as high as 23dB in which each mode converter attributes to a ~1dB insertion loss [22] A clear band gap with about 25dB extinction ratio is observed, and an improvement of 3.5dB in coupling efficiency within the slow-light wavelength region compared to the V-shape mode converter is demonstrated This highly efficient light coupling into wide slot PCWs, combined with the improved poling efficiency of the electro-optic (EO) polymer in wide slot PCWs [22, 23], provides tremendous advantages for several promising applications, including photonic integrated circuits, optical interconnects, EO modulation, and electromagnetic field sensing. Sw: slot width; Rw: rail width; WG: waveguide; SPCW: slot photonic crystal waveguide; L: length of section II of the mode converter
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