A new type of backward-wave coupled-line directional coupler with complete coupling and broadband, which is composed of a conventional microstrip and a 1D mushroom structure, is proposed. The 1D mushroom structure is employed for a double negative (DNG) transmission line. The coupler exhibits unusual characteristics such as complex propagation. The complex propagation constant of the coupled mo...

Directional couplers are critical components in photonic integrated circuits used in optical communication systems. The conventional directional couplers with laterally arranged waveguides can not achieve very short coupling lengths due to extreme sensitivity to fabrication variations and limitations to produce uniformly very narrow gap layers.1) Vertical directional couplers, however, can obta...

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We overview our recent theoretical results on spatio-spectral control, diffraction management, and broadband all-optical switching of polychromatic light in periodically curved one and two dimensional arrays of coupled optical waveguides. In particular, we show that polychromatic light beams and patterns produced by white-light and supercontinuum sources can experience wavelength-independent no...

We demonstrate that a concentric ring coupler can be employed for nonlinear switching of the angular momentum of light carried by an optical vortex. We find different types of stationary vortex states in the nonlinear coupler and study coupling of both power and momentum of an optical vortex launched into one of the rings, demonstrating that the switching takes place well below the collapse thr...

An ultra-compact plasmonic-mode-assisted polarization splitter based on directional coupler is proposed and investigated analytically and numerically. A large modal birefringence of > 0.69 is estimated, enabling a clean polarization separation within 5.6 1m. Keywords-Polarization splitters; surface plasmons; plasmonic waveguides

An ultra-compact (coupling length ~ 8.77 m) silicon polarization splitter and rotator is demonstrated based on a bent directional coupler. The peak TM-TE coupling efficiency reaches 96.6%. The crosstalk values are < -10 dB over a wavelength range of 40 nm.