We proposed a new type of transverse electric (TE) polarized mode-order converter based on a deeply-etched polygonal slot on a silicon-on-insulator waveguide. Along the transverse direction of the waveguide, two irregular boundary surfaces of the slot can introduce high-contrast index modulation on guided modes, leading to multimode interference in the slot. Therefore, when the slot is optimized, we can achieve efficient mode conversions based on the multimode interference. As examples, mode converters from the fundamental TE mode (TE 0 ) to the first-order TE mode (TE 1 ) and to the second-order TE mode (TE 2 ) have both been demonstrated with a short device length (<24.0 μm), a high mode conversion efficiency (>97.6%), and a low modal crosstalk (< −20.0 dB) over a broad wavelength range from 1500 to 1600 nm (∼100 nm). In addition, based on different polygonal slots, other types of mode conversions such as from TE 1 to TE 3 and from TE 2 to TE 1 have be realized. Fabrication tolerance of the proposed structure is analyzed. Owing to the high efficiency and compact size, the proposed structure could be applied to on-chip mode division multiplexing systems for high-density integration.

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Hybrid free space optical (FSO)/radio frequency (RF) systems have been proved to be reliable links for high-data-rate wireless backhauls. In this paper, we present a unified performance analysis of the hybrid FSO/RF transmission system which transmits the identical data in both links and implements two popular diversity combining schemes, namely, selection combining (SC) and maximal ratio combining (MRC), in the receiver. Specially, for the FSO link, the Gamma-Gamma turbulence with pointing errors under heterodyne detection (HD) and intensity modulation/direction detection (IM/DD) is considered in our analysis while the general κ-μ shadowed fading which unifies popular RF fading models is employed for the analysis of the RF link. As a result, unified closed-form expressions of outage probabilities and average bit error rates for different modulation schemes are derived. Analytical and Monte Carlo simulation results are provided to characterize the performance of the hybrid FSO/RF link which is compared to the single FSO link and the single RF link. The agreement between the analytical and simulation results confirms the unification of various FSO channels and RF fading scenarios into a single closed-form expression.

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