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We have proposed an ultracompact mode-division (de)multiplexer ((de)MDMUX) based on an asymmetrical directional coupler (ADC) with SiO 2 top cladding, where a taper-etched silicon wire and a hybrid plasmonic waveguide (HPW) are used. By carefully selecting the structural dimensions, TE 0 mode from the input port 1 (I 1) is gradually coupled into the wide multimode waveguide (MMW) and then transformed to TE 1 mode while that from the input port 2 (I 2) just passes through the bar branch and outputs directly, forming an efficient two-mode (de)multiplexer. With the aid of the HPW as well as the taper-etched wire, coupling length is reduced and fabrication tolerance is enlarged to some extent. From the results, such device has a total length of only 17. 1 μ m with a short coupling length of 4. 1 μ m , and it provides a low crosstalk (CT) of -25.6 (-27.7) dB and a low insertion loss (IL) of 0.51 (0.04) dB at the wavelength of 1. 55 μ m when TE 0 mode is input in the I 1 (I 2). [ABSTRACT FROM AUTHOR]

A compact and polarization-independent three-guide power splitter using subwavelength gratings (SWGs) on the SOI platform is proposed and analyzed in detail, where the SWG structures are located at both sides of the central input waveguide and the inner sides of the two outside waveguides. The introduced SWG structures can effectively enhance the coupling strength for TE mode, while that for TM mode is hardly affected. Consequently, by carefully choosing the structural parameters, the input TE mode can be evenly coupled from the central input waveguide to the outside waveguides, with the same coupling length for TM mode, thus a polarization-independent power splitter is realized. Results show that a compact power splitter of 8.5 μ m in coupling length is achieved with an insertion loss (IL) of 0.1 dB (0.085 dB) and reflection loss (RL) of −39 dB (−46 dB) for TE (TM) mode at the wavelength of 1. 55 μ m , and the operation bandwidth is up to 170 nm (from 1.48 to 1. 65 μ m) when IL <0.8 dB, RL <−20 dB and splitting ratio (SR) ∼ 1.001 for both polarizations. In addition, fabrication tolerances to the key structural parameters are presented and field evolution through the device is illustrated [ABSTRACT FROM AUTHOR]