Abstract

Mode-division multiplexing technology holds great promise for addressing the ever-increasing demand for data transmission capacity. This paper proposes a compact adiabatic mode (de)multiplexer [(de)MUX] using a subwavelength grating (SWG) waveguide in the silicon-on-insulator platform, with optimization for the ${{\rm TE}_0} {\text -} {{\rm TE}_1}$ and ${{\rm TE}_0} {\text -} {{\rm TE}_2}$ mode (de)MUXs. By introducing an SWG waveguide, the coupling strength of waveguides can be enhanced, making it possible for the realization of more compact adiabatic mode (de)MUXs. The adiabatic evolution lengths for ${{\rm TE}_0} {\text -} {{\rm TE}_1}$ and ${{\rm TE}_0} {\text -} {{\rm TE}_2}$ mode (de)MUXs are only 10 µm and 17.5 µm, respectively. The numerical simulation shows that the operating bandwidth of the proposed device is beyond 200 nm. For the ${{\rm TE}_0} {\text -} {{\rm TE}_1}$ mode (de)MUX, the insertion loss and mode crosstalk of ${{\rm TE}_0} {\text -} {{\rm TE}_1}$ mode conversion within the whole wavelength range of 1450–1650 nm are less than 0.25 dB and ${-}{32.0}\;{\rm dB}$, respectively. For the ${{\rm TE}_0} {\text -} {{\rm TE}_2}$ mode (de)MUX, the insertion loss and mode crosstalk of ${{\rm TE}_0} {\text -} {{\rm TE}_2}$ mode conversion within the entire bandwidth are less than 0.26 dB and ${-}{27.4}\;{\rm dB}$, respectively. The ${{\rm TE}_0} {\text -} {{\rm TE}_1}$ and ${{\rm TE}_0} {\text -} {{\rm TE}_2}$ mode (de)MUXs can be cascaded to form a three-mode (de)MUX. For ${{\rm TE}_0} {\text -} {{\rm TE}_0}$, ${{\rm TE}_0} {\text -} {{\rm TE}_1}$, and ${{\rm TE}_0} {\text -} {{\rm TE}_2}$ processes within the entire bandwidth, the mode crosstalks are less than ${-}{33.5}\;{\rm dB}$, ${-}{26.1}\;{\rm dB}$, and ${-}{25.8}\;{\rm dB}$, respectively. The device is scalable to the conversion of ${{\rm TE}_0}$ mode to higher-order mode.

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