Abstract
Higher-order mode conversion plays a vital role in on-chip multimode applications. Here, we propose an efficient silicon-based higher-order mode conversion scheme that can achieve the mode-order conversion from ${{\rm{TE}}_0}$ to ${{\rm{TE}}_1}$ (${{\rm{TE}}_0} {-} {{\rm{TE}}_1}$) mode and from ${{\rm{TE}}_0}$ to ${{\rm{TE}}_2}$ (${{\rm{TE}}_0} {-} {{\rm{TE}}_2}$) mode, respectively. These mode conversion functions are realized by etching subwavelength grating (SWG) slots on a silicon waveguide, where the design of the SWG slot pattern matches with the required ${{\rm{TE}}_1}$ (${{\rm{TE}}_2}$) higher-order mode. According to the calculations, the mode conversion length is only 3.3 µm (4.32 µm) with the mode conversion efficiency (CE) 92.1% (95.6%), mode crosstalk (CT) ${-}{17.5}\;{\rm{dB}}$ (${-}{16.7}\;{\rm{dB}}$), and insertion loss 0.65 dB (0.5 dB) for the ${{\rm{TE}}_0} {-} {{\rm{TE}}_1}$ (${{\rm{TE}}_0} {-} {{\rm{TE}}_2}$) mode converter at $\lambda = {1.55}\;{\rm{\unicode{x00B5}{\rm m}}}$. Moreover, device bandwidths over 110 nm (${\rm{CE}} \gt {{90}}\%$ and ${\rm{CT}} \lt - {{15}}\;{\rm{dB}}$) and other higher-order mode conversions can also be achieved using the proposed scheme (e.g., ${{\rm{TE}}_0} {-} {{\rm{TE}}_3}$ and ${{\rm{TE}}_0} {-} {{\rm{TE}}_4}$ mode converters). We believe such a device scheme would help increase the transmission capacity of on-chip multimode multiplexing transmissions by leveraging more mode channels.
© 2021 Optical Society of America
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