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In this letter, we designed and experimentally demonstrated a compact mode converter in silicon-on-insulator (SOI) waveguide based on conformal dielectric metasurface, which uses polygonal slot structure to manipulate the wavefront of guided modes. Mode conversion from TE0 to TE2 mode can be realized within an ultracompact size ($\sim 7.66~\mu \text{m}$) by designing the arrow-like slot structure. With the help of asymmetric directional coupler (ADC), the TE0-to-TE2 mode converter was measured in the experiment with low insertion loss (IL) (< 0.5 dB) and low crosstalk (CT) (<−8.0 dB) from 1525 to 1565 nm. Moreover, a TE0-to-TE1 mode converter using another polygonal slot structure was also experimentally demonstrated. Our proposed mode converter shows great potential in high-density integration of photonic devices for on-chip mode control. [ABSTRACT FROM AUTHOR]