摘要： Mode-division multiplexing (MDM) is attractive to enhance the link capacity of optical interconnects by using multiple mode-channels in multimode bus waveguides. As sharp waveguide bends are very important for realizing dense photonic integrated circuits, here ultra-sharp multimode waveguide bends for MDM systems are proposed and demonstrated by using subwavelength grating waveguide structures on silicon. An ultra-sharp S-bend with a radius of 10 μm is realized for the ?rst time to enable a low-loss and low-crosstalk MDM optical interconnect with three mode-channels. For this proposed ultra-sharp subwavelength grating multimode waveguide bend (SMWB) with a 90° bending angle, the theoretical excess losses for the TE0, TE1, and TE2 modes are 0.1–0.3 dB, 0.18–0.22 dB, and 0.3–0.5 dB, respectively, in a wavelength band of 1500–1600 nm. Meanwhile, inter-mode crosstalks are very low (less than ?30 dB) for all mode-channels. For the fabricated 90°-SMWB, the excess losses for the TE0, TE1, and TE2 modes are 0.1–0.3 dB, 0.2–0.4 dB, and 0.3–0.7 dB while the inter-mode crosstalk is approximately ?22 dB in a wavelength band of 1520–1600 nm. The proposed SMWB is also extended for more than three mode-channels.