Ultra-Compact Multimode Waveguide Bend With Optimized Dual Bezier Contours

Mode-division multiplexing (MDM) is an effective solution to extend the capacity of optical communication system. Multimode waveguide bend (MWB), one of the key components, is essential to realize high integration density and flexible layout of MDM systems. Here we propose and demonstrate a MWB with dual Bezier contours. By optimizing the inner and outer boundaries of the waveguide independently, an ultra-compact MWB with radius of curvature as well as width varying along the waveguide has been demonstrated. The four-mode MWB, with an effective radius of $15~\mu $ m, has the calculated average excess loss of < 0.036 dB and the inter-modal crosstalk of <-34 dB within the bandwidth of 100 nm theoretically. For the fabricated device, the measured average excess loss is < 0.039 dB and the inter-modal crosstalk is <-18 dB over the broad wavelength range from 1520 to 1600 nm for all the four modes. Such MWB also has the advantages of large width-deviation tolerance and simple fabrication process.