Wideband non-degenerate two-photon absorption in low-loss multimode silicon waveguides for nonlinear optical tuning between C and 2-μm wavebands

All-optical signal processing has a wide range of applications in optical computing, communication, switch and so on, where intensity modulation is highly desired. In this work, we propose and demonstrate a study of all-optical intensity modulation via nonlinear tuning based on two photo absorption (TPA) between C and 2-μm wavebands. By using multimode silicon waveguide with Euler bends for low-loss optimization, we design and fabricate a 12.3-cm silicon waveguide, achieving a minimum propagation loss of 0.23 dB/cm at C band and 0.87 dB/cm at 2-μm waveband. The waveguide is fabricated over 220-nm silicon-on-insulator (SOI) platform. 8.9 dB extinction ratio (ER) of TPA is experimentally realized above a 400-nm spectral distance at 2-μm waveband with a C-band pump. A mode loop structure assisted by mode-division-multiplexing (MDM) is proposed to enhance the TPA effect, with 1.6-dB extra ER improvement obtained.