Optical Autocorrelator Based on InSe-Integrated Silicon Waveguide

We demonstrate an on-chip single-shot autocorrelator by integrating few-layer InSe onto a silicon waveguide. With the strong second-order nonlinearity of InSe, a strong second harmonic generation (SHG) signal happens when counter-propagating pulses overlap within the InSe-integrated silicon waveguide. By mapping the spatial intensity distribution of the SHG signal into the time domain, the temporal profile of the pulse and group index of the waveguide modes were characterized successfully. Benefiting from the large second-order nonlinearity of InSe and the enhanced light-matter interaction provided by the silicon nanophotonic structure, our device can operate with pulse peak power down to 11 mW that is over two orders lower than that of the conventional integrated silicon autocorrelators, reaching a sensitivity of 2.4 × 10^-8 W². Our device demonstrates the promising potential of ultrafast optical pulse measurements in photonic integrated circuits.