Broadband 200-nm second-harmonic generation in silicon in the telecom band

Silicon is well known for its strong third-order optical nonlinearity,exhibiting efficient supercontinuum and four-wave mixing processes.A strong second-order effect that is naturally inhibited in silicon can also be observed,for example,by electrically breaking the inversion symmetry and quasi-phase matching the pump and the signal.To generate an efficient broadband second-harmonic signal,however,the most promising technique requires matching the group velocities of the pump and the signal.In this work,we utilize dispersion engineering of a silicon waveguide to achieve group velocity matching between the pump and the signal,along with an additional degree of freedom to broaden the second harmonic through the strong third-order nonlinearity.We demonstrate that the strong self-phase modulation and cross-phase modulation in silicon help broaden the second harmonic by 200 nm in the O-band.Furthermore,we show a waveguide design that can be used to generate a second-harmonic signal in the entire nearinfrared region.Our work paves the way for various applications,such as efficient and broadband complementarymetal oxide semiconductor based on-chip frequency synthesizers,entangled photon pair generators,and optical parametric oscillators.