Self-organized nonlinear gratings for ultrafast nanophotonics
Daniel D. Hickstein, David R. Carlson, Haridas Mundoor, Jacob B. Khurgin, Kartik A. Srinivasan, Daron A. Westly, Abijith S. Kowligy, Ivan I. Smalyukh, Scott A. Diddams, Scott B. Papp
We present the first demonstration of automatically quasi-phase-matched second-harmonic generation using femtosecond pulses. The high-confinement geometry of silicon-nitride nanophotonic waveguides provides group-velocity matching, which enables efficient second- harmonic generation over a broad bandwidth. We confirm the presence of self-organized gratings by using nonlinear optical microscopy to record the first direct images of photo-induced nonlinear gratings. Furthermore, we demonstrate how these waveguides enable simultaneous 𝜒(2) and 𝜒(3) nonlinear processes, which we utilize to stabilize a laser frequency comb. Finally, we derive the equations that govern self-organized grating formation for femtosecond pulses and explain how nanophotonic waveguides could enable scalable, reconfigurable nonlinear optical systems.