Abstract

Integrated silicon nitride (SiN_x) waveguides and microresonators are extensively studied for nonlinear demonstrations, including parametric amplification, optical parametric oscillation and supercontinuum generation, since SiN_x is a mature, versatile and efficient platform for third-order nonlinearity. Recently, its lack of second-order nonlinearity (χ⁽²⁾) has been overcome with all-optical poling (AOP) [1], relying on multiphoton absorption interference of optical fields to inscribe a χ⁽²⁾ through coherent photogalvanic effect (PGE) [2]. As such a self-organized quasi-phase matching (QPM) grating for second-harmonic generation (SHG) can be spontaneously obtained by solely launching a pump light in a waveguide, or in a seeded fashion by also injecting the pump SH which reduces the time and power requirements and increases the achievable efficiencies [2]. While the existence of trap states in SiN_x makes it possible to unlock the coherent PGE, measurements on trap locations indicate that traps in stochiometric SiN_x are 1.4 eV deep [3]. As such previous demonstrations were focused on pumping at 1550 nm (SH with 1.6 eV energy) [1] and 1064 nm (SH with 2.3 eV energy) [4] for stochiometric SiN_x (Si₃N₄). However, the depth of the traps is a limitation for AOP for longer wavelengths. In this work, we demonstrate all-optical inscription of QPM gratings in the 2000 nm region leveraging silicon-rich SiN_x waveguides.

© 2023 IEEE