Mid-IR All-optical poling in silicon nitride waveguides
Résumé
Integrated silicon nitride (SiNx) waveguides and microresonators are extensively studied for nonlinear demonstrations, including parametric amplification, optical parametric oscillation and supercontinuum generation, since SiNx 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 SiNx makes it possible to unlock the coherent PGE, measurements on trap locations indicate that traps in stochiometric SiNx 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 SiNx(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 SiNx waveguides.