Supermode-based Second Harmonic Generation in a Nonlinear Interferometer.

The nonlinear directional coupler (NDC) is a core device in integrated optics with application for instance in all-optical switching [1] . Recently, the χ (2) NDC has found a flourishing field of application: quantum optics. Its key strengths in quantum information processing as a source of entangled photons and entangled field quadratures are actively explored. Particularly, strong continuous-variable entanglement in a second harmonic generation (SHG) configuration has been predicted when supermodes are excited at the input of the NDC [2] . Supermode-based SHG has remained elusive up to now. Here we experimentally demonstrate classical supermode-based SHG through a specifically-designed integrated nonlinear interferometer ( Figure 1a ) made of linear (LDC) and nonlinear (NDC) directional couplers (DC) with a fully-fibered pump.