Time-resolved ultrafast all-optical switching in directional couplers with second-order nonlinearity

Nonlinear directional couplers (NLDC) allow for ultrafast all-optical switching. To date, various types of NLDCs have been studied, predominantly based on the Kerr [1] or cascaded quadratic nonlinearity [2] in second-harmonic generation (SHG). In the later case the switching can occur at lower powers because of a propagating-wave resonance effect. While a number of experiments to characterise the pulse propagation in Kerr-type couplers exist, till now the temporal behavior of short pulses in the NLDC with quadratic nonlinearity has never been studied experimentally. Several important questions such as the reason for incomplete switching and possible pulse compression factors remain unanswered. In this work we experimentally measure the pulse reshaping in a NLDC with second-order nonlinearity and show that pulse compression, break-up and back-switching play an important role in the switching process.