Broadband slow-light enhancement of nonlinear effects with plasmonic structures

An upper limit of achievable nonlinearities in term of the maximum nonlinear index change Aw_max exists for any Kerr nonlinear material, because of optical damage, saturation, or high-order effects. Taking advantage of slow-light effects, a photonic-crystal waveguide can enhance nonlinear effects and achieve more effective nonlinearities than the bulk material, i.e., Δn_eff > Δw_max. However, this slow-light enhancement relies on a structural resonance and is thus narrowband. Here we report broadband slow-light enhancement of nonlinear effects using plasmonic metal-dielectric-metal (MDM) waveguides. We show that MDMs structure with a thin nonlinear dielectric layer can have strikingly large effective nonlinearity, more than ten times that of the material nonlinearity, over a large bandwidth. This is because MDM structures are uniquely capable of combining broadband slow-light effects and efficient use of the nonlinear material. We expect this work to advance the development of high performance Kerr nonlinear nanophotonic devices.