Broadband slow-light enhancement of nonlinear effects with plasmonic structures

An upper limit of achievable nonlinearities in term of the maximum nonlinear index change Awmax 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., Δneff > Δwmax. 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.