Investigation On Optical Nonlinearity In A Fano Resonant Silicon Photonic Crystal Slab

Since the invention of laser,the nonlinear optics has made great progress in many fields and become an important part of modern optics.Third harmonic generation(THG)is one of the most common and widely used nonlinear optical effect.In the pre-existing nonlinear optical experiments,for the sake of intense interactions between light and matter,high power laser is necessary.On the other hand,in order to improve the conversion efficiency of THG,the size of nonlinear crystals is often large.With the development of integrated optoelectronic devices,the realization of optical nonlinearity in micro-nano size has become the focus of attention.The metal micro-nano structures,which can generate local surface plasmon resonance(LSPR)at the interface of metal and dielectric,have been used to enhance local electromagnetic field and light-matter interactions,thus achieving the purpose of enhancing nonlinearity.The field enhancement effect of LSPR can reduce the demand for pump power,however,the metal materials suffer from high absorption losses and low damage threshold,which may limit the conversion efficiency of THG.As an alternative,recent developments have led to a new direction aiming at dielectric micro-nano structures.Different from metal structures,dielectric micro-nano structures show very low absorption losses.Benefiting from the strong near-fields enhancement in dielectric micro-nano structures,nonlinear responses have been obviously strengthened.In this work,we experimentally demonstrate an enhancement of THG employing a Fano-resonant silicon photonic crystal slab(PCS).Taking advantage of strong third-order nonlinearity of silicon in near-infrared band,the locally boosted electromagnetic fields give rise to THG in the visible region by 2 orders of magnitude.The highest THG power is 32 nW,in the meanwhile,the conversion efficiency is 2.1 × 10.Moreover,we show the power dependence of THG intensity and investigate the tunability of THG by changing the structure parameters of the silicon PCSs.