Switchable self-defocusing and focusing in nearly isotropic photonic crystals via enhanced inverse diffraction

Abstract

Generally, optical diffraction is only weakly dependent on the refractive index of a medium in which light propagates. In this paper, diffraction in a nearly isotropic Kerr photonic crystal (PhC) made of silicon pillars embedded in nonlinear carbon disulfide ambient was reversed and enhanced by its linear refractive index, which is negative and much less than unity. The effective nonlinear refractive index coefficient n 2 of the PhC was found by fitting spectral broadening induced by self-phase modulation. The enhanced inverse diffraction, attributed to positive n 2 , allows self-defocusing in one single PhC. More interestingly, the same PhC can selectively exhibit dual functionalities, i.e., self-defocusing and self-focusing, based on the wavefront property of a given input beam. Our results may pave the way for protecting nanostructured photonic devices from laser damage and provide a method for controlling wavefronts.

The Refractive Index Of Photonic Crystal Fibers As A Function Of Some Parameters And Temperature

“…[18]. The propagation of light in a homogeneous medium, optical diffraction occurs, a geometrical effect leading to a spatial broadening the beam propagation direction, depends on refractive index of the media [19]. Self-focusing is a nonlinear optical phenomenon refers to the nonlinear process counteracts against natural propagation of an optical beam when power exceeds a critical value of origin self-focusing in the nonlinear refractive index, 𝑛 = 𝑛° + 𝑛2𝐼, where any increase in the intensity , 𝐼, leads to 𝑛2>0, this produces a convergent wave front through the nonlinear phenomenon of self-phase modulation (SPM) during the beam propagation in the medium [20].…”