Enhanced third order nonlinear effects in AlGaAs nanowires

Abstract

We report the first observation of self-phase-modulation enhancement in 500 nm wide, Kerr nonlinear AlGaAs nanowaveguides.The development of single-mode sub-wavelength waveguides (nanowaveguides) is today an issue of great scientific and technological interest. Such optical nanowire structures are capable of providing superior light confinement and are thus ideal for nonlinear optics applications [1]. To date, sub-micron diameter silica waveguides have been fabricated and have been used to observe super-continuum generation [2]. Other nonlinear glasses such as lead silicate, tellurites, and bismuth have also been employed along these lines. In view of the above, it will be certainly of interest to explore the possibility of fabricating such high index-contrast nanowires using highly nonlinear materials such as for example semiconductors. Quite recently we have fabricated and tested prototype AlGaAs optical nanowires. Given the fact that AlGaAs exhibits a nonlinearity that is three orders of magnitude higher than that of silica, the prospect of realizing sub-µm 2 nanowires may eventually lead to low-power nonlinear devices with sub-millimeter interaction lengths. In this paper we report the first observation of spectral broadening (SPM) enhancement in nonlinear AlGaAs nanowires.The nanowires were fabricated by deep etching of a multilayer MBE structure on a GaAs wafer. The structure of each nanowire waveguide (including the tapers) is shown in Fig. 1. The length L of the nanowire was varied from 0 to 700µm in 100µm steps. The nanowire width W for the experiments was set at 500nm. In the vertical direction the structure is as follows: The substrate is GaAs on top of which sequentially was deposited a 4200nm cladding layer of Al 0.7 Ga 0.3 As, a 500nm core of Al 0.2 Ga 0.8 As, a 300nm upper cladding of Al 0.7 Ga 0.3 As and a cap layer of 100nm GaAs. The layer structure was etched down to a depth of 2300nm, (as shown in the SEM picture of Fig. 1), to form a single mode waveguide at 1550 nm. The resulting modal area for the single mode guide was estimated to be ∼0.3µm 2 . Fig. 1: (Left) Single channel as viewed from above; (Right) SEM picture of the nanowire structure.a1438_1.pdf CMA1.pdf 1-55752-813-6/06/$25.00 ©2006 IEEE