Bispectral second-harmonic-generation in snake-shaped AlGaAs nanowires

High-contrast nonlinear nanophotonics is being increasingly recognized for its potential under different configurations, spanning from high-Q resonators to multi-pole nanoantennas, and nanowires. To confine photons at the... [ view full abstract ]

High-contrast nonlinear nanophotonics is being increasingly recognized for its potential under different configurations, spanning from high-Q resonators to multi-pole nanoantennas, and nanowires. To confine photons at the nanoscale by total internal reflection, such devices rely on a high-refractive-index core surrounded by low-index cladding in one or more dimensions, and therefore they typically consist of semiconductor nanostructures that either lie on an oxide substrate or are suspended in air. Here we focus on periodically bent AlGaAs suspended nanowires with sub-wavelength cross section (about 0.1 µm height and 1 µm width) and macroscopic length (about 1 mm), whose χ⁽²⁾ nonlinearity benefits from a combination of birefringent phase matching and directional quasi-phase matching and results in second harmonic generation (SHG) in the telecom fiber wavelength range, with an efficiency η_SHG≈10^-3W^-1. Based on an Al_0.18Ga_0.82As epitaxial layer on a [100] GaAs wafer, electron-beam lithography and inductively coupled plasma etching, we fabricated monolithic snake-shaped nanowires consisting of cascaded half-circles with opposite curvatures [1]. Since a 90^o rotation around the (100) zinc-blend axis is equivalent to a crystallographic inversion [2], a virtual χ⁽²⁾ grating was implemented with a period equal to four 90^o bends. By end-fire injecting a continuous-wave pump beam into the nanowires, we systematically reveal two distinct quasi-phase-matching spectral features whose separation in wavelength is set by the radius of curvature. While SHG in these nanowires can be seen as the unravelled version of the previously demonstrated SHG in a suspended microdisk [3], this is the first observation of a dual quasi-phase-matching resonance in a grating-less homogeneous waveguide.

REFERENCES

[1]    R. T. Horn and G. Weihs, “Directional Quasi-Phase Matching in Curved Waveguides”, arXiv: 1008.2190 (2010).

[2]     Y. Dumeige and P. Feron, “Whispering-gallery-mode analysis of phase-matched doubly resonant second-harmonic generation”, Phys. Rev. A 74, 063804 (2006).

[3]     S. Mariani et al., “Second-harmonic generation in AlGaAs microdisks in the telecom range”, Optics Letters 39, 3062 (2014).