Circular anisotropy of the third harmonic generated in tilted silicon nanowire array

A.S. Ustinov, L.A. Osminkina, D.E. Presnov, L.A. Golovan
Photonic spin Hall effect, i.e., splitting of opposite spin photons perpendicular to the incident plane of impinging light beam, is of great interest for modern photonics with its potential applications in such devices as beam splitters, demultiplexers by photonic spin degree of freedom, chiral molecule sensors, etc. Here, we report on numerical simulation and experimental detection of this effect in an array of densely arranged tilted silicon nanowires (SiNWs) of about 100 nm in diameter. We
more » ... mpared scattering of fundamental near-infrared radiation and the third harmonic (TH) generated in the structures. The latter case approves high sensitivity of nonlinear optical process to local fields within the structure, thus allowing us to probe the sub-wavelength evolution of photons in it. Numerical simulations of circularly polarized light scattering by a single SiNW and a group of 13 SiNWs used as a geometrical approximation of the real SiNW array indicate maintenance of helical modes in SiNWs for the light incident at an oblique angle to their axis. Helical guided-like mode structure in SiNWs evidences synthetic gauge field for photons resulting in its turn in asymmetric scattering diagram both for fundamental frequency and the TH. SiNWs were formed by means of metal-assisted chemical etching of (110) crystalline silicon (c-Si). They were tilted to the c-Si substrate at an angle of 45°. The array demonstrated significant linear light scattering preventing it from exhibiting of circular anisotropy. Nevertheless, experiment on the TH generation pumped by femtosecond laser pulses at 1250 nm has demonstrated significant difference in the TH signals for cases of left-and right-handed circularly polarized fundamental radiation. The effect was detected for oblique (60°) light incidence on SiNWs, whereas for the laser radiation propagating along the SiNWs or perpendicularly to them TH signal did not depend on the pump radiation photon helicity sign. Thus, we have demonstrated polarization-dependent routing of circularly polarized nearinfrared radiation in a SiNW array, which is evidenced by different TH generation efficiencies in such structure in response to incident radiation with circular polarization of opposite signs. [1] Y. Liu, Y. Ke, H. Luo et al., Photonic spin Hall effect in metasurfaces: a brief review
doi:10.24412/cl-35039-2021-21-148-148 fatcat:5klnj7j7hvdbxkgz32dsoqca3i