Enhanced nonlinear optical response from individual silicon nanowires

We report about the experimental observation and characterization of nonlinear optical properties of individual silicon nanowires of different dimensions. Our results show that the nonlinear light has different components, with one of them corresponding to the second-harmonic generation (SHG). The SHG strongly depends on the polarization of the optical excitation and nanowire diameter, and gives access to the local electromagnetic field intensity distribution. Furthermore, we show that the second harmonic, when observed, is enhanced compared to bulk silicon and is sensitive to optical resonances supported by the nanowires. This offers different perspectives on the definition of silicon-based nonlinear photonic devices.

Figure 1

(a) Schematic view of the setup used for SHG measurements. The second beam passing through the time-delay line is used for interferometric autocorrelation experiments only (BS: beam splitter). (b) Elastic light-scattering mapping of an isolated Si-NW. (c) Nonlinear emission mapping. Insets: The FWHM taken along the dashed line.

Figure 2

Spectra of SHG and nonlinear photoluminescence of NW300 in TE and TM configurations with excitation at $\lambda =840$ nm on the center of the NW. The laser polarization was fixed while the samples were rotated by ${90}^{\circ }$. The SHG signals of ${\mathrm{LiNbO}}_3$ and a 200-nm-thick Si layer of silicon on quartz are shown for comparison. The average power density was 3.84 mW/$\mu {\mathrm{m}}^2$ for Si materials and 0.92 mW/$\mu {\mathrm{m}}^2$ for ${\mathrm{LiNbO}}_3$

Figure 3

SHG maps of NW300 for (a) TE polarization, (b) TM polarization, and (c) intensity profiles along the NW axis.

Figure 4

Intensity profiles along the NW300 axis as a function of the excitation wavelength for two different detection windows [SHG filter (solid line) and PL filter (dashed line)], and for both polarization configurations (TE : curves on left side, TM : curves on right side).

Figure 5

SHG maps for (a) [(d)] TE and (b) [(e)] TM polarizations in the case of NW50 [NW80]. Normalized elastic light-scattering spectra compared to Mie theory for (e) NW50 and (f) NW80.