Circularly Polarized Light Emission from Semiconductor Planar Chiral Nanostructures

We demonstrate circularly polarized light emission from InAs quantum dots embedded in the waveguide region of a GaAs-based chiral nanostructure. The observed phenomenon originates due to a strong imbalance between left- and right-circularly polarized components of the vacuum field and results in a degree of polarization as high as 26% at room temperature. A strong circular anisotropy of the vacuum field modes inside the chiral nanostructure is visualized using numerical simulation. The results of the simulation agree well with experimental results.

Figure 1

(a) Schematic of designed chiral nanostructure. Gammadion and waveguide-core layers are fabricated of GaAs. Typical scanning electron microscopy image of a chiral photonic crystal with a left-twisted gammadion is also shown. Length of white scale bar corresponds to $1\mu \mathrm{m}$. Values of the indicated structural parameters are given in the text. (b) Measured ellipticity spectra in the zero-order transmitted light of the chiral photonic crystals. Gray (red) [black (blue)] line indicates the result obtained with the left- [right-]twisted gammadion sample.

Figure 2

Left- ($I_{\mathrm{LCP}}$) and right-circularly polarized ($I_{\mathrm{RCP}}$) components of PL spectra from left-twisted (top) and right-twisted (bottom) chiral photonic crystals with a linewidth $\alpha =146\mathrm{nm}$. Inset shows PL spectra without nanostructures. (b) Spectra of the DOP of chiral photonic crystals with left- gray (red) line] and right-twisted [black (blue) line] gammadions with a linewidth $\alpha =146\mathrm{nm}$. (c) Spectra of the DOP of chiral photonic crystals with different linewidths. Broken line indicates wavelength of 1004 nm.

Figure 3

(a) Distribution of electric field intensity induced by left- and right-circularly polarized light with the same amplitude ($|{\mathit{E}}_L^t{|}^2$ and $|{\mathit{E}}_R^t{|}^2$, respectively) at normal incidence tuned to 1004 nm, sliced on the $xz$ plane including the center of the sample with a 146 nm linewidth. Substrate is modeled as a semi-infinite slab of GaAs. White lines indicate interfaces of the GaAs layer. (b)–(d) In-plane distribution of electric field intensity induced in samples with linewidths $\alpha$ of (b) 146 nm, (c) 177 nm, and (d) 200 nm by left- (left-hand side) and right-polarized (right-hand side) light at normal incidence. Vertical position of the calculated planes is 570 nm, as indicated by red lines in (a). Calculated and experimentally determined degrees of polarization are shown on the right. (e) Dependence of the DOP of sample with linewidth $\alpha =146\mathrm{nm}$ on the $z$ position. Red line indicates position of emitter layer. Blue, red, and green areas indicate the gammadion, waveguide-core, and clad layers, respectively.