Advanced architectures for coupling III-V nanowires to photonic integrated circuitry

Abstract

This work implements a hybrid device based on a semiconductor quantum dot embedded within a nanowire to bridge a non-continuous curved waveguide structure. The geometry takes advantage of evanescent coupling between the photonic structures to recover single photons emitted from both outputs of the device. Auto- and cross-correlation measurements were performed on different output facets of the device. We demonstrate single-photon emission from both ends of the nanowire for both neutral, X and XX, and charged X-, excitonic complexes. We further demonstrate the cascaded XX-X emission by collecting each complex from a different facet. This work lays the foundation for on-chip architectures which utilize multi-directional integration of quantum emitters.

Figures (7)

• Figure 1: False colour SEM images with SiO$_2$ in grey, Si$_3$N$_4$ in blue and InP in purple. (a) Straight Si$_3$N$_4$ waveguide with a tapered InP nanowire on top. (b) Curved waveguide with a nanowire on the side. (c) Segmented waveguide with a nanowire bridging the gap. (d) As in (c) but with an additional waveguide for cross-pumping.
• Figure 2: Finite element simulations were performed for the two different hybrid coupling approaches. (a) Top-down view of the photonic integrated circuit. The quantum dot emitter (here a dipole) is located at the midpoint of the InP nanowire (NW) which is tangent to the curved Si$_3$N$_4$ waveguide. The emission from the quantum dot is emitted into the nanowire and couples into the waveguide as it bends away. The total power coupled into the waveguide as a function of nanowire radius, $r_{\text{nw}}$, is shown in the inset. (b) Revised coupling design that makes use of a gap in the Si$_3$N$_4$ waveguide with tapered sections at the gap. The inset shows the improved transmittance between both HE$_{11}$ polarizations in the nanowire and the TE/TM modes in the Si$_3$N$_4$ ridge waveguide.
• Figure 3: PL spectrum measured on a gap-coupled device showing three dominant peaks identified as the excitonic complexes $X$, $XX$ and $X^-$. The inset shows the integrated intensity as a function of pulsed excitation power at 80 MHz for each complex: linear ($\mathrm{n}\sim1$) for $X$ and $X^-$ and approaching quadratic ($\mathrm{n}\rightarrow 2$) for $XX$Sek_JAP2010.
• Figure 4: (a) Schematic of the setup for measuring $g^{(2)}(\tau)$. The excitonic complex to be measured is first filtered then directed to a beamsplitter with the output ports sent to two SNSPD detectors. (b, d, f) PL decay traces and (c, e, g) auto-correlation measurement for the three complexes, $X$, $XX$, and $X^-$, respectively, plotted semi-logarithmically. The excitation rate used in each measurement is shown in the figure as a fraction of the saturation power, $P_{\text{sat}}$.
• Figure 5: High-resolution PL of the (a) $X$, (b) $XX$ and (c) $X^-$ peaks measured at excitation powers indicated. Model fits are shown in purple. For the neutral complexes, the two peaks that constitute the doublets are shown in blue and red.