Low-Photon-Number Optical Switching with a Single Quantum Dot Coupled to a Photonic Crystal Cavity

We demonstrate fast nonlinear optical switching between two laser pulses with as few as 140 photons of pulse energy by utilizing strong coupling between a single quantum dot (QD) and a photonic crystal cavity. The cavity-QD coupling is modified by a detuned pump pulse, resulting in a modulation of the scattered and transmitted amplitude of a time synchronized probe pulse that is resonant with the QD. The temporal switching response is measured to be as fast as 120 ps, demonstrating the ability to perform optical switching on picosecond timescales.

Figure 1

(a) Scanning electron micrograph showing a fabricated device and illustrating pump-probe measurement. A pump and probe field with relative time delay $\Delta \tau$ are injected into the waveguide via grating couplers. Probe transmission depends on whether the two pulses excite the cavity simultaneously or at different times. (b) Low power PL measurement of the cavity. (c) Cavity scatter under broadband LED excitation as a function of temperature. Dotted lines indicate the temperature dependence of QD and the cavity. (d) Scattering spectrum taken at 39 K when the QD is resonant with the cavity.

Figure 2

Cavity scattering spectrum for (a) $0.1\mu \mathrm{W}$ and (b) $14.5\mu \mathrm{W}$ pump field powers. The dashed red line shows the cavity scattering spectrum with only the pump field (no signal). The solid blue line shows the scattering spectrum of the probe, with the pump scatter subtracted. (c) Theoretical scattering spectrum as a function of incident pump power before the grating.

Figure 3

Probe scattering intensity as a function of sample temperature for delays of 0 (green triangles) and 4 ns (red circles), (a) collected from the cavity and (b) collected from the output coupler. Scattering spectrum with the pump only indicated as a solid blue line in panel (a).

Figure 4

Cavity probe scattering intensity as a function of pump-probe delay. The solid line represents theoretical fit.

Figure 5

(a) Switching contrast as a function of the pump pulse energy (in the waveguide) for three different values of $\Delta ={\omega }_p-{\omega }_{qd}$. Solid lines indicate the numerically calculated values. (b) Plot of $E_{3\mathrm{dB}}$ as a function of $\Delta$. The solid line represents numerically calculated values.