Highly directed emission from self-assembled quantum dots into guided modes in disordered photonic-crystal waveguides

We explore the dynamics and directionality of spontaneous emission from self-assembled In(Ga)As quantum dots into transverse-electric-polarized guided modes in GaAs two-dimensional photonic-crystal waveguides. The local group velocity of the guided waveguide mode is probed, with values as low as ∼1.5%c measured close to the slow-light band edge. By performing complementary continuous-wave and time-resolved measurements with detection along and perpendicular to the waveguide axis, we probe the fraction of emission into the waveguide mode (β factor). For dots randomly positioned within the unit cell of the photonic-crystal waveguide, our results show that the emission rate varies from ≥1.55ns-1 close to the slow-light band edge to ≤0.25ns-1 within the two-dimensional photonic band gap. We measure an average Purcell factor of ∼2× for dots randomly distributed within the waveguide and maximum values of β∼90% close to the slow-light band edge. Spatially resolved measurements performed by exciting dots at a well-controlled distance of 0-45 μm from the waveguide facet highlight the impact of disorder on the slow-light dispersion. Although disorder broadens the spectral width of the slow-light region of the waveguide dispersion from δEd≤0.5 to >6meV, we find that emission is nevertheless primarily directed into propagating waveguide modes. The ability to control the rate and directionality of emission from isolated quantum emitters by placing them in a tailored photonic environment provides much promise for the use of slow-light phenomena to realize efficient single-photon sources for quantum optics in a highly integrated setting.