  Semiconductor quantum dots embedded in micro-pillar cavities are excellent
emitters of single photons when pumped resonantly. Often, the same spatial mode
is used to both resonantly excite a quantum dot and to collect the emitted
single photons, requiring cross-polarization to reduce the uncoupled scattered
laser light. This inherently reduces the source brightness to 50 %. Critically,
for some quantum applications the total efficiency from generation to detection
must be over 50 %. Here, we demonstrate a resonant-excitation approach to
creating single photons that is free of any cross-polarization, and in fact any
filtering whatsoever. It potentially increases single-photon rates and
collection efficiencies, and simplifies operation. This integrated device
allows us to resonantly excite single quantum-dot states in several cavities in
the plane of the device using connected waveguides, while the cavity-enhanced
single-photon fluorescence is directed vertical (off-chip) in a Gaussian mode.
We expect this design to be a prototype for larger chip-scale quantum
photonics.
