  We demonstrate the emission of indistinguishable photons along a
semiconductor chip originating from carrier recombination in an InAs quantum
dot. The emitter is integrated in the waveguiding region of a photonic crystal
structure, allowing for on-chip light propagation. We perform a
Hong-Ou-Mandel-type of experiment with photons collected from the exit of the
waveguide and we observe two-photon interference under continuous wave
excitation. Our results pave the way for the integration of quantum emitters in
advanced photonic quantum circuits.
