We review the basic light-matter interactions and optical properties of chip-based single photon sources, that are enabled by integrating single quantum dots with planar photonic crystals. A theoretical framework is presented that allows one to connect to a wide range of quantum light propagation effects in a physically intuitive and straightforward way. We focus on the important mechanisms of enhanced spontaneous emission, and efficient photon extraction, using all-integrated photonic crystal components including waveguides, cavities, quantum dots and output couplers. The limitations, challenges, and exciting prospects of developing on-chip quantum light sources using integrated photonic crystal structures are discussed.A sequence of optical pulses (top right) interacting with a single quantum dot embedded in a photonic crystal system, resulting in the emission of a train of single photons on-chip.

Spontaneous emission rate enhancements from a single quantum dot embedded in a finite-size, planar photonic-crystal waveguide are investigated. Short waveguide lengths of only 10 to 20 unit cells are found to produce very large Purcell factors associated with a waveguidelike sharp resonance feature in the local density of photon states. Aided by theoretical insight and rigorous computational calculations, we explain the physics behind these remarkable emission enhancements and subsequently propose a "single-photon gun" with on-chip unidirectional collection efficiencies greater than 60% into an output wire waveguide. The advantages over recent proposals for infinitely long photonic-crystal waveguides are highlighted.

A theoretical formalism to calculate the spontaneous emission rate enhancement ͑Purcell factor͒ and propagation mode ␤ factor from single quantum dots in a planar-photonic-crystal waveguide is presented. Large Purcell factors for slow light modes, and enormous ␤ factors ͑Ͼ0.85͒ over a broadband ͑10 THz͒ spectral range are subsequently predicted. The local density of photon states is found to diverge at the photonic band edge, but we discuss why this divergence will always be broadened in real samples, most notably due to structural disorder. Applications towards "on-chip" single photon sources are highlighted.

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