The key figures of merit for integrated optical components include the device footprint and operating energy consumption, both being major contributors to the purchase and operating cost, respectively. Slow light in silicon photonic crystal (PhC) devices has the potential to significantly reduce both, through enhanced light matter interactions, for both linear and non-linear optics applications. However, for all applications a precise control over the slow-down factor and reduced optical losses are paramount. In this paper, we present our work on various low-loss slow light systems based on PhC technology. We discuss the ability to control the group index and propagation loss of a PhC waveguide through appropriate device design - dispersion and loss engineered waveguides. This control, providing us with a free choice of group index ranging from 5 to 100, has already led to a range of non-linear optical applications, such as third harmonic generation, four-wave mixing and photon pair generation. We extend this approach to kagome lattice based PhCs and show that group indices exceeding 100 000 are possible in photonic crystal based geometries. We further discuss the post-fabrication control over slow light in PhC waveguides. Here both permanent, passive control is possible - through post-processing of the PhC devices - and adaptable, active control, through electro-optic or thermo-optic tuning. We apply the latter to a coupled cavity geometry that displays a transmission peak analogous to electromagnetically induced transparency and show a tuneable delay of 300ps with a delay loss of approximately 15dB/ns.
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