Photonic crystals (PhC) are periodically structured electromagnetic media, in which light within some frequency ranges cannot propagate through the structure. Such frequency ranges are commonly referred as photonic band gaps (PBG). The length scale of the periodicity of the dielectric map is comparable to the wavelength of light propagating in the structure. This is an electromagnetic analogue of a crystalline atomic lattice, where the latter acts on the electron wavefunction to produce the familiar band gaps. It has been known since 2001 that the strong dispersion in specific PhC structures can generate slow propagating electromagnetic modes often but not exclusively in the vicinity of the photonic band-edge. Slow light, with small group velocity (vg), is one of the most promising features of the two-dimensional (2D) PhCs. It is therefore very interesting to study the slow light behaviours as well as other PhC properties for both the passive devices for integrated optics applications and active devices for light sources. This thesis investigates both aspects, on one hand we studied the slow light dispersion properties of passive structures. All the passive devices are operating in the Near-Infrared (NIR) wavelengths. This part of work was first started by the building-up of the entire fabrication platform with state of the art Electron Beam lithography (EBL) on Silicon-On-Insulator (SOI) material system. Various slow light PhC structures based on dispersion band-edges were investigated, e.g. PhC line defect waveguides and PhC coupled cavity waveguides. On the other hand, we investigated active slow light structures constituting in band-edge lasers in the Terahertz (THz) frequency range. The active layers of the THz sources are inter-subband quantum cascade (QC) structures. Due to its intrinsic TM polarised emission, we investigated electrical pumped pillar-type PhC QC lasers that have complete PBGs in TM. We developed a BCB planarization technique to enable the metallization and electrical pumping on these isolated pillars.