Review on the Optimization Methods of Slow Light in Photonic Crystal Waveguide

Slow light in photonic crystal waveguide (PCW) is now being heavily investigated for applications in optical devices. However, slow light with high group index in perfect PCW is usually accompanied by large group velocity dispersion (GVD), which would severely limit the bandwidth of slow light, deform optical pulses, and disturb its practical applications. In this review, various optimization methods that are proposed to overcome these drawbacks are introduced and compared. These methods rely largely on the ability to modify the slow light properties of PCWs with a change in their structural parameters or a change in their effective refractive indexes through external agents. For each optimization method, the corresponding group index, GVD, bandwidth, and normalized delay-bandwidth product are all presented along with the physical parameters, the potential advantages, and the fabrication complexity of PCW that enable them. Finally, the key problems and future development directions of slow light in PCW are discussed.