Coupling light in photonic crystal waveguides: A review

•Efficient light coupling techniques for on-chip integration of slow light devices.•Comparative study of various issues in coupling photonic crystal waveguide.•Design of nanophotonic waveguides for efficient coupling.•Issues related to modal mismatch between fiber and chip.

Submicron scale structures with high index contrast are key to compact structures for realizing photonic integrated structures. Ultra-compact optical devices in silicon-on-insulator (SOI) substrates serve compatibility with semiconductor fabrication technology leading to reduction of cost and mass production. Photonic crystal structures possess immense potential for realizing various compact optical devices. However, coupling light to photonic crystal waveguide structures is crucial in order to achieve strong transmission and wider bandwidth of signal. Widening of bandwidth will increase potential for various applications and high transmission will make easy signal detection at the output. In this paper, the techniques reported so far for coupling light in photonic crystal waveguides have been reviewed and analyzed so that a comprehensive guide for an efficient coupling to photonic crystal waveguides can be made possible.