  The field of microelectromechanical Systems (MEMS) for photonic integrated
circuits (PICs) is reviewed. This field leverages mechanics at the nanometer to
micrometer scale to improve existing components and introduce novel
functionalities in PICs. This review covers the MEMS actuation principles and
the mechanical tuning mechanisms for integrated photonics. The state of the art
of MEMS tunable components in PICs is quantitatively reviewed and critically
assessed with respect to suitability for large-scale integration in existing
PIC technology platforms. MEMS provide a powerful approach to overcome current
limitations in PIC technologies and to enable a new design dimension with a
wide range of applications.
