“…Metasurfaces have attracted increasing attention in the manipulation of the phase, amplitude, polarisation and wavefront of electromagnetic waves due to their appealing qualities including their compactness, easy integration and low loss [1][2][3][4]. Among these functionalities, the phase modulation is of particular importance [5] since it can lead to diverse relevant applications such as holographic imaging [6], polarisation manipulations [7], wavefront control [8,9], and absorbers [10,11]. Although various metasurfaces, either based on metals or based on all-dielectrics, have been designed or demonstrated to achieve full 360 • phase modulations [1,12], most of these metasurface-based phase modulators are passive devices and cannot be actively tuned after fabrication.…”