Widely Tunable GRIN Lenses Using Negative Dielectrophoretic Manipulation of Phosphate Nanosheets Colloid

Tunable gradient refractive index (GRIN) lens has attracted increasing attention from researchers due to its promising applicability in various optical and electronic applications. However, the polarization-insensitive, large sized, and focal-length-controllable GRIN lens is highly difficult to implement due to the lack of available functional materials with the property of tunable refractive index. Herein, a two dimensional (2D) α-ZrP nanocolloid is introduced to fabricate a GRIN lens in which the 2D nanosheet density distribution is precisely controlled by negative dielectrophoresis. Interestingly, the geometrical 2D shape of nanosheets plays an essential role in reducing optical light scattering in colloids and enhancing the dielectrophoretic controllability of nanosheet distribution. Moreover, despite the nematic assembly of 2D nanosheets in colloids, the birefringence effect is negligible, and polarization-independent properties are obtained. Using a simple nanocolloidal cell with designed electrodes and various thicknesses, not only tunable lenses with either positive or negative focal lengths but also wide tunable lenses across positive and negative focal lengths are successfully demonstrated. Thus, the results reveal new possibilities for 2D nanocolloids in tunable GRIN optical applications.