Inverse design of dielectric nanostructures for optical trapping

Optical trapping in nanostructures has usually been achieved utilizing the strong field gradients of plasmonics resonances. However, given the inherent optical losses in metals to heat dissipation, their use can prove detrimental to biological trapping settings and can affect other trapping properties. Dielectric nanostructures do not suffer these intrinsic losses, but it remains challenging to design dielectric structures with strong field gradients. In this work, we use inverse design by topology optimization to design a dielectric nanostructure that confines light to trap nanoparticles in air. The obtained trapping potential is deep enough – with a trapping depth below -10 k_BT – to overcome thermal fluctuations.