Optomechanical device actuation through the optical gradient force

Optical forces are widely used to manipulate microparticles such as living cells, DNA and bacteria. The forces used in these 'optical tweezers' originate from the strongly varying electromagnetic field in the focus of a high-power laser beam. This field gradient polarizes the particle, causing the positively and negatively charged sides of the dipole to experience slightly different forces. It was recently realized that the strong field gradient in the near-field of guided wave structures can also be exploited for actuating optomechanical devices, and initial theoretical work in this area was followed rapidly by several experimental demonstrations. This Review summarizes the rapid development in this field. First, the origin of the optical gradient force is discussed in detail. Several experimental demonstrations and approaches for enhancing the strength of the effect are then discussed. Finally, some of the possible applications of the effect are reviewed.