Tunable Optical Trap Induced by Focal Shift and Focal Switch in a Focusing Apodized Optical System

Focal shift and focal switch induced by a three- portion apodizer, whose center annular portion has continuously changing phase shift, is theoretically investigated. Numerical simulations show that for the certain geometrical parameters of the proposed apodizer, the focal shift occurs and can be adjustable continuously by changing the phase shift of its center annular portion, and the focal switch may also be changed simultaneously. The possibility of constructing optical trap by use of the apodizer is also discussed.