Design of multilevel spiral phase Fresnel zone plates

Optical techniques are widely used for trapping of particles. One such technique involves the use of passive diffractive optical elements. Recently, a novel passive diffractive optical element, a spiral phase Fresnel zone plate (FZP) was proposed [1]. In this paper, we present an improved version, of the earlier reported element, that will allow for a compact optical configuration for generation of elliptical donut beams. This compact design enables easy insertion of the device into optical trapping experiments for micro level trapping. The proposed multilevel spiral phase FZP can be used for applications such as trapping by illuminating it with a narrow spectral width laser as shown in Fig. 1(a). The simulated 3-D structure of the proposed multilevel spiral phase FZP is shown in Fig. 1(b).