<title>Large-aperture continuous-phase diffractive optical element for beam transform</title>

Abstract

Beam transform, such as to obtain uniform focal spot with flat top, steep edge, low side lobes and high light efficiency, can be realized well by diffractive optical element (DOE). The DOE has many advantages, such as high light efficiency and strong phase distribution design flexibility. To increase the light efficiency and decrease large-angle scattering, continuous phase DOE should be used. The phase design is competed by a kind of multi-resolution hybrid algorithm based on hill-climbing and simulated annealing, which exploits sufficiently strong convergence ability of the hill climbing and global optimization potential of the simulated annealing. A kind of phase distribution with good geometrical structure and diameter 80 mm is obtained by choosing disturbance function, receipt and refused probability and so on. The simulated results show that the light efficiency is more than 95 percent, and the non-uniformity is less than 5 percent. Because the etching depth is direct proportion to the exposure time, to obtain continuous phase DOE, a kind of hollowed-out mask, namely gray-scale mask is used to control exposure time of each are. The mask is manufactured by linear cutting machine. The continuous phase DOE with diameter 80mm is fabricated by ion-etching with the mask. Finally, the tolerance of manufacturing error including depth error and alignment error are analyzed.