Optimization of continuous-profile blazed gratings using rigorous diffraction theory

Surface-relief elements with a high diffraction efficiency play an importan t role in the industrialization of diffractive optics. Optimal methods for the design, analysis, and fabrication of diffracting structures are essenti al for producing high quality applications. With direct laser beam writing it is possible to produce deep continuous-profile diffractive lenses and gr atings with periods on the order of few micrometers. The finite size of the writing beam cannot be neglected as the period becomes comparable to the w avelength of the laser. We present optimization results for deep continuous -profile blazed gratings with periods between 4 and 6 mu m designed to work in the 3rd, 4th, or 5th diffraction order in the visible range. These grat ings possess large diffraction angles, and thus they appear in the outer zo nes of diffractive lenses with a high numerical aperture (NA). Optimization of the profiles is essential for practical applications, since the diffrac tion efficiency drops significantly because of smoothing caused by the fini te size of the writing beam. The proposed optimization scheme utilizes the simulated annealing method and models the diffraction with the rigorous cou pled wave analysis. Improvements of several tens of percents in the diffrac tion efficiency are achieved. The sensitivity of the optimized structures t o fabrication errors is analyzed. (C) 2000 Elsevier Science B.V. All rights reserved.