Abstract
We describe a method for designing nonperiodic fine grating structures such as a small F-number diffractive cylindrical lens, to be fabricated by direct-writing electron-beam lithography. The design is based on a resist development simulator for estimating a proximity effect of electron dose and the finite difference time domain (FDTD) method for simulating an electromagnetic field. The surface profile and electron dose distribution are simultaneously optimized to obtain the high diffraction efficiency. For the design of a diffractive lens of 50 µm width and 25 µm focal length, the calculated diffraction efficiency is 49% for 650-nm-wavelength light, which is slightly lower than that of a diffractive lens profile optimized by electromagnetic analysis without restrictions on fabrication limits.
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