Electron-beam lithography to improve quality of computer-generated hologram

The quantized errors in computer generated holograms (CGH) have been analysed theoretically. In order to evaluate quantitatively the influence of these errors on the quality of reconstructed image, a signal-to-noise ratio (SNR) is introduced. It is found that the SNR of a reconstructed image is very sensitive to the accuracy of amplitude and phase. Improving the accuracy of amplitude and phase is much more effective for improvement of CGH image quality than simply increasing the sampling cells. The accuracy of amplitude and phase of a sampling cell is represented by the fidelity of sampling cell geometry. CGH plates with the same encoded image have been fabricated by both conventional photoreduction method and e-beam direct write method. The reconstructed images from both plates have been compared. The experimental result has confirmed the theoretical analysis: e-beam direct write can produce CGHs with quality superior to conventional photoreduction technique (C) 2002 Elsevier Science B.V. All rights reserved.