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標題: Generation of Two-Dimensional Optical Reference Signals Based on Parametric Minimum Cross Entropy
作者: Su, Y.S.
Wu, T.C.
Wang, C.H.
Chang, M.K.
Project: Ieee Photonics Technology Letters
期刊/報告no:: Ieee Photonics Technology Letters, Volume 23, Issue 12, Page(s) 813-815.
In this letter, a novel design of two-dimensional (2-D) zero reference codes (ZRCs) based on parametric minimum cross entropy (PMCE) is proposed to generate 2-D optical zero reference signals (ZRSs) with low second maximum for grating alignment systems. An optical ZRS is necessary to obtain an absolute measurement in grating alignment systems. A method to acquire an optical ZRS is by means of illuminating two identical superimposed ZRCs. Because the movement between the two ZRCs is in two-axis, 2-D ZRCs are required. However, they are hard to design due to the high computational complexity, especially for large codes. The proposed PMCE method not only reduces the second maximum of 2-D optical ZRSs, but also decreases the computational complexity. Simulation results indicate that there are 8.33%similar to 22.22% reductions in the second maximum of several 2-D optical ZRSs, as compared with those of the recently proposed cross-entropy (CE) method. The PMCE method proves to be a powerful tool for the design of 2-D ZRCs.
ISSN: 1041-1135
DOI: 10.1109/lpt.2011.2140368
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