利用有限差分時域法及傅立葉光學研究奈米多層膜結構之光學特性

Abstract

本論文以有限時域差分法(finite-difference time-domain method)及傅立葉光學(Fourier optics approach)，研究近場光碟片之超解析效應之光學作用機制。首先，我們分別探討銻薄膜(Sb-type)及氧化銀(AgOx-type)近場光碟片中，不同的奈米結構對其近場電磁場分佈及遠場讀出訊號之影響。而研究結果發現，近場光碟片中的奈米結構可將次波長記錄點之消散訊號(evanescent signal)耦合至遠場，且奈米結構會影響遠場讀出訊號之行為，而光與奈米結構交互作用所引發之侷域表面電漿增強場可提高耦合出消散訊號之效益。 另外，為了探討近場光碟片中的奈米隨機結構所扮演的角色，我們利用簡化的傅立葉光學模型及統計平均方法，計算近場光碟片之讀出對比訊號(readout contrast signal)，以此與近場光碟之載子雜訊比(carrier-to-noise ratio, CNR)比較，同時研究隨機孔洞之形狀與尺寸對讀出對比訊號之影響。除了讀出對比訊號外，我們還計算出近場光碟片之讀出波形，進一步驗證讀出對比訊號之結果。

Near-field optical disk structure has been an attractive topic in ultrahigh density optical data storage. Evanescent signals of subwavelength recording marks can be retrieved from optical interactions between reading laser beam and near-field active layer in near-field optical disk. In this dissertation, we use the 2-D finite-difference time-domain method (FDTD) and Fourier optics approach to study the mechanism of near-field optical disk. Near-field optical properties and far-field responses of near-field optical disks with various kinds of nanostructrures are studied by FDTD. Results show that evanescent signals of subwavelength recording marks are coupled to propagating waves by nanostructures. Furthermore, a simplified Fourier optical approach is used to study the influence of random nanostructure in near-field active layer. The general properties of near-field optical disk with random nanostructure are analyzed by statistical average. The readout contrast signal and waveform of near-field optical disk with random nano apertures is derived. Results show that resolution of near-field optical disk is influenced by the size of aperture.