光折變體積全像術之波長多工於高密度分波多工器之應用

A Dense Wavelength Division Multiplexing Scheme using Wavelength Multiplexing in Photorefractive Volume Holography

吳啟守(Chi-Shou wu)

指導教授 ： 孫慶成 ； 陳相村

中原大學/理學院/應用物理研究所/碩士(2002年)

https://doi.org/10.6840/cycu200200396

摘要

在光纖通訊系統中，高密度分波多工器對於增加通訊容量是一很重要的關鍵架構。設計高密度分波多工器有不同的方法、且各有其優缺點。一個成功的高密度分多工器必須有相當多的通道數（3dB的頻寬愈小或通道間距愈小，則通道數會增加）和在實際使用中的環境達到穩定之要求。因為體積全像已經使用不同的多工技術，包括：角度多工、波長多工、和相位多工以增加儲存容量。從此很容易使人聯想到體積全像可能可以用來做為高密度分波多工器。一般來講，反射式體積全像比穿透式體積全像具有更小的光柵週期，所以反射式體積全像比穿透式體積全像具有更大的儲存容量。體積全像的儲存容量決定於布拉格檢選度，而計算此檢選度有不同的理論，包含：耦合波理論、Born’s approximation、和最近的相位疊加法，由於耦合波理論可以考慮入射光與全像光柵之間線性和非線性的交互作用。所以由此理論所得之布拉格靈敏度可以視為最精確的結果，然而其對高密度分波多工器基本設計所須的HWFZ（一階零點半寬）或FWHM（半高全腰寬）並無法提供直接的公式以用來做計算。
本文證明相位疊加法所得之布拉格檢選度在低繞射效率時與耦合波理論所得之布拉格檢選度一致，為了使每一波長的頻寬相等，我們必須知道反射式體積全像之波長檢選度HWFZ與波長或入射角之關係，本文率先使用相位疊加法推導出此二種解析解，並以下述方法使用於體積全像高密度分波多工器設計。
由於每一中心波長的HWFZ隨著記錄波長增加而增加，因此本文率先結合角度和波長多工之技術，提供一設計的方法使得在光纖傳輸視窗S、C、L波帶中之每一波長的頻寬相等。運用此一技術，本文完成一高密度分波多工器之設計，此一設計是假設有一在1550nm波長中能夠感光的鈮酸鋰晶體，利用厚度為1cm的晶體達成一2048通道（其通道間距為0.05nm）之高密度分波多工器。

關鍵詞：高密度分波多工器、光纖通訊、光折變、反射式全像、體積全像、角度多工、波長多工、鈮酸鋰。

關鍵字

高密度分波多工器

並列摘要

Dense-wavelength division multiplexing (DWDM) is an important scheme for increasing communication capacity in fiber optic communication. There are various approaches for implementing DWDM and each approach has its advantages and disadvantages. A successful DWDM should have a large number of channels (for which a narrow 3-dB bandwidth or channel spacing is needed), and environmental resilience. Since volume holography has been used in information storage with various multiplexing schemes, including angular, wavelength, and phase multiplexing, for increasing the storage capacity, it is easy to conclude that there is a potential application of volume holography in DWDM. Since the grating period in a typical reflection hologram is much smaller than that of a transmission hologram, a reflection hologram can result in a larger storage capacity than that of a transmission hologram. The information storage capacity of a volume hologram is determined by its Bragg selectivity. There are various approaches for calculating this selectivity, which includes the Coupled Wave Theory, Born’s Approximation, and recently, the Phase Summation Method. Since the Coupled Wave Theory can take into account both linear and nonlinear interaction between the incident light and the hologram grating, the Bragg selectivity derived from this theory represents the most accurate result. However, it provides no formula for predicting either the HWFZ (half width at first zero) or the FWHM (full width at half maximum), which is essential for designing appropriate bandwidth in DWDM.
This thesis has verified that the Bragg selectivity calculated by using the Phase Summation Method in the regime of low diffraction efficiency is the same as that of Coupled Wave Theory. This thesis is the first to derive a formula for calculating HWFZ for the Bragg selectivity of reflection hologram using the Phase Summation Method. This thesis also proposes a DWDM scheme using volume holography and is the first to establish a unique design protocol for DWDM using a reflection hologram as detailed below.
However, the HWFZ for each center wavelength increases as the wavelength increases. In order to make the bandwidth of each center wavelength must be equal. This thesis is the first to propose an innovative approach to combine both angular multiplexing with wavelength multiplexing in order to keep the bandwidth constant within the S, C, and L band of the fiber transmission window. Using the above results, this thesis has provided a DWDM design, which consists of 2048 channels and a channel spacing of 0.05nm using a photorefractive crystal of LiNbO3 and reflection holography.

Keywords：Dense wavelength division multiplexing, fiber optic communication, Photorefraction, reflection hologram, volume holography, angular multiplexing, wavelength multiplexing, LiNbO3

並列關鍵字

Dense-wavelength division multiplexing (DWDM)

參考文獻

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