應用全像光學交換元件於光網路與光延遲線

Abstract

本論文提出以全像光學交換元件設計多種的光連線網路與光延遲線。全像光學交換元件是三維結構，具有垂直入射與輸出、緊密、容易製造、同軸耦合與重量輕等特性。在系統應用上，具有較高的設計彈性，且容易對準。在適當設計下，可以得到具有高偏極化選擇的全像元件。緊密性與設計彈性是全像光學交換元件的重要特性，運用這些特性建立多種的光連線網路時，可以藉由彈性調整這些元件尺寸，消除所有內部連線。因此，這種元件會適合用以建立各種的光連線網路。 首先要討論的，是1*2與2*2全像偏極化分光元件的結構與工作原理。該分光元件與電光調制半波片結合之後，可以設計出多種的光學交換元件，例如1*2、2*1、2*2與高訊號雜訊比的2*2交換元件。 原先使用稜鏡偏極化分光元件設計光延遲線系統時，不論是延遲路徑或非延遲路徑，都是建立在自由空間之中。因此，光延遲線系統不僅需要大量空間來配置所有元件，同時更需要精確的對準。應用全像光學交換元件以設計光延遲線系統時，除長時間延遲線以外，不論是延遲路徑或非延遲路徑，短、中時間延遲線都可建立在一個緊密結構，而不需要任何額外元件，可節省整個系統使用空間。 為了改善光連線網路的性能，我們也提出了環狀交越（cyclic crossbar）網路與改良的Benes網路。環狀交越網路與矩形交越網路的結構相似，但是這兩種網路結構在系統損失差、交叉點數與訊號雜訊比等特性有一些不同。由於環狀交越網路每一條連結路徑的交換元件數都相同，因此這種網路結構的系統損失差為零，這也使得它的訊號雜訊比與交換元件的損失無關，然而矩形交越網路的訊號雜訊比不僅會隨著輸入/輸出數的增加而降低，而且還會隨著交換元件損失的增加而快速地降低。提出改良的Benes網路則是為了提升Benes網路的訊號雜訊比，同時保有與Benes網路具有最少驅動電路數的特性。 在運用全像光學交換元件建立多種型態的光連線網路時，例如Benes網路、雙層（double-layer）網路、環狀交越網路、以環狀交越結構設計的Clos網路與主動分光/主動光合併（active splitters/active combiners）網路，運用緊密性與設計彈性在最佳化設計後，可以有效消除所有的內部連線。這不僅可以大量地減少整個系統的空間，而且可以減少所需的元件數。

In this dissertation, optical interconnection networks and photonic delay lines with holographic optical switching elements have been proposed. Holographic optical switching elements perform polarization-dependent characteristics. The holographic optical switching elements are three-dimensional devices. Normally incident input and output coupling with these compactness, easy fabrication, on-axis coupling, and lightweight devices provide better flexibility and easier alignment for system applications. With suitable designs, highly polarization-selective holographic elements can be achieved. The holographic optical switching elements are three-dimensional devices. The flexibility and compactness of holographic optical switching elements are also important characteristics. Utilizing the characteristics, the dimensions of the holographic optical switching elements can be adjusted, which may eliminate the necessity of interconnection lines between switching elements to build many types of networks. Therefore, they are more suitable for building optical interconnection networks. The structures and the operation principles of the 1□2 and 2□2 holographic polarization beam splitters will be first discussed. Combined with electro-optic halfwave plates, several types of switching elements, such as 1□2, 2□1, 2□2, and higher contrast ratio 2□2 switching elements will be discussed in detail. Using prism polarization beam splitter to design a photonic delay line system has been proposed previously, in which the delay and non-delay paths are built in free space. Therefore, this photonic delay line system not only needs a large space to allocate all components but also needs more accurate alignments. When using holographic optical switching elements to build the photonic delay line system, both delay and non-delay paths are constructed in a compact structure except the long time delay. Because the structures of moderate and short time photonic delay lines are compact, they do not need any extra components such as mirror and optical path in free space. Cyclic crossbar network and modified Benes network will be presented to improve the performance of optical interconnection networks. The cyclic crossbar network is proposed to replace the rectangular crossbar network. The rectangular crossbar network has two drawbacks: one is that it has non-zero differential system insertion loss and the other is that its signal-to-noise ratio is reduced by both the increase of the network dimension and the insertion loss of switching elements, although it has advantages of easy connection-path rebuilding, wide-sense nonblocking, and no crossover in its interconnection lines. The cyclic crossbar network eliminates the differential system insertion loss, makes signal-to-noise ratio independent of insertion loss of switching elements, and still maintains the original advantages. The modified Benes network is proposed to obtain a higher signal-to-noise ratio with the same number of drivers as the Benes network. Finally, Benes network, double-layer network, cyclic crossbar network, Clos network with cyclic crossbar structure, and active splitters and active combiners network will be built with holographic optical switching elements. After optimum design, the unique features of compactness and flexibility of holographic optical switching elements efficiently eliminate all interconnection lines between switches. Not only the spaces of all systems are significantly saved but also the number of required components is reduced.