光分碼多重擷取(Optical Code-Division Multiple-Access, OCDMA)技術提供彈性與安全性的網路傳輸，使用者可以同時地非同步擷取網路系統，因此，非常適合應用於區域網路的架構下。在一維頻域振幅編碼 (SAC)中，早期所採用的M-sequence codes、Hadamard codes等可以消除多重擷取干擾（MAI），但是在使用者多的干擾情況下會產生嚴重的相位引致強度雜訊（PIIN），進而影響系統的效能。
　　近年來，有一種新的編碼方式，修正原先的展時編碼轉換成頻域編碼用於頻域振幅編碼中，這種編碼由於碼的交互相關性低，可以減少碼在頻域上的波長碰撞，大幅地降低系統的強度雜訊，而MQC codes是屬於這類的編碼之ㄧ。由於光訊號的單極性(unipolar)特性，一維編碼的長度必須夠長以提供更多的使用者。然而，此類系統受限於光源頻寬有限，編碼的長度如果過長會使得系統變的不切實際。因此，二維編碼的出現是為了改善之前一維編碼的缺點，但仍保有其優點與特性。
　　在本篇論文中，我們提出一個新的二維編碼架構，這種編碼是由頻域編碼和空域編碼兩部份組合而成。頻域的編碼是採用MQC codes，其編解碼裝置是利用可調式布雷格光柵(FBGs)來完成；空域的編碼採用M-sequence codes，其編解碼裝置是分別利用分光器(splitter)或集光器(combiner)來完成。我們將這一個新的二維編碼應用於非同步之光分碼多重擷取系統上，分析其效能並與先前提出的二維編碼系統做比較。
　　在我們所提出的系統架構，不僅增加編解碼器的可調性，提供消除多重擷取干擾的能力，避免光路路遊時間的效應等多項優點，而且在某一固定的錯誤率下能夠大幅地提升使用者上線的數目。這是一套低成本、架構簡單又容易實現的光分碼多重擷取系統。

　　Optical code-division multiple access (OCDMA) techniques not only provide a flexible and secure transmission, but also allow multiple users access the network asynchronously and simultaneously, therefore, they are the most suitable solutions in local area network. In early one-dimensional (1-D) spectral-amplitude coding (SAC) systems using M-sequences codes or Hadamard codes can eliminate the multiple access interference (MAI), but there will be serious phase-induced intensity noise (PIIN). This intensity noise will result in system performance　degradation when a large number of users involved.
　　In recent years, a code family such as Modified Quadratic Congruence (MQC) codes that modified time-spreading codes to spectral amplitude coding codes can significantly reduce the effect of PIIN. This is because the low cross-correlation value between two different codewords can decrease beating among wavelengths, so, the system has a better performance. Due to the unipolar characteristic of optical signals, the code length has to be long enough to support more users. However, the bandwidth of optical source is the limited-factor for spectral amplitude coding and the system will become impractical as the code length longer. Hence, the development of two-dimensional (2-D) codes is to improve several shortcomings of former ones but advantages are still preserved.
　　In this thesis, we propose a new 2-D code family for frequency/spatial SAC OCDMA system and the associated coding/decoding scheme. In frequency domain, we utilize MQC codes and the coding/decoding device is based on tunable fiber Bragg gratings (FBGs); in spatial domain, we adopt M-sequence codes and the coding/decoding device is based on splitter/combiner. We apply this new 2-D code family in an asynchronous optical CDMA system and analyze the proposed system performance. Comparisons with former system using 2-D codes are also shown for a reference.
　　In our proposed system configuration, it has several advantages including tunability, the ability of MAI cancellation, and no round-trip time delay problem. Moreover, the number of active users is increased under a given bit-error-rate (BER). This is a low cost, simple, and easy implementation OCDMA system.

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