半導體雷射遭光脈衝注入之非線性動態及其於渾沌通訊應用之研究

Nonlinear Dynamics and Its Application in Chaotic Communication of Semiconductor Lasers Subject to Repetitive Optical Pulse Injection

涂修遠(Hsiu-Yuan Tu)

指導教授 ： 林凡異

國立清華大學/電機資訊學院/光電工程研究所/碩士(2007年)

摘要

在本論文中，主要探討半導體雷射遭光脈衝注入所產生的非線性動態和鎖頻 (frequency locking) 的現象。在非線性動態方面，可藉由改變光脈衝注入的強度和脈衝重複的頻率產生不同的非線性狀態，其中主要可區分為脈衝 (pulsing) 和波動 (oscillation) 兩種不同的狀態。吾發現在不同的光脈衝注入強度時，其個別會依循不同之倍數週期路徑 (period-doubling route) 進入渾沌脈衝 (chaotic pulsing) 或渾沌波動 (chaotic oscillation) 的狀態。相較於鬆弛震盪 (relaxation oscillation) 之頻率，此渾沌態之頻寬有二至四倍之頻寬增益 (bandwidth enhancement)。另一方面，藉由改變不同光脈衝注入的頻率，被注入之雷射將產生具有不同旋轉數 (winding number) 的鎖頻狀態。
在應用層面上，利用半導體雷射遭光脈衝注入所產生的非線性動態現象，吾亦探討其於渾沌通訊方面上之可行性。此光脈衝注入渾沌通訊系統相較於傳統的光注入通訊系統有許多優點，如高頻寬、抗雜訊，以及高保密性。其基本原理是利用非線性動態所產生的渾沌態作為渾沌載波 (chaotic carrier)，將所需要傳輸的訊號利用ACM (Additive Chaos Modulation) 的加密方式傳送至接收端，再利用同步化的效應可以解密出所傳輸的訊息，以達到保密通訊的效果。於此系統中，當訊噪比 (SNR) 大於30 dB 時此系統的誤碼率 (bit-error-rate) 可以達到低於傳統通訊上所要求的標準值10-9。

關鍵字

光注入 ； 渾沌 ； 鎖頻

並列摘要

The nonlinear dynamics and frequency locking of semiconductor lasers under repetitive optical pulse injection are studied numerically. Different dynamical states, including pulsation and oscillation states, are found by varying the intensity and the repetition frequency of the injection pulses. Through individual period-doubling routes, the laser enters into chaotic pulsation (CP) states and chaotic oscillation (CO) states, respectively.
Moreover, the bandwidths of the chaos states are also investigated. The time series and power spectra of frequency-locked states with di®erent winding numbers, which is the ratio of the oscillation frequency and the repetition frequency of the injection pulses, are
shown.
Chaotic communication of semiconductor lasers under repetitive optical pulse injection is demonstrated and investigated numerically. The advantages of this chaotic
communication system include large bandwidth, robust, and high security compared to the chaotic communication system based on constant optical injection. In this system, the chaotic carrier is generated by injecting repetitive pulses to a semiconductor laser. The message is encoded to the chaotic carrier with additive chaotic modulation (ACM)
method, while decoding is realized by synchronizing a receiver laser with a transmitter laser. For a signal-to-noise ratio (SNR) above 30 dB, a bit-error-rate (BER) below the benchmark of 10-9 set by the conventional communication is achieved.

並列關鍵字

optical injection ； chaos ； frequency locking

參考文獻

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