基於半導體雷射非線性動態產生之可調式超寬頻與高頻微波信號及其應用之研究

Photonic Generations of Tunable Ultra Broadband and High Frequency Microwave Signals and Their Applications Based on Nonlinear Dynamics of Semiconductor Lasers

阮于珊(Juan, Yu Shan)

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/博士(2012年)

https://doi.org/10.6843/NTHU.2012.00039

摘要

本論文主要內容為實驗證實利用半導體雷射非線性動態可產生可調式超寬頻及高頻微波信號，與其於微波光電之應用。在本論文中，我們提出及研究周期性光脈衝注入 (repetitive optical injection) 及雙光注入 (dual-beam optical injection) 之新式光注入結構，發現其系統具有低系統複雜度、高可靠度、高穩定性、及低雜訊干擾等特色。再者，亦發現利用新式光注入架構可產生之微波信號具有極寬頻、高度穩定、及極窄頻線寬等優點。

基於光電回饋系統之非線性動態，藉由準確調整回饋強度及延遲時間，周期性連續光脈衝信號可以自發性產生於主雷射之輸出端。將其應用於周期性脈衝光注入系統中，藉由調整注入派衝光之周期及脈衝強度，發現相較於等幅 (cw) 光注入系統更豐富的非線性動態，其中最重要的莫過於鎖頻態 (frequency-locked state)，基於光注入產生之頻寬增益效應，於振幅擾動限制±5 dB情況下可產生超寬頻 (20 GHz) 之電梳 (microwave frequency comb)，可更進一步應用於微波光電之途。

為進一步分析產生之寬頻電梳特性，於頻域上，我們量測並比較每個梳線之單邊帶相位雜訊 (single-sideband phase noise)；於時域上，測得29 ps 之脈衝寬度及18.7 ps之定時抖動 (rms timing jitter)。發現產生之寬頻電梳具有高度的穩定性及低雜訊干擾，非常適合進一步之應用。另外，我們亦實驗論證利用產生之寬頻電梳於頻率轉換 (frequency conversion)、通訊廣播 (broadcasting)、及任意通道選擇 (arbitrary channel selection) 具有良好的系統效能及轉換效率。

實驗上我們亦研究透過光脈衝注入系統產生之超寬頻訊號通過光纖傳輸 (ultra-wideband (UWB) -over-fiber)之可能性，利用2公里長之光纖及一對寬頻天線驗證後，發現超寬頻訊號通過光纖傳輸 (ultra-wideband (UWB) -over-fiber)之可行性。並得知產生之超寬頻訊號具有極寬頻寬，具有93%之部分頻寬 (fractional bandwidth)，其遠遠超過Federal Communications Commission (FCC) 所設之規範。

再者，在無任何外在頻率穩定機制情況下，利用鎖相雙光注入系統可產生約120 GHz 之高頻可調式微波訊號。為比較與其他機制所產生之微波訊號如單光注入 (single-beam injection)、光混合 (optical mixing)、非鎖相雙光注入 (unlocked dual-beam injection)，這些系統所產生之光譜及頻譜均被仔細比較並討論。我們發現鎖相雙光注入所產生之微波訊號具有較寬之可調性及較低之功率擾動。

在本論文中，我們亦將所產生之超寬頻及高頻微波訊號與市面上量產產品及其他利用方法產生之訊號作比較，發現我們所提出的系統具有窄線寬、低雜訊、高穩定性、較寬可調範圍、及低系統複雜度之優勢。

關鍵字

周期性光脈衝注入 ； 雙光注入 ； 鎖頻 ； 電梳 ； 單邊帶相位雜訊 ； 超寬頻訊號通過光纖傳輸

並列摘要

Photonic generations of both tunable ultra broadband and high frequency microwave signals and their applications utilizing nonlinear laser dynamics are investigated experimentally. New injection schemes including optical pulse injection and dual-beam injection are proposed and studied, which can generate microwave signals with very broad bandwidths and high frequencies. The proposed systems have the advantages of compactness, low power consumption, high reliability, less system complexity, good spectral purity, and high stability.

Nonlinear dynamics of semiconductor lasers under optical pulse injection in a hybrid system are investigated and studied for ultra broadband microwave generation. By varying the delay time, regular pulsing states with different pulsing frequencies are generated from a master laser subject to optoelectronic feedback. After injecting a pulse train optically into the slave laser, the microwave frequency combs with bandwidths greater than 20 GHz within a ±5-dB amplitude variation and very low phase noise are obtained benefiting by the bandwidth enhancement effect through optical injection.

To analyze their stabilities and spectral purities, single-sideband (SSB) phase noise of each microwave frequency comb line is measured. At an offset frequency of 200 kHz, a single sideband phase noise of -60 dBc/kHz (-90 dBc/Hz estimated) in the 1st harmonic is measured while a noise suppression relative to the injected regular pulsing state of the master laser of more than 25 dB in the 17th harmonic is achieved. A pulsewidth of 29 ps and a rms timing jitter of 5.7 ps are obtained in the time domain for the microwave frequency comb generated. Furthermore, utilizing the microwave frequency comb generated, frequency conversion, broadcasting, and arbitrary channel selection are demonstrated experimentally.

Demonstration of ultra-wideband (UWB) over fiber based on optical pulse-injected semiconductor laser is also realized. The UWB signals generated are fully in compliant with the Federal Communications Commission (FCC) mask for indoor radiation, while a large fractional bandwidth of 93\% is achieved. To show the feasibility of the UWB-over-fiber with the proposed scheme, the quality of the UWB signals transmitted through a 2 km single-mode fiber and a pair of broadband horn antenna are examined.

Moreover, utilizing a dual-beam optical injection scheme, photonic generation of broadly tunable microwave signals of around 120 GHz is also investigated without the need for a microwave reference source. Optical and power spectra of the microwave signals generated with the dual-beam optical injection scheme are compared with those generated with the optical mixing, the single-beam injection, and the unlocked dual-beam injection schemes. The signal generated with the dual-beam injection scheme shows better tunability and less power fluctuation.

As have been demonstrated in this study, compared to commercial products and microwave signals generated by conventional means using laser dynamics, the proposed schemes have the advantages of narrow linewidths, low SSB phase noise, good spectral purity, widely tunable range, and less system complexity in generating ultra broadband and high frequency microwave signals.

並列關鍵字

repetitive optical injection ； dual-beam optical injection ； frequency-locked ； microwave frequency comb ； single-sideband phase noise ； (ultra-wideband (UWB) -over-fiber

參考文獻

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