利用光注入半導體雷射非線性動態產生線性啾頻訊號及其於雷射測距的應用

Linearly Chirped Signal Generation and Its Application in Range Finding Utilizing Optically Injected Semiconductor Laser System

陳俊銘(HASH(0x877c87c))

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(2006年)

https://doi.org/10.6843/NTHU.2006.00677

摘要

在本論文中以數值模擬的方式利用光注入半導體雷射非線性動態的特性產生線性啾頻訊號(linearly chirped signal)。光注入系統包含一組雷射波長相近的主雷射與副雷射，其產生的非線性動態包含穩定鎖定區(stable-locking)、渾沌振盪區(chaotic oscillation)、週期一振盪區(period-one)、週期二振盪區(period-two)與其他高階的振盪區。我們將運用四種調變的方式來產生線性啾頻訊號，包括(1)在穩定鎖定區以直接電流調變方式調變副雷射、(2)在穩定鎖定區調變主雷射、(3)在週期一振盪區調變光注入強度，(4)在週期一振盪區電流調變主雷射。在不同架構中，研究調變係數(modulation index)、調變週期、掃頻的頻寬(bandwidth)、頻率變化率(chirp rate)與頻率變化的線性度等參數之間的相互關係。運用穩定鎖定區的特性，可以用直接調變方式產生一個掃頻的頻寬大於30 GHz，且頻率變化具有很好的線性程度。利用P1區的特性，不需要複雜昂貴的電子儀器，即可產生振盪頻率在RF範圍的訊號，但是頻率隨時間變化的線性程度較差。
在Intensity Modulation Continuous Wave(IMCW)雷射測距系統中，由於雷射光強度的振盪頻率會隨著時間線性變化，將此訊號朝向物體發射，參考訊號與反射訊號之間會有個延遲時間，訊號混合後在頻譜上會產生一個差頻，利用這頻率可以計算受測物體的距離。差頻在頻譜上會有個線寬(linewidth)，線寬會影響空間上的解析度。我們研究了掃頻的頻寬與線性度對線寬的影響，驗證利用非線性動態產生的訊號在雷射測距上的效果(performance)。我們發現線性度對解析度有很大的影響，而利用穩定鎖定區所產生的訊號有較佳的線性度，因此在測距的應用上有較好的空間解析度，解析度可以達到1.5公尺。

關鍵字

線性啾頻訊號 ； 線性度 ； 半導體雷射非線性動態

並列摘要

We numerically simulated the characteristics of linearly chirped signal generation utilizing optically injected semiconductor laser. The optically injected laser system consists of two lasers with similar intrinsic parameters and wavelength. The slave laser is injected by the master laser. By tuning the operating parameters, the optically injected semiconductor laser can be operated in different instable regions. There are stable-locking, chaotic oscillation (CO), period-one oscillation (P1), period-two oscillation (P2) and high order oscillation regions. Four schemes will be used to generate linearly chirped signal: (1) direct current modulation on slave and on (2) master laser, respectively, while the slave laser is operated in stable-locking region. (3) The third scheme is modulating the injection strength of the slave laser directly while which is operated in the P1 region. (4) The last one is modulating the injection strength by current modulation on the master laser while the optically injected slave laser is operated in the P1 region. The relation between modulation index, modulation period, bandwidth and chirp rate will be studied. We also show the dependence of linearity on chirp rate. We can generate a linearly chirped signal with bandwidth more than 30 GHz and with high linearity when the laser is operated in stable-locking region. On the other hand, a complicate electronics free method can used to generate signal in RF range by utilizing period-one oscillation region.
The signal used in the intensity modulation continuous wave (IMCW) laser ranging system is a linearly chirped signal. The signal will be transmitted toward the target and the reflected signal will be collected by a photo-diode. The frequency difference between the two signals caused by the delay time of reflected signal can be used to estimate the range of the target. We investigate the effect of linearity and bandwidth on the linewidth that determinates the resolution of the ranging system. We show the high linearity of the linearly chirped signal generated by laser operating in and a 1.5 m resolution is achieved.

並列關鍵字

HASH(0x8789cf0) ； HASH(0x8789d68) ； HASH(0x8789de0)