摘要
输出波长间隔均匀的多波长掺铒光纤激光器在很多领域,如波分复用通信系统、光纤传感、光学仪器和微波光子系统中都有重要的应用。然而掺铒光纤在室温下是均匀展宽的介质,由此产生的模式竞争使激光器谐振腔中很难实现稳定的多波长振荡。为了研究能够在室温下实现稳定多波长输出的掺铒光纤激光器,本文采用了在激光谐振腔中引入正弦相位调制和偏振烧孔的方法来抑制腔中模式竞争。
在激光谐振腔中,使用正弦信号对半导体光波导进行驱动。这样,半导体光波导可以等效成两个器件:一个对光信号产生移频反馈效果的正弦相位调制器,和一个诱使掺铒光纤中产生偏振烧孔的非线性相位延时器。通过实验,得到了10波长输出的稳定光谱。相邻波长间隔为0.32nm,功率谱比较平坦,起伏小于5dB。结果表明,相位调制和偏振烧孔的共同作用,可以有效的抑制由于掺铒光纤的均匀展宽效应引起的模式竞争。
在本文中,还使用了Matlab对仿真模型进行了数值模拟。数值模拟方面的主要工作包括:推导了基于高双折射光纤的Sagnac光纤环形镜的传输特性,分析了其作为梳状滤波器的优点;从光信号在半导体光波导中相位变化出发,分析了其作为非线性相位延时器和正弦相位调制器的原理。在介绍铒离子性质的基础上,将铒离子的速率方程用Mueller矩阵的形式表示出来,用来描述掺铒光纤中光信号功率和偏振态的传输情况。
Fiber lasers that oscillate simultaneously at multiple wavelengths with an accurate wavelength spacing are of great interest for many applications such as dense wavelength-division multiplexed (DWDM) communications, fiber-optic sensors, optical instrumentation, and microwave photonic systems. But erbium-doped fiber (EDF) is a homogeneous gain medium at room temperature, which lead to strong mode competition and unstable lasing. So it is different to obtain simultaneous multiwavelength lasing in erbium-doped fiber lasers. For realizing a stable multiwavelength erbium-doped fiber laser at room temperature, sinusoidal phase modulation and polarization hole burning are introduced in the laser cavity to suppress the mode competition.
A semiconductor optical waveguide is driven by a sinusoidal signal in the laser cavity. It can be classified here as two optical devices: a sinusoidal phase modulator and a nonlinear phase retarder. The sinusoidal phase modulator produces frequency shift for the fiber laser, and the nonlinear phase retarder introduces polarization hole burning in the erbium-doped fiber. Stable lasing with multiple wavelengths up to 10 and wavelength spacing of 0.32nm was demonstrated at room temperature. The power fluctuation was less than 5dB. It indicated that the phase modulation and polarization hole burning are propitious to suppress the mode competition owing to the homogeneous broaden line.
The numerical model is simulated in Matlab language in our study. Follows are the main points: the transmission characteristics of Sagnac loop mirror based on high-birefringence fiber are deduced. It can be see that the loop can be considered as a comb filter with an accurate wavelength spacing. Based on the analysis of phase shift in the semiconductor optical waveguide, it shows that the semiconductor optical waveguide works as a sinusoidal phase modulator and a nonlinear phase retarder. With the introduction of erbium ion dependencies, a Mueller matrix form of the erbium ion rate equations is presented to propagate powers and polarization states in the EDF.
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