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图 1是激光器的实验装置图。激光器为直腔结构,一个中心波长为974 nm、最大输出功率为823 mW的激光二极管(laser diode, LD)作为抽运源。工作波长为1020 nm~1080 nm的波分复用器(wavelength division multiplexer, WDM)将抽运光耦合到长度为80 cm的掺镱光纤(Yb501)中。一个90 ∶10的耦合器(optical coupler, OC)OC2提取腔内10%的能量作为激光器的输出,掺镱光纤和耦合器OC2之间放置一偏振控制器(polarization controller, PC)PC3以协助激光器锁模,左右两端的腔镜分别为Sagnac环反射镜和半导体可饱和吸收镜(semiconductor saturable absorber mirror, SESAM), 总腔长为7.5 m。其中Sagnac反射镜还起着滤波器的功能,它由一个50 ∶50的耦合器OC1、两段长度分别为7 cm和17 cm的保偏光纤(polarization maintaining fiber, PMF)以及两个偏振控制器PC1、PC2组成,其透射谱的周期可以写成如下形式[17-18]:
$ \Delta \lambda=\frac{\lambda^2}{\Delta n\left|L_1 \pm L_2\right|} $
(1) 式中,λ为信号光的波长,Δn为保偏光纤的双折射率差,在实验中,其值约为4×10-4,L1和L2分别为PMF1和PMF2的长度。
图 2是用自发辐射光源在不同PC状态下测得的透射谱线。由图 2可知,滤波谱线的谷值位置可以通过调节腔内PC调谐,而且它们周期相同,约为12 nm,与理论值11 nm相近。换句话说,可通过调节PC来实现波长的调谐功能。
单波长和双波长可调谐的掺镱锁模光纤激光器
Tunable single-wavelength and dual-wavelength ytterbium-doped mode-locked fiber lasers
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摘要: 为了获得不同中心波长的锁模脉冲,采用带有保偏光纤的Sagnac环滤波器和半导体可饱和吸收镜搭建了结构紧凑的可调谐锁模激光器,并进行了实验验证。结果表明,当该激光器工作在单波长锁模状态时,具有良好的波长调谐功能,其输出波长在1031 nm~1040 nm范围内连续可调;该激光器还能输出稳定的双波长异步脉冲序列,两波长间隔在10 nm左右,且各波长的带宽可通过偏振控制器调节。该研究可以为搭建结构紧凑的可调谐激光器提供设计方案。
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关键词:
- 激光器 /
- 可调谐激光器 /
- Sagnac环滤波器 /
- 掺镱光纤激光器
Abstract: In order to obtain mode-locked pulses with different center wavelengths, a compact tunable mode-locked laser was built by using Sagnac loop filter with polarization maintaining fiber and semiconductor saturable absorber mirror. And the experimental verification was carried out. The results show that, the laser has a good wavelength tuning function when it operates in a single wavelength mode locked state, and its output wavelength is continuously adjustable in the range of 1031 nm to 1040 nm. The laser can also output a stable dual wavelength asynchronous pulse sequence, with the interval between the two wavelengths about 10 nm, and the bandwidth of each wavelength can be adjusted by the polarization controller. This research can provide a design scheme for building a compact tunable laser.-
Key words:
- lasers /
- tunable laser /
- Sagnac loop filter /
- ytterbium-doped fiber laser
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图 4 单波长输出特性
a—不同抽运功率下的输出光谱图 b—输出功率随抽运功率变化图 c—不同时间下的光谱图 d—1031 nm~1040 nm连续调谐的锁模光谱
Figure 4. Characteristic of single wavelength
a—spectra at different pump powers b—output power at different pump powers c—spectra at different time d—tunable single-wavelength mode-locked laser from 1031 nm to 1040 nm
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