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Wavelength tunable mode-locked pulse fiber laser based on figure-of-eight cavity

February 2008
ACTA PHOTONICA SINICA 37(2):212-215

February 2008
37(2):212-215

Authors:

Taiyuan University of Technology

Experimental study of the wavelength tunable passively mode-locked Er-doped fiber laser based on figure-of-eight cavity is presented. Wavelength tunable and stable mode-locked pulses are obtained by utilizing the additive pulse mode-locking technique based on nonlinear optical loop mirror associated with tunable fiber grating filter. On the condition that the pump power of EDF As is fixed, by adjusting the tunable filter and orientation of polarization controllers, the mode-locked pulses at 1.1 MHz repetition rate with average output power fluctuation less than 0.8 dBm, and tunable range from 1548 nm to 1570 nm are obtained. The self-starting of the mode-locked fiber laser can be obtained, and the mode-locked operation can be hardly influenced by the environment disturbance.

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第37 卷第 2期

2008 年2月　　　　　　　　　　　　光　子　学　报

ACTA P HO TONICA SINICA Vol. 37 No. 2

February 2008

3国家自然科学基金 (60577019)和山西省留学回国人员科

研基金(2004217)资助

Tel :035126014447 　Email :office2science @tyut . edu . cn

收稿日期:2006209211

8字形腔波长可调谐锁模脉冲光纤激光器3

郭雄英1 ,2 ,杨玲珍1,贺虎成1,曹玲1,王云才1

(1太原理工大学理学院物理系 ,太原 030024)

(2新疆大学物理系 ,乌鲁木齐 830046)

摘　要:采用非线性光纤环形镜加脉冲锁模技术及可调谐光纤光栅滤波器 ,对8字形腔被动锁模掺

铒光纤激光器进行了波长可调谐输出的实验研究1在EDFA 抽运光功率一定的情况下 ,通过调节

偏振控制器和可调谐光纤光栅滤波器 ,获得了光谱稳定、重复频率 1. 1 M Hz、输出功率起伏小于

0. 8 dBm、中心波长在 1 548～1 570 nm 内连续可调的短脉冲输出.该激光器可实现自启动锁模 ,且

长时间稳定工作无需任何调整1

关键词:激光技术;光纤激光器;8 字形腔;非线性光纤环形镜;波长调谐

中图分类号: TN248 　　　　文献标识码:A 　　　　文章编号 :100424213(2008)022021224

0　引言

利用加成脉冲锁模技术实现的锁模光纤激光

器,具有结构简单、稳定性好、易于自启动的特点.在

实现全光纤结构的同时 ,可以不受载流子恢复时间

限制获得飞秒量级的超短脉冲[124 ] ,可广泛应用于光

纤通信、医学、物理学以及光化学等领域 1其中 ,基

于非线性光纤环形镜加成脉冲锁模技术的光纤激光

器(8字形腔激光器),由于非线性光纤环形镜具有

与强度相关的透射特性 ,可以像可饱和吸收体一样

窄化脉冲 ,使得锁模激光器输出脉冲较窄、工作稳

定、背景噪声低且可以在很宽的波长范围内进行调

谐1而波长可调的超短脉冲光源是高速波分复用/

光时分复用通信系统中的关键器件之一 ,因此近年

来对基于非线性光纤环形镜的可调谐被动锁模光纤

激光器的报道层出不穷1

1993 年,Noske D U 等人用腔内 F2P滤波器实

现频域稳定 ,同时用反馈环路技术实现时域稳定 ,在

8字形腔铒镱共掺被动锁模激光器中获得了光谱带

宽1. 8 nm ,中心波长在 20 nm 范围内连续可调的锁

模脉冲输出[5]11997 年,Tsun T O 等人在 8字形被

动锁模掺铒光纤激光器内放置一段较长的色散位移

光纤得到了脉宽 125 fs ,能量 0. 5 nJ 的高能量飞秒

脉冲 ,中心波长在 6. 5 nm 范围内可调[ 6 ] 12000 年,

Jeon M Y 等人在 8字形被动锁模掺铒光纤激光器

中插入声光可调滤波器 ,得到了光谱带宽约 7 nm ,

调谐范围 50 nm 的可调谐光纤激光器[7] 12005 年,

我国的马海全等人采用非线性光纤环形镜被动锁模

的掺 Yb3 + 光纤激光器 ,获得了中心波长在 1 030～

1 081 nm范围内连续调谐的锁模脉冲输出 ,在中心

波长 1 053 nm 时,测得光谱带宽 6 nm、脉冲宽度

234 p s、重复频率 3. 8 M Hz[8 ]1然而 ,利用上述方法

实现的波长可调谐锁模脉冲光纤激光器 ,其共同特

点是输出光谱较宽1

本文采用非线性光纤环形镜作为被动锁模器

件,窄线宽的光纤光栅滤波器作为波长调谐器件 ,实

现了被动锁模掺铒光纤激光器的波长可调谐输出 ,

利用偏振控制器和偏振相关光隔离器构成的强度均

衡器[ 9210] ,实现了各波长光脉冲间的强度均衡 ,获得

了输出功率平坦、波长从 1 548 nm 到1 570 nm 连

续可调的锁模脉冲序列 ,从而为其它科学研究工作

提供了中心波长可调谐的窄线宽短脉冲源1

1　实验装置及原理

8字形腔波长可调谐锁模脉冲掺铒光纤激光器

的实验装置如图 1 ,该激光器由 150 m 长的普通单

模光纤(Single Mode Fiber ,SMF)、掺铒光纤放大器

(Erbium2Doped Fiber2Amplifier ,EDFA)、光纤偏振

控制器 (Polarizatio n Cont roler , PC )、光环形器

图1　波长可调谐锁模脉冲光纤激光器实验装置

Fig. 1 　Experimental setup of wavelength tunable

mode2locked pulse fiber laser

2期郭雄英 ,等:8 字形腔波长可调谐锁模脉冲光纤激光器

(Circulator)、可调谐光纤光栅滤波器(Tunable

Fiber Bragg Grating , TFBG)、偏振相关光隔离器

(Polarization Dependent Isolator ,PDI)和光纤耦合

器(Optical Coupler ,OC)构成1实验采用的掺铒光

纤放大器 (武汉邮电科学研究所 EDFA2BA )在

1 530～1 565 nm范围内增益平坦度小于 0. 1 dB ,

EDFA1 为锁模激光腔内提供增益 , EDFA2 对锁模

脉冲进行腔外放大;反射型可调谐光纤光栅滤波器

的调谐范围为 32 nm ,其3 dB 带宽小于 0. 35 nm1

该激光器的振荡腔结构与传统的 8字形腔略有不

同,仅用一个偏振控制器 PC1 对腔内参量进行调

节,这样减小了腔内的插入损耗 ,使自启动变得更容

易;用功率分光比为 99 ∶1的耦合器 OC2 代替掺杂

光纤 ,非对称地放置在环镜中用来打破环镜的对称

性1其工作原理为:初始光脉冲 (由噪声引起)从

3 dB耦合器 OC1 的一端进入环镜后 ,被分成相向传

输、等强度的两束光.这两束光先后受到由耦合器

OC2 引起的损耗 ,因而在环镜中传输时具有不同的

光强.由于光纤的非线性 Kerr 效应 ,相向传输的两

束光在普通单模光纤中传输时 ,将受到与强度相关

的自相位调制和交叉相位调制等非线性效应的作

用,产生不同的非线性相移 ,形成非线性相移差 ,且

相向传输两束光之间所获非线性相移差在光脉冲峰

值处最大.当光脉冲峰值处所获非线性相移差等于

π时,经由 3 dB 耦合器输出时发生干涉相长 ,而脉

冲的前后两翼由于其强度较低 ,所获非线性相移较

小,发生干涉相消 ,从而产生自幅度调制的脉冲窄化

效应.光脉冲在激光腔内往复运转 ,便可形成稳定的

锁模脉冲 ,最后经由 90 ∶10 耦合器 OC3 输入到

EDFA2 中进行再放大.采用可调谐光纤光栅滤波器

对放大后的锁模脉冲进行波长选择 ,从而实现锁模

脉冲光纤激光器的可调谐输出1

该激光器实现功率平坦输出的关键器件是偏振

相关光隔离器和偏振控制器 PC21偏振控制器 PC2

和偏振相关光隔离器相当于一个强度均衡器 ,通过

调节偏振控制器 PC2 可使光脉冲具有不同的偏振

状态 ,偏振相关光隔离器将偏振态的差异转变为透

射率的差异 ,因此通过调节偏振控制器 PC2 可以控

制各波长光脉冲的透射率 ,从而实现各波长光脉冲

间的强度均衡 ,减小输出功率起伏 ,扩大调谐范围1

2　实验结果和讨论

实验中利用带宽 500 MHz 的实时示波器

(Tektronix TDS3052)来观测激光器输出的时域特

性,用最小分辩率为 0. 06 nm 的光谱仪

(Agilent86140B)观测激光器输出的频域特性 ,利用

光功率计(PMS21BF)检测光纤激光器的输出功率 ,

超快光电探测器 (XPDV2020)结合带宽为 50 GHz

的示波器(Agilent86100B)测量脉冲的宽度1

图2给出了当 EDFA1 、EDFA2 泵浦功率分别

为100 mW 和99 mW 时,对EDFA2 输出端进行观

测,所获被动锁模脉冲光谱图(a)、脉冲序列图(b)和

脉冲宽度图 (c),其重复频率 1. 1 M Hz ,中心波长

1 559 nm ,谱宽 9 nm ,脉宽 464 ps ,平均输出功率

11. 2 dBm1在此条件下 ,采用腔外滤波法[ 11 ] ,对该

锁模掺铒光纤激光器进行了波长可调谐输出实验研

究,在整个滤波过程中保持偏振控制器 PC1 波片方

位角以及 EDFA 抽运功率不变 1实验上通过联合

调节可调谐光纤光栅滤波器和偏振控制器 PC2 波

片的方位角 ,实现了输出波长从 1 548 ～1 570 nm

连续可调谐 ,波长调谐范围达 22 nm ,边模抑制比在

20 dB 以上 ,各输出波长 3 dB 线宽小于 0. 35 nm1

图2　经 EDFA2 放大后锁模脉冲结果

Fig. 2 　Output results of mode2locked pulse after amplified by EDFA2

　　图 3分别给出了在 1 548 nm 和1 559 nm 处滤

波后得到的光谱图1从图中可以看出 ,信噪比均大

于20 dB ,但是光谱中具有很大的噪声基底.这是因

为该可调谐光纤光栅滤波器属于反射型滤波器 ,端

面反射使得反射光谱中存在一定的反射背景.因此 ,

如果采用滤波特性较好的滤波器则可大大提高输出

信号的信噪比 ,消除噪声 1图4给出了对激光器输

出脉冲滤波后得到的平均输出功率和脉冲宽度随波

长的变化情况 ,从图中可以看出 ,在1 548～1 570 nm

的波长调谐范围内 ,激光器输出功率起伏小于

312

光　子　学　报 37 卷

0. 8 dBm ,脉冲宽度略有改变 ,脉冲宽度的改变主要

是由所用光纤光栅滤波器引起的 ,由于该光纤光栅

滤波器是通过拉伸光纤长度来实现波长调节的 ,而

光栅本身周期的改变会引起光纤光栅色散的改变 ,

色散的变化导致了脉冲宽度的改变1

3　结论

采用非线性光纤环形镜加成脉冲锁模技术结合

可调谐光纤光栅滤波器 ,实现了被动锁模掺铒光纤

激光器的波长可调谐输出 ,获得了重复频率为

1. 1 M Hz 、输出功率起伏小于 0. 8 dBm 、中心波长在

1 548～1 570 nm 内连续可调的短脉冲输出1该激

光器腔内没有加入色散补偿器件 ,且腔长较长 ,导致

输出脉冲宽度较宽 ,重复频率较低1可以预见 ,如果

在8字形腔中采用一段正色散光纤进行啁啾补偿、

进一步优化环镜长度和增益光纤长度、采用滤波性

能更好的可调谐滤波器 ,并结合谐波锁模技术 ,则可

得到脉宽更窄、重复频率更高、调谐范围更广的窄线

宽光脉冲输出1

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2期郭雄英 ,等:8 字形腔波长可调谐锁模脉冲光纤激光器

Wavelength Tunable Mode2locked Pulse Fiber Laser

Based on Figure2of2Eight Cavity

GUO Xiong2ying1 ,2 , YA N G Ling2zhen1, HE Hu2cheng1, CAO Ling1, WAN G Yun2cai1

(1Ph ysics D ep art ment , Coll ege of S cience , T ai yuan U niversi ty o f Technol ogy , T ai yuan 030024 , China)

(2Physics Dep artment , X injiang University , Urumqi 830046 , Chi na

Received dat e :2006209211

Abstract : Experimental st udy of t he wavelength tunable passively mode2locked Er2doped fiber laser based

on figure2of2eight cavity is p resented. Wavelength tunable and stable mode2locked pulses are obtained by

utilizing the additive p ulse mode2locking technique based o n nonlinear optical loop mirror associated with

tunable fiber grating filter. On the condition that t he pump power of EDFAs is fixed , by adjusting the

tunable filter and orientation of polarization controllers , t he mode2locked p ulses at 1. 1 M Hz repetitio n rate

wit h average outp ut power fluctuation less than 0. 8 dBm , and tunable range from 1 548 nm to 1 570 nm

are obtained. The self2starting of t he mode2locked fiber laser can be obtained , and the mode2locked

operation can be hardly influenced by the environment disturbance.

Key words:Laser t echnique ; Fiber la ser ; Figure2of2ei ght cavit y ;No nlinea r op tical loop mirror ; Wavele ngt h

tenability

GUO Xiongying 　was born in 1980. Now she is pursuing her M. S. degree at Xinjiang

University and engaged in her thesis at Taiyuan University of Technology. Her research work

mainly focuses on nonlinear fiber optics and ultra2short pulse generation in fiber laser.

512

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Mar 2012

By introducing the rotatable in-line polarizer into the ring cavity of nolinear polarization rotatation (NPR), the all fiber structure of passively mode-locked ring laser is simplified. The Erbium-doped mode-locked laser with the tuning range of 20 nm is achieved by adjusting the polarizer, 1/2 wave plate and the 1/4 wave plate together. Furthermore, the mode-locked pulses with dual-wavelength are observed during the tuning process. On the other hand, when removing the 1/2 wave plate from the configuration, the mode-locked laser can also be obtained by only adjusting the polarizer and the 1/4 wave plate. The tunable process is presented and analyzed.

Experiment Study on a Tunable Fiber Laser Using Optical Circulator and Tunable Fiber Bragg Gratings

Article

May 2009

A simple and effective tunable fiber laser is presented. The linear-cavity laser consists of a three-port optical circulator (OC), a tunable fiber Bragg grating (TFBG), a segment of high-concentration erbium doped fiber (EDF), and a wavelength division multiplexing (WDM) coupler. By using an OC as the total-reflection mirror and a strain-induced uniform FBG as a partial-reflection mirror and a wavelength selector, a tunable wavelength is obtained. With single TFBG, a single wavelength lasing with a maximum wavelength tuning range of 6.00 nm, from 1543.50 to 1549.50 nm, is achieved experimentally. Within this tuning range, the full-width at half maximum (FWHM) of the laser output is smaller than 0.01 nm and the side mode suppression ratio (SMSR) is better than 50 dB.

Amplitude-equalized high-order arbitrary numerator rational harmonic mode-locked pulse generation in fiber-ring lasers using nonlinear polarization rotation

Article

Full-text available

Mar 2005
OPT EXPRESS

We report the amplitude-equalized high order arbitrary numerator rational harmonic mode-locked (RHMLed) pulse generations based on the technique of nonlinear polarization rotation in the fiber-ring laser. The numerator effect on the amplitude uniformity of RHMLed pulse train is first investigated. It is demonstrated that the high order RHMLed pulse train with uniform amplitude can be achieved by choosing a proper numerator. The pulse amplitude equalization in up to the 10th order RHMLed pulse train is observed when the numerator is equal to 3 instead of 1. It is important that the technique may be useful to generate the high-speed pulse trains with uniform amplitude by using the high order RHMLing technique.

Stretched pulse Yb3+:silica fiber laser

Article

Full-text available

Mar 1997

We report what we believe to be the first results on short-pulse generation in Yb(3+) :silica fiber. By applying the stretched pulse technique in a unidirectional, polarization-switch Yb(3+) fiber laser incorporating a prism-based dispersive delay line, we obtain self-start mode locking and 100-pJ pulses that can be compressed to give clean chirp-free <100-fs pulses. We believe such sources to have great potential for use not only in all-solid-state, high-power femtosecond pulse systems based on Yb(3+) :silica glass but also as seeds for conventional Nd(3+) :glass amplifier chains.

Spectral and temporal stabilisation of a diode-pumped ytterbium-erbium fibre soliton laser

Article

Full-text available

Jan 1994

A diode-pumped ytterbium-erbium 'figure of eight' laser is stabilised by the inclusion of a bandwidth-limiting element inside the cavity. Transform limited solitons with durations of 1.35ps are generated, continuously tunable over 20nm. Temporal stabilisation is imposed through amplified feedback of light reflected by the nonlinear loop mirror.

Self-stable 10GHZ actively mode-locked

Article

Jan 1999

The actively mode-locked fiber laser has two kinds of instability. It is proposed a novel method to overcome the short term instability by exploiting nonlinear polarization rotation. The long term instability is removed by feedback used to control fiber cavity length. It is made the actively mode-locked fiber ring laser operation stabily for more than 8 times. The pulse width was 10ps, the spectrum width was 0. 317nm, the product of time-bandwidth was 0. 403, wavelength was 1535-1564nm, the tunable range was 39nm.

Observation of the stability of all fiber femto-second lamp-house

Article

Feb 2001

Figure-of-eight cavity Yb3+-doped fiber mode-locked lasers

Article

Sep 2005

The experimental study of Yb3+-doped fiber lasers using the nonlinear optical loop mirror (NOLM) for mode-locked operating is reported in this paper. The fiber laser can generate 2.05 mW average power of 234 ps pulse duration at a repetition rate of 3.842 MHz, and operating center wavelength is 1053 nm, spectrum width is about 6 nm. The operating center wavelength can be tuned from 1030 nm to 1081 nm, the self-starting of the mode-locked fiber laser can be achieved easily, and the mode-locked operation can be hardly influenced by the environment disturbance in days. It can be used for a seed in the high energy mode-locked fiber laser system successfully, furthermore, it can be applied in science and engineering as a center wavelength-tunable mode-locked fiber laser hopefully.

Experimental study of ultrashort pulse Yb3+-doped fiber laser

Article

Feb 2005

The experimental study of the Yb3+-doped fiber ring laser of ultrashort pulse is reported, which is pumped by 976 nm semiconductor laser. In the normal dispersion, using the additive pulse mode-locking based on nonlinear polarization evolution, the Yb3+-doped fiber laser can oscillate in the mode-locked state by adjusting the position of the polarization controller (PC) and reducing the loss in the cavity. The output characteristics of the fiber laser are shown by oscillograph in the time domain. If pump power is not changed, along with the change of the polarization of the pulse, the changes of output pulse maintain stable and unstable states. In the unstable region, the pulse becomes irregular. When PC is in a proper position, the laser operates a stable and mode-locked state by adjusting the PC1 and PC2 carefully. The maximum output power of the laser is 9.46 mW, at the repetition rate of 15.4 MHz corresponding to ∼10 nm spectrum width.

High-energy femtosecond figure-eight fiber laser

Article

Aug 1997
OPT COMMUN

A simple figure-8 fibre laser that generates femtosecond pulses with large pulse energy is reported. The pulsewidth is 125 fs and pulse energy is 0.5 nJ. The high energy is achieved by pulse stretching effect by using an erbium-doped fibre in the amplifier with normal dispersion and the narrow pulsewidth is obtained by means of a long length of dispersion shifted fibre. Furthermore, the pulses are made stable by introducing a gradual twist to the dispersion shifted fibre. The central wavelength and the spectral width of the pulses can be tuned by simply adjusttng the polarisation-controllers in the loop. No additional components are required.

Low threshold, 290 fs erbium‐doped fiber laser with a nonlinear amplifying loop mirror pumped by InGaAsP laser diodes

Article

Nov 1991
APPL PHYS LETT

290 fs soliton pulses at 1.56 μm have been successfully obtained for the first time from a laser‐diode pumped erbium‐doped fiber laser with a nonlinear amplifying loop mirror. The laser was pumped by InGaAsP laser diodes and the threshold for starting the pulse oscillation was 50 mW. The passive mode‐locking continued to a pump power level as low as 10 mW. The repetition rate was uncontrollable and varied between the fundamental repetition rate of 5 MHz and 1.2–2 GHz.

Wideband wavelength tunable modelocked fibre laser over 1557-1607 nm

Article

Mar 2000

An electronically wavelength tunable modelocked fibre laser operating over a 50 nm range using an all-fibre acousto-optic tunable filter is presented. The tuning range is 1557-1607 nm, for a 70 m long erbium-doped fibre (EDF) with a 270 ppm concentration

Wavelength tunable mode-locked pulse fiber laser based on figure-of-eight cavity

Abstract

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