Two-wave mixing by means of dynamic Bragg gratings recorded by saturation of absorption in erbium-doped fibers

We present experimental results of two-wave mixing in single-mode Er-doped optical fibers for which dynamic Bragg reflectance gratings are formed as a result of saturation of fiber-optic absorption (i.e., by means of the effect of spatial hole burning). The gratings are probed by the same recording waves at lambda approximately = 1549 nm and are detected as periodic changes of the intensity of light reflected from a Sagnac interferometer (with a piece of the doped fiber included) observed when periodic phase modulation is induced in one of the waves. Both rectangular and sinusoidal modulation were used, which permitted evaluation of the grating recording time (tau(g) approximately = 3 ms for OFS-Fitel EDF-HG980 fiber) and the grating amplitude, which proved to be approximately 6-7 times lower than expected from measurements of saturation of fiber-optic absorption by one wave only.     

Power scaling of resonantly cladding-pumped, Yb-free, Er-doped LMA fiber lasers

The results of the recent major efforts in power scaling of resonantly cladding-pumped Yb-free Er fiber lasers are presented. Commercially available Yb-free Er-doped large mode area Er60-20/125 (LMA) DC fibers were tested in two regimes: (i), as a booster amplifier in a single-frequency (SF) MOPA configuration and, (ii), in a Bragg grating (FBG) based narrowband fiber laser configuration. We obtained ～28.5 W of output power at 1590 nm, the highest power reported so far out of Yb-free Er-doped LMA fiber with resonant cladding pumping. The achieved optical-to-optical conversion slope efficiency of ～56.6% is also believed to be the highest efficiency ever reported from Yb-free Er-doped fiber laser with resonant cladding pumping.     

Amplitude of the dynamic phase gratings in saturable Er-doped fibers

Dynamic population gratings recorded via local saturation of optical absorption/gain in rare-earth (Er, Yb) doped fibers demonstrate contributions of the amplitude and phase components. Quantitative comparison of the experimentally observed amplitude grating efficiency with that evaluated from spatially uniform saturation of the fiber optical absorption usually shows a significant discrepancy. The grating amplitude proves to be significantly weaker than its theoretical evaluation. The first results on quantitative comparison of the recorded phase grating amplitudes with spatially uniform photo-induced refractive index change in Er-doped fibers at three essentially different wavelengths (1485, 1526, and 1568 nm) are reported. As for the amplitude grating component, the experimentally observed phase grating amplitude is inferior to its theoretical evaluation; this discrepancy is spectrally dependent and is also significantly reduced in the short-wavelength region 1480–1490 nm on the Er³⁺ ion absorption.     

基于色散调谐宽带扫频光纤激光器及其在光纤光栅解调中的应用

报道了一种基于色散调谐技术的宽带扫频掺铒光纤激光器。通过在主动锁模光纤激光器腔内引入较大色散,利用锯齿波电信号调制电光调制器的调制频率,可以实现激光器扫频输出。应用扫频激光器可将光纤光栅反射中心波长的变化转变为时域上信号间隔变化,适用于光纤光栅传感解调。搭建了扫频光纤激光器,利用掺铒光纤作为增益介质,研究了扫频范围的影响因素。通过优化实验参数,实验得到的扫频带宽达到43 nm,接近增益带宽,扫频速度为50 Hz。利用搭建的扫频激光器进行了光纤光栅传感解调,灵敏度约为0.68 ms/nm,验证了解调原理。     

8字形腔波长可调谐锁模脉冲光纤激光器

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.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 MHz、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.     

Diode-lasers based apparatus and method for single-mode fibers spectral splice loss measurements

Arc-discharge fusion splicing is widely used in the telecommunication industry for joining single-mode optical fibers to Er-doped fiber coils. These coils are used as the gain medium in erbium-doped amplifiers (EDFAs). The quality and integrity of splicing these coils to fibers can impact key EDFA performance parameters. This article describes an automated splice loss and Er-doped fiber absorption measurement system. The measurement system is equipped with 1310, 1550 and 1563 nm DFB lasers, broadband light source, InGaAs detectors and fiber-optic internal standards. Furthermore, the article describes a method for measuring splice loss between Er-doped fiber and the fibers spliced to coil ends. The system controls splice loss between SM-28 or HI980 fiber and Er-doped fiber to 0.094 ± 0.052 dB at 1550 nm. Moreover, the system can measure accurately Er-doped fiber absorption to within ±3.19% at 1563 nm.     

高频调制大功率窄线宽分布反馈光纤激光器

研制了一种窄线宽光纤激光器.在有源相移光栅后加一段掺铒光纤,当用980 nm抽运光注入时,首先形成了分布反馈(DFB)光纤激光器,而残余抽运光将铒纤中铒离子从基态抽运到了激发态,对DFB激光实现了有效放大,实现了对残余抽运光的充分利用,节省了功耗、降低了成本;同时利用温控技术克服了DFB光纤激光器的温度敏感问题;将相移光栅黏贴于片状压电陶瓷(PZT)的表面实现了高频调制.实验研制的激光器的最高调制频率为2 kHz、输出功率为15.6 dBm,线宽为300 kHz. 关键词： 分布反馈光纤激光器 窄线宽 大功率 高频调制     

Transient two-wave mixing in a linear configuration of an adaptive interferometer based on Er-doped fiber with saturable absorption

We report results of transient two-wave mixing (TWM) in Er-doped fibers with saturable absorption in a linear configuration of an adaptive interferometric vibrometer with essentially different powers of recording waves. The TWM signal modulation depth detected in the weak (reflected) wave was shown to be twice as strong as in the symmetric configuration with equal recording powers. In accordance with theoretical predictions, the experimentally observed TWM signal amplitude grew continuously with the fiber optical density in the whole investigated range of alpha(0)L approximately 0.2-4. At the recording wavelength 1492 nm it proved to be quite close to the theoretical limit of approximately alpha(0)L/2 for weakly absorbing fibers, and in 1-m-long fiber of high optical density reached maximal value of approximately 0.8. The TWM response time went down with the recording light power and for P(0) approximately 10 mW was in the submillisecond region.     

Tunable dual-wavelength fiber laser based on a single fiber Bragg grating in a Sagnac loop interferometer

We propose a simple dual-wavelength Er-doped fiber laser configuration based on a dual-wavelength fiber Bragg grating written on the splice joint between two different fibers for wavelength-selective filter in the Sagnac loop interferometer. The wavelength separation between the adjacent lasing wavelengths is 1.12 nm and the side-mode suppression ratio (SMSR) is over 55 dB. The output power variation is less than 0.8 dB over a two-minute period. Moreover, the lasing wavelength can be effectively tuned using the thermal heating method.     

Single-mode fiber laser based on core-cladding mode conversion

A single-mode fiber laser based on an intracavity core-cladding mode conversion is demonstrated. The fiber laser consists of an Er-doped active fiber and two fiber Bragg gratings. One Bragg grating is a core-cladding mode converter, and the other Bragg grating is a narrowband high reflector that selects the lasing wavelength. Coupling a single core mode and a single cladding mode by the grating mode converter, the laser operates as a hybrid single-mode laser. This approach for designing a laser cavity provides a much larger mode area than conventional large-mode-area step-index fibers.     

Stable Dual-Wavelength Oscillation of an Er-Doped Fiber Ring Laser at Room Temperature

We propose a simple Er-doped fiber laser configuration for achieving stable dual-wavelength oscillation at room temperature, in which a high birefringence fiber Bragg grating was used as the wavelength-selective component. Stable dual-wavelength oscillation at room temperature with a wavelength spacing of 0.23 nm and mutually orthogonal polarization stages was achieved by utilizing the polarization hole-burning effect. An amplitude variation of less than 0.7 dB over an 80 s period was obtained for both wavelengths.     

Stable Dual-Wavelength Oscillation of an Er-Doped Fiber Ring Laser at Room Temperature

We propose a simple Er-doped fiber laser configuration for achieving stable dual-wavelength oscillation at room temperature, in which a high birefringence fiber Bragg grating was used as the wavelength-selective component. Stable dual-wavelength oscillation at room temperature with a wavelength spacing of 0.23 nm and mutually orthogonal polarization stages was achieved by utilizing the polarization hole-burning effect. An amplitude variation of less than 0.7 dB over an 80 s period was obtained for both wavelengths.     

Active Q switching of a fiber laser with a microsphere resonator

We propose and demonstrate an active Q-switched fiber laser using a high-Q microsphere resonator as the Q-switching element. The laser cavity consists of an Er-doped fiber as the gain medium, a glass microsphere reflector (coupled through a fiber taper) at one end of the cavity, and a fiber Bragg grating reflector at the other end. The reflectivity of the microsphere is modulated by changing the gap between the microsphere and the fiber taper. Active Q switching is realized by oscillating the microsphere in and out of contact with the taper. Using this novel technique, we have obtained giant pulses (maximum peak power approximately 102 W, duration approximately 160 ns) at a low pump-power threshold (approximately 3 mW).     

基于光纤环形激光器和光放大的100 km光纤布拉格光栅传感系统

在基于掺铒光纤-拉曼混合放大的可调光纤环形激光器的光纤布拉格光栅(FBG)传感系统结构基础上,提出了延长传感距离的新方法。该方法以环形掺铒光纤激光器作为光源,采用双波长拉曼放大的方法对信号进行低噪声的双向放大,系统中间的两段掺铒光纤再利用剩余的抽运功率产生自发辐射光和放大传感信号,使得整个系统能够在超长的传感距离上获得很高的信噪比。实验表明使用一只40 mW的掺铒光纤放大(EDFA)抽运源、一只170 mW的拉曼抽运源和一只2 W的拉曼抽运源,可以使整个系统的传感距离达到100km,并且传感系统的光纤布拉格光栅反射信号均能获得超过57 dB的优良信噪比,从而实现在超长距离上的光纤布拉格光栅传感。     

采用WDM技术的光纤Bragg光栅传感网络

采用绝对测量原理的波长调制技术,光纤Bragg光栅可组成并行、串行和阵列WDM拓扑结构.分析表明,光纤Bragg光栅网络的工作原理类似于一个多宽带平面镜.利用光谱仪可测量上述光纤Bragg光栅网络的反射谱,其中,光源是宽带为～40nm的掺饵光纤放大器.当网络中的光纤Bragg光栅受扰动后,受扰光栅的反射谱发生相应的变化,即Bragg波长发生相应的偏移.结果表明,当事先确定了光纤光栅的波长调制范围,反射的峰值波长能反应光纤光栅传感网络的信息.值得注意的是～3nm的波长调制范围可满足～100℃和～2000με的参量测量.     

Yb：Er共掺杂对掺铒光纤激光器中自脉冲行为的抑制作用

为了进一步提高镱铒共掺杂光纤激光器的实用性，对镱铒掺杂光纤激光器的自脉冲现象进行了理论分析。利用掺杂光纤中铒离子对的可饱和吸收的作用而引起自脉冲运转及离子对互作用模型作为理论基础建立系统模型，通过理论计算分析了共掺杂镱后掺铒光纤的有效抽运速率，证明了镱铒共掺杂可以提高有效抽运速率。使用这种光纤，可以使抑制光纤激光器中离子对导致的自脉冲效应所需的抽运功率水平大大降低。半导体激光器输出的抽运功率足以抑制由离子对导致的自脉冲，提供稳定激光运转。在研制稳定单频或高重复频率锁模光纤激光器方面，这种可用激光二极管抽运的镱铒共掺光纤具有很大的潜力。     

Femtosecond fiber laser at 780 nm for two-photon autofluorescence imaging

We present an Er-doped fiber(Er:fiber)-based femtosecond laser at 780 nm with 256 MHz repetition rate, 191 fs pulse duration, and over 1 W average power. Apart from the careful third-order dispersion management, we introduce moderate self-phase modulation to broaden the output spectrum of the Er:fiber amplifier and achieve 193 fs pulse duration and 2.43 W average power. Over 40% frequency doubling efficiency is obtained by a periodically poled lithium niobate crystal. Delivering through a hollow-core photonic bandgap fiber, this robust laser becomes an ideal and convenient light source for two-photon autofluorescence imaging.     

+1/-1相位掩模板和532nm激光下低损耗As_2S_3硫系光纤布喇格光栅的制备

采用改进型Sagnac干涉光栅写入系统,利用532nm准带隙光曝光源和带+1/-1衍射级的相位掩模板,在两种不同直径的低损耗As_2S_3硫系玻璃光纤上刻写布喇格光栅,并研究曝光期间光栅的动态特性.实验表明,As_2S_3光纤布喇格光栅透射峰值随光纤直径的减小而增强;在曝光过程中,布喇格波长先是较快地向短波长方向移动,随着曝光时间的延长,布喇格波长缓慢地向长波长方向回复.曝光时间为800~1 000s时,在包层直径为140μm的As_2S_3光纤上获得质量良好的布喇格光栅光谱,其透射峰值可达-2.6dB,带宽为0.37nm.对As_2S_3硫系光纤纤芯的光敏性分析结果表明,折射率调制幅度和平均折射率变化随曝光时间分别可达到10-4和10-3数量级.