孤子光脉冲的产生及其应用研究

利用非线性偏振旋转技术实现自起振被动锁模.在掺铒光纤环形腔激光器中产生了中心波长为1563.3 nm、重复频率为12.5 MHz、脉冲宽度为352.0 fs、3 dB光谱宽度为7.8 nm的孤子光脉冲.采用该孤子光脉冲作为抽运光源，经掺铒光纤放大器放大后，输入到101 m长的高非线性光子晶体光纤中，获得了20 dB带宽约为240 nm的超连续激光光谱.实验详细观测了光脉冲随抽运功率的变化及超连续激光光谱的形成过程，分析了其形成机理.研究表明：当抽运功率较低时，光谱加宽主要由高阶孤子的分裂引起；随着抽运功率的增加，高阶孤子分裂成基本孤子的数目逐渐增大，光谱进一步加宽；当抽运功率增加到受激拉曼散射的阈值时，受激拉曼散射成为光谱展宽的主要原因；抽运功率进一步增加时，受激拉曼散射、参量四波混频等非线性的共同作用将使光谱进一步加宽且变得光滑. 关键词： 孤子光纤激光器 超连续 光子晶体光纤     

Direct mid-infrared femtosecond pulse shaping with a calomel acousto-optic programmable dispersive filter

Direct amplitude and phase shaping of mid-infrared femtosecond pulses is realized with a calomel-based acousto-optic programmable dispersive filter transparent between 0.4 and 20 μm. The shaped pulse electric field is fully characterized with high accuracy, using chirped-pulse upconversion and time-encoded arrangement spectral phase interferometry for direct electric field reconstruction techniques. Complex mid-infrared pulse shapes at a center wavelength of 4.9 μm are generated with a spectral resolution of 14 cm(-1), which exceeds by a factor of 5 the reported experimental resolutions of calomel-based filters.     

Wavelength-agile fiber laser using group-velocity dispersion of pulsed super-continua and application to broadband absorption spectroscopy

A swept-wavelength source is created by connecting four elements in series: a femtosecond fiber laser at 1.56 μm, a non-linear fiber, a dispersive fiber and a tunable spectral bandpass filter. The 1.56-μm pulses are converted to super-continuum (1.1–2.2 μm) pulses by the non-linear fiber, and these broadband pulses are stretched and arranged into wavelength scans by the dispersive fiber. The tunable bandpass filter is used to select a portion of the super-continuum as a scan-wavelength output. A variety of scan characteristics are possible using this approach. As an example, an output with an effective linewidth of approximately 1 cm^-1 is scanned from 1350–1550 nm every 20 ns. Compared to previous scanning benchmarks of approximately 1 nm/μs, such broad, rapid scans offer new capabilities: a gas sensing application is demonstrated by monitoring absorption bands of H₂O, CO₂, C₂H₂ and C₂H₆O at a pressure of 10 bar. Received: 5 August 2002 / Revised version: 23 September 2002 / Published online: 22 November 2002 RID="*" ID="*"Corresponding author. Fax: +1-608/265-2316, E-mail: ssanders@engr.wisc.edu     

Numerical analysis of stimulated inelastic scatterings in ytterbium-doped double-clad fiber amplifier with multi-ns-duration and multi-hundred-kW peak-power output

We investigate the stimulated Brillouin scattering (SBS) and the stimulated Raman scattering (SRS) in an ytterbium-doped double-clad fiber amplifier that outputs optical pulses with multi-ns-duration and multi-hundred-kW peak-power. The ytterbium-doped double-clad fiber amplifier is simulated by a model which is composed of a set of propagation-rate equations. The simulated results show that SBS and SRS will deform the output signal pulse in both the time domain and the spectral domain, and degrade the performance of the ytterbium-doped double-clad fiber amplifier seriously. It is shown in our simulation that the troublesome SBS can be effectively suppressed by broadening the signal linewidth to a critical value of 0.07 nm in our calculation, and the effect of SRS can be suppressed using a large-mode-area fiber with proper length. The model and the simulated results are very useful for designing an ultra-high-power ytterbium-doped double-clad fiber amplifier.     

啁啾脉冲堆积用于光脉冲整形

报道了一种利用100 ps啁啾脉冲堆积产生2．2 ns任意整形脉冲的脉冲整形系统。采用掺Yb~(3 )光纤锁模振荡器得到稳定的锁模光脉冲序列,将该锁模脉冲通过啁啾光纤光栅展宽并通过1 nm带宽的高斯形光谱滤波器滤波,得到标准的100 ps高斯形啁啾脉冲序列,将此脉冲选单经过光纤延迟线组成的32路脉冲堆积器,得到了精度为32 bit的重复频率为1 Hz的2．2 ns任意整形光脉冲。研究了堆积脉冲的特性,分析了宽带啁啾堆积整形脉冲的光谱时间扫描特性对激光驱动惯性约束聚变打靶束匀滑的优化作用。实验测得了该系统输出的2．2 ns整形光脉冲具有小于50 ps的上升沿,与100 ps啁啾脉冲的时间抖动小于4 ps。     

滤波对8字腔掺铒光纤激光器锁模运转的影响

构建了基于损耗非对称非线性光学环镜的8字腔掺铒光纤锁模激光器,并讨论了腔内滤波带宽对腔内脉冲演化和激光器输出特性的影响.在非线性光学环镜中引入双向输出耦合器,耦合器和传输光纤位置的不对称产生非互易性,实现锁模运转.利用自制的可调谐滤波器实验研究了滤波带宽对激光器的影响.当滤波带宽为2.1 nm时,腔内脉冲的演化过程受滤波和孤子效应的共同作用,激光器顺时针和逆时针输出脉冲半高全宽分别为583.7fs和2.94 ps.随着滤波带宽增大,滤波的作用逐渐减弱,激光器两路输出脉冲参数逐渐接近,并接近傅里叶变换极限脉冲.当滤波带宽较大时,腔内脉冲的演化过程受增益谱和孤子效应的共同作用,激光器顺时针和逆时针输出脉冲均为变换极限脉冲,半高全宽约为440 fs.通过调节滤波器中心波长实现了对激光器输出脉冲光谱的连续调谐,调节范围大于30 nm.     

A high-sensitive fiber curvature sensor using twin core fiber-based filter

A high-sensitive fiber curvature sensor is proposed and experimentally demonstrated in a large measurement range by using a twin core fiber (TCF)-based filter as sensor head. Applying the coupled-mode theory and equivalent refractive index model, we theoretically anticipate the “blue shift” of the transmission dips of the TCF-based filter when sensor head is bent. Experimentally, we fabricate an 86.9 mm TCF-based filter with a free spectral range of 49 nm and characterize its curvature performance by measuring the wavelength shift. A nonlinear “blue shift” of the wavelength is observed when we increase the curvature. The relationship between wavelength shift and curvature is a second-order polynomial function. In the range from 0 to 9.30 m^?1, the maximum sensitivity is up to ?14.7 nm/m^?1. The measurement range can be further increased by selecting a shorter TCF.     

Generation of multi-wavelength square pulses in the dissipative soliton resonance regime by a Yb-doped fiber laser

Multi-wavelength square pulses are generated in the dissipative soliton resonance(DSR) regime by a Yb-doped fiber laser(YDFL) with a long cavity configuration. The spectral filter effect provided by a passive fiber with low-stress birefringence facilitates the establishment of multi-wavelength operation. Through appropriate control of the cavity parameters,a multi-wavelength DSR pulse can be generated in single-and dual-waveband regions. When the multi-wavelength DSR works in the 1038 nm waveband, the pulse duration can broaden from 2 ns to 37.7 ns. The maximum intra-cavity pulse energy is 152.7 nJ. When the DSR works in the 1038 nm and 1080 nm wavebands, the pulse duration can be tuned from2.3 ns to 10.5 ns with rising pump power. The emergence of the 1080 nm waveband is attributed to the stimulated Raman scattering(SRS) effect. Our work might help a deeper insight to be gained into DSR pulses in all-normal-dispersion YDFLs.     

利用光谱滤波器实现自启动的全光纤超短脉冲掺Yb3+光纤激光器

讨论了利用光谱滤波器实现自启动的被动锁模掺Yb³⁺光纤环形激光器的锁模机理,并研制出全光纤结构超短脉冲掺Yb³⁺光纤环形激光器.使用980 nm二极管激光器作为抽运源,高掺杂浓度掺Yb³⁺光纤作为增益介质.在净群速度色散为正的环形腔中加入光谱滤波器,抑制Yb³⁺离子在1030 nm强发射峰的同时,通过对啁啾脉冲的光谱滤波实现脉冲压缩.光谱滤波器与光纤非线性偏振旋转效应相结合,实现了激光器在1053 nm可自启动、十分稳定的锁模运转.激光器锁模阈值功率300 mW,平均斜率效率18.3%,最大输出功率53.07 mW,对应最大输出脉冲能量3.2 nJ.锁模光脉冲中心波长1053.6 nm,3 dB带宽10.84 nm,重复频率16.45 MHz.锁模脉冲宽度为皮秒量级,经腔外光栅对压缩至188 fs. 关键词： 3+光纤激光器')" href="#">掺Yb³⁺光纤激光器 自启动锁模 全光纤     

Ultrashort pulse compression and delivery in a hollow-core photonic crystal fiber at 540 nm wavelength

We have fabricated a bandgap-guiding hollow-core photonic crystal fiber (PCF) capable of transmitting and compressing ultrashort pulses in the green spectral region around 532 nm. When propagating subpicosecond pulses through 1 m of this fiber, we have observed soliton-effect temporal compression by up to a factor of 3 to around 100 fs. This reduces the wavelength at which soliton effects have been observed in hollow-core PCF by over 200 nm. We have used the pulses delivered at the output of the fiber to machine micrometer-scale features in copper.     

基于光纤中超短脉冲非线性传输机理与特定光谱选择技术的多波长飞秒激光的产生

高集成、高可靠性宽调谐飞秒激光源在超快光谱学、量子光学及生物成像等研究与应用领域具有重要价值.如在生物多光子显微成像中,具有适中能量的宽调谐飞秒激光源不仅可满足多种生物组织荧光激发所需的峰值功率与激发波长,而且也可以显著提升非线性荧光产生效率、成像分辨率以及增大成像穿透深度.采用自主研发的高可靠性全保偏光纤飞秒激光器作为抽运源,基于低色散光纤中高峰值功率飞秒激光脉冲非线性传输引起的光谱加宽机制,本文开展了多波长全光纤飞秒激光产生技术研究.通过采用中心波长在980, 1000,1050, 1070与1100 nm的带通滤波片选择性地对单模光纤输出光谱中最左边与最右边光谱旁瓣进行滤波,在上述中心波长处分别可获得203, 195, 196, 187与194 fs的激光输出.本文提出的基于全光纤飞秒激光脉冲在单模光纤中非线性传输引起的光谱加宽机制与特定光谱选择技术的实验方案为高集成、高可靠性宽调谐飞秒激光源的实现提供了新的研究途径.     

单模石英光纤中受激喇曼散射的研究

利用连续光纤激光器为泵浦源,对单模石英光纤中的受激喇曼散射进行了实验研究.在较低功率泵浦下,观察到由自发喇曼散射向受激喇曼散射演化的过程中,光谱不断变窄;当Stokes波信号功率较强时,观察到光谱峰值相对于泵浦波的频移量从440 cm－1转化到490 cm－1.在改进耦合系统后,不仅观察到一级喇曼频移,并且观察到了高阶Stokes光.在产生多级喇曼光谱时能量移动比较复杂,每两级的喇曼频移间隔并不完全相同.     

Stable mode-locked fiber laser using 49 cm long bismuth oxide based erbium doped fiber and slow saturable absorber

A stable mode-locked fiber laser employing a 49 cm long bismuth oxide based erbium doped fiber (Bi-EDF) by using a slow saturable absorber is demonstrated. Near transform limited short pulses with a repetition rate of 8.27 MHz are obtained at a wavelength of 1560 nm with a maximum spectral width of 15 nm. Results indicate that pulse characteristics are strongly dependent on pump power rather than spectral width. Moreover the Time-Bandwidth products (TBWP), pulse duration, the energy fluctuation and timing jitter decrease with increasing pump power. The pulse width is continuously varied from 1.2 ps to less than 300 fs. It produces stable mode locking with a maximum spectral width of 15 nm, minimum timing jitter of 4 ps and energy fluctuations of 2.5%. The pulse train was amplified using a two-stage amplifier up to 447 mW average power corresponding to peak powers of 177.3 kW.     

Tunable third-harmonic generation in a solid-core tellurite glass fiber

A solid-core tellurite glass fiber with 1.8?dB/m loss at 1.55?μm was made by using the built-in casting preform fabrication method and rod-in-tube fiber drawing technique. Pumping a 10?cm fiber piece with picosecond pulses of 3-5×10(12)?W/cm(2), 0.1% of the fundamental power limited by the coherence length of 0.3-5?μm was converted into visible third-harmonic power tunable over a broad near-IR wavelength ranging from 1500 to 1680?nm. Frequency conversion from the mid-IR to near-IR was found to be even more efficient due to the longer coherence lengths of 12-20?μm in the wavelength range of 2200-2500?nm.     

Mid-infrared ZnGeP2 parametric oscillator directly pumped by a pulsed 2 microm Tm-doped fiber laser

We have demonstrated what we believe to be the first mid-infrared optical parametric oscillator (OPO) pumped directly by a pulsed Tm-doped fiber laser. The Tm-fiber pump laser produces 30 ns pulses with a repetition rate of 30 kHz at a wavelength of 2 microm. The ZnGeP2 (ZGP) OPO produces 20 ns mid-IR pulses in the 3.4-3.9 microm and 4.1-4.7 microm spectral regions simultaneously. More than 658 mW of mid-IR output power has been generated with a total OPO slope efficiency greater than 35%.     

Ultrafast continuum mid-infrared spectroscopy: probing the entire vibrational spectrum in a single laser shot with femtosecond time resolution

Until now, ultrafast IR spectroscopy has been limited by the bandwidth of optical parametric amplifiers, typically 100-400 cm(-1). Here we present the first example of transient IR spectroscopy using a continuum laser source to probe the entire mid-IR region with ultrafast time resolution. The continuum source is based on focusing the fundamental, second harmonic, and third harmonic of 1 mJ, 25 fs, 800 nm pulses in air, generating ～150 fs continuum mid-IR pulses that span the frequency range of <400 to >5000 cm(-1) or, conversely, <2 to >25 μm. We characterize the spectral and temporal properties of dicarbonylacetonato rhodium(I) in hexane. We further demonstrate the versatility of the method by measuring the very fast and broad (>1500 cm(-1)) spectral changes following IR excitation associated with the 7-azaindole-acetic acid heterodimer in carbon tetrachloride.     

Analysis of bottlenecks in DWDM fiber optic communication system

This paper deals with the limiting factors like Stimulated Brillouin Scattering (SBS), Stimulated Raman Scattering (SRS) and Four Wave Mixing (FWM) in DWDM Fiber Optic Communication. The variation of SBS threshold power level for the spectral width of the source is analyzed and it is found that addition of spectral width in the source lowers the SBS effect. By reducing the SBS effect, we could transmit more optical power in a single channel and maintain high OSNR. Similarly the effect of phase mismatching (dispersion) and wavelength spacing on both FWM and SRS are analyzed. This work aims at finding the optimal value of spectral width, dispersion and channel spacing, thereby exploring the possibilities of increasing the overall capacity of the fiber optic trunk line.     

岩心显微拉曼光谱成像方法的研究

虽然用激光拉曼光谱显微探针研究岩心中碳质物的工作已有很大进展,但是通常对诸如岩心等样品物性的光谱学(红外、拉曼和荧光等)微探针实验研究多是局限于对经过复杂处理分离出的微小样品或样品中个别点得到的结果,缺乏对复杂样品各组分(或基团)的空间分布及其相互关系的研究。近年来新发展起来的光谱成像分析系统将光谱技术与成像技术有机地结合起来融为一体,可在光谱和空间两个方面对目标样品进行分析和识别,但是用拉曼显微成像光谱研究岩心的工作则少有报道。文章报道了应用“串行-成像”(series-or indirect-imaging,Mapping)和“并行-成像”(parallel-or direct-imaging, Imaging)两种方式对含油岩心进行了显微拉曼光谱成像的研究。从光谱分辨率和空间分辨率以及工作效率等方面对两种方式所得试验结果进行了比较和评估。     

Chirped pulse amplification in single mode Tm:fiber using a chirped Bragg grating

We report femtosecond pulse generation and chirped pulse amplification in Tm:fiber. A mode-locked oscillator operating in the soliton regime produced 800 fs pulses with 5 nm spectral bandwidth, at 40 pJ pulse energy. This oscillator seeded a pre-amplifier that utilizes a Raman soliton self-frequency shift to produce wavelength tunable pulses with 3 nJ energy, reduced pulse duration of 150 fs, and increased bandwidth of 30 nm. For further amplification, the pulses were stretched up to 160 ps using a chirped Bragg grating (CBG). Stretched pulses were amplified to 85 nJ after compression in single-mode Tm:fiber and recompressed with the CBG as short as 400 fs. Compressed pulses were coupled into a highly nonlinear tellurite fiber to investigate the potential of this ultrashort pulse 2-μm fiber source as a pump for mid-IR supercontinuum generation.     

Spectrally scanned,repetitively pulsed erbium-doped fiber laser for spectral and temporal multiplexing of fiber Bragg grating sensors

An erbium-doped fiber laser that emits a series of spectrally scanned pulses is used to monitor an array of fiber Bragg grating (FBG) sensors. The cavity for this Fabry-Perot laser is formed by two spectrally selective reflectors: a rotating mirror-grating combination for scanning the reflectance peak wavelength and a fiber Fabry-Perot interferometer (FFPI) with a periodic reflectance spectrum. During a scan of the rotating mirror, the laser produces a set of Q-switched pulses over the 1522-1568-nm spectral range at each of the FFPI reflectance peak wavelengths. This laser is used to simultaneously demonstrate wavelength-division multiplexing of FBGs with reflectance peaks in different spectral regimes and time-division multiplexing of FBGs with overlapping spectra. The spectral location of the FBG peaks was determined to an accuracy of 1.4 pm.