Controllable photoinduced optical attenuation in a single-mode optical fiber by irradiation of a femtosecond pulse laser

Novel optical attenuation fibers were fabricated by the irradiation of a focused infrared femtosecond pulsed laser onto the core of a silica glass single-mode optical fiber. Optical attenuation at a wavelength of 1.55 microm proportionally increased with increasing numbers of irradiation points and was controllable under laser irradiation conditions. The single-mode property of the waveguide and the mode-field diameter of the optical fiber were maintained after irradiation of the femtosecond laser. It is suggested that the attenuation results from optical scattering at photoinduced spots formed inside the fiber core.     

中红外可调谐大能量飞秒脉冲激光产生

可调谐中红外飞秒光纤激光器具有非常普遍的应用,从而引起了人们的广泛关注。目前,非线性光纤中的拉曼孤子自频移效应是实现大范围可调谐飞秒脉冲激光的理想方法之一。然而,非线性光纤中其他高阶非线性效应的产生通常会限制拉曼孤子脉冲的能量提升。本文提出了利用有源掺杂光纤作为非线性介质和增益介质实现可调谐大能量中红外飞秒激光脉冲的方法。在理论上研究了有源掺杂非线性光纤中高阶孤子劈裂和孤子自频移效应的产生,以及线性增益对波长移动拉曼孤子能量、脉宽、光谱的影响。结果表明,通过为波长红移的低能量拉曼孤子提供线性增益,孤子脉冲的能量得到了显著提升且保持了其单脉冲特性,脉冲宽度为45 fs,且孤子脉冲的波长可通过所提供的增益进行大范围调谐。因此,利用有源掺杂光纤作为非线性介质是实现大能量可调谐中红外飞秒脉冲激光的一种有效方法。     

Spectral superbroadening of subnanojoule Cr:Forsterite femtosecond laser pulses in a tapered fiber

Spectral superbroadening of subnanojoule femtosecond Cr:forsterite laser pulses is demonstrated for the first time in experiments with a tapered fiber. Coupling 40-fs 0.6-nJ pulses of 1.25-μm Cr:forsterite laser radiation into a tapered fiber with a taper waist diameter of about 2 μm and a taper waist length of 90 mm, we observed the spectra spanning more than two octaves at the output of the fiber. These experimental results open new horizons for the creation of compact femtosecond systems based on Cr:forsterite lasers and tapered fibers for optical metrology and biomedical applications.     

Two-octave spectral broadening of subnanojoule Cr:forsterite femtosecond laser pulses in tapered fibers

Spectral broadening of femtosecond Cr:forsterite laser pulses is enhanced due to the use of tapered fibers. Supercontinuum generation with unamplified subnanojoule femtosecond Cr:forsterite laser pulses is observed for the first time. With 40-fs 0.6-nJ pulses of 1.25-μm Cr:forsterite laser radiation coupled into a tapered fiber having a taper waist diameter of about 2 μm and a taper waist length of 90 mm, we observed the spectra spanning more than two octaves at the output of the fiber in the regime of anomalous group-velocity dispersion. This result opens the way for the creation of compact femtosecond Cr:forsterite laser plus tapered fiber systems for optical metrology and biomedical applications. Received: 23 October 2001 / Accepted: 16 January 2002 / Published online: 14 March 2002     

掺Er光纤飞秒激光器载波包络位相偏移的探测

本文介绍了基于掺Er光纤飞秒激光器光学频率梳中光学部分的研制. 实验上采用重复频率为230 MHz的掺Er光纤飞秒激光器,通过放大、光谱展宽以及单臂f—2f系统,在优化及分析相关参数影响的基础上,获得了~30 dB信噪比f₀的输出,为光纤光学频率梳的建立奠定了基础. 关键词： 掺Er光纤激光器 光学频率计量 光纤光学频率梳 光谱展宽     

光纤法布里-珀罗干涉温度压力传感技术研究进展

光纤法布里-珀罗干涉温度和压力传感器具有灵敏度高、制作简单、成本低、体积小和抗电磁干扰能力强等优点,已被广泛应用于军事和民用领域.在某些环境恶劣,如具有强电磁干扰和腐蚀性,或提供给传感器的安装空间非常有限的特殊工业领域,微型光纤温度和压力传感器发挥着重要的作用,国内外诸多高校、科研院所都在对其进行研究.本文综述了光纤法布里-珀罗干涉仪的基本原理、制备技术、及其压力和温度传感应用的研究进展.详细介绍了湿法化学腐蚀制备法、电弧放电制备法、飞秒激光制备法、聚合物辅助制备法等常见光纤法布里-珀罗腔传感器的制作工艺,分析了不同制作工艺的优缺点;详细介绍了光纤法布里-珀罗干涉仪在温度传感、压力传感和温压一体传感领域的应用;最后对光纤法布里-珀罗干涉温度压力传感器的发展进行了总结和展望.     

1040nm泵浦的光子晶体光纤超连续光谱产生性能退化研究

光子晶体光纤已经被广泛应用于由飞秒脉冲激光源产生超连续光谱。当激光源的重复频率较低时,由光子晶体光纤产生的超连续光谱随时间的变化过程较为缓慢,通常不被注意到。而在天文光谱仪定标等应用中,需要使用GHz至几十GHz量级的高重复频率激光源。此时,可观察到光子晶体光纤的超连续光谱产生性能在有限时间内产生显著的退化。在1 040 nm飞秒激光泵浦条件下,通过测试三种不同气孔占空比的光子晶体光纤的超连续光谱产生性能演化,发现超连续光谱的退化进程随光纤气孔占空比的增大而加速。观察发生光谱退化后的光子晶体光纤样品,发现在光纤上超连续光被产生的区段出现多个不同颜色的亮点,呈现有方向性的光泄露现象。针对光泄露现象,通过测量光纤的吸收光谱线,证实了实验中超连续光谱退化的主因并非是光纤熔融石英材料中大量非桥氧色心产生。针对光泄露具有方向性这一特征,提出了经由多光子吸收作用在光纤纤芯中形成长周期光栅的理论。为探究影响光子晶体光纤超连续光谱产生性能的退化的因素,以达到光谱退化抑制的目的,首先通过改变了光纤的拉锥参数,期望增强光纤熔融石英材料的光子耐受性。实验结果证实了该方法的有效性较为有限。其次,从保持激光源的平均功率,降低激光脉冲的峰值功率和保持激光脉冲的峰值功率,降低激光源平均功率两个方面入手,对激光源进行调制。实验结果证明,光纤单位时间内接受的高峰值功率脉冲总量是影响其超连续光谱产生性能的最重要因素。在天文光谱仪定标的应用中,对超连续光谱光功率的需求并不高,使用斩波器降低光子晶体光纤入射光的平均功率是减缓超连续光谱产生性能退化过程的有效且简单可行的方法。     

具有几个光振荡周期的飞秒激光脉冲

从麦克斯韦方程组出发 ,推导出了具有几个光振荡周期的飞秒激光脉冲在非线性光纤中传输的方程和非线性光纤的折射率。给出了描述具有几个光振荡周期的飞秒激光脉冲在非线性光纤中传输方程的解。研究了在非线性光纤中自相位调制导致具有几个光振荡周期的飞秒激光脉冲频谱展宽 (脉宽压缩 )的详细物理过程。研究了非线性光纤中飞秒光孤子产生的条件     

Biosensing based on two-photon fluorescence measurements through optical fibers

We have performed two-photon fluorescence detection in a new scheme in which femtosecond laser pulses were delivered thorugh an optical fiber for nonlinear excitation and the emitted fluorescence was collected through the same fiber. Single-mode fibers were determined to give higher detection efficiency than multimode fibers, consistent with theoretical considerations. The utility of fiber-optic sensing based on two-photon fluorescence detection was proved by an experiment that measured the uptake of a targeted drug delivery agent into cultured cancer cells.     

使用FBG及更短光纤的高效Er3+-Yb3+共掺双包层光纤放大器

提出在光纤放大器中,使用光纤布喇格光栅作为泵浦光反射镜,所需的双包层光纤可以缩短,同时至少保持了与没有光纤布喇格光栅作为反射镜时光纤放大器相同的性能.基于速率及传输方程,对使用和不使用光纤布喇格光栅的铒、镱共掺双包层光纤放大器的性能进行了数值模拟.结果表明,使用光纤布喇格光栅作为反射镜时光纤放大器可以获得与无光栅时相同的输出功率,但仅仅需要后者长度一半的光纤,无论是前向泵浦还是后向泵浦.对后向泵浦方式并使用光纤布喇格光栅作为反射镜,可获得最高的输出功率及光增益,同时使用了较短的光纤.     

基于光纤微结构加工和敏感材料物理融合的光纤传感技术

将功能敏感材料与光纤在物理层面进行有机融合,充分发挥光纤传感器在结构集成、材料集成等方面的优势,将有望发展新型的光纤传感器件和系统.本文综述了飞秒激光光纤微加工技术分别在标准的单模光纤和光纤光栅上制备微结构,再结合敏感材料制备技术,实现在物理层面上光纤传感器材料和结构的集成和融合,探索实现新型高性能的光纤传感新技术.     

利用飞秒激光加工碳纤维(英文)

为验证光学加工碳纤维材料的可行性,利用飞秒激光和连续激光对碳纤维块体材料进行了加工。获得了利用飞秒和连续激光加工的表面形貌。与连续激光加工相比,利用脉宽40fs的激光加工效率较高,加工区边缘形貌较好,加工质量较高。通过不同激光功率下加工孔径尺寸的研究获得了飞秒激光加工阈值在1012W/cm2量级。研究结果证明了光学加工碳纤维体材料的可行性。     

Microstructure fibers as frequency-tunable sources of ultrashort chirped pulses for coherent nonlinear spectroscopy

Microstructure fibers are shown to allow the creation of new tunable sources for femtosecond nonlinear spectroscopy. These fibers provide a high efficiency of frequency upconversion of regeneratively amplified femtosecond pulses of a Cr:forsterite laser, permitting the generation of subpicosecond anti-Stokes pulses with a smooth temporal envelope and a linear positive chirp. These pulses from a microstructure fiber were used to measure the spectra of coherent anti-Stokes Raman scattering (CARS) of toluene solution by cross-correlating these pulses with the femtosecond second-harmonic output of the Cr:forsterite laser in boxcars geometry (XFROG CARS). PACS 42.65.Wi; 42.81.Qb     

飞秒激光在双折射微结构光纤中模式控制的四波混频效应的实验研究

利用飞秒激光脉冲在长度为10cm，包层具有大空气比的双折射微结构光纤中通过高阶模相位 匹配的四波混频获得了波长可调谐的反斯托克斯波.实验中脉冲宽度为35fs，中心波长820nm ，单脉冲能量4nJ的飞秒激光脉冲耦合到长轴直径为5μm，短轴为46μm的双折射微结构光 纤中.在高阶模传输情况下，通过调制耦合光的偏振方向，获得了具有不同中心波长的反斯 托克斯波.通过对比分析，讨论了输入光的偏振态对双折射微结构光纤中高阶模式下四波混 频效应的影响情况.理论计算分析很好的解释了实验结果. 关键词： 微结构光纤 飞秒脉冲激光 四波混频     

Phase-matched four-wave mixing of isolated waveguide modes of high-intensity femtosecond pulses in a hollow photonic-crystal fiber

Hollow-core photonic-crystal fibers with a special dispersion profile are shown to allow phase-matched nonlinear optical interactions of isolated air-guided modes of high-intensity femtosecond laser pulses confined in the hollow fiber core. We present theoretical and experimental studies of the four-wave mixing of fundamental and second-harmonic pulses of a Cr:forsterite laser with an initial pulse duration of about 50 fs and an intensity on the order of 10¹⁴ W/cm² in waveguide modes of a hollow photonic-crystal fiber with a core diameter of about 13μm.     

Attosecond relative timing jitter and 13 fs tunable pulses from a two-branch Er:fiber laser

We present what is believed to be the first direct measurement of the relative timing jitter between the two parallel pulse trains of a two-branch femtosecond erbium-doped fiber laser, operated without active stabilization. The system provides independently tunable pulses in the near infrared with durations down to 13 fs. Using an interferometric optical cross-correlator, the phase-noise spectral density is measured with high sensitivity in a range from 1 Hz up to the Nyquist frequency of 24.5 MHz. We find an integrated jitter of 11 attoseconds directly after the amplifier stages and 43 as after propagation through free-space optics and nonlinear fibers for frequency conversion.     

Fiber chromatic dispersion measurement based on wavelength-to-time mapping using a femtosecond pulse laser and an optical comb filter

A novel method for the measurement of chromatic dispersion of an optical fiber based on wavelength-to-time mapping using a femtosecond pulse laser (FSPL) and an optical comb filter is proposed and experimentally evaluated. In the proposed approach, the spectrum of an ultrashort optical pulse generated by an FSPL is sliced by an optical comb filter. The spectrum-sliced optical pulse is then coupled into the optical fiber under test. Thanks to the chromatic-dispersion-induced wavelength-to-time mapping in the optical fiber under test, a time-domain waveform similar to the sliced spectrum is generated at the output of the optical fiber, with different frequency components having different time delays. The time delay vs. frequency data are then recorded for the estimation of the chromatic dispersion by using least square fitting. Chromatic dispersions of two types of optical fibers with different lengths are tested. The measured dispersion values agree well with those measured by the conventional modulation phase shift (MPS) method.     

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.