Double-clad photonic crystal fiber coupler for compact nonlinear optical microscopy imaging

A 1 x 2 double-clad photonic crystal fiber coupler is fabricated by the fused tapered method, showing a low excess loss of 1.1 dB and a splitting ratio of 97/3 over the entire visible and near-infrared wavelength range. In addition to the property of splitting the laser power, the double-clad feature of the coupler facilitates the separation of a near-infrared single-mode beam from a visible multimode beam, which is ideal for nonlinear optical microscopy imaging. In conjunction with a gradient-index lens, this coupler is used to construct a miniaturized microscope based on two-photon fluorescence and second-harmonic generation. Three-dimensional nonlinear optical images demonstrate potential applications of the coupler to compact all-fiber and nonlinear optical microscopy and endoscopy.     

双包层大模场面积保偏掺镱光子晶体光纤研究

采用改进的化学气相沉积法和溶液掺杂法制备出掺镱石英光纤预制棒,以该预制棒为有源纤芯制备芯区直径约为30μm的双包层保偏掺镱光子晶体光纤.模拟计算得到该保偏光纤的模场面积约232μm2,双折射系数B为5×10-5.利用该光纤分别进行了脉冲激光和连续激光的放大测试实验,在国内首次实现了高效率的飞秒激光放大,2 m长的光子晶体光纤可得到1.64 W的激光输出,激光放大斜率效率为49.8%.同时5 m长的光纤还能够实现8.12 W的连续激光放大输出,斜率效率达到55.9%,具有较高的斜率效率.此外,该光纤消光比约10 dB,具有良好的保偏特性.     

Double-clad fiber laser design for particle image velocimetry and material science applications

We have developed models to design actively Q-switched Yb-doped Double-Clad fiber lasers in various configurations. Based on these simulations, we present the design of two specific cavities: the first one is able to emit a pair of sub-nanosecond pulses separated by more than 500 ns for Particle Imagery Velocimetry applications. The time delay between the pulses can be adjusted by proper choice of the length of an un-doped fiber inserted in the cavity. The second cavity designed allows to emit long 150 ns pulses exceeding a few millijoules per pulse. Applications concern in this case materials science and combustion. In all cases, the rise time of the EOM is an essential parameter.     

Double-clad Cr4+:YAG crystal fiber amplifier

A novel double-clad Cr4+:YAG crystal fiber is demonstrated by use of a codrawing laser-heated pedestal growth method. Up to 10 dB of gross gain at a wavelength of 1.52 microm is achieved at a pump power of 0.83 W, which, to our knowledge, is the first Cr4+-doped fiber amplifier in the optical fiber communication band.     

Coherent Raman scanning fiber endoscopy

Coherent Raman scattering methods allow for label-free imaging of tissue with chemical contrast and high spatial and temporal resolution. However, their imaging depth in scattering tissue is limited to less than 1 mm, requiring the development of endoscopes to obtain images deep inside the body. Here, we describe a coherent Raman endoscope that provides stimulated Raman scattering images at seven frames per second using a miniaturized fiber scanner, a custom-designed objective lens, and an optimized scheme for collection of scattered light from the tissue. We characterize the system and demonstrate chemical selectivity in mouse tissue images.     

Er-Yb共掺双包层光纤的研制

报道了溶液掺杂法制备Er-Yb共掺双包层光纤的技术.采用改进的化学汽相沉积研制工艺,制作了SiO2-P2O5-F的光纤阻挡层和SiO2-GeO2-P2O5的疏松芯层,利用疏松芯层在YbCl3、ErCl3溶液中的浸泡吸收作用,成功研制出Er、Yb离子浓度比分别为1∶13和1∶8两个光纤样品,其中样品2在976 nm泵浦波长处的有效吸收系数最大达到2 dB/m,分析和讨论了光纤的损耗谱和荧光特性.     

Double-clad Tm3+-doped silica fiber laser with Bragg grating inscribed directly into active core by femtosecond laser

We report for the first time to inscribe the Fiber Bragg Grating (FBG) in Tm³⁺-doped multimode double-clad silica fiber by 800 nm femtosecond laser with a phase mask. The 1.35 μm period Bragg grating is written into the fiber core, which is responded to the laser center wavelength located at nearly 1960 nm. Continuous wave total output power of 11.5 W is obtained under the launched pump power of 29.8 W, corresponding to a slope efficiency of 45.0% and a conversion efficiency of 38.6%.     

高功率掺镱双包层光纤激光器中光纤损伤及其理论分析

针对高功率掺镱双包层光纤激光器热效应引起的光纤损伤情况,由热传导方程,结合边界条件推导了两端泵浦情况下双包层光纤激光器光纤内的温度分布及热效应引起的应力分布,并对光纤内的温度分布和应力分布进行了数值模拟.结合模拟结果,对光纤的损伤进行了解释,分析了引起光纤热效应的主要因素.对两端泵浦情况的模拟与分析符合高功率光纤激光器的实际工作情况,这对优化高功率光纤激光器的设计有一定的参考价值.     

大功率多波长可转换双包层光纤激光器

在多模掺镱双包层光纤上,利用相位掩模法直接写制Bragg光栅作为激光器后腔镜,得到多波长激光输出.在室温下,通过调节偏振控制器可以得到稳定的单波长及多波长的激光输出,输出波长范围在1 056～1 061 nm,线宽均小于0.02 nm.在25 W的976 nm激光泵浦下,激光器得到功率为6 W的多波长输出.     

双包层光纤激光器泵浦吸收效率的模场计算方法

提出一种计算双包层光纤激光器泵浦吸收效率的新方法.该方法是建立在模式分析基础上的,对对称的和偏心的双包层光纤结构都适用.我们的数值计算结果与以前的射线方法结果基本一致,但我们的方法更为精确一些.     

窄线宽线形腔调Q双包层掺钕光纤激光器

对LD泵浦调Q双包层掺Nd³⁺光纤激光器进行了实验研究.在Littrow结构的体光栅与二向色镜构成的线形腔结构中,利用声光Q开关(AQM)调Q,在1064nm得到了光谱线宽约为0.08nm稳定的激光脉冲序列.脉冲重复频率从1kHz到10kHz可调.在重复频率1kHz时得到脉冲宽度约800ns,最大单脉冲能量180μJ,脉冲峰值功率225W,激光平均功率180mW,并对激光输出脉冲能量进行了计算,计算结果与实验符合很好.     

Depixelation of coherent fiber bundle endoscopy based on learning patterns of image prior

We present an iterative method of eliminating pixelation artifacts from an endoscopic image acquired from a coherent fiber bundle imager. Our proposed approach for decoupling the honeycomb effect from the obtained sample image was formulated by using the prior probability for an approximate Bayesian framework in which the ideal complete image can be estimated by maximizing the posterior probability from the observed image. The maximization of the posterior probability from the original mask image (the mirrored fiber bundle imager structure) and the observed image (the sample image of the United States Air Force chart) has been performed by learning the image priors in the space of Markov random fields. By iteratively estimating the probability distribution, we reduced the noise effects from the mask image and recovered the ideal shape of the image. This method was efficient for automatically learning the sliding patch from the combination of projected kernels. The mask and observed images were obtained from en face images of the Fourier domain optical coherence tomography based on a common path interferometry scheme.     

掺镱双包层光纤激光器的径向偏振振荡

通过在腔内放置汇聚型布儒斯特角轴锥体,并对增益光纤采用双端泵浦, 实验上实现了掺镱双包层光纤激光器的径向偏振模振荡.对增益光纤的末端做了斜角抛光,抑制了光纤端面间的寄生振荡,减小了在低泵浦功率下被放大的自发辐射光份额.该激光器的域值约为175 mW,斜率效率13.8%,激发波长约1085 nm.当泵浦功率达到最大值460 mW时,获得了39 mW的激光输出功率,其光束偏振纯度和圆柱形对称性有显著改善.     

高功率双包层光纤激光器温度场动态分析

基于动态热传导方程,对高功率双包层光纤激光器的热效应进行了数值模拟,研究了高功率双包层光纤激光器内部温度场的空间及时间特性.计算表明,对于芯径为15 μm的光纤,开启泵浦光后约20 s光纤温度达到稳定值,关闭泵浦光后约20 s光纤冷却到室温,如采用脉冲泵浦,温度分布将随时间变化,波动频率与泵浦频率相同,泵浦频率越高波动越小,越接近相同平均功率的连续泵浦.     

掺Yb3+双包层光纤中的绿光荧光分析

普通单模光纤与掺Yb³⁺双包层光纤熔接后,当用波长为976nm激光耦合时,实验观察到掺Yb³⁺双包层光纤中呈现绿色的荧光并用光谱仪进行了测试分析表明:绿色荧光的产生为Yb³⁺离子间相互作用引起合作能量转移(CET)过程,这种能量转移过程将降低光纤激光器和光纤放大器的量子效率。     

Effect of image fiber on the speckle fringe pattern in image fiber-guided DSPI endoscopy

The effect of using an image fiber on the speckle fringe visibility in an endoscopic DSPI is analyzed here. An endoscope system was designed and developed, using image fiber as the speckle pattern image conduit, to work in the out-of-plane speckle interferometric configuration and experiments were carried out using a curved phantom tissue specimen as the test target. Experimental results obtained using the developed system are compared with that obtained using conventional DSPI system. To obtain a relative and quantitative comparison of the quality of the fringes obtained employing the two methods, an evaluation method that can give a quantified ‘score’ is proposed here.     

脉冲泵浦掺镱双包层光纤激光器的动力学研究

对脉冲泵浦的掺镱双包层光纤激光器进行了实验研究.采用重复频率1-10 kHz、脉宽100 μs的976 nmLDs泵浦,实现了脉宽小于10 ns的稳定激光脉冲输出.并对该激光器的动力学过程进行了分析,首次提出了在脉冲泵浦光纤激光器中产生ns脉冲是瑞利散射和受激布里渊散射共同作用的结果.     

多光束纳秒紫外激光制作硅表面微结构

使用波长351 nm的半导体泵浦全固态脉冲激光器（DPSSL）作为光源,经过位相光栅分束,形成干涉光场,在硅表面直接刻蚀微结构,制作了周期为0.55 µm,槽深可达55 nm的一维微光栅和周期为1.25 µm,刻蚀深度45nm的正交微光栅结构。给出了微光栅形貌结构的扫描电子显微镜(SEM)和原子力显微镜(AFM)的测量结果。正交微光栅的一级衍射效率在1.8%到6.3%之间。该研究是改变硅表面微结构,优化硅材料特性的一种新方法,并扩展了大功率激光刻蚀在表面微加工领域的应用。     

掺Yb双包层光纤激光器的时域特性和光谱特性研究

实验观测了掺Yb3+双包层光纤激光器的时域特性和光谱特性. 研究了抽运功率、腔损耗对激光器工作特性的影响. 研究发现, 利用单镜腔结构的光纤激光器, 可产生自脉动、受激布里渊散射和受激喇曼散射等非线性效应; 而采用双镜腔结构可有效抑制自脉动特性, 提高激光器工作的稳定性, 并对实验现象进行了定性的分析.