级联掺磷光纤喇曼激光器的解析优化

讨论了二级级联喇曼光纤激光器的解析解和优化设计.通过引入几何平均功率、增益因子和归一化光纤有效长度,将描述泵浦光和斯托克斯光沿喇曼增益光纤分布的微分方程组简化成代数方程组,在对泵浦光采用线性传播近似后,获得了二级级联喇曼激光器的解析解.所获得的解析解同数值模拟结果吻合得很好.利用该解析解可方便和快速地讨论级联喇曼激光器的优化设计,计算不同泵浦功率下的最佳光纤长度、输出光纤光栅反射率和转换效率.泵谱功率越大,最佳光纤长度越短,最佳输出光纤光栅反射率越小.     

3μm与2μm级联振荡Ho3+:ZBLAN光纤激光器的动态特性分析

基于传输速率方程，对Ho³⁺:ZBLAN光纤激光器的动态特性——上能级粒子数以 及输出激光功率的弛豫振荡特性进行了数值分析.通过忽略光纤参数对传输方向的依赖性，抽运光 和信号光的功率传输方程被分别简化处理.结果表明，在⁵I₆能级的 粒子数首先经历 一次弛豫振荡后，⁵I₆和⁵I₇能级的粒 子数交替弛豫振荡并达到稳态；同 样，在3μm波长的激光功率首先经历一次弛豫振荡后，3μm和2μm波长的激光功率交替弛豫 振荡并达到稳态，而且，弛豫振荡时的峰值功率远大于稳态时的激光功率. 关键词： 光纤激光器 动态特性 光纤激光理论 钬光纤     

基于级联跃迁的2.8 μm低掺铒氟化物光纤激光器数值分析与优化

2.8 μm和1.6 μm激光级联跃迁的工作方式,可以有效解决低掺铒氟化物光纤中自终止效应导致的2.8 μm激光功率提升难题.建立基于低掺铒氟化物光纤2.8 μm和1.6 μm激光级联跃迁的中红外光纤激光器数值模型,系统分析了2.8 μm和1.6 μm激光波长对2.8 μm激光功率和转换效率的影响.计算结果表明,选取1610 nm作为级联激光工作波长,能有效平衡2.8 μm激光下能级⁴I_13/2粒子向基态⁴I_15/2和激发态⁴I_9/2的跃迁过程,实现2.8 μm波段激光输出功率和效率的提升.此外,计算了1.6 μm激光腔反馈对2.8 μm激光功率和效率的影响,结果表明,仅通过光纤端面提供的弱反馈即可实现1.6 μm激光振荡,从而获得高效率2.8 μm激光输出.     

光纤光栅温度传感理论与实验

从光纤光栅温度传感模型出发，理论分析研究了光纤光栅的温度传感特性，推导了光纤光栅温度传感的一阶、二阶和有效线性灵敏度系数的解析式，计算了各灵敏度系数的理论值，实验得到了反射波长与温度的二次多项式，对比分析了理论与实验结果，讨论了石英的力学参数对光纤光栅温度传感特性的影响、反射波长与温度的线性及非线性的适用范围等问题. 关键词： 光纤光栅 光纤传感 温度传感     

光纤参变放大器光纤长度的优化设计

随着高输出功率掺铒光纤放大器和高非线性光纤的出现和使用,光纤参变放大器(OPAs)中出现了越来越多的增益饱和现象,这是光放大器中应该尽量避免的。对此,提出了依据光纤参变放大器的光纤非线性系数、抽运光功率、信号输入功率等参量对光纤长度进行优化设计的解决思路。明确提出最佳光纤长度的概念,即在其他参量一定的情况下使信号增益或信号输出功率达到最大所需的最小光纤长度,而且最佳光纤长度有利于提高光纤参变放大的增益带宽和波长转换带宽。通过数值积分求解描述光纤参变放大过程的非线性耦合方程,并运用控制变量法深入研究了最佳光纤长度与光纤非线性系数、抽运光功率、信号输入功率的关系。最后用最小二乘法进行数据拟合确定系数,得到简洁、实用的最佳光纤长度解析表达式。与已有实验结果比较表明,该解析式可很好地用来计算和优化光纤参变放大的光纤长度。     

基于重构等效啁啾制作光纤光栅编解码器的光码分多址系统实现

在光码分多址(OCDMA)系统中，光纤布拉格光栅(FBG)编解码器是极具竞争力的核心器件，满足光接入网低成本、高性能的要求. 将重构等效啁啾 (REC) 技术制作的FBG作为编解码器运用于OCDMA系统. 实验采用一对511个码片、编码速率为6.4×10⁹/s的FBG编解码器，在编码匹配的情况下能恢复出输入信号，与编码非匹配的情况相比获得了8 dB的功率增益.这为REC技术制作的编解码光栅在OCDMA系统中的应用提供了实验依据. 关键词： 光纤布拉格光栅 光码分多址 重构等效啁啾 编解码器     

石英基掺Tm3+光纤激光器特性的理论分析

基于速率方程理论建立了石英基掺Tm³⁺光纤激光器³H₆—³H₄抽运方式的理论模型,采用龙格-库塔 (Runge-Kutta) 法对该模型进行了数值分析,得出抽运光与激光功率在掺Tm³⁺光纤中的分布特性,并对Tm³⁺光纤长度、Tm³⁺的掺杂浓度等因素对掺Tm³⁺光纤激光器性能的影响进行 关键词： 3+光纤激光器')" href="#">石英基掺Tm³⁺光纤激光器 龙格-库塔法 抽运效率 掺杂浓度     

非线性光纤环镜在受激布里渊散射慢光级联系统中的可行性研究

基于非线性光纤环镜(NOLM)的脉冲压缩特性,分析了NOLM在基于受激布里渊散射(SBS)慢光级联系统中对延迟脉冲的影响.利用环形结构来模拟多次级联,有效地降低了系统的复杂度,得到了在不同抽运光功率和级联次数下脉冲的延迟输出特性.理论分析表明,NOLM可以有效地抑制SBS慢光级联系统中延迟脉冲的展宽,抽运光功率决定了展宽因子的变化趋势及最终稳定值的大小,展宽因子在级联4次时趋于稳定值,恰当选取抽运光功率可实现脉冲的零展宽延迟;改变抽运光功率和级联次数可以实现延迟量的连续可调,且延迟量理论上不受限制;增大抽 关键词： 慢光 脉冲压缩 非线性光纤环镜 受激布里渊散射     

基于光纤环形腔激光器的可调谐全光波长转换器的研究

在光纤环形腔激光器中引入周期极化反转铌酸锂(PPLN)光波导，用该激光器产生的连续光作为抽运光和控制光，使其与外加的信号光发生非线性效应实现可调谐波长转换.介绍了基于准相位匹配的PPLN光波导中的和频与差频级联型全光波长转换器的基本原理.对抽运光、信号光、控制光以及转换光的光功率随着PPLN光波导的变化进行了模拟.还对转换效率随着转换光波长的变化进行了数值计算.实验验证了该波长转换器的可调谐性. 关键词： 周期极化反转铌酸锂 和频与差频 可调谐全光波长转换 光纤环形腔激光器     

级联χ2过程产生高量值高阶非线性相移

基于位相失配三倍频(Δk≠0)转换,构建了产生高阶非线性相移的χ(2)级联非线性过程.此过程不涉及三阶等其他非线性效应,仅表现为纯的五阶非线性,所感应的非线性相移正比于I2.进一步的数值计算研究表明χ(2)级联五阶非线性相移不仅符号可控,而且具有丰富的饱和特性,其量值远高于χ(2)级联三阶非线性相移 关键词： 级联非线性相移 倍频     

Theoretical Study for Wavelength Conversion of Cascaded Second-Order Nonlinearity in Silica Fiber

In this paper, A novel wavelength divison multiplexing (WDM) nets is proposed by use of cascaded second-order nonlinearities (⁽²⁾:⁽²⁾) in the D-fiber grating after periodically thermal/electric-field poling, and is theoretically analyzed for the first time. The coupled mode equations of the ⁽²⁾:⁽²⁾ nonlinearities are derived, and the analytic expressions for the electric-field amplitude of converted light wave and the conversion efficiency are obtained under the small signal approximation, which are well consistent with numerical calculations. Both analytic expressions and numerical results show that, under the phase matching, is proportional to the logarithm of the square of pump light power, and the 4th power of the grating length L and the second-order nonlinearity d. The calculated results also show that and of this fiber grating can be reached over -17dB and 120nm, respectively. With the increase of L, increases rapidly while decreases quickly. The results of simulated calculations and theoretical analysis show that the cascaded ⁽²⁾:⁽²⁾ process is different from quasi-phases-matched difference-frequency generation.     

Wideband wavelength conversion using double-pass cascaded χ:χ interaction in lossy waveguides

We report the wavelength conversion based on double-pass cascaded nonlinear interaction (χ⁽²⁾:χ⁽²⁾) of sum and difference frequency generation in quasi-phase matched lithium niobate waveguides and compare it with double-pass cascaded second harmonic generation and difference frequency generation with and without waveguide loss. It is shown that the efficiency decreases considerably even for the low-loss waveguide compared to the lossless one especially for long waveguides and to achieve the higher efficiency for the same length, the amount of the extra power to compensate the loss increases. Also, an increased detuning of pump wavelength is proposed to flatten the response with a small efficiency penalty. The detuning- and loss-compensating pump powers can be found using the design diagrams in which the criteria for the design of waveguide length and the assignment of pumps power to obtain the desired efficiency, ripple and bandwidth are presented assuming a 75-nm pump wavelength difference.     

用光谱分辨的双光束耦合方法测量χ（2）:χ（2）级联非线性相移

针对重要的χ^(2):χ^(2)级联非线性相移,在理论上论证了可以用光谱分辨的双光束耦合方法来测量χ^(2)：χ^(2)级联非线性相移,在实验上研究了飞秒时域级联非线性相移随波矢失配置的变化规律。这一新疑的测量方法灵敏度高,实际使用简单,应用低能量的飞秒激光振荡器,就能方便地测量微弱χ（2）晶体的级联非线性相移。     

Detection of a new SRS‐promoting phonon mode and cross‐cascaded χ(3)‐nonlinear lasing in single crystals of calcite (trigonal CaCO3)

For calcite (CaCO₃), one of the pioneer crystals in nonlinear optics, new results of stimulated Raman scattering (SRS) spectroscopy are presented. Among them are the discovery of a new SRS‐promoting vibration mode with ω_SRS2 ≈︁ 282 cm^‐1 and its participation, together with the main SRS mode ω_SRS1 ≈︁ 1086.5 cm^‐1, in cross‐cascaded (χ⁽³⁾ ↔ χ⁽³⁾) nonlinear‐lasing generation, as well as the observation of efficient self‐upconversion via cascaded parametric four‐wave processes of one‐micron Stokes and anti‐Stokes χ⁽³⁾‐lasing into the UV‐region of third harmonic generation. The investigations show that calcite is able to generate a χ⁽³⁾‐lasing comb of more than two octaves bandwidth. The article also gives a brief review on the discovery and study of the SRS‐effect in natural crystals (minerals), which have expanded our ability to study the photon‐phonon nonlinear‐laser interactions in crystalline materials. A short summary of information about χ⁽³⁾‐lasing properties of the triangular planar structure units in SRS‐active crystals is included.     

Orthorhombic YAlO3 – a novel many‐phonon SRS‐active crystal

In single crystals of orthorhombic YAlO₃, widely known as a host‐matrix for Ln³⁺‐lasant ions, many‐phonon stimulated Raman scattering interactions as well as different manifestations of cascaded and cross‐cascaded nonlinear χ⁽³⁾↔χ⁽³⁾ processes are initiated by picosecond laser pulses. The scientific and applicative potential of YAlO₃ crystals is considerably expanded by the demonstration of its SRS properties. In particular, the studies revealed the manifestation of eight χ⁽³⁾‐active vibrational modes. The corresponding Stokes and anti‐Stokes lines have been assigned and the steady‐state Raman gain coefficients related to the strongest phonon mode have been estimated. In addition, a short review presents the stimulated emission channels of its Ln³⁺‐ions together with some χ⁽³⁾‐nonlinear laser properties of crystals belonging to the binary Y₂O₃‐Al₂O₃ system.     

Observation of all-optical wavelength conversion based on cascaded effect in periodically poled lithium niobate waveguide

We experimentally demonstrate multi-channel wavelength conversion through the cascaded second-order nonlinear processes in periodically poled lithium niobate waveguide in the optical communication wavelength band of 1.5 μm. The normalized conversion efficiency as high as 90% W⁻¹ cm⁻² is obtained. Wavelength conversion over a broad wavelength range of 66 nm has been confirmed.     

Nonlinear optical response of silver and copper nanoparticles in the near-ultraviolet spectral range

The nonlinear optical response of silver and copper nanoparticles synthesized by ion implantation in silica glasses is studied in the near-ultraviolet spectral range at a wavelength of 354.7 nm. The real and imaginary parts of the third-order nonlinear susceptibility χ⁽³⁾ of composite materials are measured. It is shown that the quantity Imχ⁽³⁾ is due to saturated absorption, while Reχ⁽³⁾ is due to the self-defocusing effect in composite materials.     

Efficient cascaded difference frequency conversion in periodically poled Ti:LiNbO3 waveguides using pulsed and cw pumping

Using an FM-mode-locked Ti:Er:LiNbO₃ waveguide laser as the fundamental source, wavelength conversion by cascaded χ⁽²⁾:χ⁽²⁾-difference frequency generation with a conversion efficiency of up to +3(-4.6) dB was demonstrated at a pulse repetition rate of about 2 (10) GHz. In addition, multi-channel conversion was demonstrated with a fully packaged wavelength converter using a continuous fundamental source. Received: 29 May 2001 / Revised version: 10 August 2001 / Published online: 2 November 2001     

Laser crystals and ceramics: recent advances

After a brief examination of known insulating laser crystals and the stimulated emission channels of their generating activator ions, this article reviews recent advances in the development of novel lasing crystals and ceramics, as well as inorganic and organic nonlinear‐laser crystals for χ⁽³⁾ and cascaded χ⁽³⁾ ↔ χ⁽²⁾ frequency converters. Several new modern attractive technologies in the physics and techniques of crystalline lasers are also discussed.     

Hindered rotation and phase transition in sodium gallohydride according to the NMR data

Polycrystalline sodium gallohydrides with different hydrogen isotope compositions, NaGaH₄, NaGaH_2.56D_1.44, and NaGaD₄, were studied over the temperature range 100–375 K by the ²H, ²³Na, and ^69,71Ga NMR methods in magnetic fields of 1.4, 1.88, and 7.04 T. The data on spin-lattice deuteron relaxation T ₁(²H) were used to determine the activation energy (～35 kJ/mol) of anion rotational motions and quadrupole coupling constant (QCC) χ _Q ⁰ (²H) = 90 kHz for the rigid lattice. To within measurement errors, the activation energy and ²H QCC were independent of the isotope composition. The low-temperature ²H NMR line was a doublet with ²H QCC χ(²H) = 70 kHz. The difference between χ ₀ and χ(T) was interpreted in terms of the librational averaging of the electric field gradient (EFG) according to the Bayer equation. The frequency of librations at 113 K was estimated (31 cm^?1). The shape of the ^69,71Ga NMR line was indicative of second-order quadrupole interaction with a nonzero asymmetry parameter η of the EFG tensor. Temperature variations in the QCC and η parameter at gallium were considered using the distorted tetrahedron model. The η value changed from 0.65 to zero (axial EFG tensor symmetry characteristic of tetragonal lattices) over the temperature range 140–295 K and again increased to 0.3 at 300–365 K, which was evidence of a change in the orientation of the distorted tetrahedral anion in the lattice. Changes in the asymmetry parameter were in agreement with the phase transition in sodium gallohydride recorded as a heat capacity jump.