光子晶体光纤包层可见光及红外宽带色散波产生

对光子晶体光纤包层3个空气孔之间节区的传光特性进行了分析, 对比了纤芯与包层节区传光的模场面积、非线性系数及色散特性, 得到光子晶体光纤包层节区具有小芯、高非线性的特点.在包层空气孔较大的情况下, 得到了双零色散曲线.根据色散曲线, 分析了色散波产生的相位匹配特性, 得到了色散波中心波长随抽运波长及功率的变化规律.制备出了所设计的光子晶体光纤, 实验得到了在可见光及红外大于300 nm的宽带色散波, 并给出了色散波随抽运波长及功率的变化规律.实验和理论分析结果一致, 为波长变换及超连续宽带光源的研究奠定了基础. 关键词： 光子晶体光纤 色散波 相位匹配 非线性     

Core-suction technique for the fabrication of optical fiber preforms

A novel technique, named "core suction," for fabricating optical fiber preforms has been devised. The technique involves drawing the molten nonconventional core glass material into the cladding tube to form the preform. The developed technique is simple, inexpensive, and shows great potential for fabricating preforms of highly nonlinear nonconventional glasses as the core material. Preforms were made with Schott SF6 and a lead-tellurium-germanate glass in silica cladding tubes, and these preforms were then pulled into fibers.     

Pockels介质平板中的光波传输

本文讨论了非线性对称平板波导中的TE波的偶模及奇模的传输问题.平板波导的芯区材料是由Pockels介质所构成,包层与衬底是相同的线性材料.Pockels介质的介电系数为ε=n²+α|E|,故问题归结为求解芯区的传输方程.本文给出了芯区、包层及衬底中光波的解析解以及传播常量β的本征值方程等.     

负折射率介质光纤的导模异常特性分析

对芯层为负折射率介质,敷层为普通介质的光纤的导模进行了研究,并对芯层与敷层介电常数比值（ξ）和磁导率比值（η）变化对导模色散特征的影响进行分析.分析表明负折射率光纤具有许多不同于常规光纤的反常特征,如存在表面波模,存在TM00模和TE00模以及存在多个单模传输模式和单模传输区间等.同时对负折射率介质光纤的单模传输条件进行了分析,发现单模传输模式和传输区间随ξ和η的不同而改变.     

Differentiating core and cladding attenuation in single-mode fiber

The measured attenuation of single-mode fibers is determined by loss contributions from both the core and the cladding. These regions can have different attenuation characteristics. In such a case, a shift in the ratio of core to cladding power of the LP₀₁ mode, due to a change in the cutoff wavelength, will result in a change of the measured attenuation spectrum. We have developed a technique to separate core and cladding attenuations and, by way of example, use the individual effects of radiation, hydrogen, and impurities on the core and cladding region of single-mode fibers to highlight the usefulness of the technique.     

非线性包层光纤中TE0模的传播特性分析

本文对具有Kerr非线性包层和线性匀芯的光纤在不同光功率下的传播特性进行了理论分析和数值计算.结果表明,在适当光功率下,当模折射率N等于芯折射率n_f时,芯场变得相当均匀,而包层场迅速衰减.对于自聚焦包层,当从N<n_f逐渐变到N>n_f时,芯场剖面越过N=n_f从凸变凹.在拐点,芯场成为均匀的.论文给出了模场分布和光功率与模折射率的关系.指出纤芯出现匀场预期会在光纤器件、光电子器件、光子器件中得到应用.     

Uniform Core Field in Symmetrical Planar Waveguides and Circular Fibers with Nonlinear Claddings

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Uniform Core Field in Symmetrical Planar Waveguides and Circular Fibers with Nonlinear Claddings

It is known that no uniform electric field profile exists in a planar linear waveguide. The uniform core field can be shown to exist in symmetrical planar waveguides and circular fibers with nonlinear claddings. Theoretical analysis and numerical calculations are carried out to show that when the modal index equals to the core refractive-index, the core field becomes uniform at an appropriate optical power. Analysis for a step-index circular fiber with nonlinear cladding have also shown that the core field becomes uniform under similar conditions. The occurrence of a uniform field in a waveguide core may believe to have promising applications in waveguide, optoelectronic and photonic devices.     

Large-core single-mode channel waveguide based on geometrically shaped leaky cladding

We propose a leaky channel waveguide structure for large-mode-area single-mode operation. The proposed structure is characterized by a uniform rectangular core and a specially designed cladding, through which all the confined modes are leaky. Single-mode operation is ensured by choosing the waveguide parameters properly so that the differential leakage loss between the first two modes is sufficiently high. A general power-law cladding geometry profile is considered, which is solved by the effective-index method in conjunction with the transfer-matrix-method to obtain the effective indices and leakage losses of the modes. We show that, with a suitable choice of cladding parameters, the waveguide can demonstrate extended single-mode operation in the wavelength range 750–1600 nm with a core area as large as 100 μm². Such a large confinement area for mode propagation can effectively suppress nonlinear optical effects. The waveguide is expected to find applications in the design of high-power lasers and amplifiers. PACS 42.82.-m; 42.82.Et; 42.79.Gn; 42.55.-f; 42.82.Bq     

Analysis of Nonlinear TE Waves in a Periodic Refractive Index Structure with a Nonlinear Cladding

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Propagation of ultrashort pulses in a nonlinear long-period fiber grating

By solving a pair of normalized nonlinear coupled-mode equations, we analyze in detail the propagation of ultrashort optical pulses in a nonlinear long-period fiber grating and investigate the conditions for the grating to function as an optical limiter or a saturable absorber. We show that the function of the grating depends on whether the nonlinear effect counteracts or enhances the detuning effect, and the nonlinear effect can be weakened significantly by the group-delay difference between the core mode and the coupled cladding mode. We present simulation results to illustrate these effects and discuss the physical conditions required for an effective operation of a nonlinear long-period grating.     

1 550 nm单模锥形光纤模场的演化特性

根据光纤模式传输理论,结合单模锥形光纤的结构,使用有限差分光束传播法(FD-BPM)仿真了1 550 nm波长下光纤模式的传输,分析包层内模场和纤芯内模场之间的相互影响。仿真结果表明:因为包层模的存在,随着包层内模式数的减少和纤芯对模场约束状态的变化,锥形光纤纤芯内不同区域模场分布变化明显,模场的均方根宽度在不同区域有不同程度的起伏。通过数值计算得到了光纤内模场能量的分布,发现因为包层模的存在,纤芯内模场能量减小速度比没有包层模时的速度要慢。     

Calculation of nonlinear modes guided by step-index fibers with finite cladding thickness

A circular optical fiber consisting of a nonlinear core bounded by a nonlinear cladding with a finite thickness is considered here. In this paper, the influence of the cladding radius in comparison with the core radius in the Power – effective index relations P(/k ₀) is examined. Numerical results indicate that the radius ratio between the cladding and the core is an important factor in changing the Power – effective index relations P(/k ₀) when the cladding has a stronger nonlinearity than that of the core.     

Nonlinear planar waveguides with gracled-index core: power series solution

Abstact Solutions are presented for a class of nonlinear, planar waveguides with graded-index linear film and nonlinear cladding and/or substrate. The solutions are based on a powerseries expansion for the field in the core and, for several interesting examples, can be expressed explicitly - without the need to solve any eigenvalue equation. For more general problems, the solution can be described in a form that is directly analogous to that for the asymmetric step-index waveguide. Some interesting differences between the mocles of the step-and graded-index waveguides are illustrated.     

Design of temperature-compensated elliptical core birefringent fibres

A new type of temperature compensated birefringent optical fibre is reported. The proposed fibre is designed aiming to minimising the stress birefringence by matching the thermal expansion coefficients between the core and the cladding and maximising the geometric birefringence by increasing the refractive index difference between the core and the cladding and increasing the core ellipticity. The optimum dopant concentrations satisfying the requirements is determined by solving a set of nonlinear algebraic equations. The fibre aimed at satisfying the requirements is fabricated and characterised. The experimental results show that the temperature dependence of the fibre birefringence is 6.97 × 10⁻⁴/°C. Methods of further improvement of the compensation are discussed and an alternative dopant material, titanium, for the improvement is suggested.     

Propagation characteristics of a segmented cladding fiber

We propose a novel optical fiber design that consists of a uniform core and a segmented cladding formed by alternate regions of high and low refractive indices in the azimuthal direction. The structure is analyzed by use of the radial effective-index method, and the propagation characteristics of the structure are studied. The fiber has a highly dispersive cladding and shows characteristics similar to those of photonic-crystal fibers and holey fibers. The novel fiber offers the possibility of single-mode operation over a wide range of wavelengths with a large core diameter.     

非线性包层多量子阱波导的TE波

给出用以分析非线性包层多量子阱波导ＴＥ模光学非线性与双稳性的理论公式与计算方法。指出用均方根等效折射率法解本征方程是有效的简化方法。用本文方法分析了模折射率对波导总功率的依赖关系,芯区功率与总功率之间的双稳性以及模场分布与模折射率的关系。讨论了波导参数对光学非线性、双稳性及模场的分布的影响。     

On the structure of waveguiding regions for high-order core modes of solid-core photonic-crystal fibers

Waveguiding properties of the higher-order modes in solid-core photonic-crystal fibers are studied numerically. The dispersion diagram is calculated for glass fibers with refractive indices of 1.611 with a hole-to-period ratio of 0.5 and 0.8. It is shown that, below the cutoff of the higher-order core modes, frequency regions exist within which these modes may propagate due to bandgaps in the cladding. In other words, the guiding effect in the solid-core fibers may result both from total internal reflection and from resonant reflection by the periodic cladding.     

用转移矩阵法研究LNN型非线性平面光波导

用转移矩阵法数值分析了芯区和衬底为非线性介质、覆盖层为线性介质结构平面光波导的传播特性,包括TM的模场分布和功率与有效折射率之间关系的分析.解析地表达了模式本征方程和功率分布,对非线性介质中电场强度与介质非线性系数的关系进行了研究.计算结果表明,TM的模场分布和功率与有效折射率及介质的非线性系数有关.     

复合纺丝法制备聚合物瓣状光纤的研究

瓣状光纤(SCF)由高折射率均匀芯层和高低折射率区域交替的皮层组成, 可有效地实现大纤芯单模运行。提出了采用复合纺丝法一步制备瓣状光纤。采用聚碳酸酯(PC)和聚甲基丙烯酸甲酯(PMMA)成功地制备截面符合设计要求的聚合物瓣状光纤。所制光纤的纤芯直径为40 μm。并用白光作为光源, 考察了所制光纤在500～1000 nm波段范围的出射光谱。从出射光谱可以看出, 所制光纤在730～830 nm波段范围内透射率比较高。通过截断法对所得光纤在500～1000 nm波段范围的传输损耗进行测试, 结果表明所制光纤的传输损耗比较大, 最大为30 dB/m。采用532 nm绿色激光作为光源, 通过CCD采集60 cm所得光纤的光斑。