Evaluation of dimensionless vector and scalar propagation constants for single-mode graded index fibers by a simple technique

We present simple but accurate analytical expressions for prediction of scalar and vector propagation constants for single-mode graded index fibers. Our formulation is based on the recently developed Chebyshev power series expression for the fundamental mode of graded index fibers. Taking parabolic index fiber as example, we show that our estimations agree excellently with the exact results. The concerned calculations involve very little computations.     

Analysis of splice loss in single-mode fibres using a Gaussian field approximation

By using a Gaussian field approximation to the fundamental mode in a single-mode fibre, a very simple formula is derived for the splice loss in the two fibres when transverse, longitudinal and angular misalignments exist simultaneously. It is shown that the effects of the three misalignments on the splice loss are more significant for step-index fibres than for parabolic-index fibres, and also that matching oil in the gap between the fibres is effective for the end separation, but produces a reverse effect for the tilt. Calculated coupling efficiency between step-index fibres is compared with the experimental data reported so far, and good agreement between them is observed.     

Bend loss calculation in single-mode graded-index fibers using variational fields

Calculation of bend loss for single-mode graded-index fibers utilizes the fundamental modal field. Using some of the single and two parameter scalar variational approximations available in the literature for this mode, the bend loss has been computed. The exact results are obtained using a well known numerical method. The accuracies of the results obtained from the use of these variational fields have been compared.     

A simple but accurate method for prediction of splice loss in single-mode dispersion shifted trapezoidal as well as dispersion flattened graded and step W fibers

We present simple and accurate analytical expressions for transmission coefficient at the splice for both angular offset and transverse offset in case of single-mode dispersion shifted trapezoidal as well as dispersion flattened graded and step W fibers. Here, we employ the recently developed simple series expression for fundamental modal field for such fibers. The evaluation of the concerned parameters based on our formalism requires very little computations. We show that our estimations match excellently with the exact numerical results in case of the said fibers. Further, splices being highly tolerant with respect to longitudinal separation, we restrict our investigations to the cases of transverse and angular mismatches only. The present study should find application in all optical technology involving said kinds of fiber.     

A simple technique for evaluation of transmission coefficient at the splice with angular offset and transverse offset for first higher mode propagation in graded index fibers

We present simple and accurate analytical expressions for transmission coefficient at the splice with angular offset and transverse offset in case of first higher mode propagation in graded index fibers. We employ the simple series expression for first higher order modal field for graded index fiber. The evaluation of the concerned parameters based on our formalism requires very little computations. Here, we show that our estimations match excellently well with the exact results in case of step and parabolic index fibers. Further, splice being highly tolerant for longitudinal separation, our analysis is judiciously restricted to the case of transverse and angular mismatches only. The analysis should find application in dual mode graded index fiber in all optical technology.     

Diode-lasers based apparatus and method for single-mode fibers spectral splice loss measurements

Arc-discharge fusion splicing is widely used in the telecommunication industry for joining single-mode optical fibers to Er-doped fiber coils. These coils are used as the gain medium in erbium-doped amplifiers (EDFAs). The quality and integrity of splicing these coils to fibers can impact key EDFA performance parameters. This article describes an automated splice loss and Er-doped fiber absorption measurement system. The measurement system is equipped with 1310, 1550 and 1563 nm DFB lasers, broadband light source, InGaAs detectors and fiber-optic internal standards. Furthermore, the article describes a method for measuring splice loss between Er-doped fiber and the fibers spliced to coil ends. The system controls splice loss between SM-28 or HI980 fiber and Er-doped fiber to 0.094 ± 0.052 dB at 1550 nm. Moreover, the system can measure accurately Er-doped fiber absorption to within ±3.19% at 1563 nm.     

金属包层渐变折射率介质光波导的传输特性与损耗

用金属包层介质光波导损耗的微扰理论及藉助多层近似法用递推公式分析渐变折射率波导传播常数的方法,对几种类型的金属包层渐变折射率介质光波导的传输特性与损耗进行分析和讨论,得到了与精确数值计算结果相吻合的结果.     

Fibre splice loss: a simple method of calculation

Abstact We evaluate the loss encountered when splicing between two circular single-mode fibres with unmatched parameters. Our method represents a significant improvement in simplicity over other methods, with only an insignificant degradation of accuracy. We use Galerkin's method, but expand the field of both fibres in terms of the same set of basis functions, leading to considerable simplicity: the overlap integral is simply the inner (dot) product of the eigenvectors. Integration is thus avoided. We assume that weakly guiding conditions prevail.     

Character of similaritons formed in a single-mode fiber without gain

Based on the numerical and experimental studies, a nonlinear-spectronic character of similaritons formed in a single-mode optical fiber without gain is demonstrated. It is shown that the combined action of the Kerr-type nonlinearity and normal dispersion of the fiber leads to the formation of similaritons. The temporal envelop, spectral and phase profiles of such similaritons have a nearly parabolic shape in their central energy-carrying parts.     

Light propagation in multi‐step index optical fibres

This paper reviews the theoretical analysis of light propagation we have carried out on multimode multi‐step index (MSI) optical fibres. Starting from the Eikonal equation, we derive the analytical expressions that allow calculating the ray trajectories inside these fibres. We also analyse the effects of leaky rays on the transmission properties of MSI fibres. For this purpose, a single analytical expression for the evaluation of the ray power transmission coefficient is calculated. Afterwards, we investigate the effects of extrinsic and intrinsic coupling losses on the performance of MSI fibres, providing analytical expressions to calculate the coupling loss and, also, determining the most critical parameters. Finally, we carry out a comprehensive numerical analysis of the fibre bandwidth under different source configurations.     

Stable single-mode operation of a Q-switched laser by a simple resonator length control technique

A simple extension to the technique of “pre-lase” Q-switching ensures that a TEM₀₀ mode, Q-switched NdYAG laser produces single longitudinal mode oscillation on every shot.     

Spontaneous emission of two quantum dots in a single-mode cavity

The spontaneous emission spectrum from two quantum dots （QDs） that are strongly coupled with a single-mode nanocavity is investigated using rigorous numerical calculations and simple analytical solutions of quantum dynamics. The emission spectra both from the side and along the axis of the cavity are considered. Modification of two parameters, the coupling strength and the detuning between the transition frequencies of the two quantum dots, allows us to efficiently control the shape of the spontaneous emission spectrum. Different profiles and their physical origins can be well understood in the dressed-state picture for the light-QD interaction in the on-resonance and off-resonance situations. In the on-resonance situation, the emission spectra exhibit symmetric features, and they are not altered by the asymmetry in the coupling pa- rameters. The axis spectra show two emission peaks while the side spectra have three emission peaks. In the off-resonance situation, the emission spectra always show an asymmetrical three-peak feature. When the two QDs have different decay parameters, singular features （a peak or a dip） can take place at the frequency of the cavity mode, and this is attributed to the unbalanced process of the emission and absorption of a single photon.     

Stationary properties of a single-mode laser system with non-Gaussian and Gaussian noise

A single-mode laser system with non-Gaussian and Gaussian noise is investigated. The stationary mean value and the normalized variance of the laser intensity are numerically calculated under the condition that the stationary probability distribution function (SPDF) is derived. The SPDF as a function of the laser intensity exhibits a maximum. The maximum becomes smaller with the increase of the correlation intensity or the non-Gaussian parameter, where the later is a measure of the deviation from the Gaussian characteristic. The maximum becomes larger as the correlation time increases. The laser intensity stationary mean value decreases with the increase of the correlation intensity or the non-Gaussian parameter while increases with the correlation time increasing. The laser intensity normalized variance increases with the increase of the correlation intensity or the non-Gaussian parameter while decreases as the correlation time increases.     

Statistical properties of a single-mode laser driven by additive and multiplicative coloured noises with a coloured cross-correlation for different correlation times

We study a system for a single-mode laser driven by additive and multiplicative coloured noises with a coloured cross-correlation. The analytical expression of the stationary intensity distribution (SID) for the laser is derived in the case of three different correlation times. The influences of each stochastic parameter on the SID are discussed, the effects of the noise "colour" and the cross-correlation of noises on the mean intensity , the variance, λ_2(0), and the skewness,λ_3(0) of the single-mode laser are investigated. We find that there are colourful phase transitions for the SID above a threshold, and re-entrant transitions induced by the "colour" of the additive noises. Further research of the curves of -τ_i, λ_2(0)-τ_i, and λ_3(0)-τ_i (i=1,2,3) (where τ_i is the correlation time) shows that the output intensity not only increases with the additive noise correlation time τ_2 and the cross-correlation time τ_3, but also the quality of the output of laser beams is optimized.     

Stochastic resonance in a single-mode laser driven by frequency modulated signal and coloured noises

By adding frequency modulated signals to the intensity equation of gain--noise model of the single-mode laser driven by two coloured noises which are correlated, this paper uses the linear approximation method to calculate the power spectrum and signal-to-noise ratio (SNR) of the laser intensity. The results show that the SNR appears typical stochastic resonance with the variation of intensity of the pump noise and quantum noise. As the amplitude of a modulated signal has effects on the SNR, it shows suppression, monotone increasing, stochastic resonance, and multiple stochastic resonance with the variation of the frequency of a carrier signal and modulated signal.     

Group index dispersion of holey fibres measured by a white-light spectral interferometric technique

We present a new white-light interferometric technique to measure the group index of holey fibres over a wide wavelength range. The technique utilizes an unbalanced Mach–Zehnder interferometer with a fibre under test of known length placed in one of the interferometer arms and the other arm with adjustable path length. In a first step, the differential group index of the fibre is measured over a wide wavelength range. In a second step, the fibre is replaced by the reference sample of known thickness and group dispersion to determine precisely the group index of the fibre at one specific wavelength. The group index as a function of wavelength is measured for two different holey fibres, one made of pure silica glass and the other made of SK222 glass. For both fibres, the wavelength dependence of the group index of the outer cladding and modes supported by the fibre is measured.     

单模激光驱动的超混沌系统的完全同步

利用主动-被动同步法实现了由单模激光驱动的超混沌系统的完全同步.根据稳定性理论,对系统进行了一般分解.以单模激光Lorenz系统和四维超混沌Chen系统为例,验证了这种方法的有效性.仿真模拟结果表明,这种同步方法是快速有效的.利用这种同步方法可以实现对任意高维混沌系统的混沌同步,具有一定的普适性.     

调频信号的单模激光线性模型随机共振

对单模激光增益模型的光强方程加入调频信号,用线性化近似方法计算了以δ函数形式关联的两白噪声驱动下光强的输出功率谱及信噪比. 结果表明,信噪比随抽运噪声和量子噪声强度的变化可出现典型随机共振,受调制信号振幅的影响,信噪比随载波信号频率和调制信号频率的变化出现抑制、单调上升、共振、抑制和共振等几种情况. 关键词： 抽运噪声 单模激光 随机共振 调频信号     

交叉色关联噪声驱动的单模激光系统统计性质研究

采用交叉色关联的加性色噪声和乘性色噪声驱动的单模激光立方模型,通过诺维科夫理论和福克斯近似以及斯特拉托诺维奇近似,得到反映激光统计性质的强度关联函数C的表达式;研究关联时间τ、净增益系数a₀和交叉关联强度λ对强度关联函数C的影响.数值模拟发现,在阈值以上（a₀>0）时,关联函数C随关联时间τ的增大而增大;在阈值以下（a₀<0）时,关联函数C随关联时间τ的增大而减小.无论在阈值以上还是阈值以下,关联函数C均随交叉关联强度λ的增大而减小.在C-a₀曲线上存在单峰. 关键词： 单模激光 交叉关联 强度涨落 强度关联函数     

调幅波的单模激光线性模型随机共振

对单模激光增益模型的光强方程加入调幅波，用线性化近似方法计算了以δ函数形式关联的两白噪声驱动下光强的输出功率谱及信噪比. 结果表明，信噪比不但随着抽运噪声和量子噪声强度的变化出现随机共振，而且随着高频载波信号频率和低频调制信号频率的变化也出现了随机共振. 关键词： 抽运噪声 单模激光 随机共振 调幅波