Coupling coefficients evaluation of a directional coupler using gain guided and index antiguided fibers

In this paper, we have investigated the mutual and self coupling characteristics of directional couplers using two individual gain guided and index antiguided fibers, which can deliver robust single mode operation with large mode area, respectively owing to the combined adequately large gain coefficients in the core; Some interesting and distinguishing properties from conventional index guided fiber couplers are obtained that: The variations of coupling coefficients are complex-valued and spatially damping oscillated, but not exponential-like decreasing as conventional index guided couplers.     

Simulation and experimental characterization of Raman/EDFA hybrid amplifier with enhanced performance

We present simulation and experimental characterization of a hybrid amplifier comprising of a Raman amplifier and an erbium doped fiber (EDF) amplifier, with enhanced performance. The incorporation of a pumped EDF section in a fiber Raman amplifier (FRA) employing a dispersion compensating fiber is demonstrated to provide superior performance than a sole FRA system. The hybrid amplifier is characterized in terms of single channel gain and noise figure, and the results of measurements are shown to be in close agreement with the simulated results. Polarization-dependent gain (PDG) and multi-channel measured and simulated gain characterization of the Raman/EDFA hybrid amplifier are also presented.     

高功率光子晶体光纤放大器内超短脉冲的放大传输特性

由速率方程和功率传输方程得到信号脉冲平均功率和增益系数随脉冲传输距离的变化关系.利用Ginzburg-landau方程,在信号脉冲功率的不断增强和增益系数的不断变化的情况下,研究超短脉冲的传输演化特性,发现信号脉冲平均功率、能量和增益系数等参量受到色散和非线性效应的影响相对较小,而信号脉冲的峰值功率、时域和频域特性则易受到色散和非线性效应的影响.探讨了在非线性作用下,脉冲分裂和展宽等所导致的脉宽不稳定性对传输特性的影响,表明研究脉冲传输问题时,引入脉宽不稳定性有利于提高数值模拟准确度.     

氟磷共掺杂二氧化硅光纤预制棒的表面晶化

对F、P共掺杂光纤预制棒退火后的表面晶化行为进行了研究.由改进的化学汽相沉淀法制备的氟和磷共掺杂二氧化硅光纤预制棒玻璃样品在6 h的1 150 ℃控温加热处理后,其表面发生晶化.用X-射线衍射仪观测其晶相,主要为α-方石英,可使玻璃具有二阶光学非线性;用光学显微镜观察了其表面形貌并对结晶微粒的大小进行测量,知晶粒大小在十几到几十μm之间,会造成散射损耗的增加.实验结果,还显示氟对结晶过程有很大的影响.     

A theoretical and experimental study on all-normal-dispersion Yb-doped mode-locked fiber lasers

We report on a theoretical and experimental study of an all-normal-dispersion (ANDi) Yb-doped mode-locked fiber laser, in which nonlinear polarization rotation (NPR) is used to realize mode-locking without any dispersion compensation. Based on the coupled nonlinear Schrdinger (CNLS) equation, a model simulating the mode-locked process of an allnormal-dispersion ring fiber laser is developed, which shows that the achievement of stable mode-locking depends on the alignment of the polarization controller (PC) along the fast-polarization axis of the fiber, the birefringence intensity, and the net cavity dispersion. According to the theoretical analysis, stable mode-locked pulses with pulse duration 300 ps and average output power 33.9mW at repetition rate 36MHz are obtained.     

Reliability in reconstruction of the axisymmetric refractive index profiles from transverse interferograms. Accurate versus approximate methods: A comparative study

A mathematical formalism related to the approximate as well as the accurate interferometric data reduction schemes is briefly outlined and subsequently applied in the reconstruction of the assumed (Luneburg) axisymmetric refractive index distribution. The presented comparative analysis confirms the generally held opinion that the approximate methods (“straight-line” and Kokubun-Iga approaches) may provide quite reasonable results in the examination of refractively inhomogeneous disturbances characterized by weak gradient and moderate index variation. On the other hand, the accurate scheme for transverse interferometric data interpretation and reduction, based on the close-form correlation between the fringe shift and the deflection function, [1] remains the only method for reliable reconstruction of strongly refracting index profiles, independently of magnitude of refraction and ambiguity of the fringes. This fact is of considerable importance for transverse interferometry of fibers (preform rods) and/or GRIN-rod lenses characterized by high numerical apertures.     

Paraxial designing of planar waveguide variable-index focusing elements: Part 1—lenses of circular symmetry

A paraxial ray equation is used to evaluate refractive index profiles for a family of radially symmetric planar waveguide lenses. Two cases are considered: the (theoretically) full-aperture solution, and the solution with smooth index variation (non-full-aperature case). In deriving the latter case a new method has been applied that consists of the proper choice of a continuous deflection function. Both types of index profiles are described by exceptionally simple formulas.     

Dispersion Robustness of Millimeter Waves Generated by Up-Conversion Strategies

Abstract

The performance degradation caused by transmission along dispersive single-mode fibers of optically generated millimeter-wave signals using up-conversion is theoretically assessed and validated by numerical simulation. Up-conversion techniques based on optical double sideband, optical single sideband, and optical carrier suppression are considered. The generation of 60 GHz by frequency tripling using the optical single sideband is shown to be particularly tolerant to the fiber dispersion. The practical imbalance of Mach-Zehnder modulators is taken into account for optical carrier suppression modulation, where the finite extinction ratio is found to increase tolerance to fiber dispersion.     

Two-Frequency Brillouin Fiber Laser Based on Bragg Grating Fabry-Perot Cavity

Abstract

A novel and simple two-frequency Brillouin fiber laser is presented. It is based on a fiber Fabry-Perot cavity with fiber Bragg gratings as reflectors. The model of stimulated Brillouin scattering in fiber grating–based Fabry-Perot resonator is investigated. The laser allows conversion efficiency of close to 100% and suppresses the higher-order Stokes waves. The theoretical prediction is presented and the experimental demonstration is realized.     

Relative Intensity Noise in Optical Single Side Band Systems with Multiple In-Line Amplifiers: Analysis and Validation

Abstract

This article analyzes and validates through simulation the influence of fiber nonlinearity, dispersion, and loss on the Relative Noise Intensity (RIN) spectrum at fiber output in externally modulated optical single side band (OSSB) systems. The analysis includes the RIN generated by the laser source, the effect of the OSSB modulator, and noise generated by the in-line optical amplifiers. The analysis takes into account conversion between phase noise and intensity noise introduced by fiber transmission. It is shown that, depending on the operating conditions, the system performance may be predominantly affected either by the laser RIN or by the noise generated by the in-line optical amplifiers. The impact of the OSSB modulator can be relevant when the RIN of the system is dominated by the laser noise and should therefore be considered.