光纤中的交叉相位调制不稳定性研究

在同时考虑四阶色散和五阶非线性的情况下,以扩展的非线性薛定谔方程为基础,研究了有损光纤中双光束交叉相位调制(XPM)不稳定性.结果表明:由于四阶色散的影响,在光纤的正、反常色散区,XPM所致的调制不稳定性可发生在两个频谱区;正、负五阶非线性的存在分别对XPM不稳定性起加强和减弱作用.     

Second-order theory for self-phase modulation and cross-phase modulation in optical fibers

The authors develop a second-order perturbation technique for the study of self-phase modulation (SPM) and cross-phase modulation (XPM) effects in optical fibers. When the dispersion distance is much shorter than the nonlinear length, it is found that the difference between the first- and second-order solution is negligible. However, as the dispersion distance increases, nonlinearity becomes a stronger perturbation, and the first-order theory is not adequate to describe the SPM effects. However, the results obtained using the second-order perturbation technique is in good agreement with numerical simulations even when the dispersion distance is longer than the nonlinear length. When pulses of different channels are copropagating in a fiber, they undergo amplitude distortion and timing shift due to XPM. The perturbation technique presented in this paper accounts for both amplitude distortion and timing shift of a pulse due to XPM.     

Prediction of transmission penalties due to cross-phase modulationin WDM systems using a simplified technique

Cross-phase modulation (XPM) is a dominant impairment in WDM networks employing high bit-rates and narrow channel spacing. The optimization of future networks requires rapid and accurate techniques to predict XPM-induced penalties. We demonstrate the accuracy of predicting penalties from the distortion of a CW probe channel and show that as a consequence, XPM penalties can be calculated by a simplified numerical technique     

Control of spectral characteristics of dispersive optical fibers byannealing

Novel optical fibers fabricated from optical glasses with different dispersive characteristics are annealed under various conditions. Spectral properties of such dispersive fibers are greatly changed by annealing. It is shown that one of core and cladding index spectra can be shifted largely by annealing in case of fiber glasses with different transformation temperatures. We can therefore control properties of annealed dispersive fibers by adjusting the heat treatment     

Effects of the cross-phase modulation on the propagation of femtosecond optical pulses in photonic crystal fibers

The propagation of two femtosecond pulses in the region with minimum group-velocity dispersion, influenced by the cross-phase modulation (XPM) in photonic crystal fiber (PCF), is investigated in this paper. The adaptive split-step Fourier method is used to simulate the generalized nonlinear Schr?dinger equations (GNSE). The numerical results show that the combination of the Raman scattering and XPM can make the spectrum and the pulse shape changed, inducing the pulse compression and supercontinuum generation. The Raman effect from molecular vibrations, which can make the pulse spectrum in anomalous-dispersion region to be more symmetrical, is also discussed.     

Birefringence caused by thermal stress in elliptically deformed core optical fibers

Birefringence and polarization dispersion introduced by thermal stress in single-mode fibers with elliptical core are formulated here in terms of fiber structure parameters, thermal expansion coefficients, and thermoelastic constants. Thermal stress distribution and birefringence characteristics are estimated within first-order perturbation with respect to fiber core ellipticity. Normalized frequency dependence of birefringence and polarization dispersion is also derived in this paper. Birefringence and polarization dispersion in elliptical core fiber are seen to depend on thermal stress rather than geometrical anisotropy for relatively small relative index differences. Numerical examples are presented for germanosilicate, borosilicate, and phosphosilicate glass fibers.     

Analysis of the cross-phase modulation in dispersion compensatedWDM optical fiber systems

Wavelength-division-multiplexed (WDM) optical systems are affected by cross-phase modulation (XPM) due to Kerr effect. In this letter, dispersion compensated optical WDM systems affected by XPM are investigated by an analytical model. The theoretical results fit rather well with previous simulations performed in the case of fully compensated and under compensated optical fiber links     

无线上网卡造成的干扰分析

详细记录了一次极为特殊的网络干扰排查经历，叙述了干扰的监测、分析、排查过程，对今后干扰排查工作具有借鉴意义。     

无线上网卡功率失控引起的干扰分析

7月4日,我站接到中国联通衢州分公司的干扰投诉,衢州市开化县供电局楼顶的CDMA基站第二扇区上行283信道(频率833.49MHz)带内底噪值从-80dBm上升到-60dBm左右,覆盖区域内电话无法接入。接到     

在用广电信号与火炬传递信号的干扰分析

石家庄市是北京2008奥运会火炬传递城市之一,“祥云”火炬将从革命圣地西柏坡传递到市内主会场。虽然火炬传递时间短,但前期无线电安全保障工作涉及面广、任务重、难度大、要求高。在奥运火炬传递这项庞大的系统工程中．无线电安全保障和优质服务起着关键作用．其协调、管控水平是体现北京奥运会“科技奥运”理念的一个重要方面。     

High-birefringence optical fibers by preform deformation

High-birefringence optical fibers have been fabricated using a preform deformation technique in which an initially round preform is locally heated and squeezed from two sides. This technique has been used to make both polarization-preserving and single-polarization fibers. A novel feature of these new fibers is their rectangular shape which facilitates location of the principal axes and increases resistance to polarization breakdown from external perturbations. These fibers have circular cores, low loss, and excellent polarization holding.     

基于相位-强度调制转换的光纤色散精确测量方法

在分析光纤色散导致的相位-强度调制转换的基础上,提出了一种利用电光相位调制的光纤色散扫频测量方法。方法的原理为光纤色散使相位调制信号获得附加相移并产生周期性衰落,从衰落曲线的特征性凹陷频率确定出光纤色散。实际运用中,由于凹陷频率附近的信号弱,因此噪声大且不稳定。为了解决这一问题,通过衰落曲线的多项式拟合,进一步提高凹陷频率和光纤色散的测量精度。实验中,对长光纤或者短光纤分别测试以验证本文方法对于不同色散的适应性。实验结果表明,本文方法的相对误差小于0.22%。使用矢量网络分析仪(VNA)和相位调制器进行测试,可工作于不同光波长,适用于测量不同种类的光纤的色散;并且可以利用简单的实验系统,实现光纤色散的大小和符号的测量。     

The influence of cross-phase modulation on optical FDM PSK homodynetransmission systems

A combination of optical frequency division multiplexing (FDM) and phase-shift-keying (PSK) homodyne detection can increase transmission capacity. However, phase sensitive transmission systems, especially repeatered ones, suffer from data-dependent optical amplitude fluctuation that is converted to phase fluctuation by fiber nonlinearity. The authors discuss how this data-dependent amplitude fluctuation affects the error rate performance of optical FDM PSK homodyne detection systems. If only the optical amplitude fluctuation induced by phase modulators is taken into account, the allowable power fluctuation to keep the power penalty at 0.5 dB at a bit error rate (BER) of 10^-10 is below 0.17 mW for BPSK homodyne detection and 0.09 mW for QPSK homodyne detection. However, if only the amplitude fluctuation induced by the fiber chromatic dispersion is taken into account, the allowable number of repeaters to keep a 0.5-dB power penalty due to XPM at a BER of 10^-10 is 1 for BPSK homodyne detection and below 5 for QPSK homodyne detection     

Light intensity profiles of surface-emitting InGaAsP LED's: Impact on coupling to optical fibers

Light intensity profiles of 1.3-µm surface-emitting InGa AsP/InP LED's were measured using an infrared vidicon imaging technique. Typical light spot profiles were shown to have uniform intensity only over a small spot, with significant Gaussian tails around the periphery. Profiles were measured versus current. Narrowing of the light spot via current crowding was observed. A previous model for current crowding in stripe-geometry lasers was modified to calculate intensity profiles of circular-contact LED's. The model qualitatively predicts the observed changes in the profile shape with varying current and epitaxial-layer parameters. Measured efficiencies η of coupling LED power to optical fibers are usually lower than calculated for an ideal Lambertian source of uniform intensity. The observed profile is shown here to be responsible for the reduced η. For example, η of a uniform 25-µm spot is calculated to be ∼30-percent higher than that of a spot with typical Gaussian spreading and a width of 25 µm at half-maximum intensity, both butt-coupled to a 50-µm core, graded-index fiber. Lensing schemes to improve η were designed assuming uniform light spots, A ray-tracing calculation shows here that spherical lenses improve η equally well in the presence of Gaussian tails around the light spot.     

All-optical switching of grating transmission using cross-phase modulation in optical fibres

All-optical modulation of the transmission of a grating by picosecond laser pulses (1064 nm) in an optical fibre is demonstrated. The photosensitive grating is reflecting in the visible (514.5 nm) and the modulation is achieved by changing the refractive index through cross-phase modulation.<>     

Changing multimode dispersive fibers into single-mode fibers byannealing and guided mode analysis of annealed fibers

Dispersive fibers whose refractive index differences change greatly with wavelength are fabricated from optical glasses with different index dispersions. The fibers have several guided modes, and are changed into single-mode fibers by annealing under suitable conditions. The number of guided modes is investigated by measuring the bending loss and the mode lines of annealed dispersive fibers. The annealed single-mode fibers support only the fundamental mode over broad spectral ranges and no second guided mode at any wavelength     

RMS width of pulses in nonlinear dispersive fibers

An approximate analytical expression for the root means square (RMS) width of pulses propagating in nonlinear, dispersive fibers is derived. This result is useful for predicting how far a pulse can travel before it suffers significant distortion due to the combined influence of the nonlinearity of the refractive index and the dispersive properties of the fiber. This theory applies to pulses operating near the zero-dispersion wavelength where dispersion alone has a negligible influence, but where the combined influence of nonlinear self-phase modulation and dispersion can produce a significant effect     

Polarization and dispersive properties of elliptical-hole photoniccrystal fibers

We survey the properties of photonic crystal fibers with elliptical air holes, examining mode shapes, birefringence, group velocity walkoff and dispersion, and cutoff conditions. We find new types of behavior for each quantity and demonstrate the possibility achieving large birefringence with zero walkoff in the single-mode regime. We show that the dispersive properties of the vector modes are closely tied to those of the so-called fundamental space filling modes, and that at long wavelengths, the fibers exhibit a single-polarization single-mode regime of propagation without the presence of material anisotropy     

Demonstration of chirping manipulation of laser diode chirped optical pulses utilising cross-phase modulation in optical fibres

A new method to manipulate the chirp characteristics of laser-diode pulses is proposed, utilising the cross-phase modulation in optical fibres. Chirping manipulation of a red-shift chirped pulse from a 1.3 mu m gain-switched distributed-feedback laser diode is first demonstrated by compensating for the residual chirp through the blue-shift chirp induced by a 1.3 mu m intense YAG pump pulse.<>