Soliton switching study using new normalized nonlinear Schrödinger equations

Soliton switching in a nonlinear directional coupler (NLDC) is studied by using new normalized nonlinear Schrödinger equations (NLSE). The resulted equations have one parameter κL_D only, this feature greatly simplifies the numerical study of soliton coupling in a NLDC, and it enables us to derive the soliton switching conditions based on numerical analysis. Numerical results show that most of the input soliton energy remains in the launched waveguide when input soliton normalized peak power is bigger than 2.5. It is contrary to the existing theoretical expectations which were derived using variational approach. The fundamental soliton switching conditions is also expressed in terms of input soliton pulse width. In addition, it is found that frequency chirp degrades soliton switching performance in a NLDC.     

Switching Dynamic Analysis for Twin-Core Fibre Coupler Using Supermode Theory

Characteristics of optical switching in a twin-core fibre coupler are numerically analysed under short pulse input by using supermode theory. The dynamic nonlinear coupled superlnode equations are derived, The numerical results show that the input pulse width determines the power transfer and the pulse temporal profile in the output ports. The optimal switching characteristics can be obtained by selecting an appropriate initial pulse width. In addition, the switching characteristic curves are insensitive to the input pulse shape for either fundamental soliton pulse or Gaussian pulse input, but sensitive to pulse sharpness. A reduced switching power and a sharper switching transition can be obtained by using the sharp super-Gaussian pulse.     

Gain-induced soliton switching in fiber nonlinear directional coupler

With study for switching characteristics and output coupling ratio of fiber nonlinear directional couplers (NLDC), we found that the influence elements on the switching characteristics and output coupling ratio had gain of core 1 and 2, nonlinear coefficient of those, the input power and width of input soliton. We also found numerically that switching efficiencies were improved by controlling gain of core 1, different output coupling ratio would be obtained by controlling gain of core 1 or 2. And we can change the gain by changing pump power of the optical fiber amplifiers. From this, we also made fiber coupler which output coupling ratio was changeable.     

掺铒光纤环镜中超短光孤子的放大与压缩Ⅱ.环镜及输入脉冲特性对放大结果的影响

最近的研究发现,用掺铒光纤环镜放大并压缩超短光孤子不仅能避免常规掺铒光纤放大器中由于非线性效应引起的孤子畸变,而且可克服绝热放大技术中放大器长度随输入脉宽增大而指数规律增大的困难。进一步研究了环镜及输入脉冲特性对放大结果的影响。数值计算表明,对于确定的输入脉冲,当环镜参量(环镜长度、增益、耦合器功率耦合系数)在较大范围内变化时,环镜放大器的孤子输出性能基本稳定。对于确定的环镜,输入脉冲形状的变化、初始输入功率的起伏以及高阶效应等因素对放大结果的影响较小;相对而言,初始频率啁啾对输出孤子宽度的影响较大,但对输出孤子质量的影响并不严重。     

Optical switching in a coupler with saturable nonlinearity

Abstact We report in this paper a numerical study of optical switching in couplers with saturable nonlinearity. Regions that characterize different coupling behaviour are revealed. It is shown that, in the presence of saturation, a Gaussian pulse should be used instead of solitons for negligible pulse splitting between the coupler arms. Nearly complete switching is possible depending on the input optical power and the index saturation parameter.     

Vector soliton switching in a fiber nonlinear directional coupler

This paper reports a detailed numerical study of soliton switching in a high as well as low birefringent nonlinear coupler. It is shown that by controlling the polarization angle one can have nearly 100% transmission with excellent switching characteristics. It is shown that soliton remains stable during its propagation inside the coupler. However it is observed that high birefringent coupler exhibits relatively better soliton stability. We show that the coupler could be used as a soliton switch even at an input peak power less than the critical power, the power at which 50-50 power sharing takes place between the two cores, just by a judicious choice of the polarization angle.     

三芯非线性光纤耦合器中的短脉冲光开关

利用变分法研究三芯非线性光纤耦合器中的短脉冲光开关,解析分析线性三耦合非线性Schr?dinger方程的结果与数值模拟符合得很好.并且得到在非线性光纤耦合器中孤子的耦合长度和开关阈值,与连续波情况和两芯光纤耦合器的结果不同. 关键词： 光纤耦合器 光开关 耦合长度 开关阈值     

Femtosecond pulse switching in a fiber coupler with third order dispersion and self-steepening effects

A numerical study of femtosecond pulse propagation and switching in a dual-core nonlinear directional coupler with the consideration of third order dispersion and self-steepening effects is reported. The Split Step Fourier Method (SSFM) is used to investigate the switching characteristics of nonlinear directional couplers. It is observed that the energy transfer from core to core is not affected by changing the input pulse shapes except super-Gaussian. While the normalized coupling co-efficient and the input peak power dominate the coupling characteristics, the effects of third order dispersion (TOD) and self-steepening (SS) are also reported.     

Dark soliton switching in an NLDC in the presence of higher-order perturbative effects

Dark soliton switching in a nonlinear directional coupler in the presence of intermodal dispersion, cross-phase modulation (CPM), third-order dispersion, Raman effect, and self-steepening effect is reported for the first time. It is shown that, with the exception of CPM, all of the other perturbative effects have almost no effect on the switching characteristics of the dark soliton switch, which is an improvement over the corresponding bright soliton switch. Although the CPM increases the critical power of dark soliton switching, the soliton pulse remains stable inside the coupler during its propagation.     

A new soliton communication band for optical networking redundancy using a Gaussian soliton generation

We present a novel communication band of the tunable multi-Gaussian soliton system, whereas the large bandwidth signals of the spatial soliton pulses can be generated after propagating within the nonlinear ring resonator system. A Gaussian pulse input with 20 ns pulse width, 2 W peak power, the center wavelength at 1300 nm is propagated into the nonlinear ring resonator system. Using the appropriate parameters relating to the practical device such as micro-ring radii, coupling coefficients, linear and nonlinear refractive index, we found that the multi-soliton pulse obtained have shown the potential of application for a new dense wavelength division multiplexing (DWDM) band. The soliton pulse width and free spectrum range of 400 and 7 fm are obtained, respectively, which can be used to increase the channel capacity in soliton communication. Furthermore, the soliton power obtained is available for system and link redundancy, where the output soliton power of 12 W is achieved.     

Phase-induced switching in fiber nonlinear directional coupler

A numerical study of soliton switching characteristics and the maximum output coupling by the relative phase change of a control pulse is carried out for input powers, coupled coefficient and input soliton width. It is shown that input powers ratio, coupled coefficient and input soliton width play important roles in this mode of soliton switching and that these effects may lead to useful soliton switching if the relative phase of the control pulse is monitored judiciously.     

Analysis of a gained nonlinear directional coupler pulse switch

We have investigated the switching performance of a gained (nonlinear directional coupler) NLDC switch in the presence of both 2nd and 4th order gain nonlinearities. In this system, we have achieved a nearly complete pulse switching at half beat length of the coupler which implies about 40% reduction in the switching length as compared to the switching length reported in Trillo et al. (1988). We have shown that at the half beat length the output energy of each branch is equal to that of the input energy and hence the gained NLDC switches have ability to be cascaded. Our initial investigations reveal that this gained NLDC switch has remarkable performance and potential to be used in ultra-fast optical communication systems.     

Chirp-controlled soliton fission in tapered optical fibers

Manipulation of the input pulse chirp during supercontinuum generation in tapered fibers provides precise control of the soliton fission process taking place in the taper waist. Simulations and experiments demonstrate that controlling this pre-chirp by a pulse shaper can be applied to compensate for deleterious effects due to untapered fiber pigtails. Temporal and cross-correlation frequency resolved measurements are utilized to show, that the control of the soliton fission dynamics can be obtained by manipulating the input pulse chirp through the imposition of a quadratic spectral phase. PACS 42.65.Wi; 42.65.Tg; 42.81.Qb; 42.81.DP     

Nonlinear copropagation of two optical pulses of different frequencies in photonic crystal fibers

A theoretical investigation of the nonlinear copropagation of two optical pulses of different frequencies in a photonic crystal fiber is presented. Different phenomena are observed depending on whether the wavelength of the signal pulse is located in the normal or the anomalous dispersion region. In particular, it is found that the phenomenon of pulse trapping occurs when the signal wavelength is located in the normal dispersion region while the pump wavelength is located in the anomalous dispersion region. The signal pulse suffers cross-phase modulation by the Raman shifted soliton pulse and it is trapped and copropagates with the Raman soliton pulse along the fiber. As the input peak power of the pump pulse is increased, the red-shift of the Raman soliton is considerably enhanced with the simultaneous further blue-shift of the trapped pulse to satisfy the condition of group velocity matching. PACS 42.65.Tg; 42.81.Dp     

Soliton content of arbitrarily shaped light pulses in fibers analysed using a soliton-radiation beat pattern

Arbitrarily shaped light pulses propagating down a fiber may contain one or several solitons and a radiative background. A novel computer-assisted method is introduced to identify the composition. This technique does not suffer from restrictions of applicability to integrable systems. As an example we identify the soliton content in a chirped Gaussian pulse. PACS 42.81.Dp; 42.65.Tg     

All-optical Steerable Directional Coupler Using Kerr Dark Spatial Soliton Waveguides

1.IntroductionOpticalspatialsolitoninduced-waveguidesareofgreatresearchinterestrecently[1-8]becauseoftheirPOtentialapplicationinopticalcommunicationsandopticalcompution.Asoliton--inducedwaveguidecanguidelightinself--focusingorself--defocusingKerr-typemediabecausethesolitonbeaminducesarefractive-indexprofileequivalenttoanordinarydielectricwaveguide.Soliton-inducedwaveguidecansupPOrtmanymodesofaprobebeampropagatingcoaxiallyalongthesolitonwaveguideSoliton-inducedwaveguideshaveadvantageovertheir…     

含负折射介质的反向定向耦合器的时空不稳定性研究

研究含负折射介质的不对称反向定向耦合器中的时空调制不稳定性(MI),探讨了输入功率、前向波和后向波功率比和通道间的耦合系数等对时空MI的影响。结果表明:在这种新型耦合器中只有当横向波数超过一定阈值时才会产生MI,增加输入功率或减少前向波和后向波的功率比都会扩大MI增益谱的范围并最终使MI区域重合,而降低耦合器通道间的耦合系数可减少MI的增益峰值但拓宽增益谱的范围。负折射介质的电磁参数可调谐特性为实现MI的主动调控和孤子的形成提供了新的方法和手段。     

Design and simulation of a switch based on nonlinear directional coupler

In this paper, we have analyzed a nonlinear photonic crystal directional coupler by the finite difference time domain method. We have tried to increase the coupling efficiency and also reduce the coupling length in linear and nonlinear states in this device. In this coupler, refractive index of the rods of the central row is tuned by input signal power due to nonlinear Kerr effect; therefore, input signal beam can be controlled so as to be exchanged between two output ports. Physical length is chosen to be 24a so as to have the highest output power ratio and also the smallest amount of power required for nonlinear performance.     

Amplification and compression of ultrashort fundamental solitons in an erbium-doped nonlinear amplifying fiber loop mirror

A nonlinear amplifying loop mirror constructed from erbium-doped fiber is proposed for simultaneous amplification and compression of ultrashort fundamental solitons. Numerical simulations show that, unlike conventional erbium-doped fiber amplifiers in which nonlinear effects lead to serious degradation of pulse quality, the proposed device performs efficient high-quality amplification and compression of ultrashort fundamental solitons while it almost completely preserves the soliton nature of the input pulses. Moreover, the performance of the device is insensitive to small variations in the loop length and in the power-splitting ratio of the coupler.     

Raman effects in the infrared supercontinuum generation in soft-glass PCFs

Measurements of the Raman gain spectra in the SF6 and SF57 highly nonlinear glasses demonstrated twice as high Raman shift in comparison with the fused silica. Numerical simulation predicted that a large Raman shift in combination with high nonlinearity can significantly reduce the required input pulse intensity for supercontinuum in these glasses, retaining the necessary degree of coherence. We found that the degradation of the SC coherence due to Raman soliton jitter can be effectively controlled by a correct choice of input intensity and fiber length. Also it was found that a high degree of coherence correlates with the spectrum shape in the vicinity of the Raman threshold, providing an convenient experimental observable. PACS 42.65.Tg; 42.81.Dp; 42.72.Ai