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.     

实现暗态的三芯耦合波导设计及其非线性脉冲传输特征

暗态效应被广泛应用于量子信息处理.通过纤芯结构的设计,在三芯耦合波导中实现了该量子效应,并数值研究了非线性对暗态的影响.研究发现,在几个耦合长度内,当波导1中的输入为归一化功率等于1的低能量光脉冲时,波导2与3中没有光传输;当入射光的归一化功率增大到1000时,波导2与3中依然没有明显光传输,且对比度超过4个数量级.然...     

A 1 × 7 fibre coupler with Kerr nonlinearity

We study for the first time the evolution of the guided field in a 1×7 fibre coupler with a third-order nonlinearity. An analytical solution of the nonlinear coupled-mode equations is presented in terms of the Weierstrass function. In particular, we found that contrary to the equal power distribution in the linear limit, a cross-state appeared if the coupler was initially excited in the central core and a certain input power was chosen. Finally, we analyse the far-field pattern of the coupler output.     

Dissipative discrete spatial optical solitons in a system of coupled optical fibers with the Kerr and resonance nonlinearities

The propagation of monochromatic radiation in a system of weakly coupled single-mode optical fibers with saturable amplification and absorption and Kerr nonlinearity of the refractive index is analyzed. Conditions of stability and bistability of plane-wave regimes are determined. Discrete dissipative optical solitons are found and their stability is studied. The hysteresis dependences of the peak intensity of the discrete solitons on the value of the Kerr nonlinearity and the input beam intensity are demonstrated. The numerical estimates of the parameters of the spatial dissipative discrete solitons are presented.     

自陡对光纤耦合器调制不稳定性的影响

当考虑自陡效应时,从光纤耦合器的耦合模方程出发,用偶奇超模对其进行了重写。讨论了当输入条件使奇偶超模的其中之一被单独激发时光纤耦合器中的自陡效应对调制不稳定性的影响。结果表明:在光纤耦合器中不论是正常色散区还是反常色散区,当输入功率一定时,随着自陡参数的增大,调制不稳定性增益谱较多地显示出了强度变弱和宽度变窄,最终导致光纤耦合器的超模发生畸变。     

Design parameters for two-mode-interference couplers with varying nonlinearity

Different coupler cross-section designs of two-mode-interference couplers with varying nonlinearity are discussed with a view to minimizing the critical switching power. It is found that a linear inner region can be advantageous for some configurations. The optimization procedure employed here is quite general and can be easily applied to different coupler cross-section shapes.     

细菌视紫红质膜的光吸收非线性特性研究

对细菌视紫红质（ＢＲ）膜的光学吸收非性进行了研究,分别测量了细菌视紫红质光照前后的光吸收谱,结果显示它的吸收发生了明显的变化。用Ｚ扫描法研究了它的光学非线性,理论计算的结果表明它具有较大的光学非线性系数,且测量它的透过率随光强变化的关系曲线和理论模拟发现它对６３２．８ｎｍ波和匠光具有饱和吸收特性。     

超短脉冲倍频中三阶非线性效应的影响及补偿

 为了提高超短脉冲二倍频的转换效率和改善出射倍频光的脉冲形状,对超短脉冲倍频中三阶非线性效应的影响进行了理论分析和数值模拟,并采用初始相位失配的方法来补偿三阶非线性效应的影响。结果表明：用KDP晶体二倍频中心波长为800 nm的超短脉冲,当入射功率密度大于100 GW/cm²时,三阶非线性效应是倍频转换效率的主要影响因素。对脉宽为50 fs,入射功率密度为250 GW/cm²的超短脉冲在KDP晶体（2 mm）中的二次谐波变换,当初始相位失谐0.9 mrad时,转换效率提高了10%,同时由三阶非线性效应引起的强度调制得到明显抑制,出射基频光和倍频光的脉冲形状得到明显改善。     

Adiabatic geometric phase in the nonlinear coherent coupler

We introduce the concept of geometric phase to the nonlinear coherent coupler. With considering the adiabatic change of the distance-dependent phase mismatch, we calculate the adiabatic geometric phase related to the supermode of the coupler analytically. We find that the phase depends on the input light intensity explicitly. In particular, in the low and high intensity limits, the phase equals half of the area on the Poincare sphere enclosed by the evolution loop of the system. At the critical intensity where different supermodes merge, the phase diverges, which can be considered as the signal of a continuous phase transition.     

Why variational approximation reduces solition switching in nonlinear couplers to the CW case

Use of the variational approximation to describe soliton propagation in a nonlinear optical coupler is shown formally to reduce the problem to one with the same form as CW operation of a coupler, albeit with a different form of nonlinearity.     

Nonlinear directional couplers with asymmetrical distribution of nonlinearity

An analytical solution is given for the nonlinear directional coupler with asymmetrically placed nonlinearity. It is shown that the distribution of nonlinearity influences the critical power value and changes the transmission characteristics.     

All-optical limiting using nonlinear directional couplers composed of a self-focusing and a self-defocusing waveguide

We numerically demonstrate the all-optical limiting features in a mismatched nonlinear directional coupler (NLDC) composed of a self-focusing and a self-defocusing waveguide for both continuous wave and pulse cases. The working conditions required are analyzed. To obtain the limiting feature, the propagation constant of the self-focusing waveguide should not be larger than that of the self-defocusing waveguide. Cascaded asymmetric NLDCs are investigated to improve the limiting characteristics. The limiting threshold and the limiting output power can be adjusted by varying the coupler length or the ratio of the nonlinearity coefficients of the self-defocusing and self-focusing waveguides. Analytical solutions are presented in the case of a continuous wave. For the pulse case, numerical solutions show that the top part of the output pulse, if it exceeds the limiting threshold, will be tailored, while the rising and falling edges of the output pulse are almost the same as the input pulse. There is almost no pulse breakup. The influence of the second order dispersion and the intermodal dispersion on the limiting characteristics are analyzed. PACS 42.79.Gn; 42.79.Ta     

Novel effects in non-linear coupling

Non-linear couplers should be important in optical circuitry, especially in switching applications. In a non-linear coupler the oscillation in energy between the two cores depends on the initial light intensity. New effects which can occur in non-linear coupling are presented, using an analysis which includes an interaction coefficient. For a coupler formed from identical guides, the complete forms for the two invariants are given. Energy components are considered, and it is shown that, for a certain input energy, there is no coupling. In this case there is no oscillation in energy levels, so energy launched in one guide will remain in that guide. The energy required for switching to occur depends on the interaction coefficient as well as the non-linearity.     

同轴对称型主耦合器的研制

 为更进一步提高注入器的性能,注入器使用的耦合器采用同轴对称耦合。给出了同轴对称耦合器的理论计算、具体设计以及实验情况。经过对模型耦合器多次微波传输测量调试以及对各个部位反射的细致分析,最后获得了较好的结果,证明了该耦合器的实用性和可行性。     

Bloch oscillation and Landau\ben Zener tunnelling in a modulated optical lattice in a photovoltaic photorefractive crystal

We theoretically study the beam dynamical behaviour in a modulated optical lattice with a quadratic potential in a photovoltaic photorefractive crystal.We find that two different Bloch oscillation patterns appear for the excitation of both broad and narrow light beams.One kind of optical Landau–Zener tunnelling also appears upon the Bloch oscillation and can be controlled by adjusting the parameter of the optical lattice.Unlike the case of linear potential,the energy radiation due to Landau–Zener tunnelling can be confined in modulated lattices of this kind.For high input intensity levels,the Landau–Zener tunnelling is suppressed by the photovoltaic photorefractive nonlinearity and a symmetry breaking of beam propagation from the modulational instability appears.     

Nonlinear directional coupling between plasmonic slot waveguides

A numerical investigation of nonlinear switching in plasmonic directional couplers made of two dielectric slab waveguides with metallic claddings is presented. We assume Kerr-nonlinear dielectric and study the influence of geometrical parameters, metallic losses, and metal nonlinearities on coupler characteristics. We observe a general trade-off between losses and nonlinearity levels required for the switching operation. Underlying physical mechanisms that affect the coupler performance are discussed. The obtained results can be useful in design and optimization of the nonlinear plasmonic couplers.     

双光子吸收对光子晶体定向耦合全光开关的影响

 利用时域有限差分方法,在非线性条件下,考虑双光子吸收效应的同时,建立了分析2维光子晶体定向耦合波导光开关的模型。数值计算结果表明,对于长度较短的波导耦合器件,在强控制光和非线性条件下,双光子吸收效应会对波导的耦合作用产生一定的影响,从而改变入射光的透射特性,使光开关控制的动态过程发生变化。故而在设计全光开关器件时,对强控制光条件下的非线性双光子吸收效应有必要作为影响因素考虑进去。     

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…     

All optical logic gates based on an asymmetric nonlinear directional coupler

The performance of three different asymmetric dual core nonlinear directional couplers which includes an increasing and a decreasing self-phase modulation profile (SPM) was investigated. The asymmetry is associated to the SPM profile of one of the channels. Looking at the transmission characteristics of the device, through the direct- and cross-channel, we did a study of the extinction ratio (Xratio) of the devices. It was observed that in the operation of the three couplers, the performance of AND, XOR and OR gates are dependent on the nonlinearity profile of the coupler. For all configurations, an AND port with gain was observed. We can conclude that to operate the asymmetric coupler as a logic gate one has to control the nonlinearity profile to optimize the transmission characteristics thorough the extinction rate coefficient (Xratio).     

A novel fringe adaptation method for digital projector

Aimed to obtain high-quality sinusoidal fringe projection, a new method to correct the output fringe of digital projector is presented. The method is based on the proposed fringe transform model, which describes the relationship of the input and output fringe pattern. Firstly, a series of fringe patterns are projected and from the fringe images, the transform function is calculated by the pattern shifting method. At last, by modifying the input fringe pattern, a standard sinusoidal output fringe can be achieved. Different from the previous methods, the waveform nonlinearity is estimated by varying the intensity of the projected fringe pixel by pixel; thus the waveform nonlinearity can be estimated precisely and the time cost is considerably reduced. Experimental results show that by modification of the input projection patterns the projector can project fringe with high-quality sinusoidal waveform leading to high performance of the projection system.