Switching behavior of a nonlinear Mach-Zehnder interferometer: Saturating nonlinearity

This paper uses the Beam Propagation Method to investigate numerically the switching behavior of a Nonlinear Mach-Zehnder Interferometer (NMZI). A saturating-type nonlinearity has been considered for the present investigations. It is shown that the input versus output characteristics change drastically when a Kerr type nonlinear medium is replaced by a saturating type nonlinear medium. In contrast to an NMZI with Kerr nonlinearity, where only quantitative behavior changes with NMZI length, quantitative as well as qualitative behaviors change in the case of a saturating nonlinearity. We propose an all-optical stabilizer and MZI with stable “ON” and “OFF” states on the basis of our investigation.     

Switching behaviour of a nonlinear Mach-Zehnder interferometer

In the present paper, a detailed investigation on the switching behaviour of a nonlinear Mach-Zehnder interferometer (NMZI) has been carried out using beam propagation method (BPM). A thorough investigation on input vs. output characteristic has been carried out by varying different parameters like length of the arms, refractive index of the linear/nonlinear arm, wavelength of the input beams and nonlinear coefficient of the material of the nonlinear arm. The input vs. output characteristic has also been investigated by shifting the balance point of the NMZI. The present paper provides a physically intuitive understanding of the effect of change in different parameters of the NMZI on its switching behaviour.     

Single-photon all-optical switching using coupled microring resonators

We study the nonlinear phase response of a microring resonator coupled to a bus waveguide and the use of this nonlinear phase shift to store information in the microring resonator and enhance the switching characteristics of a Mach-Zehnder interferometer (MZI). By introducing coupling between adjacent microring resonators, the switching characteristics of the MZI can be exponentially enhanced as a function of the number of microring resonators, when compared to the linear enhancement for uncoupled resonators. With only a few moderate-finesse microring resonators, the switching power can be reduced to attowatt level, allowing for photonic switching devices that operate at single-photon level in ordinary optical waveguides.      

A new scheme of all-optical adder logic operation based on nonlinear property of the material and polarization encoding technique

Optical nonlinear materials have been used for several digital logic and arithmetic operations. These operations are conducted in real time domain as per their operational speed is concerned. In this paper authors propose a new method of all optical half adder scheme. This type of switching is based on polarization properties of light along with nonlinear properties of material. As the state of polarization of light ensures that the field intensity level of the light signal is the same in whole operation, the scheme may be extended to some wide applications in all optical parallel computation and information processing.     

All-optical switching in subwavelength metallic grating structure containing nonlinear optical materials

All-optical switching based on a subwavelength metallic grating structure containing nonlinear optical materials has been proposed and numerically investigated. Metal-dielectric composite material is used in the switching for its larger third-order nonlinear susceptibility (approximately 10(-7)esu) and ultrafast response properties. The calculated dependence of the signal light intensity on the pump light intensity shows a bistable behavior, which results in a significant switch effect. It rests on a surface plasmon's enhanced intensity-dependent change of the effective dielectric constant of Kerr nonlinear media, corresponding to a transition of the far-field transmission from a low- to high-transmission state. The study of this switching structure shows great advantages of smaller size, lower requirement of pump light intensity, and shorter switching time at approximately the picosecond level.     

Ultrafast optical switching in Kerr nonlinear photonic crystals

Nonlinear photonic crystals made from polystyrene materials that have Kerr nonlinearity can exhibit ultrafast optical switching when the samples are pumped by ultrashort optical pulses with high intensity due to the change of the refractive index of polystyrene and subsequent shift of the band gap edge or defect state resonant frequency. Polystyrene has a large Kerr nonlinear susceptibility and almost instantaneous response to pump light, making it suitable for the realization of ultrafast optical switching with a response time as short as a few femtoseconds. In this paper, we review our experimental progress on the continual improvement of all-optical switching speed in two-dimensional and three-dimensional polystyrene nonlinear photonic crystals in the past years. Several relevant issues are discussed and analyzed, including different mechanisms for all-optical switching, preparation of nonlinear photonic crystal samples by means of microfabrication and self-assembly techniques, characterization of optical switching performance by means of femtosecond pump-probe technique, and different ways to lower the pump power of optical switching to facilitate practical applications in optical information processing. Finally, a brief summary and a perspective of future work are provided.     

Ultrafast optical switching in Kerr nonlinear photonic crystals

Nonlinear photonic crystals made from polystyrene materials that have Kerr nonlinearity can exhibit ultrafast optical switching when the samples are pumped by ultrashort optical pulses with high intensity due to the change of the refractive index of polystyrene and subsequent shift of the band gap edge or defect state resonant frequency. Polystyrene has a large Kerr nonlinear susceptibility and almost instantaneous response to pump light, making it suitable for the realization of ultrafast optical switching with a response time as short as a few femtoseconds. In this paper, we review our experimental progress on the continual improvement of all-optical switching speed in two-dimensional and three-dimensional polystyrene nonlinear photonic crystals in the past years. Several relevant issues are discussed and analyzed, including different mechanisms for all-optical switching, preparation of nonlinear photonic crystal samples by means of microfabrication and self-assembly techniques, characterization of optical switching performance by means of femtosecond pump-probe technique, and different ways to lower the pump power of optical switching to facilitate practical applications in optical information processing. Finally, a brief summary and a perspective of future work are provided.     

Beyond the absorption-limited nonlinear phase shift with microring resonators

We show that the nonlinear phase shift produced by a ring resonator constructed from a given nonlinear optical material can be greater than the phase shift produced by a single pass through an infinite length of the same material when linear and nonlinear absorption are taken into consideration. The figure of merit (defined by the phase shift times the throughput) also improves for the ring resonator over that of the native nonlinear absorbing material. We finally show that these benefits of using the ring resonator as a nonlinear phase-shifting element can enhance the switching characteristics of a Mach-Zehnder interferometer.     

Resonant nonlinear optics of backward waves in negative-index metamaterials

The extraordinary properties of resonant four-wave mixing of backward and ordinary electromagnetic waves in doped negative-index materials are investigated. The feasibility of independent engineering of the negative refractive index and the nonlinear optical response as well as quantum control of the nonlinear propagation process in such composites is shown due to the coherent energy transfer from a control field to a signal field. Laser-induced transparency, quantum switching, frequency-tunable narrow-band filtering, amplification, and realizing a miniature mirrorless optical parametric generator of the entangled backward and ordinary waves are among the possible applications of the investigated processes.     

Entangled photon states generation and regeneration using a nonlinear fiber ring resonator

We propose a simple system of the entangled photon states generation and regeneration using a standard diode laser, a Mach Zehnder Interferometer (MZI) and a fiber optic ring resonator (FORR). Light from the diode laser is launched into an MZI and circulated in the FOOR, without any optical pumping components included in the system. The nonlinear light pulses are generated by a Kerr nonlinear effects type, while the resonance peaks are formed by the four-wave mixing of light pulses in the FORR. The entangled photons can be performed by using the polarization control device, and then detected by the avalanche photo-detectors, where the entangled photon visibility is plotted and seen. Similarly, the entangled photon states can be easily formed by using the appropriated coupling ratios into a fiber coupler, then into a ring resonator, i.e. without an MZI. The use of the entangled photons generation based on a fiber optic scheme for quantum teleportation, quantum key distribution via optical wireless link, and the system of the entangled photon states recovery by using a fiber ring resonator incorporating an erbium-doped fiber (EDF) have been investigated and discussed. The feasibility of dense coding using multi-entangled photons generation based on the fiber optic scheme and the effect of the entangled state walk-off along the optical fiber are also discussed, respectively.     

柱面非线性麦克斯韦方程组的行波解

柱面电磁波在各种非均匀非线性介质中的传播问题具有非常重要的研究价值.对描述该问题的柱面非线性麦克斯韦方程组进行精确求解,则是最近几年新兴的研究热点.但由于非线性偏微分方程组的极端复杂性,针对任意初边值条件的精确求解在客观上具有极高的难度,已有工作仅解决了柱面电磁波在指数非线性因子的非色散介质中的传播情况.因此,针对更为确定的物理场景,寻求能够精确描述其中更为广泛的物理性质的解,是一种更为有效的处理方法.本文讨论了具有任意非线性因子与幂律非均匀因子的非色散介质中柱面麦克斯韦方程组的行波精确解,理论分析表明这种情况下柱面电磁波的电场分量E已不存在通常形如E=g(r-kt)的平面行波解;继而通过适当的变量替换与求解相应的非线性常微分方程,给出电场分量E=g(lnr-kt)形式的广义行波解,并以例子展示所得到的解中蕴含的类似于自陡效应的物理现象.     

Performance of nonlinear photonic crystal devices at high bit rates

I investigate theoretically the performance limits for all-optical switching devices incorporating photonic crystals made of nonlinear materials operating at high bit rates. I compare two switching techniques--shifting of the photonic bandgap and the more traditional interferometric method enhanced by slow wave propagation in photonic crystals-and show that the latter always has an advantage. I also demonstrate that the benefits provided by the photonic crystal in the interferometer are still severely limited by the dispersion and become significant only in materials combining high nonlinearity, high index contrast, and high damage threshold.     

微扰的耦合非线性薛定谔方程的近似求解

将直接微扰方法应用于可积的含修正项的非线性薛定谔方程，通过近似解与精确解的比较确定了直接微扰方法的可靠性.继而，将该方法应用于微扰的耦合非线性薛定谔方程，并获得了该微扰方程的可靠的近似解. 关键词： 直接微扰方法 微扰 耦合非线性薛定谔方程 近似解     

界面与低维体系的非线性光学研究

自诞生以来,非线性光学始终是物理学中的一门前沿领域,拥有引人入胜的丰富现象与广泛应用。文章结合作者近年来的研究,简要介绍了表面非线性光谱学的原理、发展与近况,及其与低维材料体系结合所拓展出的新方向。     

Low switching power 2 × 2 thermo-optic switch using direct ultraviolet photolithography process

A Multimode Interferometers–Mach Zehnder Interference (MMI–MZI) polymer 2 × 2 thermo-optic switch is proposed using the thermo-optical effect of polymer materials and fabricated by simple direct ultraviolet photolithography process. We utilize a cross-linkable negative photoresist as core material. Once exposed to ultraviolet light through a photomask, the waveguide strips can be obtained upon development. The experiment results show that the switch has a low switching power of less than 7.5 mW.     

Application of He's variational iteration method to nonlinear heat transfer equations

Instead of finding a small parameter for solving nonlinear problems through perturbation method, a new analytical method called He's variational iteration method (VIM) is introduced to be applied to solve nonlinear heat transfer equations in this Letter. In this research, variational iteration method is used to solve an unsteady nonlinear convective-radiative equation and a nonlinear convective-radiative-conduction equation containing two small parameters of ε₁ and ε₂ and evaluate the efficiency of straight fins. VIM can apply to the nonlinear equations with boundary or initial conditions defined in different points just with developing the correction functional using the extra parameters such as Cn, as used in this Letter.     

红外光谱辐射计探测器高阶非线性响应校正方法

针对傅里叶变换红外光谱辐射计辐射定标需要黑体辐射面充满仪器视场的技术特点,分析了由于入射光子流较高导致红外探测器产生非线性响应误差的机理.通过仿真包含非线性误差的黑体辐射数据,研究了非线性误差对光谱产生的影响,并根据卷积和交叉迭代两种校正方法,提出了适合校正高阶非线性响应误差的迭代方法—梯度下降法.利用傅里叶变换红外光谱辐射计进行辐射定标实验,对比卷积、交叉迭代和梯度下降法三种校正方法的效果,结果显示三种校正方法均可有效减小非线性误差,分别使拟合优度提高了0.15%,0.29%和0.39%,梯度下降法校正后的光谱数据更为准确.     

Mach-Zehnder interferometer switch with a high extinction ratio over a wide wavelength range

We have realized a novel Mach-Zehnder interferometer (MZI) thermo-optic switch that can operate over a much wider wavelength range than a conventional MZI switch. We constructed the novel MZI switch by incorporating a phase-generating coupler (PGC) as an optical coupler. The PGC generates a nonlinear wavelength-dependent phase, which functions as a virtual wavelength-dependent delay part that cancels out the wavelength dependence of a MZI. We fabricated the novel MZI switch on a silica-based planar light-wave circuit and achieved a low insertion loss of less than 1.6 dB and a high extinction ratio of 30 dB over a wide wavelength range of 160 nm.     

Towards the origin of the nonlinear response in hybrid plasmonic systems

Plasmonic systems are known for their distinct nonlinear optical properties when compared to purely dielectric materials. Although it is well accepted that the enhanced nonlinear processes in plasmonic-dielectric compounds are related to the excitation of localized plasmon resonances, their exact origin is concealed by the local field enhancement in the surrounding material and the nonlinearity in the metal. Here, we show that the origin of third-harmonic generation in hybrid plasmonic-dielectric compounds can be unambiguously identified from the shape of the nonlinear spectrum.     

Dual field nonlinear dielectric spectroscopy in a glass forming EPON 828 epoxy resin

Results of the dual field nonlinear dielectric spectroscopy (NDS) studies in supercooled glass forming epoxy resin EPON 828 are presented. For the NDS, changes of dielectric permittivity induced by DC (rectangular) or AC (sine-wave) pulses of a strong electric field were probed by a weak radio frequency electric field. A clear stretched exponential (x < 1) decay after switching off the DC pulse and a single exponential decay (x = 1) after switching off the AC pulse were found. The same results are presented for preliminary studies in superpressed low molecular glass former di-isobutyl phthalate. This observation may be considered as an argument for the heterogeneous picture of supercooled glass forming materials. The temperature dependences of the stationary responses related to DC and AC strong electric field excitations are also shown. The sensitivity of the applied set up made it possible to detect NDS outputs even for electric fields E(strong) < 10 kV cm(-1), qualitatively weaker than in similar 'nonlinear, dielectric' experimental studies on glass forming materials carried out so far.