A new approach to all-optical half-adder by utilizing semiconductor optical amplifier based MZI wavelength converter

Semiconductor optical amplifier (SOA) has already been established itself as a strong all-optical switching element for conducting super fast optical operations. Many all optical logic operations have been proposed by the use of SOA. Here in this paper the authors proposed a new method of implementing all-optical frequency encoded logic operations and half-adder by the use of SOA as well as Mach Zehnder interferometer. The advantage of frequency encoding has been strongly exploited here.     

半导体光放大器的稳态增益饱和特性

高速全光逻辑门是实现光分组交换、光计算和未来高速大容量光传输的关键器件,近年来受到广泛的关注。半导体光放大器（SOA）因为具备体积小、工作波长范围宽、响应时间短及良好的非线性特性等优点,成为研制高速全光逻辑器件的首选。采用分段模型分析了SOA的稳态增益饱和特性,通过数值求解载流子速率方程和光传输方程对其特性进行了仿真实现。结果表明,SOA在入射光功率不同时会表现出明显的非线性;在一定范围内增加光功率,SOA增益持续增加,继续增加入射光功率,SOA逐渐进入饱和吸收状态,增益反而降低。     

Interferometric ultrafast SOA-based optical switches: From devices to applications

All-optical switches are fundamental building blocks for future, high-speed optical networks that utilize optical time division multiplexing (OTDM) techniques to achieve single channel data rates exceeding 100 Gb/s. Interferometric optical switches using semiconductor optical amplifier (SOA) non-linearities perform efficient optical switching with < 500 fJ of control energy and are approaching optical sampling bandwidths of nearly 1 THz. In this paper, we review work underway at Princeton University to characterize and demonstrate these optical switches as processing elements in practical networks and systems. Three interferometric optical switch geometries are presented and characterized. We discuss limitations on the minimum temporal width of the switching window and prospects for integrating the devices. Using these optical switches as demultiplexers, we demonstrate two 100-Gb/s testbeds for photonic packet switching. In addition to the optical networking applications, we have explored simultaneous wavelength conversion and pulse width management. We have also designed high bandwidth sampling systems using SOA-based optical switches as analog optical sampling gates capable of analyzing optical waveforms with bandwidths exceeding 100 GHz. We believe these devices represent a versatile approach to all-optical processing as a variety of applications can be performed without significantly changing the device architecture.     

A novel method of developing all-optical frequency encoded memory unit exploiting nonlinear switching character of semiconductor optical amplifier

The very fast running optical memory and optical logic gates are the basic building blocks for any optical computing data processing system. Realization of a very fast memory-cell in the optical domain is very challenging. In the last two decades many methods of implementing all-optical flip-flops have been proposed. Most of these suffer from speed limitation because of low switching response of the active devices. In our present communication the authors propose a method of developing a frequency encoded memory unit based on the switching action of semiconductor optical amplifier (SOA). Nonlinear polarization rotation characters of SOA and ‘SOA based Mach-Zehnder Interferometer’ switch, i.e. ‘SOA-MZI’ switch, are exploited for the purpose of some switching action with least switching power (<−3 dB_m) and high switching contrast ratio (20 dB). Here two logic states (‘0’ state and ‘1’ state) of the memory is encoded by two different frequencies, which will remain unchanged throughout the data communication irrespective of loss of light energy due to reflection, refraction, attenuation, etc. Though the SOA based switch runs with the operational speed 100 Gb/s, still due to the presence of the other optical components in the memory unit, the overall speed of the proposed system will come down to 10 Gb/s.     

Remote optical control of an optical flip-flop

We experimentally demonstrate control of a holding-beam-enabled optical flip-flop by means of optical signals that act in a remote fashion. These optical-control signals vary the holding-beam power by means of cross-gain modulation within a remotely located semiconductor optical amplifier (SOA). The power-modulated holding beam then travels through a resonant-type SOA, where flip-flop action occurs as the holding-beam power falls above and below the switching thresholds of the bistable hysteresis. Control is demonstrated using submilliwatt pulses whose wavelengths are not restricted to the vicinity of the holding beam. Benefits of remote control include the potential for controlling multiple flip-flops with a single pair of optical signals and for realizing all-optical control of any holding-beam-enabled flip-flop.     

基于半导体光放大器中非线性偏振旋转效应单一光缓存环全光时隙交换处理能力研究

对基于半导体光放大器(SOA)中非线性偏振旋转效应(NPR)效应的单一光缓存环多数据包的全光时隙交换(TSI)处理能力进行了理论和实验研究,在使用归纳法导出单一缓存环实现多数据包全光时隙(TSI)必要条件的基础上,针对各种全光TSI操作要求得出了相应光数据包的调度方案,在实验上,以基于SOA中NPR效应的单一光缓存环实验系统,开展了多数据包全光TSI操作的实验研究,根据上述光数据包理论调度方案进行相应系统参数设定,进行了速率为10 Gb/s的3个和4个数据包的全光TSI实验,实验结果与理论预期相符合,研究成果为减少昂贵SOA元件的用量、简化基于光缓存环全光TSI系统的结构提供了可靠依据,对推进全光TSI技术的发展具有重要意义。     

半导体光放大器的光-光互作用及其应用

半导体光放大器（SOA）中的非线性系数约为普通光纤的10^9，为光子晶体光纤的10^7，而且有4种光-光互作用，即交叉增益调制（XGM）、交叉相位调制（XPM）、交叉偏振调制（XSM）及四波混频（FWM），可以灵活地组成各种光信号处理器件，如波长变换器、全光触发器、全光逻辑、全光时钟恢复、全光缓存器……等，正成为整个光信号处理的基础。文章介绍了它们的原理和简单应用。     

Theoretical analysis and performance investigation of ultrafast all-optical Boolean XOR gate with semiconductor optical amplifier-assisted Sagnac interferometer

A comprehensive theoretical model of an ultrafast all-optical Boolean XOR gate implemented with a semiconductor optical amplifier (SOA)-assisted Sagnac interferometer is presented. The model accounts for the SOA small signal gain, linewidth enhancement factor and carrier lifetime, the switching pulses energy and width and the Sagnac loop asymmetry. By undertaking a detailed numerical simulation, the influence of these key parameters on the metrics that determine the quality of switching is thoroughly investigated and simple design rules are extracted for their proper selection so as to ensure optimum operation. The obtained results are in good agreement with the published experimental measurements and confirm the feasibility of realizing the gate at 10 Gb/s with fairly high performance. The model can be extended for studying more complex all-optical circuits of enhanced functionality in which the XOR gate is the basic building block.     

增益半导体光放大器的特性

为满足半导体光放大器（SOA）在光纤到户FTTH系统接入网中的广泛应用,提出了基于光纤光栅外腔反馈型GC-SOA结构的全光增益机制,窄线宽激光光源经可变衰减器、隔离器和光纤光栅注入到SOA中,SOA的输出光经隔离器和光纤光栅送至光谱分析仪,通过光纤光栅反馈输入SOA形成钳制激光。对GC-SOA的阈值特性、增益特性及开关特性进行分析,结果表明:当注入电流小于GC-SOA的阈值电流时,增益随注入电流的增加而增加;当注入电流大于GC-SOA的阈值电流后,其增益不再随注入电流的变化而变化,实现了SOA的增益稳定,使SOA的饱和输出功率得到了提高。     

基于半导体光放大器偏振旋转的全光缓存器

全光缓存器可实现数据包在光域内的缓存,是全光路由、伞光计算以及全光交换的关键部件之一.提出了一种基于半导体光放大器(SOA)中非线性偏振旋转(PR)的光纤环型全光缓仃器结构;提出了一种利用偏振主态(PSP)寻找两个正交线偏振态以及在线实时测量光纤中偏振态的方法.通过改变SOA的注入电流,实现了对两个正交偏振态转化的控制,利用这两个正交的线偏振态,实现了信号的"写"人和"读"出.利用该结构的缓存器,实现了2.5 Gb/s的1024 bits数据包6圈的缓存.缓存后的信号波形良好.     

Design of ultrafast all-optical PolSK DMUX based on semiconductor optical amplifiers

A novel ultrahigh-speed all-optical demultiplexer (DMUX) with polarization-shift-keying (PolSK) modulation input signals is proposed. This design is based on four-wave mixing (FWM) in a semiconductor optical amplifier (SOA). For analyzing each amplifier, we use finite-difference method (FDM) based on solution of the traveling wave coupled equations. Using numerical simulation, the all-optical DMUX is theoretically realized at 40 Gb/s. We also study the relation between optical confinement factor and thickness of active layer of the SOA section successfully, and investigate the increasing effect of confinement factor on the DMUX optical output power. With this work, the confinement factor is increased from 0.3 to 0.48, and as a result, the output power approximately twice of its initial value is achieved. Moreover, the effects of polarization dependence of SOA on the output performance of all-optical DMUX for PolSK signal are theoretically investigated in detail.     

All-optical carry lookahead adder with the help of terahertz optical asymmetric demultiplexer

An all-optical model of carry lookahead adder (CLA) implemented with a semiconductor optical amplifier (SOA)-assisted Sagnac interferometer (TOAD) is presented. The model accounts for the SOA small signal gain, linewidth enhancement factor, the switching pulses energy and width and the Sagnac loop asymmetry. Adder is a very basic component in a central processing unit. The CLA is the highest speed adder nowadays. Theoritical model is presented and verified through numerical simulation. The method promises both higher processing speed and accuracy. The model can be enhanced the functionality in which carry lookahead adder is the basic building block.     

全光波长变换器消光比特性的理论研究

半导体光放大器（SOA）是具有优良非线性效应的光子器件,在光开关、波长变换、光逻辑运算中有重要的应用。从SOA载流子的速率方程和耦合波方程出发,建立了基于SOA的交叉增益调制波长变换理论模型,并利用分段模型分析方法,对SOA的交叉增益调制波长变换的消光比特性进行了详细的研究。研究结果表明,适当增大信号光功率、减小探测光功率并选择合适的波长差和SOA长度,可以有效地提高传输信号的消光比。     

SOA-assisted Sagnac switch and investigation of its roadmap from 10 to 40 GHz

Future broadband optical communications networks will rely on all-optical switches to perform a set of processing functions exclusively in the optical domain. Interferometric optical switches using semiconductor optical amplifier (SOA) nonlinearities can perform efficient optical switching with few tens of fJ control energies and short fiber lengths allowing for monolithic integration. In this paper we present work performed with a three terminal SOA-assisted Sagnac interferometer. We review all-optical Boolean AND and XOR logic results at 10 GHz and 10 Gb/s for full duty cycle and pseudo-random data pattern operation, respectively, achieved with adequate contrast ratios, remarkably low switching energies and low pattern dependence. The ability of the device to be cascaded was proved up to 10 GHz by recirculating stably for hours arbitrary pattern profiles. Finally, and in view of the extension of photonic networks single channel data rates beyond 40 Gb/s, the performance of the switch was simulated in terms of its critical parameters. The obtained results showed that full switching operation at 40 GHz or higher is feasible either by deploying gain recovery reduction techniques in bulk and quantum well SOAs or alternatively other technologically advanced optical devices, such as quantum dot SOAs.     

基于太赫兹光非对称解复用器结构的低开关能量、高线性度全光采样门实验研究

利用多量子阱结构的非线性半导体光放大器(SOA)构建的太赫兹光非对称解复用器(TOAD), 实验实现了一个开关能量低至25 fJ, 线性度高达0.99的全光采样门. 详细分析了采样脉冲功率和非对称偏移量分别对采样窗口形状、宽度和幅度的影响, 并研究了不同采样窗口宽度下TOAD的开关能量及线性度的变化规律.     

An all optical frequency encoded demultiplexer with tri-state logic

Optics has already been established its significant application over electronics using the nonlinearity of optical medium. The use of semiconductor optical amplifier (SOA) as a nonlinear medium has remarkably extended in the field of optoelectronic technology due to his high switching speed and high extinction ratio. The SOA based devices are used in multifunctional way mainly in switching, multiplexing, de-multiplexing and wavelength conversion. Here in this paper the authors propose a new demultiplexer scheme with the broad area semiconductor optical amplifier (BSOA) using the frequency encoding techniques and tri state logic. Frequency encoding techniques and tri-state logic in optics are already been established as a potential mechanism.     

Effect of amplified spontaneous emission on semiconductor optical amplifier based all-optical logic

The performances of all-optical logic gates XOR, AND, OR, NOR and NAND based on semiconductor optical amplifier (SOA) have been simulated including the effects of amplified spontaneous emission (ASE). For the parameters used, all-optical logic gates using SOA are capable of operating at speed of 80 Gb/s.     

All-optical 40 Gbits/s packet regeneration by means of cross-gain compression in a semiconductor optical amplifier

We experimentally demonstrate all-optical reshaping of 40 Gbits/s packets by using cross-gain compression in a semiconductor optical amplifier (SOA). This scheme, which is based on cross-saturation effects between two conjugate signals copropagating in a single SOA, is wavelength preserving and polarization independent and does not suffer from any transient effect at packet edges. We report evidence of noise redistribution and packet reshaping by means of the bit-error rate versus threshold measurements for different input optical signal-to-noise ratios.     

All-optical flip-flop based on vertical cavity semiconductor optical amplifiers

We report the operation of an all-optical set-reset (SR) flip-flop based on vertical cavity semiconductor optical amplifiers (VCSOAs). This flip-flop is cascadable, has low optical switching power (~10 microW), and has the potential to be integrated on a small footprint (~100 microm(2)). The flip-flop is composed of two cross-coupled electrically pumped VCSOA inverters and uses the principles of cross-gain modulation, polarization gain anisotropy, and highly nonlinear gain characteristics to achieve flip-flop functionality. We believe that, when integrated on chip, this type of all-optical flip-flop opens new prospects for implementing all-optical fast memories and timing regeneration circuits.     

All-optical switching and nonlinear optical properties of HBT in ethanol solution

This paper demonstrates an all-optical switching model system comprising a single pulsed pump beam at 355 nm and a CW He--Ne signal beam at 632.8 nm with 2-(2^\prime -hydroxyphenyl)benzothiazole (HBT) in ethanol solution. The origins of the optical switching effect were discussed. By the study of nonlinear optical properties for HBT in ethanol solvent, this paper verified that the excited-state intramolecular proton transfer (ESIPT) effect of HBT and the thermal effect of solvent worked on quite different time scales and together induced the change of the refractive index of HBT solution, leading to the signal beam deflection. The results indicated that the HBT molecule could be an excellent candidate for high-speed and high-sensitive optical switching devices.