High-speed, all-optical XOR gates using semiconductor optical amplifiers in ultrafast nonlinear interferometers

We will review three recently-proposed high-speed, all-optical Exclusive OR (XOR) gates operating at 40 and 85?Gb/s, which were demonstrated using ultrafast nonlinear interferometers (UNIs) incorporating semiconductor optical amplifiers (SOAs). The first 40-Gb/s XOR gate was obtained using a dual UNI configuration. The second is a 40-Gb/s XOR gate without additional probe beam required, where the only inputs launched into the setup were data A and B. The XOR logic of data A and B is the sum of two components (A)B and(A)B , each of which was obtained from the output of UNI via cross-phase modulation (XPM) in SOAs. Furthermore, an 85-Gb/s XOR gate is, by far, the fastest XOR gate realized by SOAs, which was also demonstrated using a dual UNI structure. The operating speed of the XOR gate was enhanced by incorporating the recently proposed turbo-switch configuration. In addition, the SOA switching pulse energies of these XOR gates were lower than 100 fJ.     

基于QD-SOA-XGM的全光逻辑或非门研究

为了改善基于交叉增益调制效应的量子点半导体光放大器全光逻辑或非门的性能,研究了QD-SOA-XGM全光逻辑门的码型效应特性,用两个连“1”脉冲和单个“1”脉冲的峰值功率来衡量,即P30/P20。研究结果表明:第一级输入电流越小,逻辑或非门的性能越好,而第二级输入电流对或非门性能影响很小;在一定范围内,输入连续光功率越大、有源区长度越长、有源区宽度越宽、最大模式增益越大、损耗系数越小,或非门输出效果越好。     

Comprehensive analysis of two cascaded semiconductor optical amplifiers for all-optical switching operation

This paper presents numerical calculations and experimental results for two cascaded semiconductor optical amplifiers (SOAs) in a counterpropagating configuration for an all-optical switching operation. A detailed theoretical analysis with regard to the gain evolution and the extinction ratio (ER) through the SOAs' cavities show that the two cascaded SOAs have improved performance over the single SOA configuration. A measured ER up to 20 dB is obtained for close contra-directional signal wavelengths and for a wide range of optical input powers. An all-optical switching operation is realized for 2.5-GHz data pulses, and its feasibility is demonstrated with an ER higher than 12 dB over a wide range of wavelength.     

基于LOA-XGM全光逻辑与门的理论研究

提出了基于线性光放大器(LOA)的交叉增益调制(XGM)原理来实现全光逻辑与(AND)运算的理论模型,通过Simulink模块构建,使其更好地仿真出逻辑输出结果,并且分析不同参数对与输出结果的影响。结果表明:由于LOA利用有源区两侧的分布式布拉格反射镜(DBR)对入射光的增益形成了很好的钳制,使其具有良好的线性增益特性,因而利用级联LOA实现逻辑门运算时所发生的畸变远比在SOA中小;适当地选择输入信号光的波长范围和光功率,会得到更优的逻辑与运算结果。     

Ultrafast all-optical AND gate based on cascaded SOAs with assistance of optical filters

An ultrafast all-optical logic AND gate is realised based on two cascaded Semiconductor optical amplifiers (SOAs) each followed by an optical filter to accelerate the effective recovery process of the SOAs. 40 Gbit/s operation with return-to-zero signals has been achieved with SOAs, the 90-10% recovery time of which is much greater than the single bit period. Clear open eyes with quality factor of 6.3 are observed. The proposed AND gate has a potentially loose requirement on input pulse width     

Reconfigurable All-Optical Logic Gates for Multi-Input Differential Phase-Shift Keying Signals: Design and Experiments

Differential phase-shift keying (DPSK) signals are promising candidate for the long-haul transmission systems. However, the development of the all-optical signal processing techniques for the DPSK signals is still in its infancy, especially the all-optical logic operations. In this work, a general scheme for reconfigurable logic gates for multi-input DPSK signals with integration possibility is proposed. Benefiting from the optical logic minterms developed by two kinds of optical devices, i.e., optical delay interferometers and semiconductor optical amplifiers (SOAs), target logic functions can be realized by combining specific minterms together. The scheme is reconfigured by changing the phase control of the delay interferometers or the input wavelengths. The latter approach was adopted in the experimental trials. Although the outputs of the scheme are on-off keying (OOK) signals, the data format is compatible with all-optical decision circuits where OOK format is preferred. Two- and three-input experiments are carried out at 20 Gbit/s with nonreturn-to-zero DPSK signals. Various logic operations are demonstrated, including full sets of two- and three-input minterms, AND, NOR, XOR, and XNOR logic operations where the AND and NOR logic are derived simultaneously and the XOR and XNOR logic are convertible. The optical SNR as well as the Q-factor of the two- and three-input results are measured and compared. It shows that the input powers to the SOAs are critical in achieving good extinction ratio and the Q-factor of logic results degrades when several minterms are combined. The recovery time of the SOAs need to be optimized as well. Finally, the scaling issues of the scheme are discussed.     

All-optical multiple logic gates with XOR, NOR, OR, and NAND functions using parallel SOA-MZI structures: theory and experiment

The authors have proposed, simulated, and experimentally demonstrated all-optical multiple logic gates using two parallel semiconductor optical amplifier (SOA)-Mach-Zehnder interferometer (MZI) structures that enable simultaneous operations of various logic functions of XOR, NOR, OR, and NAND. The proposed scheme, which is optimized by adjusting the optical gain and phase differences in SOA-MZI structures with creative and systematic method, has great merits to achieve the reshaped output pulses with high extinction ratio and enable the high-speed operation at over 10 Gb/s through performance enhancement of SOAs. Its validity is confirmed through simulation and experiments at 2.5 and 10 Gb/s, respectively.     

半导体光放大器的增益透明电流测量方法研究

半导体光放大器(SOA)作为全光集成器件的核心,在全光通信和光纤传感等领域中具有重要的应用前景。值得关注的是,半导体光放大器的材料增益透明决定了它的快慢光过渡点和信号增益的起始点,因此准确测量其材料增益透明对应的注入电流,对于SOA的全面应用具有重要意义。提出了一种测量SOA材料增益透明电流的方法,并深入分析了其特点。依据材料增益透明时SOA的输出功率与入射光偏振无关的特性,实验测量了不同输入光功率条件下,入射光偏振态对输出功率影响最小时,SOA的注入电流。利用上述方法,准确地测量出给定波长输入待测SOA的增益透明电流为155mA。该方法为实现其他类型任意波长注入时SOA增益透明电流的测量提供了参考,为其全面应用奠定了基础。     

All-optical logic NXOR based on semiconductor optical amplifiers with the effect of amplified spontaneous emission

The performance of all-optical logic NXOR gate based on semiconductor optical amplifiers Mach-Zehnder interferometer(SOAs-MZI)is simulated.The effects of amplified spontaneous emission(ASE)and the input pulse energy on the system’s quality factor are studied.For the parameters used,the all-optical logic gates using SOAs are capable of operating at speed of 80Gbit/s.     

基于级联半导体光放大器实现全光逻辑与门的改进方案

基于级联半导体光放大器(SOA)实现全光逻辑与门的方案中,第一级输出信号质量直接影响逻辑与运算结果.采用载流子恢复较慢的体材料半导体光放大器用于第一级转换,在10 Gbit/s以上得不到理想的转换结果,限制了该方案实现逻辑与门的速率.利用光纤延时干涉仪(DI)和第一级半导体光放大器级联可以改善第一级输出信号质量,从而有效提高第二级全光逻辑与门的实现速率.阐述了改进方案中延时干涉仪的作用,并进行了数值模拟.根据实验结果,采用载流子恢复较慢的半导体光放大器级联延时干涉仪能够实现高速归零(RZ)信号和非归零(NRZ)信号的反码,从而得到较高速率的全光逻辑与门.实验实现了20 Gbit/s的伪随机归零和非归零信号的全光逻辑与门,对40 Gbit/s的结果进行了分析和讨论.     

Experimental study on all-optical half-adder based on semiconductor optical amplifier

We demonstrate a novel all-optical haft-adder based on two semiconductor optical amplifiers （SOAs）. Two optical bandpass filters are used to select the two idlers generated by four-wave mixing （FWM） effect of the first SOA. Therefore, the AND gate and XNOR logic are realized simultaneously. The second SOA acts as a NOT gate, in which the NOR logic is achieved with the input of the logic XNOR. As a result, the output is the sum of the two input bits and the carry. In the experiment, all-optical haft-addition calculation is achieved between two 10 Gb/s signals.     

基于级联半导体光放大器中交叉增益调制效应的新型全光逻辑与门

提出一种基于级联半导体光放大器(SOA)中的交叉增益调制(XGM)效应实现的全光逻辑与门新方案。该方案采用单端耦合半导体光放大器提高第一级半导体光放大器输出的消光比，合理控制第二级半导体光放大器的输入光功率，实现了两路2．5Gbit／s非归零(NRZ)信号的逻辑与运算。详细阐明了基于级联半导体光放大器的与门的工作原理和实验方案，分析了实验结果。根据实验结果，发现第一级半导体光放大器输出信号的消光比和信噪比对逻辑与运算结果影响较大，利用单端耦合半导体光放大器后能改善逻辑与运算结果，第二级半导体光放大器的输入抽运光功率对逻辑与运算输出的信号质量有较大的影响。合理控制这些因素，可以有效地提高该逻辑与门的输出特性。     

All-optical NOR gate based on injection-locking effect in a semiconductor laser

A scheme for all-optical NOR logic gate is proposed based on injection-locking effect in a semiconductor laser. In this scheme, signal light injection into the laser will cause frequency shift of laser modes, as a result, the probe light into the laser can be switched between injection-locked and unlocked status, and its output power will be modulated. Theoretical analysis for this scheme is carded out by using a model to describe the dynamics of the injection-locked laser. By numerical simulation, the influence of laser bias current, laser length, injected signal power and signal frequency on the output performance of NOR logic gate is quantitatively analyzed.     

7 Gbit/s optical JK flip flop design with two optical AND gates and NOR gates

This study presents a simple methodology for implementation of all optical JK flip flop for future optical high speed networks. The scheme utilizes electronic model of JK flip flop for implementation of all optical JK flip flop at the bit rate of 7 Gbit/s. Firstly, all-optical AND and NOR gates are implemented. Furthermore, with the combination of these basic gate structures, the optical model of JK flip flop is verified. This structure makes use of two optical AND gates and two optical NOR gates. This technique uses a semiconductor optical amplifier (SOA) as the nonlinear medium to produce considerable amount of cross gain and cross phase modulation to attain truth table conditions of optical JK flip flop. In this method, the number of gates is reduced as compared to earlier schemes. Rise time and fall time of 5.6 ps with contrast ratio more than 60 dB are achieved in this design.     

Simultaneous All-Optical and and nor Gates for NRZ Differential Phase-Shift-Keying Signals

A scheme for realizing all-optical logic AND and NOR gates simultaneously for nonreturn-to-zero differential phase-shift-keying signals is proposed and demonstrated based on a delayed interferometer and two semiconductor optical amplifiers. Experimental demonstration at 20 Gb/s verifies the logic integrity of this scheme. The final results are derived in the ON-OFF keying format with clear open eyes and extinction ratios over 10 dB. The proposed scheme can be expanded to realize arbitrary logic gate.     

160 Gb/s photonic crystal semiconductor optical amplifier-based all-optical logic NAND gate

The performance of an ultra-fast all-optical logic NOT-AND gate using photonic crystal semiconductor optical amplifiers (PCSOA)-based Mach–Zehnder interferometers is numerically analysed and investigated. The dependence of the quality factor (Q-factor) on the input signals’ and PCSOA operating parameters is examined, with the impact of amplified spontaneous emission included so as to obtain realistic results. The achieved Q-factor is 18 at 160 Gb/s, which is higher than when using conventional SOAs.     

Extremely fast high-gain and low-current SOA by optical speed-up at transparency

We propose a new configuration for semiconductor optical amplifiers (SOAs), called optical speed-up at transparency (OSAT), which allows to speed up the gain recovery of SOAs and their saturation power without sacrificing the gain, nor increasing the applied current. The proposed configuration is particularly well-suited for high-speed WDM or OTDM applications. It consists of an optical CW-signal injected at the transparency point of the SOA. This setup is potentially integrable on a single chip, and still relatively flexible once the device is realized.     

All-optical NAND gate using integrated SOA-based Mach–Zehnder interferometer

An all-optical NAND gate using integrated SOA-based Mach–Zehnder interferometer is proposed and demonstrated for the first time. Numerical analysis shows the switching window of the proposed NAND gate, which is synchronous with the dynamic gain experienced by the probe pulses. The effects of the SOA and input data parameters on the switching performance are discussed. The operation of the proposed NAND gate with 10 Gb/s RZ pseudorandom bit sequences is simulated and the results demonstrate its effectiveness. This NAND gate could provide a new possibility for all-optical routing in future all-optical networks.     

Low-power all-optical gate based on sum frequency mixing in APEwaveguides in PPLN

We present an all-optical gate implemented in periodically poled lithium niobate (PPLN) (LiNbO₃). Efficient mixing is achieved by using a phase-matched guided-wave interaction. A control wave at 1.537 μm is used to gate a signal at 1.552 μm, where a control power of 185 mW is sufficient to achieve 96% depletion of a low-power signal. A simple switch configuration is described whereby high-contrast low-power all-optical switching can be performed     

Optical Reshaping of 40-Gb/s NRZ and RZ Signals Without Wavelength Conversion

We experimentally demonstrate a scheme for all-optical reshaping at 40 Gb/s that is wavelength preserving and transparent to both nonreturn-to-zero and return-to-zero on-off keying signals. Eye-diagram reshaping is confirmed by means of bit-error rate versus threshold measurements on both modulation formats. The scheme is based on cross-gain compression in an semiconductor optical amplifier (SOA) and uses two SOAs that are not in interferometric configuration. Due to its working principle, this method is polarization-independent and suitable, in principle, for higher bit rates.