Cascaded SOA configuration for NRZ-OOK to RZ-QPSK format conversion

We propose and experimentally demonstrate an all-optical format conversion from two independent non-return-to-zero on-off keying (NRZ-OOK) signals to a return-to-zero quadrature phase shift keying (RZ-QPSK) signal using two cascaded SOAs. Within each SOA, the cross phase modulation (XPM) process is properly controlled by an assistant light. After evaluating its effect on XPM, a suitable power range of assistant light is chosen for the NRZ-OOK to RZ-QPSK format conversion. In the experiment, a RZ-QPSK signal is successfully obtained with opened demodulation eye-diagrams.     

OOK-to-QPSK modulation-format conversion based on two gain-transparent SOAs

In this paper, the system scheme of on–off keying (OOK) to quadrature phase-shift keying (QPSK) format conversion is proposed, which is based on two gain-transparent semiconductor optical amplifiers (GT-SOA). GT-SOA is used as a simple all-optical phase modulator, which is no effects of cross gain modulation and four-wave mixing existing in conventional SOA. The assistant light is used to speed up the SOA carrier recovery time. The principles of OOK to QPSK format conversion are expounded. The influences of the assistant light power and signal light power on the conversions are numerically analyzed. The OOK signal can still be exactly converted to the QPSK signal with the power of OOK signal being changed within a certain range.     

Simultaneous format conversion of parallel multichannel based on FWM in symmetric highly nonlinear fiber loop

A parallel multichannel format conversion scheme for elastic optical networking based on four wave mixing （FWM） in symmetric highly nonlinear fiber loop （S-HNLF-L） is proposed and the performance is evaluated and discussed. Parallel four channels format conversion from quadrature phase shift keying （QPSK） to binary phase shift keying （BPSK） signals at 40 Gb/s is theoretically analyzed and simulated. The results are helpful for the format-adaptive elastic optical networks.     

Simultaneous implementation of all-optical OR and AND logic gates for NRZ/RZ/CSRZ ON-OFF-keying signals

An all-optical scheme for simultaneously realizing OR and AND logic gates based on three-input four-wave mixing (FWM) arising in a single semiconductor optical amplifier (SOA) is proposed and demonstrated. It has the ability to process not only conventional non-return-to-zero-ON-OFF-keying (NRZ-OOK) and return-to-zero-OOK (RZ-OOK) formats but also carrier-suppressed return-to-zero-OOK (CSRZ-OOK) format signals. Firstly, the performance of 40 Gb/s logic operation is numerically evaluated by a comprehensive dynamic SOA model considering three input signal induced FWM effect. Then, 10 Gb/s experimental demonstrations with clear waveforms and high extinction ratios (ERs) further verify the logic integrity of this scheme. Thus, the OR and AND logic gates simultaneously achieved within a single logic unit is compact and cost-effective for future optical signal processing applications.     

Generation and transmission simulation of 60 G millimeter-wave by using semiconductor optical amplifiers for radio-over-fiber systems

A novel method of the millimeter-wave (MMW) generation is proposed for Radio-over-fiber systems with low phase noise by using semiconductor optical amplifiers (SOAs). The simulation results show that the method is correct. When a pump light and a signal light are input into the SOA, the converted light induced by four-wave mixing (FWM) effect is generated. The optical MMW is generated between the signal light and converted light after filtering the pump light. The electrical MMW is obtained by beating the signal light and converted light via a photo-detector. The phase noise of the system is low because the phase difference between the signal light and converted light is stable for the FWM effect. The power of MMW is increased with the increase of the pump light power and the pump current of the SOA, is decreased with the increase of the polarization azimuths of the pump light.     

Slow and fast light in quantum dot based semiconductor optical amplifiers

Recent progress in the field of quantum dot/dash based semiconductor optical amplifiers (SOAs) for slow and fast light is discussed. Room temperature fast light has been obtained in InAs/InP QDash based SOAs by means of coherent population oscillation and four wave mixing (FWM) effects. Typical optical delays amount to 55 ps at 2 GHz. Growth optimization of the QDashes allowed us to achieve high modal gain, leading to very similar performances, e.g. gain and FWM efficiency, to those of a bulk SOA. A novel approach based on linear spectrograms is also introduced to measure the phase shift induced by wave mixing in an SOA.     

All- optical phase encoded 4-to-1 phase multiplexer using four wave mixing in semiconductor optical amplifier

Optics has already showed its potency over its electronic complements in case of superfast computing and communication systems. Semiconductor optical amplifier, (SOA) with its several nonlinear properties, plays a very crucial role in the development of high-speed all-optical processor. Multiplexer and demultiplexer are the extremely important element of the processor which takes part in utilizing different actions like encoding, decoding, routing, and the different process of data conversion and generation, etc. In this paper, the authors have proposed a scheme of phase encoded all-optical phase multiplexer using four wave mixing (FWM) property of semiconductor optical amplifier. Thus, the improved tolerance against fiber-nonlinearity and higher receiver sensitivity of phase encoding method with the fast occurring processes like FWM in SOA offers higher speed in this proposed scheme of multiplexing.     

基于PolSK调制的四波混频型超快全光译码器

提出了一种新型的基于半导体光放大器（semiconductor optical amplifier, SOA）中四波混频（four-wave mixing, FWM）效应的超快全光译码器方案,方案中采用了偏振移位键控（polarization-shift-keying, PolSK）信号光.考虑SOA的偏振相关性,建立了这种全光译码器完整的偏振相关宽带理论模型.通过数值模拟的方法,从理论上实现了超快全光译码器,并研究了两输入信号光功率、SOA注入电流和SOA的偏振相关性对全光译码器输出特性的影响. 关键词： 全光译码器 偏振移位键控 四波混频 半导体光放大器     

基于光子晶体光纤中四波混频效应的单到双非归零到归零码型转换

归零(RZ)码与非归零(NRZ)码是波分复用和时分复用系统中广泛采用的两种码型, 全光NRZ到RZ码型转换能完成从波分复用到时分复用的网络接口功能, 是未来透明光子网络中一项重要的全光信号处理技术. 提出并实验证实了一种基于色散平坦高非线性光子晶体光纤中四波混频效应的单到双NRZ到RZ码型转换方法, 将一束信号光与同步时钟脉冲同时输入色散平坦高非线性光子晶体光纤中, 通过四波混频过程, 产生两个携带该数据信息的闲频光, 从而实现了单到双的NRZ到RZ码型转换功能, 码型转换器工作波长在193 nm范围可调谐, 最大转换效率为-21 dB, 最优消光比和品质因子分别为11.9 dB和7.2. 该方法的特点在于基于光纤中的四波混频效应工作, 因而具有对调制格式和比特率透明的优点, 同时, 光子晶体光纤特有的高非线与色散平坦性, 既避免了使用传统光纤需要较长的长度, 又避免了波长设置不灵活的弊端, 并具备可进一步增加带宽的能力, 且在码型转换的同时, 实现了波长转换, 完成了双通道波长组播功能. 整个系统为全光纤设计, 结构简单, 性能可靠, 并易于与现有的光纤通信系统相容, 对促进超高速大容量光子网络的发展具有重要意义. 关键词： 码型转换 四波混频 光子晶体光纤     

Slow and fast light in quantum-well and quantum-dot semiconductor optical amplifiersInvited Paper

Slow and fast light in quantum-well (QW) and quantum-dot (QD) semiconductor optical amplifiers (SOAs) using nonlinear quantum optical effects are presented. We demonstrate electrical and optical controls of fast light using the coherent population oscillation (CPO) and four wave mixing (FWM) in the gain regime of QW SOAs. We then consider the dependence on the wavelength and modal gain of the pump in QW SOAs. To enhance the tunable photonic delay of a single QW SOA, we explore a serial cascade of multiple amplifiers. A model for the number of QW SOAs in series with variable optical attenuation is developed and matched to the experimental data. We demonstrate the scaling law and the bandwidth control by using the serial cascade of multiple QW SOAs. Experimentally, we achieve a phase change of 160° and a scaling factor of four at 1 GHz using the cascade of four QW SOAs. Finally, we investigate CPO and FWM slow and fast light of QD SOAs. The experiment shows that the bandwidth of the time delay as a function of the modulation frequency changes in the absorption and gain regimes due to the carrier-lifetime variation. The tunable phase shift in QD SOA is compared between the ground- and first excited-state transitions with different modal gains.     

All-optical wavelength conversion for 10-Gb/s NRZ payload and 2.5-Gb/s OFDM label in optical-packet-switched network

Simultaneous wavelength conversion based on four-wave mixing (FWM) for 10-Gb/s NRZ payload and 2.5-Gb/s OFDM label signals in optical switching network is experimentally demonstrated. The dual-pump scheme based on FWM in semiconductor optical amplifier (SOA) is employed and simultaneous wavelength conversion for optical packet with one optical payload of 10-Gb/s non-return-to-zero (NRZ) on-off keying (OOK) signals and one optical label of 2.5-Gb/s OFDM signals are realized. The bit-error-rate performance is evaluated for both payload and label after wavelength conversion.     

Data-aided channel estimation and frequency domain equalization of minimum-shift keying in optical transmission systems

We demonstrate a digital optical communication system based on minimum shift keying （MSK） signal transmission with coherent detection. 5-Gb/s MSK signal can transmit over a 160-km standard single mode fiber （SSMF） without phase compensation. At the receiver, we use data-aided channel estimation and frequency domain equalization （FDE） techniques in the digital signal processing （DSP） algorithm, then analyze its performance characteristics compared with quadrature phase shift keying （QPSK） format. The simulation results show that the MSK format will be a potential candidate for next-generation access network.     

A Novel Method for Wavelength Conversion with Dual-pump Four-wave Mixing in a Semiconductor Optical Amplifier

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半导体光放大器中垂直双抽运四波混频效应的理论研究

建立了输入信号光偏振方向任意情况下的半导体光放大器(SOA)中 垂直双抽运四波混频(FWM)效应的完整宽带理论模型. 以基于SOA的垂直双抽运FWM型全光波长转换器为例, 通过数值模拟的方法, 理论研究了输入信号光与两抽运光功率、两抽运光与信号光之间的波长失 谐量和输入信号光偏振方向等工作参数对SOA的垂直双抽 运FWM效应及基于SOA的垂直双抽运FWM型波长转换器特性的影响.     

Analysis of non-linear refractive index influences on four-wave mixing conversion efficiency in semiconductor optical amplifiers

In this paper, we have analyzed the influences of non-linear refractive index on the four-wave mixing (FWM) characteristics in semiconductor optical amplifiers (SOAs). It has been shown that the generated FWM signal characteristics can be modified due to the variation of non-linear refractive index of the SOA's medium. The wave propagation in the SOA has been modeled using the nonlinear propagation equation taking into account gain spectrum dynamics, gain saturation, which depends on carrier depletion, carrier heating, spectral hole-burning, group velocity dispersion, self-phase modulation and two photon absorption. Simulation of optical wave evolution in the SOA has been carried out using the finite-difference beam propagation method (FD-BPM) both in time and spectral domains. Our simulation results confirm that higher FWM conversion efficiency and lower time bandwidth product are achieved for higher absolute values of non-linear refractive index. Moreover, non-linear refractive index is more efficacious for high power propagated waves in SOAs. Finally, we have studied the modification of waveguide refractive index due to the propagation of optical pulses. We have also shown that when |n₂|=1 cm²/TW, refractive index variation is in the order of 10^?4 to 10^?7 for high and low power input pulses, respectively.     

A Novel Method for Wavelength Conversion with Dual-pump Four-wave Mixing in a Semiconductor Optical Amplifier

Using a semiconductor-fiber ring laser, a novel method for the all optical wavelength conversion based on dual-pump four-wave mixing (FWM) in a semiconductor optical amplifier (SOA) is demonstrated. For the input signal with different wavelengths, only one external pump is needed. This scheme can simplify the dual-pump FWM in SOA and has nearly constant conversion efficiency and signal-to-noise ratio (SNR) over 50nm range of wavelength shifts.     

基于半导体光放大器四波混频效应的多种调制格式的波长转换实验

实验报道了利用半导体光放大器(SOA)的四波混频(FWM)效应实现多种码型的波长转换.其中对于非归零(NRZ)信号实现了从单信道到三信道的多波长转换.调制速率从10 Gb/s到40 Gb/s均实现多波长转换.对于归零(RZ)信号分别实现了20 Gb/s和40 Gb/s的RZ格式的波长转换和40 Gb/s的载波抑制归零(CSRZ)格式的波长转换,利用光纤布拉格光栅(FBG)作为带陷滤波器消除共轭光和抽运光之间的串扰.对于非归零差分相移键控(NRZ_DPSK)信号分别实现了20 Gb/s和40 Gb/s的波长转换,利用实验室自制的光纤延时干涉仪进行NRZ-DPSK信号的解调.基于FWM效应的转换光的输出消光比大于7 dB,转换后消光比退化约为3 dB.     

Theory of pulse propagation and four-wave mixing in a quantum dot semiconductor optical amplifier

A theory, combining the relations of pulse traveling into quantum dot (QD) semiconductor optical amplifier (SOA) with the four-wave mixing (FWM) theory in these SOAs, is developed. Carrier density pulsation (CDP), carrier heating (CH), and spectral hole burning (SHB) contributions on FWM efficiency are discussed. Effect of QD ground state and wetting layer are included. An additional parameter appears in the gain integral relation of QD SOAs. An equation formulating pulses in the QD SOAs is introduced. We have found that FWM in QD SOAs is detuning and is pulse width dependent. For short pulses, CH is dominant at high detunings (10–100 GHz) while at higher detunings (>100 GHz) the SHB is the dominant one. Undesired paunch behavior is shown in QD SOAs then, CDP must be reduced.     

Comparison of the compensation effects of fiber nonlinear impairments with mid-span optical phase conjugation between PDM CO-OFDM system and PDM QPSK system

The compensation effects of fiber nonlinearity in 112 Gb/s polarization division multiplexing(PDM) coherent optical systems by mid-span optical phase conjugation(OPC) based on four wave mixing(FWM) effect are studied. Comparisons of the compensation results between PDM coherent optical-orthogonal frequency division multiplexing(CO-OFDM)system and the single carrier(SC) PDM quadrature phase shift keying(QPSK) system are provided as well. The results demonstrate that nonlinear compensation effect with mid-span OPC in PDM CO-OFDM system is much more obvious than that in SC PDM QPSK system.     

Wavelength conversion in optical transport networks

The introduction of optical technology in the path layer of a transport network is analyzed; in particular, the impact of all-optical wavelength conversion is examined. Two basic optical cross-connect schemes based on space switching and on wave-length switching, respectively, and two types of wavelength converters are considered. The wavelength converters are, respectively, based on four-wave miring (FWM) in semiconductor optical amplifiers (SOAs) and on cross-phase modulation (XPM) obtained by two SOAs put in an interferometric configuration. An analysis of transmission performances of optical transport networks employing both types of wavelength conversion and both the node architectures is reported. The performances are evaluated by means of a system modeling that facilitates considering physical phenomena occurring during transmission and all the important transmission impairments. The analysis reveals that both the types of converters can be employed with different features and limitations, according to the considered network and switching architecture.