ROF系统中基于SOA非线性效应的光子上变频技术研究

在光载射频（ROF）系统中,为了将承载信息的光基带信号上变频到微波／毫米波波段,本文基于半导体光放大器（SOA）中的交叉增益调制（xGM）和交叉相位调制（XPM）效应实现了光子上变频：即实现了1．25Gb／s基带信号到30GHz的毫米波信号的转换。文中分析了SOA驱动电流的变化（50～200mA）和信号光与本振光波长间...     

Characteristics of the Wavelength Converted Signal in Wavelength Conversion Based on Cross-Gain Modulation

An analytical theory describing the frequency chirp characteristics of the wavelength converted signal in wavelength conversion based on cross-gain modulation (XGM) in semiconductor optical amplifier (SOA) is derived. By computation, we can see that low input pump power, high probe power, small line-width enhancement factor and low unsaturated single-pass gain of the SOA are favorable for reducing the frequency chirp of the wavelength converted signal. The analytical results have significance in understanding and designing wavelength converters.     

Comparison of conventional and gain-clamped semiconductor opticalamplifiers for wavelength-division-multiplexed transmission systems

We compare the output spectra and data streams of a conventional 1550-nm semiconductor optical amplifier (SOA) with its gain-clamped (GCSOA) counterpart, in order to assess the impact of gain clamping on cross-gain modulation (XGM) and difference frequency generation (DFG). Whereas the conventional SOA exhibits a large amount of crosstalk due to XGM, there is virtually no XGM present in the GCSOA. However, the XGM effect in the SOA shows evidence of diminished efficiency at moderate input levels. We observe much higher DFG levels from the GCSOA (roughly 10 dB greater than the SOA). These DFG levels are such that cascaded wavelength cross-connect devices, in-line amplifiers, and even optical gates could experience inhibited performance     

Optical gain and refractive index of a laser amplifier in the presence of pump light for cross-gain and cross-phase modulation

The wavelength dependent changes in optical gain and refractive index in a Fabry-Perot semiconductor optical amplifier are measured for various detunings of the pump wavelength from the quasi-Fermi level separation. The refractive index change is nearly constant over a very large wavelength range. We also present data for the linewidth enhancement factor due to optical injection. Estimates of the carrier densities and stimulated recombination rates are made using our optical gain model based on realistic band structure calculations for a strained quantum-well laser. Our results are very useful for ultra-broad-band wavelength conversion by cross-gain and cross-phase modulation (XGM, XPM).     

Measurement of SOA Linewidth Enhancement Factor With a Sagnac Fiber Loop

We demonstrate a novel method to measure the linewidth enhancement factor ($alpha$-factor) of the semiconductor optical amplifier (SOA). We derived theoretically the quantitative relationships among the$alpha$-factor, the cross-gain modulation, the cross-phase modulation, and the contrast ratio of an SOA-based Sagnac fiber loop. We found that the$alpha$-factor value can be calculated directly from the maximum power contrast ratio measurement. Our experiment results show that the obtained$alpha$-factor fluctuates within a small range of 5.23 to 6.83 when the bias current varies from 130 to 240 mA. Compared with existing measurement methods, our method is more attractive because of its simple configuration and better stability.     

Experimental analysis of cross-phase modulation and cross-gain modulation in SOA-injecting CW assist light

Cross-phase modulation (XPM) and cross-gain modulation (XGM) in a semiconductor optical amplifier (SOA) pumped by assist light were experimentally analyzed. A simple analysis technique for evaluating the XPM separately from the XGM was proposed utilizing a polarization-discriminating delayed interferometer. An initial phase deviation and a gain recovery time in SOA with injecting assist light were quantitatively estimated.     

基于SOA互增益调制双折射效应的全光2-4电平编码转换

提出了一种利用半导体光放大器(SOA)的互增益调制(XGM)的双折射效应实现全光2-4电平编码转换的方法.两路2-电平强度调制光信号正交偏振合波后,沿SOA的主轴进入,利用SOA的偏振调制实现被调制信号光的偏振调制,通过检偏输出4-电平强度调制光,从而实现2-4电平调制的编码转换.     

Analytical Model for Cross-Gain Modulation and Crosstalk in Quantum-Well Semiconductor Optical Amplifiers

An analytical model of the dynamic characteristics of a quantum-well (QW) semiconductor optical amplifier (SOA) is developed. Closed-form expressions for the optical gain and cross-gain modulation (XGM) for arbitrary input pulses are derived. The model takes into account the carrier capture and escape transitions between the QW and the continuum states. This model is also used to derive a closed-from expression for interchannel XGM crosstalk in multichannel SOA systems. The model/analysis provides insight into the effect of the SOA parameters on the performance of a wavelength-division multiplexed system. We found that crosstalk in a multichannel SOA system can be reduced by reducing the escape lifetime.     

40 Gbit=s reconfigurable photonic logic gates based on various nonlinearities in single SOA

40 Gbit/s reconfigurable photonic logic gates with XNOR, AND, NOR, OR and NOT functions are demonstrated, based on various nonlinearities of a single semiconductor optical amplifier (SOA), including four-wave mixing (FWM), cross-gain modulation (XGM) and transient cross-phase modulation (T-XPM). Detuning optical bandpass filters are employed to enhance the SOA modulation bandwidth.     

Theoretical and Experimental Study of High-Speed Small-Signal Cross-Gain Modulation of Quantum-Dot Semiconductor Optical Amplifiers

We numerically and experimentally investigate the high-speed small-signal cross-gain modulation (XGM) characteristics of a quantum-dot (QD) semiconductor optical amplifier (SOA). From a p-doped QD SOA operating at 1.3 $mu{hbox {m}}$, high-speed small-signal XGM responses up to 40 GHz are measured from low to high injection currents and improve at high injection currents. In the numerical model, we set up about six hundred coupled rate equations, where the carrier dynamics of QD electron and hole states are considered separately and the enhanced hole occupation due to p-type doping is included. The high-speed small-signal XGM spectra are calculated at various modulation frequencies and pump-probe detunings. We identify how the two separate XGM mechanisms of total carrier density depletion (TCDD) at low injection current and spectral hole burning (SHB) at high injection current affect the high-speed small-signal XGM behavior. From the measured and calculated results, we show that high-speed small-signal XGM responses of QD SOAs can be improved by injecting more carriers to the QD excited states, which enhances high-speed XGM induced by SHB rather than by TCDD.      

基于半导体光放大器的组播实验研究

提出了一种基于半导体光放大器(SOA)的组播实验方案,首先利用谱展宽和谱切片得到多波长脉冲源,将其作为探测光并与信号光共同注入到SOA中,利用SOA的交叉增益调制(XGM)效应,信号光与每一个波长的脉冲光发生作用,在SOA输出端通过可调光带通滤波器(TBDF)得到每一波长的变换后信号,实现光信号的组播过程。在实验中,10 Gb/s的归零(RZ)码作为信号光,而由多波长脉冲源产生的4波长脉冲光作为探测光,在探测光波长附近分别得到了与编码信号光逻辑取"非"的信号。     

Measurement of carrier lifetime and linewidth enhancement factor for 1.5- mu m ridge-waveguide laser amplifier

Semiconductor optical amplifiers are used for investigation of the effective carrier lifetime and the linewidth enhancement factor. Contrary to semiconductor lasers, semiconductor optical amplifiers allow measurement at high levels of injected carrier density. The carrier lifetime and the linewidth enhancement factor are measured with a simple dynamic self-heterodyne method. Carrier lifetimes of 750 ps at the threshold current for the SOA without antireflection coating and 200 ps at high injection have been found. The linewidth enhancement factor is measured to be between 4 and 17 which fits with a simple empirical expression.<>     

Specific Features of XGM in QD-SOA

The peculiarities of a cross-gain modulation (XGM) in quantum-dot semiconductor optical amplifier (QD SOAs) related to the inhomogeneous broadening are theoretically studied. We have solved numerically the electron rate equations for the QD SOA model including an excited state, a ground state and a continuum wetting layer (WL), and the propagation equations for the pump and the signal lightwaves. It is shown that XGM in QD SOA is possible for a comparatively large detuning close to the inhomogeneous broadening because in such a case QDs with substantially different resonant frequencies interact directly through WL.     

基于SOA的全光超宽带脉冲振幅调制方案

文章基于SOA(半导体光放大器)中的XGM(交叉增益调制)效应,提出一种实现全光UWB(超宽带)PAM(脉冲振幅调制)的方案.该方案只需要一个外部光源和一个SOA,结构简单,调制速率快.利用光通信系统软件OptiSystem对该方案进行仿真,分析了光源功率、SOA的注入电流和光源波长等系统参数对UWB PAM信号性能的...     

SOA-XGM全光波长变换器的特性分析

对基于半导体光放大器交叉增益调制实现的全光波长变换器的工作特性进行了分析，归纳了要取得较好的变换效果，应在输入信号光功率、波长、偏置电流、放大器腔体长度等方面作合理的选择，使输出信号的消光比、信噪比等指标符合要求。     

Optimization of the frequency response of a semiconductor opticalamplifier wavelength converter using a fiber Bragg grating

Cross-gain modulation in a semiconductor optical amplifier (SOA) is one of the simplest techniques for all-optical wavelength conversion. However, the finite gain recovery time of the semiconductor optical amplifier causes distortion and pattern dependence at high bit rates. Here we show that filtering the output of a semiconductor optical amplifier wavelength converter with the transmission edge of a fiber grating filter improves its frequency response. The grating sharpens the transition between the bits by converting the phase modulation at the edge to useful amplitude modulation. We determine the filtering condition that produces the optimum frequency response and reduces bit-pattern dependence for nonreturn-to-zero (NRZ) data. For small modulation, the apparent frequency response increases by the linewidth enhancement factor α_H of the SOA. In this case, pattern dependence is eliminated completely by the fiber grating filter. For large modulation, pattern dependence can be substantially reduced, but not completely eliminated. We show that after spectral filtering, the residual pattern dependence of an SOA depends only on modulation depth. For a given SOA, we find the optimum grating for minimum conversion penalty at 12 Gb/s for a wide range of operating parameters. Using a fiber grating filter reduces the required optical power for conversion in a semiconductor optical amplifier     

基于半导体光放大器的波长转换技术 及其在WDM 全光网络中的应用

本文在简单地介绍了各种波长转换技术之后,对基于半导体光放大器的交叉增益调制,交叉相位调制,以及四波混频效应的波长转换技术进行了深入地分析,为了阐明波长转换技术在WDM全光网络的中的应用,研究了一种分析模型。     

增益饱和波长转换器消光比退化研究

分析了半导体光放大器增益谱特点,对交叉增益调制波长转换输出消光比进行了数值计算,并在此基础上深入分析了消光比退化的原因,为改善波长转换器性能提供了理论依据。     

Spectral broadening of stochastic light intensity-smoothed by asaturated semiconductor optical amplifier

We present calculations of the intensity smoothing of stochastic light by a semiconductor optical amplifier (SOA). We predict spectral changes of the light that are due to amplitude-to-phase coupling in the gain medium. The intensity smoothing of noisy optical signals with an SOA carries a penalty of spectral broadening (increased phase noise) that increases with increasing alpha parameter (linewidth enhancement factor). The spectral broadening also increases with increasing strength of the intensity fluctuations being smoothed     

基于SOA中XGM效应全光超宽带高斯单边信号源的研究

提出了一种基于半导体光放大器（SOA）中交叉增益调制（XGM）效应产生高斯单边信号（monocycle）脉冲的方案。该方案只需要单个外部光源和单个SOA,结构简单;采用相向的工作方式可以改善输出信号的消光比;输出的monocycle信号光只含有一个波长,在光纤传输过程中上下脉冲不会引入时间差。利用Optisystern...