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.     

Small and large signal analysis using circuit model of InGaAs/InP based uni-travel carrier photodiode

An equivalent circuit model of uni-traveling carrier photodiode (UTC-PD) is developed from integral carrier density rate equation and few important properties of the device such as the electrical and optical characteristics are evaluated by employing advanced device physics. Circuit model incorporates chip and package parasitic of the device quite simply to provide practical behaviour of UTC-PD. We have developed small signal ac circuit model which is useful for the analysis of low power modulation characteristics of the device and dc circuit model which is advantageous to find wavelength dependent responsivity fairly accurately. At high optical input power the device bandwidth is found to be increased through enhancement of self-induced field in the absorption region and high output power can be derived from the device when absorption width is large. Such condition calls for large signal analysis. We have developed large signal circuit model by combining few mathematical transformations with small signal circuit model with different circuit element values. Our large signal model is unique that the same circuit can be used for both small and large signal analysis. With large signal model the optical power induced bandwidth improvement and output photocurrent saturation are explained. Large signal model is validated through linearity and IP3 analysis which found close agreement with the measured results.     

基于单端耦合SOA的波长转换器啁啾特性分析

提出了一种基于单端半导体光放大器（SOA）的交叉增益调制型（XGM）全光波长转换器结构, 并针对这种结构建立了动态理论模型, 以这个模型为基础分析了泵浦光功率、探测光功率、输出消光比、输入消光比对转换后信号啁啾的影响. 结果表明利用这种结构的波长转换器实现波长转换, 在提高输出消光比的同时也降低了转换光的啁啾, 较传统的波长转换器是一种改进.     

Contrast ratio and hysteresis width of optical bistability in quantum-dot vertical-cavity semiconductor optical amplifiers integrated with MEMS membrane

The characteristics of optical bistability in quantum dot vertical cavity semiconductor optical amplifier integrated with MEMS membrane have been investigated, and a closed-form model is derived taking into account the effect of the quantum dot discrete states and the membrane deflection and reflectivity. We show that small membrane deflection significantly adjusts the resonant wavelength, the contrast ratios and the hysteresis width. The shape of the input–output characteristics of the device can be adjusted to display clockwise, butterfly and counterclockwise hysteresis loops depending on the membrane deflection and the initial wavelength detuning. Our analysis reveals that the contrast ratios of the upper and lower bistable levels are totally different. Also, it has been shown that the characteristics of the bistability are strong function of the active layer linewidth enhancement factor and the membrane reflectivity.     

Analytic approach to the small-signal frequency response of saturated semiconductor optical amplifiers using multisection model

An analytic solution derived by multisection model to the small-signal frequency response (SSFR) of wavelength conversion based on cross-gain modulation (XGM) in semiconductor optical amplifiers (SOAs) is presented. The result contains details that can affect the characteristics of SSFR significantly more than previous ones.     

基于LOA-XGM波长转换器消光比特性的数值分析

建立了基于一种新型光放大器（线性光放大器）的交叉增益调制波长转换理论模型.对交叉增益调制波长转换器同向工作方式下的输出消光比进行了分析,讨论了抽运光和探测光的波长和功率等参量对转换后信号消光比特性的影响.结果表明:随着抽运光波长的增加,波长转换器的输出消光比逐渐增大,但对于探测光波长的增加,消光比反而减小；增加抽运光功率和减小探测光功率都可以获得较大的消光比；波长向下转换时的消光比明显优于向上转换时的消光比.     

基于量子点半导体光放大器全光波长变换特性

从光电集成电路的角度出发,根据量子点半导体光放大器(QD-SOA)中载流子跃迁速率方程和光场传输方程,建立了QD-SOA等效电路模型,并通过电路仿真的方法对QD-SOA的增益谱、饱和增益特性等进行了仿真和分析;利用QD-SOA的交叉增益调制研究了速率分别为40Gbps、100Gbps和160Gbps时的波长转换特性,并分析了不同的偏置电流、功率的信号光和探测光对输出信号消光比和Q值的影响,其转换速率可达到100Gbps,消光比ER约为10dB,Q值约为2.2.该研究对提高基于QD-SOA的交叉增益调制波长转换的性能具有指导意义.     

Filter-free ultrawideband generation based on semiconductor optical amplifier nonlinearities

A filter-free scheme for ultrawideband (UWB) generation with single semiconductor optical amplifier (SOA) is proposed and demonstrated. A pair of polarity-reversed optical pulses is generated due to cross gain modulation (XGM) in the pump-probe scheme, whereas the amplified pump pulse becomes sharp at its leading edge such that the power peak is shifted forward. Hence, the combination of the pump and probe signals at the SOA output is quasi-monocycle shape. Our scheme is an improved scheme to avoid exploiting optical filters and time-delay devices. The generated UWB radio frequency spectrum shows good stability when the input probe power varies from −10 dBm to 6 dBm, the probe wavelength varies in the whole C-band, and the bias current varies from 100 mA to 240 mA. Although the generated quasi-monocycle deviates from a standard Gauss monocycle to some extent, the frequency spectrum conforms to the UWB regulation. Two SOAs with different XGM dynamics are compared in generating UWB signals.     

基于XGM的SOA波长变换器噪音特性分析及优化设计

利用动态载流子恢复时间可以精确模拟基于交叉增益调制的SOA全光波长变换器的饱和增益效应,本文将SOA分段ASE噪音功率和分段动态模型结合,得到沿长度分布的ASE噪音功率,并讨论了偏置电流、泵浦光和探测光的波长、功率、SOA长度对消光比和信噪比的影响理论计算结果表明,大的偏置电流有利于提高消光比和信噪比;对于一定的输入波长,相对较大的泵浦光和相对较小的探测光变换效果好;SOA的长度存在最佳值.     

Optical ultrawideband monocycle pulse generation based on cross-gain modulation in a semiconductor optical amplifier

A novel method for generating ultrawideband (UWB) monocycle pulses based on cross-gain modulation (XGM) in a semiconductor optical amplifier (SOA) is proposed and experimentally demonstrated. Thanks to the XGM in the SOA, a pair of polarity-reversed optical Gaussian pulses is generated at the output of the SOA, to which a Gaussian pulse pump and a continuous-wave probe are applied. The two polarity-reversed optical pulses are then time delayed by two cascaded fiber Bragg gratings to introduce a time delay difference. A UWB monocycle pulse with a full width at half-maximum of 48 ps and a fractional bandwidth of 188% is generated at the output of a high-speed photodetector.     

All-optical wavelength multicasting exploiting cross-phase modulation in a dispersion-flattened nonlinear photonic crystal fiber

An all-optical wavelength multicasting scheme with tunable output wavelength and channel numbers has been proposed and demonstrated based on cross-phase modulation (XPM) in a dispersion-flattened highly nonlinear photonic crystal fiber. We show that the input signal wavelength can be simultaneously converted to four different wavelengths by filtering the broadened sideband of the continuous-wave (CW) probe beams. The experiments are carried out to investigate into the wavelength tunability, and exploit the dynamic characteristics with variable input signal powers, the ability of multicasting channels scalable, and the relationship between the multicasting signal qualities with variable optical band-pass filter (OBPF) bandwidth. The results indicate that the proposed wavelength multicasting scheme has the advantages of simple structure, efficient operation in a wide wavelength range, as well as transparent to bit rates. Moreover, the system can be upgraded to generate more multicasting channels by increasing the number of CW probe beams.     

Theoretical Study of SOA-Based Wavelength Conversion with NRZ and RZ Format at 40 Gb/s

We theoretically discuss 40 Gb/s semiconductor optical amplifier （SOA）-based wavelength conversion （WC） using a detuning optical bandpass Jilter based on ultrafast dynamic characteristics of SOA. Both the inverted and noninverted WCs are obtained by shifting the filter central wavelength with respect to the probe wavelength when input data signal is in return-to-zero （RZ） format. However, we can obtain format conversion from nonreturn- to-zero （NRZ） to pseudo-return-to-zero （PRZ） and inverted WC when the input signal is in NRZ format.     

有源-吸收分段式脊型波导半导体激光器的光双稳激射特性

本文报道了一种脊型波导有源-吸收分段结构半导体激光器中的光双稳输出特性的实验研究结果及其理论分析.给出了实验中发现的获取最大光滞回线宽度(Hysterisis)、所对应的器件结构参数以及电注入水平.此外,一种光线近似理论模型被采用来求解光输出特性从而得到了与实验近似一致的结果.     

A NOVEL SCHEME FOR XGM WAVELENGTH CONVERSION BASED ON SINGLE-PORT-COUPLED SOA

A novel scheme for wavelength conversion based on cross-gain modulation (XGM) in single-port-coupled semiconductor optical amplifier (SOA), in which the input and output share one port, is brought forward. Experimental results and theoretical analysis show that this scheme can be achieved with simple implementation, high output extinction ratio and large input dynamic range. Based on this novel scheme, 2.5 Gbit/s wavelength up conversion with 12.8 nm span has been demonstrated with the output extinction ratio as high as 15 dB.     

基于啁啾光纤光栅的粮仓测温网络研究

为了解决传统光纤光栅测温系统中单根光纤上带光纤光栅探头数量少、回波光强弱以及复用能力差的问题,设计研究了基于啁啾光纤光栅的测温系统。通过啁啾调制技术提高了回波光的带宽,从而增强了信号的可处理性并大大提高了带探测点位的数量。推导了啁啾调制的光栅周期表达式,给出了调制方法及波长范围。实验采用LPT-102型宽带光源与F-P光纤解调仪等,调制带宽为1 535.0～1 555.0 nm,并结合WR-201型温度传感器作标定。对20～60 ℃范围内每1 ℃改变进行测试,实验结果显示,传统光纤光栅探头与啁啾光纤光栅探头的测试温度误差相近,都符合设计要求。相比而言,啁啾FBG的测试数据对应的波长偏移具有较为明显的单调线性的特征,即数据稳定性更高,同时,采用啁啾FBG的系统带光纤光栅探头数量明显优于传统光纤光栅测温系统。由此可知,本系统在不增加光纤个数及不降低温度测试精度的基础上,实现了大幅提高带探测点位数量的设计要求。     

Erbium doped fiber ring laser for optical wavelength conversion

We experimentally investigate the gain saturation effect of a piece of 8 m long Erbium doped fiber (EDF), we introduce a theoretical model for the EDF ring loop, and our simulation results show very good cross-gain modulation (XGM) and wavelength conversion. We also experimentally investigate the XGM in an EDF ring loop system. Based on the study of the XGM in the EDF ring loop system, a wavelength conversion is designed with the EDF ring loop system. The EDF ring loop systems as a wavelength conversion is experimentally demonstrated by converting a sinusoidal modulated optical signal at wavelength of 1551 nm to an optical signal at wavelength of 1553.3 nm.     

Imaging characteristics of a birefringent lens under broadband illumination

This paper reports the imaging characteristics of an optical system consisting of a lens made of a uniaxial birefringent crystal sandwiched between two linear polarizers under polychromatic input illumination. The optic axis of the birefringent crystal is perpendicular to the lens axis and for an initial investigation, the spectral profile of the input beam is considered to be uniform for all wavelengths. The study reveals that if the variation of the birefringence parameters of the device with the wavelength is less, a larger bandwidth may be used without considerably deviating from the imaging characteristics under strictly monochromatic illumination. The nonlinear variation of birefringence with wavelength results in an asymmetric axial irradiance distribution. This obviates an optimal operating wavelength as well as a proper choice of the lens material. It is found that no appreciable change in image quality under diffraction-limited condition results for an input beam having 632 nm operating wavelength and 60 nm bandwidth. Therefore, it may be feasible to use this system with a white light source in conjunction with a wavelength-selective filter.     

基于多电极单端耦合半导体光放大器的交叉增益调制型波长转换器

提出了一种新型的基于多电极单端耦合半导体光放大器(SOA)的交叉增益调制(XGM)型波长转换方案，并建立了这种波长转换器完整的宽带理论模型.通过数值模拟的方法，比较了基于多电极单端耦合SOA的XGM型波长转换和基于单电极单端SOA的XGM型波长转换的输出特性，结果表明前者的输出消光比优于后者，而且啁啾特性也略有改善. 关键词： 多电极 波长转换 单端耦合半导体光放大器 交叉增益调制 消光比 啁啾     

高速CCTS光双稳激光器的研究

从速率方程出发对双区共腔（ｃｏｍｍｏｎ－ｃａｖｉｔｙｔｗｏｓｅｃｔｉｏｎ简称ＣＣＴＳ）光双稳激光器进行了精确的理论分析与计算，并对其稳态特性进行了实验研究和测试，得出了定量和定性的分析结果，同时还首次发现当激光输出高态出又出现了一次光双稳和开关效应。经研究确认是量子阱探测器的自电光效应，并提出一种可集成双逻辑功能显示的新型网络模型器件。     

光纤Bragg光栅非线性开关动态特性研究

基于光纤Bragg光栅中脉冲演变遵循的非线性耦合模方程,数值分析了光纤Bragg光栅在禁带附近由非线性光学特性导致的Bragg波长偏移。仿真结果表明：随着输入信号功率的增大,光栅的布拉格波长向长波方向移动,反射峰值下降,反射带宽变窄。进一步研究了基于此效应的全光自开关特性,结果表明：此开关的稳定时间短,并且输出脉冲形状保持良好。因此,这种具有高非线性系数的光纤光栅实现的全光开关在全光信号处理方面具有广泛的应用前景。