利用光反馈半导体激光器产生超宽带混沌脉冲信号

提出了一种基于光反馈半导体激光器的混沌特性产生超宽带(UWB)信号的新方法。一个商用的通信波段半导体激光器在外腔光反馈下实现混沌振荡,输出连续波混沌激光,经由一个电吸收调制器后,被调制为一系列混沌脉冲信号。该混沌脉冲信号的频谱特性可通过调节半导体激光器的偏置电流和反馈强度进行控制。实验分别获得了中心频率为4.0 GHz、相对带宽为181%和214%的混沌脉冲UWB信号。进一步数值仿真了偏置电流和反馈系数对混沌脉冲UWB信号频谱特性的影响,实验结果与模拟验证相符。该方法实验装置简单,UWB信号频谱特性易控,可用作未来UWB光纤无线通信系统的光生微波信号发生装置。     

基于SOA和EAM的全光超宽带脉冲波形调制

提出了一种基于半导体光放大器(SOA)和电吸收调制器(EAM)实现超宽带(UWB)脉冲波形调制(PSM)的方案,利用SOA的交叉增益调制(XGM)和增益饱和效应产生高斯单边带(monocycle)信号,利用EAM的交叉吸收调制(XAM)效应控制泵浦光与monocycle信号的叠加,进而实现UWB PSM。与其它方案相比,本文方案具有结构简单、易于控制和色散管理相对简单的优势。利用OptiSystem7.0软件进行了仿真研究,分析了输入信号功率、调制速率和光源波长对UWB PSM信号的影响,研究了UWB PSM信号在光纤中的传输特性。结果表明,本文方案对输入信号波长不敏感。给出了输入信号功率和调制速率的优化范围。     

同时产生二阶及三阶超宽带信号的研究北大核心

提出了一种利用SOA(半导体光放大器)的增益饱和效应及XGM(交叉增益调制)效应同时产生二阶及三阶UWB(超宽带)信号的方案,分析了其工作原理,并采用光子模拟软件进行了仿真实验,得到了中心频率为6GHz、相对带宽为143%的二阶信号和中心频率为8GHz、相对带宽为120%的三阶信号,两者均符合FCC(美国联邦通信委员会)对UWB信号的规定。同时,还分析了输入脉冲信号宽度、探测光及泵浦光功率对生成的UWB信号的影响。     

同时产生二阶及三阶超宽带信号的研究

提出了一种利用SOA(半导体光放大器)的增益饱和效应及XGM(交叉增益调制)效应同时产生二阶及三阶UWB(超宽带)信号的方案,分析了其工作原理,并采用光子模拟软件进行了仿真实验,得到了中心频率为6GHz、相对带宽为143%的二阶信号和中心频率为8GHz、相对带宽为120%的三阶信号,两者均符合FCC(美国联邦通信委员会)对UWB信号的规定。同时,还分析了输入脉冲信号宽度、探测光及泵浦光功率对生成的UWB信号的影响。     

基于半导体放大器实现多功能超宽带调制的研究

基于半导体放大器(SOA)的增益饱和效应,提出了一种简单的实现多功能超宽带(UWB)调制的方案。方案采用一个光源和单个SOA,可以实现脉冲波形调制(PSM)、脉冲幅度调制(PAM)和脉冲极性调制(BPM),因此实现容易、结构简单和成本低。利用OptiSystem软件对方案进行了仿真研究,分析了各参数对调制信号的影响以及信号的传输特性。结果表明,本方案对光源的波长和光源的光功率的变化不敏感,仿真输出的调制信号在单模光纤(SMF)中可传输35km。     

基于被动锁模光纤激光器的光子超宽带脉冲源

超宽带(UWB)无线通信的关键技术之一是UWB窄脉冲产生技术.为简化光子超宽带脉冲源的设计,提出采用基于光纤可饱和吸收体效应的环形腔被动锁模光纤激光器来设计光子UWB脉冲源.为了获得满足UWB室内无线通信频谱范围的脉冲,利用色散和啁啾效应展宽脉宽的原理,在激光器环形腔内使用较长的增益光纤引入大量色散效应,将光脉冲展宽以符合美国通信委员会(FCC)规定的室内UWB通信频谱范围(3.1～10.6 GHz).并根据光纤激光器谐波锁模的原理,通过控制偏振态调制输出脉冲的周期以提高脉冲重复频率.实验中,展宽的光脉冲经光电转换器转换成UWB电脉冲序列后,由宽带数字示波器进行波形观测和测量.通过调节偏振控制器,获得了可输出8种不同脉冲重复频率的光子超宽带脉冲源.     

基于半导体光放大器交叉增益调制效应的主动锁模光纤激光器

提出一种腔内损耗小的基于半导体光放大器(SOA)交叉增益调制效应(XGM)的主动锁模光纤激光器结构。使用光环行器成功减小了激光器的腔内损耗,提高了激光器的输出功率。从理论上对有理数谐波锁模过程中腔内脉冲复合的物理机制进行了详细分析。利用有理数谐波锁模技术,在调制频率为10 GHz下,得到了重复频率为30 GHz的皮秒级光脉冲序列输出,其峰值功率约0.5 mW。由于半导体光放大器的宽增益谱与滤波器的较大可调谐范围,使得激光器输出可以在较大的波长可调谐范围内保持较大功率输出。成功实现了调制频率为20 GHz的谐波锁模短光脉冲输出,可调谐范围达40 nm,峰值功率大于0.65 mW。半导体光放大器和激光器的短腔长保证了激光器的长期稳定性。     

声光调制用于全光纤激光器的光谱调谐

描述了采用压电换能器对谐振腔内增益光纤的声光调制,通过控制压电换能器的信号,实现了全光纤激光器的光谱调谐。同时,利用实验制作的可调谐激光器产生了连续可调微波信号,其频率范围1⁴.9GHz。     

载波重用微波光纤矢量信号传输系统性能研究

提出了一种基于双边带(DSB)部分载波抑制调制(OCS)方式的微波光纤传输(ROF)系统结构,实现了矢量信号的传输以及调制方式由8PSK到QPSK的转换,并使用光纤Bragg光栅(FBG)实现了光载波的重新使用,降低了系统的成本。分析了实验原理并搭建了实验链路,在中心站,采用光OCS方案产生并倍频加载了携带有1 Mbps的8PSK矢量信号的5 GHz微波信号,实验结果表明,在基站,使用FBG实现光载波重用的同时,微波信号频率由5 GHz上转换为10 GHz,传输的矢量信号调制方式由8PSK变为QPSK。通过光谱可以看出,实验链路成功实现了50 GHz nm波矢量信号的产生和传输。     

ROF中基于单个光波长与LiNdO3调制器的多频光毫米波

实验研究了一种采用单个光载波和一个单臂LiNdO3调制器同时产生多个不同频率光毫米波的光无线通信(ROF)系统。在中心站,多路不同频率的射频(RF)信号与相应的基带数据信号进行混频,再用功率耦合器将它们耦合成一路信号,输出信号用于驱动单臂LiNdO3调制器进行载波抑制调制去产生多频率的光毫米波信号。经过光纤传输后,在基站,利用光滤波器将载有不同频率光毫米波的光频成分进行分离,之后再分别进入光电检测器(O/E)进行检测。实验结果显示,采用频率为10 GHz与20 GHz的RF信号源可以产生频率为20GHz与40 GHz的光毫米波,20 GHz的毫米波携带2.5 Gb/s的下行基带数据信号在单模光纤中可以传输40km以上,因此这种方案是有效和可行的。     

Multiple ultra-wideband signal sources exploiting XPM in SFRL

A novel scheme for all-optical broadcast ultra-wideband (UWB) monocycle pulses generation based on cross-phase modulation (XPM) in semiconductor fiber ring laser (SFRL) is proposed, in which three UWB positive or negative monocycle pulses can be generated simultaneously. A comprehensive broad-band dynamic model for this kind of all-optical broadcast UWB monocycle sources is established, which is further applied to numerically analyze the impacts of injection current of semiconductor optical amplifier (SOA), the power and wavelength of the signal light on the performance of the UWB positive monocycle pulses with higher power spectral density. The results show that the spectra of the UWB positive and negative monocycle pulses generated by this scheme match the Federal Communications Commission (FCC) definition quite well. Three UWB positive monocycle pulses with better performance can be obtained when the power of signal light is at a high level, and three other UWB positive monocycle pulses with good tolerance to both the injection current of the SOA and the wavelength of the signal light can be obtained. In addition, the powers of the lasing light coupled into the SFRL should not be strong to obtain three UWB positive monocycle pulses with better performance.     

Optical UWB doublet pulse generation using multiple nonlinearities of single SOA

All-optical ultra-wideband (UWB) doublet pulse generation based on the multiple nonlinear effects of a single semiconductor optical amplifier (SOA) is demonstrated. First, a monocycle pulse is obtained by means of cross-gain modulation and self gain-saturation in the SOA, and a Gaussian pulse at conjugated light is obtained using four-wave mixing of the SOA. Secondly, the Gaussian pulse at the conjugated light is combined with the monocycle pulse by proper time delay to form a doublet pulse. The central frequency and 10 dB bandwidth of the doublet radio frequency are 5 and 6.25 GHz, respectively. The scheme is simple since only a single SOA is required.     

Photonic Monocycle Pulse Frequency Up-Conversion for Ultrawideband-Over-Fiber Applications

We demonstrate a photonic monocycle pulse frequency up-conversion scheme for ultrawideband (UWB)-over-fiber applications using nonlinear polarization rotation arising in a semiconductor optical amplifier. For the first time, we have successfully realized the photonic up-conversion of UWB monocycle pulses with an optical local oscillator signal at 24 GHz in the whole -band. The up-converted UWB monocycle pulse at 24 GHz exhibits a power spectrum density fitting the UWB emission mask. After electrical down-conversion, the UWB monocycle pulse has shown low distortion induced by the optical mixing process.     

Methods for Ultra-Wideband Pulse Generation Based on Optical Cross-Polarization Modulation

Optical methods for different type ultra-wideband (UWB) pulse generation based on cross-polarization modulation (CPM) are proposed and demonstrated in this paper. Two polarity-reverse pulses can be obtained by CPM and birefringence time delay to form a monocycle pulse. A semiconductor optical amplifier (SOA) is placed after the monocycle pulse process for doublet pulse generation. These two kinds of pulses can be employed in single-band impulse radio UWB (IR-UWB) systems. Two kinds of multi-band UWB pulses can be generated based on monocycle pulse train with proper apodization profiles, realized by hybrid photonic microwave filter and synchronous polarization modulation respectively. Experimental results show that these pulses can be used in multi-band UWB (MB-UWB) over fiber systems.      

Ultra-Wideband Pulse Generation Based on Cross-Gain Modulation in Fiber Optical Parametric Amplifier

A novel approach to generate ultra-wideband (UWB) monocycle or doublet pulse using cross-gain modulation in fiber optical parametric amplifier is demonstrated in a single experimental setup. The high-speed optical parametric process realizes the signal amplification, idler generation, and pump depletion simultaneously within femtosecond response time in the highly nonlinear fiber. After the combination of the three lightwaves with a suitable time delay between them, UWB pulse is obtained. A selective generation of monocycle or doublet pulse can be made by altering the optical attenuators without changing the wavelengths or the powers of the pump and the signal. In our experiment, high-quality UWB monocycle and doublet pulses with a fractional bandwidth of 115% and 126% were generated.      

基于SOA增益饱和效应生成UWB信号的研究

光纤传输超宽带信号(UWB over fiber)的提出解决了UWB传输距离短的问题,成为国内外研究的热点课题,如何在光域中生成UWB是该系统的关键技术之一。对称形UWB(doublet)与常用的单周期高斯脉冲信号(monocycle)相比,在低频部分的功率谱密度较低,在UWB系统中有更好的性能。为此提出了利用半导体光放大器(SOA)的增益饱和效应生成对称形UWB信号的方法,并进行了仿真实验,得到了符合美国联邦通信委员会(FCC)标准的中心频率为8.3GHz,相对带宽约为142%的对称形UWB信号,验证了该方法的可行性。     

Edge-Triggered Bi-Phase Modulation for the Generation and Modulation of UWB Pulses

We propose and demonstrate a novel scheme called edge-triggered bi-phase modulation for the generation and modulation of ultra-wideband (UWB) pulses in the optical domain. The proposed system consists of a laser diode, a Mach–Zehnder modulator (MZM), and a photodetector. An input data sequence with either return-to-zero or nonreturn-to-zero format is sent to the MZM via its radio-frequency port. The MZM is biased at the quadrature point; for an input pulse having a pulse amplitude equal to the two times the half-wave voltage of the MZM, a pair of UWB monocycles is generated with opposite polarities corresponding to the rising and falling edges of the input pulse. A proof-of-concept experiment is performed. A UWB monocycle sequence is generated when a square-wave with a frequency of 680 MHz is applied to the MZM. The generated UWB pulse has a 10-dB bandwidth of 5 GHz with a fractional bandwidth of 165%.      

Optical Generation of Binary Phase-Coded Direct-Sequence UWB Signals Using a Multichannel Chirped Fiber Bragg Grating

A novel technique to generate binary phase-coded, direct-sequence ultra-wideband (DS-UWB) signals in the optical domain is proposed and demonstrated. In the proposed system, the wavelengths from a laser array are modulated by a Gaussian pulse, which is sent to a multichannel optical frequency discriminator, to generate a UWB monocycle or doublet pulse sequence with a predetermined phase-code pattern. By tuning the wavelengths of the laser array, or by tuning the states of polarization of the wavelengths, the generated pulse shape and code pattern can be changed. The key device in the system is the multichannel dispersive chirped fiber Bragg grating (FBG), which functions, in combination with a dispersive fiber, as a multichannel frequency discriminator with a step-increased group-delay response, to ensure the generated UWB sequence to have uniform time spacing among the chips and to compensate for the fiber-induced chromatic dispersion. The proposed scheme is experimentally demonstrated. A multichannel chirped FBG is designed and fabricated. Binary phase-coded DS-UWB signals with different code patterns are experimentally generated.      

Photonic generation of ultrawideband signals using a delay interferometer

We demonstrate a novel scheme to generate ultrawideband (UWB) monocycle and doublet pulses byinputting a dark return-to-zero (RZ) signal into a delay interferometer (DI), which accords with the general features in future applied UWB system, namely, single optical source input, simple configuration and passive device. The two polarized interferential beams have a time delay and a phase difference when they propagate through the DI. By adjusting polarization controllers (PCs), the total phase difference, i.e., the sum of the relative opticalphase difference between two orthogonally polarized components caused by PCs and the optical-phase shift due to birefringence of the polarization-maintaining fiber (PMF), the orientation angle of the polarization beamsplitter (PBS) relative to the two axes of the PMF are able to be changed and controlled. When the appropriate conditions are met, UWB monocycle and doublet pulses are generated conveniently.     

Ultrawideband Pulse Generation Based on Overshooting Effect in Gain-Switched Semiconductor Laser

We demonstrate an alternative procedure to achieve ultrawideband (UWB) radio-frequency (RF) doublet impulses. It is based on the overshooting effect appearing by biasing a semiconductor laser close to the threshold with a large-amplitude signal. Specifically, with an optical bandpass filter and an electrical low-pass filter, we easily obtain doublet-like impulses whose RF spectrum meets the UWB regulations. Furthermore, we have been able to propagate such signals through an optical fiber link of 118-km length. Though the technique is not flexible in terms of waveform generation, our method constitutes a reliable, easy, and low-cost alternative for RF UWB impulse generation.