Impact of Mach-Zehnder Modulator Chirp on Radio over Fiber Links

The impact of Mach-Zehnder modulator (MZM) chirp on single sideband (SSB) and carrier suppressed double sideband (CS-DSB) modulation radio over fiber (RoF) links are investigated and simulated. Finite extinction ratio and drive signal unbalanced ratio of non-ideal MZM are considered, power variation of target microwave signal and harmonic suppression are calculated and evaluated. Our results suggest that unbalanced ratio could be optimized to minimized the power variation owing to the finite extinction ratio and improve the harmonic suppress ratio in the two kinds of RoF links. However, harmonic suppression ratio declined rapidly with the decrease of extinction ratio in the CS-DSB RoF link. For a non-ideal modulator with low extinction ratio, high quality microwave signal could be obtained in the SSB RoF link while an additional filter is required to suppress the unwanted harmonic components in the CS-DSB RoF link.     

30-GHz millimeter-wave carrier generation with single sideband modulation based on stimulated Brillouin scattering

A new technique to generate a millimeter（mm）-wave carrier of 32.57 GHz(f_LO=10.85 GHz) with single sideband modulation（SSB） for radio-over-fiber（RoF） systems is experimentally demonstrated by using stimulated Brillouin scattering（SBS）.The SSB is realized by directly amplifying the +3rd sideband of the modulated optical carrier in the process of SBS.The pump wave is provided through a double Brillouin scattering frequency shifting configuration.The use of the same laser source to generate the pump wave ensures the stability of the mm-wave generation system since the relative frequency shift between them can be eliminated.In addition, the mm-wave carrier obtains an RF power gain of 21 dB with the SBS amplification and a 3-dB bandwidth of 10kHz.     

Optical Single Sideband Modulation Using Strong Optical Injection-Locked Semiconductor Lasers

We report on the experimental demonstration of optical single sideband (SSB) modulation using a directly modulated semiconductor laser under strong optical injection-locking. Modulation sidebands with 15-dB power ratio between the lower and upper sidebands have been achieved. The longer wavelength sideband is resonantly amplified by the injection-locked laser cavity mode. The radio-frequency performance of the optical SSB after 80-km fiber transmission is significantly improved compared with a typical symmetric sideband modulation of a free-running laser. A 622-Mb/s data transmission on a 20-GHz subcarrier is demonstrated over an 80-km fiber link.     

A Novel Direct Detection Microwave Photonic Vector Modulation Scheme for Radio-Over-Fiber System

This letter demonstrates the feasibility of a novel direct detection microwave photonic vector modulation scheme for the radio-over-fiber (RoF) system. Unlike the traditional double-sideband with optical carrier suppression modulation scheme, which can carry only the on-off keying data format, the proposed scheme encodes the electrical vector signal on either the upper sideband (USB) or the lower sideband (LSB) only and a pure optical subcarrier on the other sideband. Therefore, phase and amplitude information will be preserved after direct detection. A frequency doubling scheme is employed to reduce the cost of RoF systems. Additionally, the relative intensity between USB and LSB can be easily tuned by adjusting the individual power of electrical driving signals to optimize the performance of the optical radio-frequency signals. A proof-of-concept experiment is conducted by using a 1.25 Gb/s BPSK signal at a carrier frequency of 20 GHz. After transmission over 50-km single-mode fiber, the receiver sensitivity penalty is less than 0.5 dB.     

Impact of nonlinear distortion in radio over fiber systems with single-sideband and tandem single-sideband subcarrier modulations

In radio over fiber (RoF) systems, two subcarrier modulations (SCMs), i.e., single-sideband (SSB) and tandem single-sideband (TSSB), have been widely used. Both SSB and TSSB SCMs can be obtained using optical Mach-Zehnder modulators. In this paper, the authors theoretically investigate the impact of harmonic distortion and intermodulation distortion in RoF systems for one wavelength carrying two radio frequency (RF) signals with either SSB or TSSB SCM. It is found that nonlinear distortion can be reduced when the frequency difference of two RF signals is /spl sim/ 1 GHz compared with /spl sim/ 2 GHz and higher for both TSSB and SSB SCMs, particularly for large modulation indexes. When the frequency difference of RF signals is /spl sim/ 2 GHz and beyond, either a small modulation index or a medium modulation index combined with a minimum RF of 6 GHz must be used, and a large modulation index cannot be used due to serious nonlinear distortion. Comparison of SSB and TSSB SCMs with uniform distribution of optical signal subcarriers in a dense wavelength-division-multiplexing RoF system with channel spacing of 12.5 GHz shows by simulation that SSB SCM is better (worse) than TSSB SCM for small (large) modulation indexes.     

Combating/eliminating dispersion-induced fading using suppressed carrier link for OFDM signal

We investigate the performance of 20-GHz radio over fibre (RoF) system having orthogonal frequency division multiplexed (OFDM) as radio signal using two modulation techniques – balanced detection for intensity modulation direct detection (IMDD) and coherent heterodyne detection suppressed carrier (SC) modulation. Dispersion-induced power fading is seen in conventional IMDD links due to the dependence of dispersion over frequency-dependent refractive index of the fibre. SC link is seen to compensate the power fading by terminating the direct current and even-order harmonics with the suppression of carrier along with balanced detection.     

基于窄带光纤光栅的单边带调制及其传输特性

利用自制的窄带光纤Bragg光栅(NFBG)获得了单边带(SSB)调制信号,并在标准单模光纤(G.652)上分别进行双边带(DSB)和SSB调制信号的传输,传输了155 km G.652后采用自制的啁啾光纤Bragg光栅(CFBG)进行色散补偿.结果表明,在同样的入纤光功率下获得相同的误码率(BER),SSB信号的功率代价比DSB信号的小,在BER为E-12数量级时,SSB信号的功率代价比DSB信号小0.8 dB.     

基于多频相位调制的光学单边带调制器研究

提出了一种基于多频相位调制技术实现光学单边 带调制信号产生的新型方案。当含有基频和谐波成分的多频调制信号施加到Mach-Zehnder( MZ)电光调制器上时,若驱动信号波 形选取合适,可使调制后的光信号功率集中在边带谱的一个频率成分上,其它频率成分被抑 制, 从而获得光学单边带调制信号的输出。以十频相位调制为例,计算了与之对应的光学单边带 调 制信号的光谱结构,其中信号能量利用率近88%,载波抑制比大于24dB,边频抑制比大于18 d B, 从理论上证明了本文所述方案的可行性。进一步的仿真结果显示,随着驱动信号谐波数的增 加, 载波抑制比、边频抑制比和信号能量利用率均逐渐增大。可见,为了获得优质的光学单边带 调 制信号,应在实际条件允许的情况下使用尽可能多的调制频率。此方案能量利用率相对较高 , 仅用到了一级商用MZ相位调制器,方案结构简单,是一种产生光学单边带调制信号的有效途 径。     

A novel scheme to implement duplex 60-GHz radio-over-fiber link with 20-GHz double-sideband optical millimeter-wave transmitted along the fiber

A duplex radio-over-fiber (RoF) link with a novel scheme to generate 60-GHz millimeter (mm)-wave using 20 GHz double sideband (DSB) optical mm-wave with signal carried only by its optical carrier is investigated. In the RoF downlink, the modulation frequency to generate the DSB optical mm-wave is reduced greatly. The theoretical analysis and numerical simulation show that this scheme cannot only eliminate the code form distortion caused by the time shifting of the sidebands, but also reduce the influence of the fading effect as the DSB optical mm-wave signal is transmitted along the fiber. Based on the scheme, the duplex RoF link with the frequency up- (down-) conversion of the down- (up-) link mm-wave signal is built and the uplink transmission performance is analyzed theoretically.     

基于受激布里渊散射的30GHz毫米波单边带调制生成技术

本文提出了一种基于受激布里渊散射原理的单边带调制产生30GHz毫米波的新方法,可应用于光载射频系统。该方法利用一个双布里渊散射移频结构生成泵浦光,并将其反向注入到传输信号光的25 km单模光纤;通过受激布里渊散射,直接放大受调制信号光的正三阶边带,实现光载波的单边带调制,有效改善由色散效应引入的功率涨落问题,保证了毫米波功率稳定。此外,信号光和泵浦光由同一个激光器产生,有效消除两者间的相对频率漂移,从而大大提升了毫米波生成系统的频率稳定性。通过我们的方法,实验系统所生成的毫米波功率增益了21dB,其3dB线宽为10kHz。     

Improved sideband suppression of optical SSB modulation usingall-optical Hilbert transformer

A novel optical single-sideband (SSB) modulation system using an all-optical Hilbert transformer is proposed. The sideband suppression characteristics are analysed and compared with a conventional system using an electrical transformer. The side-lobe to main-lobe peak suppression ratio exceeding 40 to 60 dB is shown, significantly outperforming the conventional system     

Performance evaluation of optical OFDM in direct detected systems based on MZM bias and drive voltages

The impact of DC bias and the RF drive voltage of the dual electrode Mach Zehnder Modulator (DE-MZM) on the transmission performance of optical orthogonal frequency division multiplexing (O-OFDM) direct detected systems is analyzed theoretically and verified by simulation. Selection of optimum bias and drive voltage is necessary to minimize the optical signal to noise ratio (OSNR) requirements and the non-linear distortions in the fiber transmission. In this paper, we compare MZM modulation techniques such as double sideband full carrier and single sideband (SSB) [biased at quadrature and minimum power transmission (MPT) point] with a novel modified SSB OFDM technique. To the best of our knowledge for the first time, a mathematical model for above modified SSB technique is developed to evaluate the OSNR requirement, chromatic dispersion of the fiber, spectral efficiency and the receiver sensitivity against other modulation techniques. Our results show that the modified SSB technique provides high spectral efficiency, receiver sensitivity and low chromatic dispersion against other the modulation techniques, while the one biased at MPT minimizes the OSNR requirements.     

双音调制星间微波光子链路信号噪声失真比优化

建立了包括光源、马赫曾德尔调制器、掺铒光纤放大器和光电探测器的双音调制星间微波光子链路模型。利用贝塞尔函数展开、傅里叶变换/反变换和Graf加法定理,推导出探测器输出信号的严格通用解析解,考虑三阶交调失真的影响,得出信号噪声失真比（SNDR）的表达式。着重分析了在不同调制方式下SNDR、基波和三阶交调信号功率随射频输入功率的变化情况。数值计算结果表明:SNDR、基波和三阶交调信号功率随射频输入功率的增大先增大后减小,存在最优的射频输入信号功率使SNDR达到最大。相同射频输入功率条件下,双边带调制SNDR大于单边带调制,适合星间微波光子链路应用。     

Generalized analysis of subcarrier multiplexing in dispersive fiber-optic links using Mach-Zehnder external modulator

A new exact analytical model is presented to analyze the dispersive transmission in subcarrier multiplexing (SCM) fiber-optic links using dual-drive Mach-Zehnder external modulator (DD-MZM). The model is very general and can be applied to almost all operating conditions of DD-MZM, such as bias point, drive level, phase shift, and modulation index difference between DD-MZM drives. The model results in simple, new, and closed-form expressions for output power spectrum, permitting an accurate and fast analysis of such links. Two special cases, double sideband (DSB) and single-sideband (SSB) modulation, are studied in detail. Some important system parameters, such as 1-dB compression point, the input third-order intercept point (IIP3), and the system capacity, are derived for the first time. Measured results for system capacity and intermodulation products of different orders match very well with the calculated results.     

Analysis of the Instantaneous Power Flow for Three-Phase PWM Boost Rectifier Under Unbalanced Supply Voltage Conditions

This paper proposes the analysis of the instantaneous power flow of three-phase pulse-width modulation (PWM) boost rectifier under unbalanced supply voltage conditions. An analytical expression for the instantaneous output power has been derived, which provides the link between the output dc link voltage and the instantaneous output power. A direct relationship between the dc link voltage ripples and the second harmonic component in the instantaneous output power has been established. Based on the input and output instantaneous power analytical expressions provided, the presence of the odd order harmonic components in the ac line currents can be explained. A simple cascaded PI control scheme has been developed for the dc output voltage control. The controller ensures that the dc link voltage is maintained constant and the supply side power factor is kept close to unity under the unbalanced supply voltage operating conditions. Simulation and experimental test results are provided on a 1.6-kVA laboratory-based PWM rectifier to validate the proposed analysis and control scheme.      

A 60-GHz-Band Analog Optical System-on-Package Transmitter for Fiber-Radio Communications

We developed an analog optical system-on-package (SoP) transmitter for a 60-GHz-band radio-over-fiber (RoF) link. The SoP transmitter consisted of an electroabsorption modulator, radio frequency amplifiers, and a bandpass filter. The 60-GHz RoF wireless link was prepared to measure the performance of the SoP transmitter. The transmission characteristics of 64-quadrature amplitude modulation (64-QAM) data of the 60-GHz RoF wireless link, including the SoP transmitter, were investigated by measuring the error vector magnitude (EVM) and signal-to-noise ratio (SNR) with a baseband frequency. The EVM of the 60-GHz RoF wireless link was between 2.25% and 2.80%, and the SNR was between 27.36 and 29.31 dB from 140 and 770 MHz, at input baseband power of -9 dBm. The noise figure had the minimum of 8.44 dB at 500 MHz. We successfully transmitted digital community antenna television (CATV) system signals through the 60-GHz RoF wireless link, including the SoP transmitter. Digital CATV signals of 86 channels could be transmitted through the 60-GHz RoF wireless link, and the total throughput was found to be 2.61 Gb/s.     

一种12倍频全双工RoF系统

为提高光载无线(RoF)通信系统倍频系数,提出了一种基于集成双平行马赫曾德尔调制器(MZM)和抑制载波光双边带调制的12倍频光生毫米波方案。理论分析了光生毫米波信号产生机理,讨论了相关参数对光生毫米波信号的影响,理论分析与仿真结果基本吻合。在此基础上设计了一种基于该方案的全双工RoF系统,通过调整基站(BS)线偏振器(Pol)偏振角度即可恢复出下行数据和上行载波。仿真结果表明,在误码率(BER)为10-9时,传输90km后上行链路功率代价为0.86dB,相同条件下下行链路功率代价仅为0.47dB。     

基于超长分布式2阶喇曼放大器的光载射频传输

为了提升光载射频传输链路的链路增益以及传输距离,采用了L波段的超长分布式2阶喇曼放大器结构对光信号进行放大。从理论上对分布式2阶喇曼放大器以及光载射频传输链路的原理进行了解释,利用信号光、1阶抽运光、2阶抽运光以及噪声之间的耦合方程组分析了它们之间的关系,并且得到了基于超长分布式2阶喇曼放大器的光载射频传输系统的1阶射频信号增益。通过数值仿真以及系统实验得到了抽运功率大小对超长分布式2阶喇曼放大器的开关增益的影响、光载射频传输系统在0GHz~7GHz范围内的频率响应及其射频增益以及该光载射频传输链路在应用超长分布式2阶喇曼放大器后的相位噪声情况。结果表明,光载射频传输在超长分布式2阶喇曼放大器的作用下获得了28.1dB的链路增益,在距离为80.94km的光链路上实现了近似无损传输,射频信号开关增益与射频信号频率无关。该研究在光载射频链路的长距离传输中有重要的应用价值。     

Size Reduction of a MMIC Direct Up-Converter at 44 GHz in Multilayer CPW Technology Using Thin-Film Microstrip Stubs Loading

This paper proposes a novel compact multilayer 44.5-GHz coplanar waveguide (CPW) single-sideband (SSB) subharmonically pumped (SHP) mixer for direct up-conversion GaAs monolithic microwave integrated circuit. It uses previously developed thin-film microstrip (TFMS) and CPW structures for capacitive and inductive loading techniques to drastically reduce its size. The SSB SHP mixer uses 50-MHz in-phase and quadrature signals to directly modulate the second harmonic of a 22.25-GHz carrier to produce the required 44.55-GHz RF output. Two pairs of antiparallel diodes reduce feedthrough of the fundamental 22.25-GHz signal to the RF output while novel CPW/TFMS-based structures provide matching. This 1.2$,times,$1.5$hbox mm^2$chip uses a lumped Wilkinson divider as a local-oscillator divider and a previously developed reduced size 90$^circ$coupler. The SSB SHP mixer acts as an up-converter with a measured conversion gain of$-hbox 10pm hbox 1 ~hbox dB$and the lower sideband suppression is greater than 23 dB across the RF bandwidth of 43.5–45.5 GHz. Additionally, it is shown that the RF port return loss is better than 20 dB, and 2$,times f _ LO$was suppressed by 21 dB over the same band. The circuit also does not require any dc bias. Compared to the conventional SSB SHP mixer, a 70% reduction in circuit area was achieved with better performances.     

Distortion of OFDM Signals on Radio-Over-Fiber Links Integrated With an RF Amplifier and Active/Passive Electroabsorption Modulators

The integration of orthogonal frequency division multiplexing (OFDM) and radio-over-fiber (RoF) techniques have made cost-effective and high-data-rate mobile wireless Internet networks possible, such as wireless broadband networks. This paper describes the distortion effects of OFDM signals fed via an RF amplifier integrated with an RoF link employing active and passive electroabsorption modulators (EAM) for chiefly broadband in-building network applications. First, peak-to-average power ratio was investigated for RoF links. Second, the adjacent channel power ratio, which estimates the degree of spectral re- growth due to the in-band and out-of-band interference resulting from distortion effects from nonlinear amplification, error vector magnitude, and system distortion effects, was also observed for the proposed system. In this study, we considered a combined Volterra-series and impulse response-based analytical model for WiBro systems and compared it to the observed measurements. We analyzed the different nonlinear distortion effects for OFDM signals driven via an RF amplifier that was integrated with an RoF link employing a distributed feedback laser as a transmitter and an active and passive InP EAM as a receiver. The results show significant agreement between the suggested analytical model and the measurement case. This study is unique in that it examines the distortion effects of RoF links with active and passive EAMs as an access point for OFDM-based wireless access networks.