A novel scheme to generate multiband millimeter wave signals for 40 GHz full duplex radio-over-fiber system

This paper proposes a new scheme to generate frequency-diversity binary phase shift keying (BPSK) signals for radio-over-fiber (RoF) system. As is well known, the frequency diversity technology has the anti frequency selective fading characteristic and RoF system is a practical solution to increase the capacity and mobility of future-proof contents delivery and serve both fixed and mobile users. In this paper, our proposal can generate 20 GHz and 40 GHz millimeter-wave (mm-wave) signals simultaneously with the data rate of 1.25 Gbit/s employing only one electrical optical phase modulator (EOPM) and one Mach-Zehnder modulator (MZM) at the central station. With one additional MZM at the base station, the full duplex transmission can be accomplished. As the downstream data is phase modulated, the optical signal can be re-used to load the upstream data and no laser diode (LD) is needed at the base station, which simplify the structure of the base station. The 20 GHz electrical carrier is also generated which can be used to demodulate the BPSK signal. The whole scheme can be used in the future duplex RoF system.     

Generation of frequency-doubling mm-wave signal using a Mach–Zehnder modulator with three arms to overcome fiber chromatic dispersion

We propose a novel method to generate optical frequency-doubling mm-wave signal by using a three-arm Mach–Zehnder modulator (MZM) for radio-over-fiber (RoF) systems. Since the optical carrier and its two 2nd-order sidebands are dominant, the 2nd-order harmonic in the photocurrent gets maximal. When the optical mm-wave signal is transmitted in standard single-mode fiber (SSMF), there is no time shift of code edges because the data signal is only carried by the optical carrier. The 2nd-order harmonic in the photocurrent consists of two beating products, so it experiences a periodical fading effect when the optical mm-wave signal is transmitted in SSMF. However, if a proper direct-current (DC) bias is applied to the data modulation arm in the MZM architecture to adjust the position of the fading nodes, the degradation on the photocurrent can be avoided. A RoF link is built based on the novel scheme by simulation, and the transmission performance of the proposed scheme is presented. The eye diagram still keeps open and clear even after 40 km transmission. Simulation results prove our theoretical analysis.     

Cancellation of the signal fading for 60 GHz subcarrier multiplexedoptical DSB signal transmission in nondispersion shifted fiber usingmidway optical phase conjugation

In millimeter-wave (mm-wave) optical double sideband (DSB) signal transmission systems, the received radio frequency (RF) power fades periodically because of the group velocity dispersion (GVD) and the self-phase modulation (SPM) of optical fibers. In this paper, cancellation of the signal fading by using midway optical phase conjugation in mm-wave subcarrier multiplexed (SCM) optical DSB signal is analyzed. Fading-free 60 GHz mm-wave optical DSB signal transmission over 100 km-long nondispersion shifted single-mode fiber at 1550 nm by using a semiconductor optical amplifier (SOA) optical phase conjugator (OPC) in the midway of optical link is experimentally demonstrated for the first time. Finally, the degradation factor of the OPC system is also discussed     

Full-Duplex 60-GHz RoF System With Optical Local Oscillating Carrier Distribution Scheme Based on FWM Effect in SOA

A full-duplex 60-GHz radio-over-fiber (RoF) system using novel optical local oscillating (LO) carrier distribution scheme to reduce the system cost and realize centralized management is proposed and experimentally demonstrated. In the proposed scheme, the optical LO carriers for producing remote electrical LO signals at the base stations (BSs) are generated together with the downlink RoF carriers at the central station (CS) via four-wave-mixing effect in semiconductor optical amplifier, and are then distributed to the BSs along with the downlink RoF signals. By down-converting the 60-GHz-band uplink signal with the remotely produced 60-GHz LO signal and reusing the optical LO carriers as the uplink optical source, only a cost-effective intermediate frequency modulator is required at each BS to transmit the uplink signal, which will dramatically reduce the whole system budget due to a large amount of BSs. Moreover, the operating frequency of each BS can be controlled remotely at the CS end to realize centralized management and convenient reconfiguration. Using the proposed scheme, 622-Mb/s signals for both directions are successfully transmitted over a 20-km single-mode fiber link and a 50-cm wireless channel with less than 0.1- and 0.2-dB power penalty for downlink and uplink, respectively.      

采用单个相位调制器产生毫米波

实验研究了采用单个相位调制器(PM)产生毫米波的方案。该方案采用电混频器将射频(RF)信号与基带信号混频后再利用相位调制器产生双边带调制(DSB)信号,经光纤传输到基站后用一个光交叉复用器(IL)分离一阶边带和中心载波,一阶边带经过光电(O/E)检测器拍频产生两倍频于射频频率的毫米波,而中心载波可以作为上行链路载波重新利用。理论分析了该毫米波的传输性能,研究发现由于色散导致两个一阶边带时延不同,码元的占空比会随着传输距离的增加而减小,将限制毫米波的最大传输距离;实验中采用频率为20 GHz射频信号产生频率为40 GHz的毫米波,速率为2.5 Gbit/s的非归零(NRZ)码作为下行链路数据,经过20 km色散光纤传输后下行链路的功率代价为0.2 dBm。     

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.     

一种克服色度色散影响的四倍频光毫米波信号产生方法

提出一种克服色度色散影响的四倍频光毫米波信号产生方法。该方法使用一个双驱动马赫曾德尔调制器,通过调整上、下两路射频信号的相位差、直流偏置点、调制系数以及基带信号增益,将数据信号仅调制到四倍频光毫米波信号的一个2阶边带上传输,解决了色度色散引起的码元走离问题,有效增加了传输距离。理论分析和仿真实验结果表明,信号在光纤中传输120 km后眼图仍然十分清晰,经过60 km传输后的功率代价约为0.45 dB。另外,基于频率再用技术,没有调制数据的另一个2阶边带信号还可以作为全双工光纤无线通信(RoF)系统的上行链路光载波,简化了基站配置。仿真实验结果表明,双向2.5 Gbit/s数据信号在光纤中传输40 km后,功率代价小于0.6 dB。     

基于两个平行马赫-增德尔调制器的光载无线传输系统

为提高光载无线(radio over fiber,RoF) 传输系统中的光波信号的利用率,本文提出了一种基于两个平行马赫-增德尔调制器 (Mach-Zehnder modulator,MZM) 的RoF传输系统。两个平行MZM经射频(radio frequency,RF) 信号调制后,产生5个光边带信号,分别是正负一阶光边带、正负二阶光边带和光载波。其中正负二阶光边带使用基带数据进行调制,经光电检测器(photodiode,PD) 拍频后产生已调数据的毫米波信号,再由天线发射出去。正二阶边带和光载波经PD拍频后产生未调制数据的毫米波,该毫米波用于接收端解调的本振信号(local oscillator,LO) 。负二阶边带信号用于上行链路的光载波。在本系统中,5个光边带信号都被充分利用,提高了光信号的利用效率。此外,还分析了该系统通过色散介质的传输特性,为RoF通信系统提供了一种实用化的解决方案。     

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。     

Multi-band QPSK signal transmission implemented with remote up-conversion and Schottky RF detectors in a 60-GHz millimeter wave radio-over-fiber system

A simple multi-band QPSK signal transmission scheme, constructed by using an optical remote up-conversion technique and a Schottky diode RF detector, is theoretically analyzed and experimentally implemented in a 60-GHz millimeter wave (mm-wave) radio over fiber (RoF) system, for the first time. There is no need for complex system architecture or any expensive high-frequency clock source in our scheme. Simulation results show that our scheme is highly tolerant to fiber dispersion, compared with the conventional 60 GHz multi-band RoF system. In the experimental demonstration, successful delivery of QPSK signals at two 60-GHz sub-bands is achieved over 50-km fiber and 4-m wireless distance.     

光载毫米波在光纤中传输色散性能研究

提出了并理论分析了一种采用单电极Mach–Zehnder调制器(SD-MZM)产生光载毫米波的方案。采用电混频器将射频信号与基带数字信号混频后再利用单电极调制器产生双边带调制信号并发送至光纤,在基站使用一个交叉复用器(IL)将双边带信号的中心载波与一阶边带信号进行分离,中心载波可用于上行链路的光载波,而一阶边带产生光载毫米波;理论分析了该毫米波的色散特性并在仿真平台上验证了其正确性,研究发现由于光纤色散引起两个一阶边带的延时不同, 从而导致毫米波能量的损失和解调信号的码间干扰,限制了毫米波的最大传输距离。     

Impact of Nonlinear Transfer Function and Imperfect Splitting Ratio of MZM on Optical Up-Conversion Employing Double Sideband With Carrier Suppression Modulation

Generation of optical millimeter-wave (mm-wave) signal using a Mach–Zehnder modulator (MZM) based on double-sideband (DSB), single-sideband (SSB), and double-sideband with carrier suppression (DSBCS) modulation schemes have been demonstrated for various applications, such as broadband wireless signals or optical up-conversion for wavelength-division-multiplexing (WDM) radio-over-fiber (RoF) network, wideband surveillance, spread spectrum, and software-defined radio. Among these schemes, DSBCS modulation offers the best receiver sensitivity, lowest spectral occupancy, the least stringent requirement of electrical bandwidth, and the smallest receiving power penalty after long transmission distance. Nonetheless, the inherent nonlinear E/O (electrical/optical) conversion response of a MZM is such that the signal quality of the optical mm-wave suffers. Fabrication tolerances make a balanced 50/50 splitting ratio of the MZM's y-splitter particularly difficult to achieve. As a result, imbalanced MZMs have a finite extinction ratio (ER) and degrade the optical carrier suppression ratio (OCSR) using DSBCS modulation. In this paper, the effect of the MZM nonlinearity and imbalanced y-splitter on optical mm-wave generation by DSBCS modulation is theoretically and experimentally investigated. A novel approach with better performance and greater cost-effectiveness than dual-electrode MZM (DD-MZM) is presented to realize a DSBCS modulation scheme based on a single-electrode MZM (SD-MZM).      

基于相位调制器产生光毫米波的全双工光纤无线通信系统

提出并实验研究了一种基于相位调制器产生光毫米波信号的全双工光纤无线通信(RoF)系统。在中心站采用相位调制器结合滤波的方法产生重复频率为40GHz的载波抑制双边带毫米波信号,利用交叉复用器分离开毫米波信号的上下边带,其中的一个边带强度调制数据速率为2.5Gbit/s的下行基带信号,另一个边带被发送到基站调制上行传输的基带数据。该系统抗色散效果好,在经过40km标准单模光纤上/下行传输数据速率2.5Gbit/s的基带信号后,双向的传输功率代价都小于0.5dBm。在光纤无线通信系统中采用相位调制器结合滤波的方法产生光毫米波,同时基于波长重用技术再生上行光载波信号,可以简化中心站和基站配置,节约系统成本。     

A Novel Scheme to Generate Single-Sideband Millimeter-Wave Signals by Using Low-Frequency Local Oscillator Signal

We have proposed and experimentally demonstrated a novel scheme to generate optical millimeter-wave (mm-wave) signals by using single-sideband modulation with low-frequency local oscillator (LO) signals. In this architecture, by incorporating the proper dc bias of the modulator in central office, the optical mm-wave carriers are generated with two times frequency of the LO signal while largely reducing the bandwidth requirement of the modulator. We quantify the optical carrier-to-sideband ratio (CSR) of downstream transmission in this radio-over-fiber (ROF) link and establish that the performance of the ROF system can be significantly improved when the optical signals are transmitted at CSR equal to 0 dB.     

Multiple-frequency basestation RoF system based on polarization multiplexed FWM in SOA

An approach of multiple-frequency millimeter-wave(mm-wave)signal generation is proposed for radio-over-fiber(RoF)system with multiple-frequency basestations(MFBSs).Two groups of orthogonally polarized signals are injected into a semiconductor optical amplifier(SOA),and subsequently ten new different wavelengths are generated via four-wave mix-ing(FWM)effect.At each MFBS,different wavelengths are filtered out using demultiplexer and then input to a photodiode(PD)to generate the mm-wave signals with the frequencies from 52 GHz to 68 GHz at the interval of 2 GHz.Simulation results verify that the proposed multiple-frequency generation for MFBS RoF system can work properly.     

New progress of mm-wave radio-over-fiber system based on OFM

This paper presents an overview on new progresses-of millimeter wave (mm-wave) radio-over-fiber (RoF) system based on mm-wave generation by optical frequency multiplication (OFM), including gen-eration of high-order optical side modes by optical modulation using dual-drive Mach-Zehnder modulator (DD-MZM) and enhancement of high-order optical side mode induced by selective amplification due to stimulated Brillouin scattering (SBS). The paper describes OFM by using DD-MZM in principle and verifies it in an experimental bidirectional 40GHz RoF system. SBS amplification enhances the generated information-bearing mm-wave in downlink and also helps in producing a pure reference mm-wave for radio frequency-intermediate frequency (RF-IF) down-conversion in uplink. These efforts pushed the OFM technology of mm-RoF systems to achieve more and more feasibility and cost-effectiveness.     

Millimeter-wave broad-band fiber-wireless system incorporating baseband data transmission over fiber and remote LO delivery

We present the first demonstration of a millimeter-wave (mm-wave) broadband fiber-wireless system which incorporates baseband data transmission in both the downstream (622 Mb/s) and upstream (155 Mb/s) directions. The local oscillator (LO) required at the remote antenna base station for up- and downconversion to/from the mm-wave radio frequency (RF) is delivered remotely via a modulation scheme that is tolerant to the effects of fiber chromatic dispersion on the detected LO carrier power. The technique employs a single dual electrode modulator located at the central office (CO) and the data and an RF signal at a frequency equal to half the LO frequency, are applied simultaneously to the device. The modulation scheme was optimized as a function of the modulator operating conditions. Simultaneous bidirectional radio transmission in the mm-wave fiber-wireless network was implemented using specially designed mm-wave diplexers located at the base station (BS) and customer unit, and a single Ka-band printed antenna array at the BS operating simultaneously in transmit and receive mode. Error-free data transmission was demonstrated for both down(34.8 GHz) and uplinks (37.5 GHz) after 20 km of single-mode optical fiber and a bit error rate (BER) of 10/sup -6/ was achieved after the inclusion of a 2-m radio link.     

Generation and Modulation of Tunable mm-Wave Optical Signals Using Semiconductor Ring Laser

Optical injection locking and cavity enhanced four-wave mixing in semiconductor ring lasers have been used to generate data modulated millimeter (mm)-wave optical signals. The scheme is shown to have multigigahertz (multi-GHz) modulation bandwidth. The 4-Gb/s data is transferred directly from an intensity modulated optical signal onto an mm-wave optical signal with the mm-wave frequency tunable in steps of 62.5 GHz and with flexible radio-frequency modulation formats over the optical carrier. Bit-error-rate and eye-diagram measurements confirm excellent signal quality.      

60-GHz Photonic Millimeter-Wave Link for Short- to Medium-Range Wireless Transmission Up to 12.5 Gb/s

In this paper, a 60-GHz photonic millimeter-wave link system for short- to medium-range broadband wireless data transmission is investigated. The system employs advanced mm-wave photonic components and radio-over-fiber (RoF) techniques for the generation of a DSB-SC optical mm-wave carrier and its subsequent on-off-keying modulation and transmission. For short-range applications, we have constructed a compact wireless RoF transmitter consisting of a high-frequency photodiode and a mm-wave antenna only. This system achieved error-free ($hbox {BER}=10^{-9}$, $2^{31}-1$ PRBS, NRZ) in-door transmission of 12.5-Gb/s signals over wireless distances up to 3.1 m with a receiver sensitivity as low as $-$ 45.4 dBm . For fixed wireless access (FWA) requiring a bit error rate of $10^{-4}$, the maximum transmission distance for 12.5 Gb/s is increased up to 5.8 m. For medium-range broadband wireless transmission an electrical radio-frequency (RF) amplifier was employed in the RoF transmitter. Here we achieved 7.5-Gb/s error-free transmission in out-door line-of-sight experiments over wireless distances of up to 36 m. Based upon the experimental results, we expect that the maximum wireless distance the system could accommodate for 12.5 Gb/s is in the kilometer range when using high-gain antennas and an RF transmitter amplifier with a sufficient bandwidth.      

System-on-Packaging with Electroabsorption Modulator for a 60-GHz Band Radio-Over-Fiber Link

A system-on-packaging (SoP) with an electroabsorption modulator (EAM) for a 60 GHz band radio-over-fiber (RoF) link is described. The system consists of an EAM device, a microstrip filter, and a low noise amplifier (LNA). The microstrip filter was used to achieve impedance matching between the EAM device and the LNA and to reject the local oscillator (LO) frequency of the heterodyne system. The frequency response and the effect of the EAM bias voltage were measured for a simple RF/optical link. A 60 GHz band RoF link with 2.5 GHz intermediate frequency (IF) was prepared to measure the transmission characteristics of the 16 QAM data.