The transmission performance of the single sideband optical millimeter-wave with BPSK signal in the duplex radio-over-fiber link

This paper has investigated the transmission performance of the single sideband (SSB) optical millimeter (mm)-wave with signal carried by the sideband in BPSK format in duplex radio-over-fiber (RoF) system theoretically and numerically. The SSB optical mm-wave signal is generated by a LiNbO₃ Mach–Zehnder modulator and there exists an optimal modulation index to generate the SSB optical mm-wave with a maximal RF photocurrent. The SSB optical mm-wave is much suitable for the duplex ROF link with the uplink lightwave recovered from the downlink because the optical carrier carries no signal. In such a duplex RoF link, although there are the spurs on the optical carrier, they have little influence on the downlink and the uplink signal even if the modulation index is large.     

Effects of Direct Current Bias-Drifting on Radio on Fiber Link

The effects of direct current (dc) bias-drifting on radio on fiber (RoF) links are quantitative investigated and simulated. Single sideband (SSB) modulation and carrier suppressed double sideband (CS-DSB) modulation RoF links are considered, power variation of targeted signal and harmonic suppression on account for bias-drifting are calculated and evaluated. Our results suggest that power variation can be maintained within 1.1 dB with dc bias drift ε less than 5% in the SSB modulation RoF link and the degradation of harmonic suppression is evident with ε exceed 2% in the CS-DSB modulation RoF link.     

The optimization design of tilt-Spectral fiber Bragg grating and its application in SSB modulation based Radio over Fiber system

Based on theoretical analysis and simulation software, the paper researched the performance of transmission after using tilt-Spectral fiber Bragg grating for SSB modulation in Radio over Fiber system. The study concluded that DSB signal can be converted to SSB signal by using tilt-Spectral fiber Bragg grating, and inhibit the carrier power. There are two ideal conditions for a best grating. First, one side of DSB signal will be completely filtered, while the other side remains the same power. Secondly, carrier power equals to sideband power in SSB signal, which means that carrier-to-sideband ratio is 0 dB. As the result, the best tilt-Spectral fiber Bragg grating is designed. Transmitting the SSB signal which is filtered by the best grating in optical fiber not only eliminates the phenomenon that output amplitude change with the transmission distance cyclically, it also enhances the transmission efficiency and receiver sensitivity.     

Influence of the modulation index of Mach-Zehnder modulator on RoF link with ASK millimeter-wave signal

In this paper, the influence of the modulation index of LiNbO₃ Mach-Zehnder modulator on the radio over fiber (RoF) link based on single sideband (SSB) optical millimeter (mm)-wave with ASK signal is theoretically and numerically investigated. Our investigation shows that there exists an optimal modulation index to generate the SSB optical mm-wave with a maximal RF photocurrent. Although the fiber dispersion distorts the code form and degrades the performance of the RF signal demodulated from the SSB optical mm-wave after fiber transmission, it does not cause the closure of the eye diagram. However, the influence of the fiber dispersion becomes more obvious as the modulation index increases. For the duplex RoF link with the optical carrier of the uplink recovered from the downlink, a larger modulation index of the downlink causes a worse crosstalk from the downlink to the uplink.     

Noiseless amplification and signal-to-noise ratio in single-sideband transmission

We study the properties of optical single-sideband (SSB) modulation with respect to signal-to-noise ratio and limits to spectral efficiency. We show that SSB signals undergo truly noiseless amplification, which can be understood in view of Heisenberg's uncertainty principle. Yet, contrary to previously published results, this phenomenon offers no advantages in terms of the signal-to-noise ratio of the amplified signal. We show that, when an intensity receiver is used, single-sideband modulation can improve spectral efficiency in the limit of a high optical signal-to-noise ratio and in the presence of a strong carrier signal.     

Simultaneous modulation and transmission of 10-Gb/s baseband and 60-GHz microwave signals in a radio-over-fiber system

A novel radio-over-fiber (ROF) scheme simultaneously to modulate and transmit 10-Gb/s baseband and 60-GHz microwave signals on a single wavelength using single-sideband (SSB) modulation technique is proposed and verified by simulation. The scheme is based on a Dual-Parallel Mach-Zehnder Modulator (DPMZM). The scheme can carry the microwave signals on either the upper sideband (USB) or the lower sideband (LSB) only and the baseband signals on the other sideband. The optical 60-GHz millimeter wave (mm-wave) carrier is generated by means of subcarrier-multiplexing (SCM) technique to carry 155-Mb/s baseband signals while 10-Gb/s baseband signals are imposed on the original optical carrier via SSB modulation. The signals with dual services are successfully transmitted over 50-km single-mode fiber.     

Cost-effective and dispersion-tolerant cascade modulation for millimeter-wave-over-fiber applications

In millimeter-wave-over-fiber (MWoF) feeder systems, the received millimeter-wave signals at the remote antennas (RAs) can suffer from signal fading by chromatic dispersion of optical fiber. This can be substantially mitigated by Mach-Zehnder modulator (MZM) based photonic up-conversion technique. In this technique, the data signals at intermediate frequency (IF) are frequency up-converted to millimeter-wave frequency by an MZM biased at its transmission null point. However, this scheme requires a costly, high-speed MZM, which will hinder the widespread of this technique for cost-sensitive MWoF applications. Hence, we propose and demonstrate a cost-effective way of reducing the cost of MWoF optical transmitters based on photonic up-conversion technique. We employ a dual wavelength source composed of a directly modulated laser and a polarimetric filter. This source is used to generate a millimeter-wave tone signal and to frequency up-convert the IF data signals to millimeter-wave frequency. The dual wavelength source is also shared with numerous RAs for further cost reduction. Our experimental demonstration performed with 30 Msymbol/s 16-quadrature amplitude modulation signals shows that we can transmit the 20 GHz millimeter-wave signals over 25 km standard single-mode fiber without any transmission penalty.     

Receiver structure and estimation of the modulation index for tamed frequency modulated (TFM) signals

Tamed frequency modulation (TFM) is a spectrally efficient constant amplitude continuous phase modulation (CPM) scheme which can be simply realized by using a frequency modulator (FM). In the implementation the modulation index of TFM is calibrated to have a nominal value of 0.5, but due to temperature variations it can drift causing time varying phase jitter. In this paper we present novel algorithms and performance results to measure and control the modulation index in a coherent receiver based on the joint reduced state sequence detector (RSSD) and per-survivor processing (PSP) carrier phase estimation. The modulation index estimator measures phase transitions in the receiver and derives estimates by comparing the result to the coding rule of the TFM signal. The estimator has acquisition and tracking ability, and the current estimate can be used to replace the nominal index value. Our simulation results show that the proposed coherent receiver with the novel modulation index estimator has less than 1 dB performance degradation compared to around 4.5 dB exploiting only the PSP carrier phase estimation.     

Comparative analysis of long-haul system based on SSB modulation utilising dual parallel Mach–Zehnder modulators

In this paper, we have proposed a long-haul optical transmission system, based on a single sideband (SSB) modulation scheme. Analytical and simulation models have been developed, optimised and demonstrated for the proposed SSB system configurations. The SSB modulation scheme was proposed to overcome dispersion in the fibre. We have shown that the related link losses can be minimized by increasing the quality of the optical signal at the modulation. We have optimised the radio over fibre configuration scheme based on dual parallel dual drive Mach–Zehnder Modulator, thereby increasing transmission length of the fibre. With the proposed SSB, by suppressing some of the harmonics and cancelling one of the sidebands, we have halved the RF power fading and interference. The developed analytical (theoretical/mathematical) model agrees very well with the simulation results using two (both) different commercial simulation tools. The optical signal is boosted while minimizing the number of repeaters. We report a SSB configuration, compensation and amplification with individual spans of 150 km, by extending the length of the link up to 3250 km. The proposed system configuration exhibits high performance with less complexity and lower cost.     

星间微波光子链路调制方式的优化

针对外调制星间微波光子链路输出信噪比优化问题,建立了基于双电极马赫 曾德尔调制器的强度调制直接探测星间微波光子链路模型,通过优化调制器调制方式来提高链路性能。用数值模拟方法得到了单边带、双边带和推挽式3种调制方式下链路输出信噪比,利用曲面投影法求得了最优调制方式时一定信噪比要求下发射端所需最小光放大器增益和对应的调制器直流偏置相位。结果表明:相同输入射频信号功率和发射光功率情况下,双边带调制输出信噪比比单边带调制高3 dB,低直流偏置相位推挽调制可以进一步优化输出信噪比。输入射频信号功率为-20 dBm,输出信噪比为17.3 dB时,所需最小光放大器增益为43.9 dB,对应的直流偏置相位为0.87。     

信号在时变等离子体中的传播特性

高速飞行器等离子鞘套由于飞行姿态调整、湍流、非均匀烧蚀等因素的影响,使其等离子体参数存在时变特性,针对这种传输介质的快速时变特性引起的电波幅度、相位上的寄生调制效应,本文利用大面积辉光放电等离子体产生装置,搭建了等离子体中信号传输实验系统,进行了S频段的单频信号与调制信号传输实验,观测验证了调制效应的存在,且其调制频率与等离子体变化频率具有一致性,进一步分析了等离子参数与寄生调制效应的关系,理论和实验结果表明:即使当载波频率大于等离子频率时,时变等离子引起的寄生调制效应也会使传输信号的星座图发生旋转,造成其判决容差裕度变小,通信可靠性下降,并且载波频率越接近等离子频率时,其寄生调制效应越强烈。     

适合传输快变信息信号的混沌调制保密通信

提出一种新的混沌调制通信方法.利用一个自适应控制器跟踪信息信号的误差对产生混沌载波的发射系统进行参数调制.同时，信息信号直接与混沌载波相乘作为发射信号驱动接收系统.在接收端，另一个自适应控制器维持收发系统的混沌同步并恢复出信息信号.由于同步误差与信息信号无关，从而实现了大幅度、快时变信息信号的混沌调制通信.理论分析和数值模拟的结果表明该方法增强了低维混沌系统的通信保密性. 关键词： 混沌调制 保密通信 自适应控制器 蔡氏电路     

高斯白噪声相位调制的激光光谱展宽

激光器是现代光学中一种常用的光源,分析其谱宽特性对于激光的研究具有重要意义.由于高性能窄线宽激光的半高全宽通常在几十M Hz以内,难以直接满足宽光谱领域的应用需求,因而无法发挥其在成本和性能方面的优势,这在一定程度上限制了激光的发展.如果在激光内部直接进行调制实现线宽展宽,又会导致频率的严重漂移,破坏稳频特性.为了在激...     

自启动的非归零/归零码和光电时钟信号发生器及码型转换

采用双波长注入一包含伪随机码发生器与相位调制器的光电振荡器可以同时得到非归零(NRZ)码,归零(RZ)码以及光,电时钟信号输出。该方案使用了光域耦合的双环路结构,在不增加有源器件的条件下实现边模抑制。相位调制器用于反馈调制并同时实现占空比可调的非归零码到归零码的转换。双波长的注入排除了编码信号在振荡器中引入的非时钟频率成分。实验给出了10 Gb/s工作速率下的结果,得到了抖动为637 fs的光信号输出。转换得到的归零码信号占空比约为33%。输出电时钟信号的相位噪声在频偏10 kHz处为-109 dBc/Hz,边模抑制比为58 dB。     

Assessment of Fiber Chromatic Dispersion Based on Elimination of Second-Order Harmonics in Optical OFDM Single Sideband Modulation Using Mach Zehnder Modulator

This work addresses the analytical and numerical investigations of the transmission performance of an optical Single Sideband (SSB) modulation technique generated by a Mach Zehnder Modulator (MZM) with a 90° and 120° hybrid coupler. It takes into account the problem of chromatic dispersion in single mode fibers in Passive Optical Networks (PON), which severely degrades the performance of the system. Considering the transmission length of the fiber, the SSB modulation generated by maintaining a phase shift of π/2 between the two electrodes of the MZM provides better receiver sensitivity. However, the power of higher-order harmonics generated due to the nonlinearity of the MZM is directly proportional to the modulation index, making the SSB look like a quasi-double sideband (DSB) and causing power fading due to chromatic dispersion. To eliminate one of the second-order harmonics, the SSB signal based on an MZM with a 120° hybrid coupler is simulated. An analytical model of conventional SSB using 90° and 120° hybrid couplers is established. The latter suppresses unwanted (upper/lower) first-order and second-order (lower/upper) sidebands. For the analysis, a varying quadrature amplitude modulation (QAM) Orthogonal Frequency Division Multiplexing (OFDM) signal with a data rate of 5 Gb/s is upconverted using both of the SSB techniques and is transmitted over a distance of 75 km in Single Mode Fiber (SMF). The simulation results show that the SSB with 120° hybrid coupler proves to be more immune to chromatic dispersion as compared to the conventional SSB technique. This is in tandem with the theoretical analysis presented in the article.     

具有快速调制功能NMR发射机的设计与实现

介绍了一种具有快速幅度、相位和频率调制功能的核磁共振射频发射机. 数字中频子系统中采用了两个级联的数控振荡器,前一级数控振荡器在FPGA内实现,用于产生基带调制信号;后一级则采用具有正交调制功能的DDS芯片,由它来完成基带信号的采样率转换、中频产生、调制和输出. 射频脉冲的相位和频率偏置的设置直接由级联NCO实现,而幅度设置则由步进衰减器和中频幅度调制共同实现. 该发射机的基本性能和功能满足常规1D/2D NMR实验需求.     

The influence of fiber dispersion on the code form of the optical mm-wave signal generated by single sideband intensity-modulation

We have theoretically investigated the transmission performance of the optical mm-wave generation by using an external modulator based on single sideband (SSB) intensity modulation. Though the SSB millimeter (mm)-wave can immune the fading effect, the baseband signals with a high bit rate are degraded greatly after transmission along fiber. The main reason is that the fiber dispersion causes the time shift of the code edges; therefore the maximum transmission distance of the baseband signals is limited. The experimental and simulation results agree well with our theoretical analysis. We also propose a novel scheme to extend the transmission distance. In this novel scheme, the data signals are modulated only onto one of the two optical carriers; hence the shift of the code edges in the down-converted signals after transmission is eliminated.     

Study of terahertz interferometric imaging using optical techniques

<正>Principles of terahertz(THz) interferometric synthetic aperture imaging with heterodyne and optical techniques are presented.A THz interferometric experiment based on optical up-conversion is set up.The received THz signal is modulated into an optical carrier and transmitted in a fiber.To simulate phase differences between two THz receivers,the output of receiver is divided and a phase shifter is placed before electro-optical modulation(EOM).Interferometric spectra of these modulated optical signals are examined at different phase shifts.Otherwise,carrier suppression and phase error calibration are discussed for THz interferometric synthetic aperture imaging.     

Millimetre-wave fibre–wireless transmission systems with reduced effects of fibre chromatic dispersion

This paper describes two techniques for the implementation of millimetre-wave (mm-wave) wireless communication systems incorporating optical fibre distribution networks. Fibre chromatic dispersion can exhibit severe effects on the transportation of mm-wave frequencies over fibre, resulting in greatly reduced post-detection rf powers. Each mm-wave fibre–wireless system demonstrated here incorporates a method for the generation and modulation of an optical mm-wave carrier, which enables the effect of fibre dispersion to be significantly reduced. One set-up is a direct-detection scheme where optical single-sideband (SSB) with carrier modulation is used to overcome fibre dispersion effects. The other system employs a self-heterodyne arrangement in which a dual-frequency optical source generates a low phase-noise mm-wave beat signal. Data transmission is achieved by externally modulating the dual-mode signal and reduced effects of fibre dispersion are observed.     

干涉型光纤水听器相位载波调制及解调方案研究

概述了直接调制光源产生相位载波的马赫－曾德尔（Ｍａｃｈ－Ｚｅｈｎｄｅｒ）干涉型光纤水听器调制解调技术。重点在于通过严密的数学推导, 定量分析了直接调制光源伴生的调幅现象对于解调过程和结果的影响, 并有针对性地提出了解决办法。同时就采用直接调制光源的相位载波零差检测方案时, 设计中如何合理选择各相关参数, 以达到最佳匹配进行了原理性探讨。给出了有关实验结果, 这些理论分析和实验结果对于全光纤化水听器阵列的研究及检测系统的设计具有十分重要的意义。