Optical Millimeter-Wave Up-Conversion Employing Frequency Quadrupling Without Optical Filtering

This study presents two optical frequency quadrupling techniques for generating high-purity millimeter-wave signals with optical carrier suppression. To our best knowledge, this investigation demonstrates for the first time that a frequency quadrupling system requires only a single integrated Mach–Zehnder modulator without an optical narrowband filter to remove undesired optical sidebands. Since no optical filter is needed, fast frequency tuning is straightforward and this approach is particularly attractive for the optical up-conversion in the wavelength-division-multiplexing radio-over-fiber systems. This study provides both theoretical analysis and experimental demonstration. The generated optical millimeter-wave signals are of very high quality with optical carrier and undesired harmonic distortion suppression ratio of more than 36 dB.      

OPM产生四倍频光载毫米波的双向ROF系统

提出一种采用单个光相位调制器(OPM)和光纤布拉格光栅(FBG)滤波器产生四倍频光载毫米波的双向光纤无线通信(ROF)系统。在中心站(CS),系统采用基带信号与射频(RF)信号混频后去驱动OPM,以产生抑制一阶边带的多边带光信号。在基站(BS),利用FBG滤波器将信号的重复频率增至4倍。实验结果显示,经过40km光纤传输后,下行链路信号的眼图清晰可见,功率代价小于1.6dB。本文方案中,由于没有额外增加激光源使得基站结构进一步简化,同时四倍频技术降低了RF信号的频率,系统成本大大降低。     

Full-duplex radio-over-fiber system with photonics frequency quadruples for optical millimeter-wave generation

We have experimentally investigated two different schemes (schemes A and B) to generate optical millimeter-wave using optical frequency quadrupling with a Mach–Zehnder modulator (MZM), and wavelength reuse for uplink connection in the radio-over-fiber (ROF) systems. For scheme A, only one MZM is used for both the optical millimeter-wave generation and signal modulation. For scheme B, two MZMs are used. In this scheme, one of MZMs is used to generate optical millimeter-wave for frequency quadrupling, and another one is used for signal modulation. In both schemes, at the base station (BS), the optical carrier can be reused to carry upstream data and delivered to the central station (CS). By experimentally comparing the performance of downstream and upstream transmission in two schemes, it can be seen that scheme B can overcome the crosstalk between the upstream and downstream signals, but scheme A cannot. Meanwhile we also show that the millimeter-wave generated in scheme B has better quality and is almost robust to fiber chromatic dispersion.     

A simplified optical millimeter-wave generation scheme based on frequency-quadrupling

This paper analyzes and demonstrates a simplified frequency quadrupling configuration for optical millimeter-wave(mm-wave)generation,in which the electrical phase shifter and optical filter are omitted.Theoretical analysis is given to reach the optimum operating conditions including direct current(DC)bias voltage,optical transmission point of the dual-parallel Mach-Zehnder modulator(MZM)bias voltage,optical transmission point of the dual-parallel Mach-Zehnder modulator(DP-MZM),amplitude of the radio frequency(RF)driving signal and the impact of the extinction ratio(EF)on the optical sideband suppression ratio(OSSR)and radio frequency spurious suppression ratio(RFSSR).Experiments prove an OSSR of 15 dB and an RFSSR of 26 dB for the new frequency quadrupling scheme at 6 GHz,8 GHz and 10 GHz of RF driving signal without any electrical phase shifter or optical filter.This system exhibits the advantage of low wavelength dependence and large frequency tunable range.     

基于偏振调制器并联产生16倍频毫米波的研究

针对高倍频毫米波的产生问题,文章提出了一种基于4个偏振调制器并联产生16倍频毫米波的方案,利用相关光边带极性的不同,使合成光信号中只保留载波和8n阶边带。经过适当选取调制指数值和光电探测器拍频后,获得16倍频毫米波信号。文章理论分析了产生16倍频毫米波信号的原理,推导出方案所产生的±8阶光边带信号的光边带抑制比为61.72 dB,16倍频毫米波信号的射频杂散抑制比为55.70 dB。仿真实验获得的光边带抑制比和射频杂散抑制比分别为60和53 dB。同时分析了射频信号相位偏移及调制指数对抑制比的影响。实验结果与理论分析吻合,验证了所提方案的可行性。     

Optical generation and distribution of continuously tunable millimeter-wave signals using an optical phase modulator

In this paper, we propose an approach to generate and distribute two wide bands of continuously tunable millimeter-wave (mm-wave) signals using an optical phase modulator and a fixed optical notch filter. We demonstrate theoretically that the odd-order electrical harmonics are cancelled and even-order electrical harmonics are generated at the output of a photodetector when the optical carrier is filtered out from the phase-modulated optical spectrum. Analysis shows that dispersion compensation is required in order to maintain the suppression of the odd-order electrical harmonics, in order to eliminate signal fading of the generated electrical signal when the optical signal is distributed using conventional single-mode optical fiber. It is experimentally demonstrated that, when the electrical drive signal is tuned from 18.8-25 GHz, two bands of mm-wave signals from 37.6 to 50 GHz and from 75.2 to 100 GHz with high signal quality are generated locally and remotely. This approach does not suffer from the direct current (dc) bias-drifting problem observed when an optical intensity modulator is used.     

Optical mm-Wave Signal Generation by Frequency Quadrupling Using an Optical Modulator and a Silicon Microresonator Filter

By adjusting the direct current (dc) bias on an electrooptic modulator to suppress the first-order sideband and subsequently using a double-waveguide micro-ring resonator to filter out the optical carrier, millimeter (mm)-wave signal was generated at a frequency of four times the 10-GHz local oscillator. A monolithic integrated silicon-based optical mm-wave signal generator by frequency quadrupling is proposed. A silicon integrated microresonator filter was fabricated and its design parameters are given. High extinction ratio optical mm-wave signal was obtained. The single sideband noise spectrum of the generated 40-GHz optical signal was measured, showing similar performance when compared with that generated by a radio-frequency synthesizer.      

Generation and distribution of a wide-band continuously tunable millimeter-wave signal with an optical external modulation technique

A new technique to generate and distribute a wide-band continuously tunable millimeter-wave signal using an optical external modulator and a wavelength-fixed optical notch filter is proposed. The optical intensity modulator is biased to suppress the odd-order optical sidebands. The wavelength-fixed optical notch filter is then used to filter out the optical carrier. Two second-order optical sidebands are obtained at the output of the notch filter. A millimeter-wave signal that has four times the frequency of the microwave drive signal is generated by beating the two second-order optical sidebands at a photodetector. Since no tunable optical filter is used, the system is easy to implement. A system using an LiNbO/sub 3/ intensity modulator and a fiber Bragg grating filter is built. A stable and high spectral purity millimeter-wave signal tunable from 32 to 50 GHz is obtained by tuning the microwave drive signal from 8 to 12.5 GHz. The integrity of the generated millimeter-wave signal is maintained after transmission over a 25-km standard single-mode fiber. Theoretical analysis on the harmonic suppression with different modulation depths and filter attenuations is also discussed.     

A Photonic Microwave Frequency Quadrupler Using Two Cascaded Intensity Modulators With Repetitious Optical Carrier Suppression

We theoretically analyzed and experimentally demonstrated a novel 4- to 40-GHz frequency quadrupler for radio-over- fiber systems. By using an optical carrier suppression modulation scheme in two cascaded intensity modulators, four-fold microwave or millimeter wave signals are optically generated without the need for an optical and electrical notch filter to remove the residual carrier components. Moreover, the limitation of high drive voltage is greatly reduced through tandem intensity modulation with pi/2 phase shift between two driving signals.     

On Frequency-Doubled Optical Millimeter-Wave Generation Technique Without Carrier Suppression for In-Building Wireless Over Fiber Applications

A novel optical millimeter-wave (mm-wave) generation scheme based on double-sideband phase modulation (DSB-PM) to achieve frequency doubling without suppressing the carrier is proposed. Theoretical analysis shows that the generated 60-GHz optical mm-wave can tolerant ${pm}$ 0.016-nm wavelength drifting with filter bandwidth ranging from 70 to 100 GHz to sustain first to second harmonic suppression ratio of 18 dB. In addition, error-free transmission of 60-GHz mm-wave at 2.5 Gb/s is experimentally demonstrated over a combined distance of 3-m wireless with 21-dBm equivalent isotropically radiated power, and 250-m fiber to best emulate an in-building network environment. Dispersion effect on the frequency-doubled PM optical mm-wave without carrier suppression is also analyzed and experimentally studied by comparing the link performance over single-mode fiber (SMF-28) and dispersion-shifted fiber (DSF), respectively.      

一种改进的载波抑制调制光毫米波信号的产生方案

为了克服光纤无线(ROF)系统中色散对光载波抑制(OCS)调制光毫米波信号传输的影响,提出一种改进的OCS调制方案。使用双驱动马赫-曾德尔调制器(MZM),通过调整两路输入射频信号相位、基带信号增益和直流偏置电压将2.5Gbit/s数据信号仅调制到(OCS)信号的一个边带上传输。理论分析表明,与传统OCS调制光毫米波信号产生方案相比,本文方案解决了色度色散引起的码元走离问题,大大增加了传输距离。仿真实验结果表明,经过110km光纤传输后信号的眼图仍然十分清晰,在BER=10-10条件下,信号经过20、40和60km光纤传输后的功率代价分别为0.78、1.7和1.9dB。     

Photonic generation of frequency 12-tupling millimeter-wave based on three cascaded-MZMs and polarization multiplexing

Optical millimeter-wave generation is a predominant approach for the generation of high-quality carrier signals for future wireless transmissions. This paper proposes an optical frequency 12-tupling millimeter-wave generation scheme using three cascaded-MZMs assisted by polarization multiplexing for carrier suppression. A three-stage MZM architecture produces the desired sixth-order sidebands along with the undesired carrier signal. The proper adjustment of polarization direction and angle of polarization rotation lead to the effective suppression of the undesired optical carrier signal. A comprehensive mathematical analysis has been accomplished to evaluate the system's performance, and the obtained results are also validated through simulation findings. The derived results demonstrate that the proposed system is capable of operating over a broad modulation index range extending from 1.5 to 4.5, thereby relaxing the stringent requirements for a constant modulation index. The proposed system generates high-purity mm-wave signals with an OSSR of 62.06 dB and an RFSSR of 54.79 dB at a modulation index of 2.6. Moreover, it is also validated that even if the system parameters like modulation index, polarizer rotation angle, and phase difference among RF driving signals deviate from their ideal values to a certain degree, the system performance remains acceptable. The involvement of polarization technique, omission of wavelength-dependent devices, and a large modulation index operating range make this methodology readily appealing for implementation in radio-over-fiber transmissions.     

基于级联双平行MZM的16倍频光生毫米波技术

为解决毫米波信号生成中存在的困难,提出了一 种基于级联双平行马赫-曾德尔调制器(DPMZM)的16倍频光生毫米波 系统。首先通过控制第1个DPMZM的直流偏压、驱动信号相位差和调制指数,完全抑制光载波 和±2阶边带,获得±4阶光边带;然后将该光波输入到另一个完全一样的DPMZM,获得±8阶光边 带和光载波输出;最后利用光滤波器(OF)滤除光载波,用光电探测器(PD)拍频得到 16倍频的毫米波输出。详细分析 了系统的工作原理,并通过仿真验证了方案的可行性。当输入射频(RF)驱动信号频率为2.5GHz时,可 得到40GHz毫米波输出,并且调制器的调制带宽仅需要 2.5GHz。本文方案具有倍频次数高、频谱纯度好等优点。     

Optoelectronic millimeter-wave synthesis using an optical frequency comb Generator, optically injection locked lasers, and a unitraveling-carrier photodiode

This paper demonstrates multi-octave, milliwatt-class millimeter-wave synthesis using three key components: an optical frequency comb generator, an optical injection-locking filter, and a unitraveling-carrier photodiode. The experimental system synthesizes 10-110-GHz millimeter-wave signals with 3-dBm output at 60 GHz. Phase noise results are also presented.     

Polarization state rotation filter for optical generation of continuously tunable millimeter-wave signal employing an external intensity modulator

A method to generate a continuously tunable millimeter-wave signal employing an optical external intensity modulator and polarization state rotation filter (PSRF) is proposed. The technique is based on the optical heterodyne, the Mach–Zehnder modulator (MZM) is biased to suppress odd-order sidebands, and the polarization-dependent PSRF is used to filter the optical carrier. A concept-proof experiment system is built to demonstrate the generation of microwave signal by beating the generated two second-order optical components. The results show that a high purity tunable microwave signal with very narrow linewidth at four times the frequency of microwave drive signal can be obtained. Moreover, the generated signal does not suffer obvious phase-noise degradation after transmission through a 25-km SSMF link. The operation principle of PSRF and the effect of its performance on the generated electrical signal are also analyzed. The proposed technique based on PSRF is very easy to implement, flexible and cost-effective to generate continuously tunable millimeter-wave signals.     

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。     

Millimeter-Wave Signal Generation Using Two Cascaded Optical Modulators and FWM Effect in Semiconductor Optical Amplifier

A novel method of optical generation millimeter-wave (mm-wave) signals employing two cascaded optical modulators and four-wave-mixing effect in semiconductor optical amplifiers is proposed. This approach is capable of generating signals of four times, eight times, and 12 times microwave source frequency with high spectral purity and stability. A mm-wave of 42 GHz (12times fundamental) with a 3-dB linewidth less than 30 Hz and a phase noise less than 83 dBc/Hz at 10-kHz offset is obtained.     

基于双平行PM调制的60GHz光毫米波RoF系统研究

提出了一种采用相位调制器产生六倍频光载毫米波的RoF系统。该系统使用一个双平行相位调制器实现六倍频的调制,通过调节相位调制器的相位偏移量,产生出抑制一阶边带的光谱,耦合相减后得到三阶边带信号,在光电检测器中拍频,产生六倍于射频信号的光载毫米波。仿真结果表明,10GHz射频信号可以产生60GHz光载毫米波信号,5Gb/s的数据信号可在单模光纤中传输10km以上。     

A Super-Tripling Technology Used in Radio-Over-Fiber Systems for Multiservice Wireless Signals Within a Millimeter-Wave Band

A super-tripling technology used in radio-over-fiber systems is presented in this letter for the optical generation and multiplexing of multiservice wireless signals within a millimeter-wave band. To realize the technology, optical carrier suppression is followed by optical single sideband with suppressed carrier modulation in the central station and optical stopband filtering in the base station is utilized. With the technology, 38.5-GHz amplitude shift keying and 41-GHz differential phase-shift keying signals both with 1.25-Gb/s data bit rate were demonstrated experimentally, and power penalties of about 1 dB at a bit-error rate of $10^{-8}$ were obtained after both signals transmitted over 10 km fiber. The spurious-free dynamic range of the link was measured to be 65 $hbox{dB}cdothbox{Hz}^{2/3}$ for the 38.5-GHz channel and 70 $hbox{dB}cdothbox{Hz}^{2/3}$ for the 41-GHz channel, both with the phase-noise at about ${-}$70 dBc/Hz.      

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.