Photonic Frequency Upconversion Based on Stimulated Brillouin Scattering

We demonstrate a method of photonic frequency upconversion useful in radio-over-fiber systems, which is based on Brillouin selective amplification. One of the optical sidebands generated from the applied radio-frequency carrier at 10.831GHz is selected and amplified by Brillouin gain. By carrying the 1-GHz intermediate-frequency (IF) signal on the optical carrier and beating them with the amplified sideband, the IF signal of 1 GHz is upconverted to 11.831 GHz. This scheme can also be applied to the IF signal with bandwidth larger than the Brillouin gain bandwidth. The upconverted 11.831-GHz signal has the phase noise of -83.3dBc/Hz at 10-kHz offset. Also, the proposed upconversion scheme shows the spurious-free dynamic range of 89.5 dBmiddotHz^2/3     

Low-Bandwidth Cost-Effective Brillouin Frequency Sensing Using Reference Brillouin-Scattered Beam

We propose a method that down-converts the electrical bandwidth for Brillouin frequency shift sensors with heterodyne detection without the need for any expensive instruments or a complicated system. We discuss the power and coherency of the stimulated Brillouin scattering light required for the reference fiber. We confirm that the frequency bandwidth measured with the proposed method is much lower (0.2 GHz) than that measurable with conventional heterodyne detection (11 GHz). Moreover, the proposed method can measure the dependence of the Brillouin frequency shift on temperature.      

基于单个偏振调制器和光交错滤波器的八倍频微波信号产生研究

提出并实验验证了一种采用单个偏振调制器(PolM)的八倍频微波信号光学产生方法。PolM在大信号调制下产生多个高阶光边带,通过调节偏振控制器(PC)和检偏器,仅获得偶数阶光边带;合理调节其调制指数(射频信号功率),使得二阶边带被完全抑制,四阶边带功率明显高于六阶及其它高阶边带。采用光交错滤波器进一步抑制光载波及六阶边带,仅保留四阶边带,经光电探测器(PD)拍频获得八倍频微波信号。仿真方案选用25GHz和50GHz信道间隔的光交错滤波器,充分利用光交错滤波器的周期滤波特性,在4个频段范围内获得了连续可调的八倍频微波信号。实验结果和理论分析有效验证了所提出方案的可行性。     

基于双平行马赫曾德尔调制器和受激布里渊散射效应的十倍频毫米波信号生成

提出了一种基于双平行马赫-曾德尔调制器(DPMZ M)和受激布里渊散射(SBS)效应的10倍频mm 波信号生成方案,具有覆盖频段高和频谱纯度高等优点。在本文方案中,低频率的射频(RF )信号通过DPMZM 对激光器发出的光波进行调制,调节直流偏置电压,使DPMZM的主调制器和两个子调制器均 工作在最小传 输点(MITP),抑制光载波和偶数边带,进一步调节两个子调制器的调制深度和移相器的相 移,抑制一阶和 七阶边带,留下三阶和五阶边带,然后利用SBS效应进行布里渊边带滤波滤除三阶边带,仅 保留五阶边带, 再经光电探测器(PD)拍频即可获得10倍频mm波信号。通过仿真实验,以10 GHz的R F信号为驱 动信号,得到了100GHz的mm波信号,验证了方案的可行性。     

基于强度调制和布里渊效应的六倍频可调毫米波信号产生

提出了一种新型的基于马赫-曾德尔调制器(MZM)和布里渊效应实现六倍频可调毫米波信号输出的方法。在本方案中,先调节MZM的直流偏置,抑制偶数边带,留下奇数边带;经过大功率掺Er3+光纤放大器(EDFA)放大之后,使两个一阶边带的功率达到布里渊阈值之上,然后采用了25km的单模光纤(SMF)作为布里渊介质,滤除一阶边带,留下三阶边带;最后经过EDFA放大和光电探测器(PD)光电转换得到六倍频的毫米波信号。因为布里渊边带滤波是窄带滤波,与波长无关,故本系统可以实现波长无关的微波信号产生。     

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.     

基于微波光子的24倍频毫米波信号生成

提出了一种基于级联双电极马赫-曾德尔调制器、光延迟线和半导体光放大器的24倍频毫米波信号生成方案。将两个双电极马赫-曾德尔调制器通过一个光延迟线级联,获得高纯度±4阶边带,进而利用半导体光放大器的四波混频效应,得到±4阶和±12阶边带,通过波分解复用器选出±12阶边带,经光电探测器拍频即可得到24倍频毫米波信号。理论分析和仿真验证结果表明,当输入信号频率为4~10GHz时,可以生成射频杂散抑制比不低于26dB的24倍频毫米波信号,且其频谱纯度高,可调谐性好。     

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。     

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.     

基于并联调制器的高倍频毫米波信号生成

为了获得更高频率的信号，采用了一种基于并联马赫-曾德尔调制器（MZM）和半导体光纤四波混频效应的二十四倍频光生毫米波方案。本振信号被并联MZM调制后可以获得高纯度的±4阶边带，在四波混频效应下，又可以生成±12阶边带，用级联的布喇格光栅滤波器滤除±4阶边带，经光电探测器拍频便可生成二十四倍频信号。结果表明，当输入本振信号为5GHz时，生成的120GHz高频微波毫米波信号射频杂散抑制比为22dB，频谱纯度很高，且具有很好的可调谐性。该研究为高频微波毫米波信号的生成提供了更高的倍频方法。     

基于光纤光栅的微波扫描单边带调制法测量光纤布里渊散射特性

利用光纤布拉格光栅(FBG)和马赫-曾德尔电光调制器实现了单边带光调制输出。基于微波扫描的单边带调制技术提出了一种测量光纤受激布里渊散射(SBS)特性的方法,可有效地将布里渊频移与布里渊增益谱的测量统一起来。对一段50m长的光子晶体光纤(PCF)的SBS特性进行了测量,得到了PCF的SBS谱的布里渊频移为9.7443GHz,布里渊增益谱线宽为22.472MHz,布里渊增益系数为7.874×10-12 m/W。     

基于FBG和偏振复用的8倍频全双工RoF系统

为简化光载无线通信系统(RoF)中心站(CS)和基站(BS)结构,提出了一种基于光纤布拉格光栅(FBG)和偏振复用技术的8倍频全双工RoF系统方案。通过设置马赫-曾德尔调制器(MZM)偏置电压和射频驱动信号幅度保留部分主载波与偶数阶边带,再利用FBG将主载波与偶数阶边带分离。结合偏振复用技术将主载波和偶数阶边带复用到X和Y两个偏振方向上,其中抑制载波偶数阶边带用于下行链路数据传输,而主载波在BS站作为上行链路载波使用。理论推导了实现机理并进行了实验验证,结果表明当使用10 GHz射频驱动时可实现稳定的80 GHz光载毫米波信号,传输20 km后下行链路和上行链路功率代价仅为0.1和0.07 dB,表现出了较好的系统性能。     

一种新型瑞利BOTDA系统的研究

搭建了一种新型的基于瑞利散射的布里渊光时域分析（Rayleigh Brillouin optical time domain analysis, RBOTDA）传感系统。该系统工作在单端,能克服传统 BOTDA双端接入的缺点;采用两个EOM并联的结构产生含有连续基底光的脉冲光,探测光由基底连续光的瑞利散射提供,避免了多种受激布里渊散射（stimulated Brillouin scattering,SBS）作用带来的干扰,信噪比更高,传感距离更长;采用双边带探测方法,有效减少泵浦脉冲的损耗与非本地效应。建模解析了该系统中的SBS作用过程,并实验验证了系统的可行性。结果表明,布里渊增益谱完好地贴合洛伦兹曲线,非本地效应得到了有效的抑制;在2.4 km光纤上,室温25℃下泵浦脉宽50 ns时,布里渊频移为10.867 GHz,布里渊线宽约为40.21 MHz。     

波长扫描型布里渊光时域反射仪

布里渊光时域反射仪(BOTDR)是一种具有广泛应用前景的分布式光纤传感器。对于特定的入射波长,自发布里渊散射光的布里渊频移与温度和应变成线性关系,通过测量光纤沿线布里渊频移分布可实现温度或应变的分布式传感。布里渊功率谱扫描是BOTDR获取布里渊频移的常用手段,已有光频差扫描与电频扫描两种方式。基于布里渊频移对波长的依赖性,提出一种波长扫描型BOTDR。采用可调谐激光器作为光源,通过扫描入射光波长,来获取布里渊功率谱,该方法兼具光频差扫描与电频扫描的优点。实验证明了该方法的可行性,对23.4km光纤进行测量,实现了5m的空间分辨率与2.2℃的温度测量精度。     

二次多项式拟合在分布式光纤传感中的应用

基于布里渊散射的分布式光纤传感中温度和应变与布里渊频移成线性关系,为了提高温度和应变测量的准确性,提出了一种改进的二次多项式拟合算法用于提取布里渊频移。该算法分为两步:首先使用一种改进的中值滤波算法对含噪布里渊谱信号进行预处理,以提高增益峰值定位的准确性；然后截取围绕峰值左右对称的一个线宽的原始布里渊谱进行二次多项式拟合以实现布里渊频移的高精度提取。以布里渊频移误差及峰值定位准确性作为衡量指标,比较研究后确定同一频率下所有空间点对应的布里渊增益作为滤波器的输入。研究了不同扫频间隔和信噪比及不同滤波窗长下改进算法的效果,同时研究了最优窗长的选择问题。结果表明,不同信噪比和扫频间隔下改进算法均能有效提高布里渊频移提取的准确性。随窗口长度增加布里渊频移误差先减少后增加,在扫频间隔为1~10MHz、信噪比为0～40dB情况下,通用的最优窗长为53~163。     

Simple distributed optical fiber sensor based on Brillouin amplification of microwave photonic signals

A simple distributed fiber sensor is proposed by Brillouin amplification and depletion of microwave photonic signals. This technique utilizes optical carrier suppression (OCS) modulation to generate two sidebands acting as the pump waves. After Fresnel reflection at the cleaved end of the fiber under test (FUT), the pump waves are converted to probe waves. By sweeping the modulated microwave frequency, the stimulated Brillouin scattering (SBS) spectra and Brillouin frequency shift (BFS) can be precisely characterized. As a result, the accurate measurement of the Brillouin frequency shift makes good determination of the distributed temperature or stain along the FUT, and the position along the FUT can be resolved and controlled by the delay of the microwave pulses. Furthermore, our proposed sensing system is implemented with a single-ended configuration which has shown many advantages such as immunity of the laser frequency fluctuation and compact setup without additional pump laser source and filters.     

Multi-band microwave photonic satellite repeater scheme employing intensity Mach-Zehnder modulators

To solve the satellite repeater's flexible and wideband frequency conversion problem, we propose a novel microwave photonic repeater system, which can convert the upload signal's carrier to six different frequencies. The scheme employs one 20 GHz bandwidth dual-drive Mach-Zehnder modulator (MZM) and two 10 GHz bandwidth MZMs. The basic principle of this scheme is filtering out two optical sidebands after the optical carrier suppression (OCS) modulation and combining two sidebands modulated by the input radio frequency (RF) signal. This structure can realize simultaneous multi-band frequency conversion with only one frequency-fixed microwave source and prevent generating harmful interference sidebands by using two corresponding optical filters after optical modulation. In the simulation, one C-band signal of 6 GHz carrier can be successfully converted to 12 GHz (Ku-band), 28 GHz, 34 GHz, 40 GHz, 46 GHz (Ka-band) and 52 GHz (V-band), which can be an attractive method to realize multi-band microwave photonic satellite repeater. Alternatively, the scheme can be configured to generate multi-band local oscillators (LOs) for widely satellite onboard clock distribution when the input RF signal is replaced by the internal clock source.     

Photonic Frequency Upconversion by SBS-Based Frequency Tripling

We describe a photonic frequency upconversion by the stimulated Brillouin scattering (SBS)-based frequency tripling method. The frequency tripling and the photonic frequency upconversion are simultaneously obtained by incorporating a dual-electrode electrooptic modulator (EOM) and a single optical source. Each electrode of the dual-electrode EOM is driven by both an intermediate frequency (IF) and a microwave radio frequency (RF) signal, respectively, along with the optical frequency tripling scheme. The dual-electrode EOM generates appropriate optical sidebands, while the IF signal is conveyed by the pump signal. After the successive SBS shifting process, one of the third optical sidebands is amplified by the narrow gain spectrum of SBS. The carrier signal at 32.493 GHz with narrow linewidth, which is amplified by 20 dB while the other signals are suppressed more than 20 dB, is obtained after photodetection. From the simultaneous frequency upconversion and tripling, an IF signal at 1 GHz is upconverted around the 32.493-GHz signal, which is tripled from the RF signal (10.831 GHz). To verify the ability of conveying broadband data that is limited in the previous method based on SBS, the upconversion of a pilot tone at 1 GHz is demonstrated, which means that the data rate exceeds 1 Gb/s. The proposed photonic frequency upconversion shows the spurious free dynamic range of 75.1 dBldrHz^2/3 , which is suitable for a wireless personal communication system adopting the analog fiber-optic link.     

基于相位调制器的宽带窄线宽的线性调频激光源的产生

提出了一种基于相位调制器(PM)和可调谐光滤波器产生线性调频激光信号的方法。该方法利用带有基频的微波线性调频信号作为相位调制器的驱动信号,窄线宽的激光种子源经相位调制器调制后产生一系列的宽带线性调频激光信号。通过可调谐光滤波器抑制其他边带保留所需阶次的线性调频激光信号。实验结果表明:当光滤波器保留正二阶调频激光信号时,获得了调频带宽为2 GHz、调频速率为6 THz/s的线性调频激光信号。在观测时间为1 ms时,测得的线性调频激光信号的瞬时线宽为3.2 kHz。该方法结构简单,易于实现,并且对调频连续波激光雷达、相干光谱分析等测量应用有重要意义。     

Stimulate Brillouin Scattering Based Broadband Tunable Slow-Light Conversion in a Highly Nonlinear Photonic Crystal Fiber

An integrated configuration is proposed to convert tunable slow light from signal to another frequency in a wide bandwidth by using a 70 m-long highly nonlinear photonic crystal fiber (HN-PCF). A 10 GHz RZ signal is delayed by a 10 Gbit/s $2 ^{31} -1$ pseudo random bit sequence (PRBS) stimulated Brillouin scattering (SBS) pump, and the slow light is converted to another frequency in a broadband by four-wave mixing (FWM). By this way, not only the slow light is converted, but the idler power is enhanced greatly. In our experiment, all-optical controlled 37.5 ps delay time is converted in a 40 nm bandwidth flatly, and 4.7 dB idler power is enhanced simultaneously. The experimental results are in good agreement with those of the theory.