基于四次乘方射频信号和级联MZM的梳线可调的光学频率梳

提出了一种基于四次乘方射频(radio frequency,RF) 信号和级联马赫- 曾德尔调制器(Mach-Zehnder modulator,MZM)的梳 线可调的光学频率梳(optical frequency comb,OFC)产生方案。利用乘方运算电路对正弦RF信号进行运算 耦合,产生的乘方RF信号驱动级联的MZM,调制器对输入光进行调制,从而产生梳线数可 调的平坦 OFC。建立了乘方RF信号驱动级联MZM产生OFC的理论模型,利用OptiSystem软件对其性能 进行了 研究。结果表明,OFC的梳线间隔是RF信号源频率的2倍,可调谐并且拓展了频谱带宽;产 生OFC的 目标梳线数是基准调制电压的4倍,实现了梳线数可调谐;调节MZM上下支臂的调制和偏置电 压差为确 定的优化值,可以使不同目标梳线数的OFC平坦度均小于0.95 dB。     

基于非线性光学差频及参量效应的太赫兹源

基于非线性光学技术的THz源具有其独特的性能和优点,将基于非线性光学差频原理和光学参量效应,从理论上研究并分析THz波与抽运光、闲频光及相位匹配角之间的关系,得到THz波输出的条件和范围,并设计出宽波段连续可调的THz源。以调QNd∶YAG激光器和光学参量振荡器(OPO)作为抽运源,以GaSe和MgO∶LiNbO3晶体作为差频非线性晶体,根据相位匹配理论及光学参量效应,搭建两套THz波产生系统。其中,基于光学参量效应的THz辐射源有效地产生出THz信号。     

产生外差输出的光学发生器

光频发生器可以发生比现用设备更低噪声和更低功耗的射频输出。由加州理工学院喷气推进实验室R．Logan申请专利的光学射频合成器产生具有1～100GHz以上频率范围的相位稳定、强度调制的光载波。利用光纤的多数应用，包括从通信到射频天文学都可从强度可调的微波和毫米波频率信号使用中获得好处。这种信号目前用光学和电子学方法产生。光外差信号振荡系统以调谐到稍不同频率f1和f2的两台连续波激光器为基础。这两台激光器的输出被组合，两个频率之差导致产生第三个频率，即拍频（f1-f2）。为产生所希望的拍频，该两激光的频率差可以选择。需…     

集成电光频率梳研究进展（特邀）

光学频率梳是由一系列离散且等间隔分布的频率成分所组成的光谱结构,作为光谱分析的天然刻度尺,其已广泛应用于光谱学、精密测量、光通信、传感等多个领域。光学频率梳根据其产生技术可分为基于锁模激光器的光学频率梳、克尔微腔光学频率梳、电光频率梳。电光频率梳由于其频率间隔可调、梳齿功率较高、可实现微波到光波的转换等优势,得到了充分发展。但传统电光频率梳的产生器件存在体积大、功耗高的缺点,限制了其进一步应用。随着微纳加工技术的不断发展,越来越多的材料应用于片上集成光学器件,包括硅、氮化硅、氮化铝、磷化铟、铌酸锂、砷化铝镓等。集成电光频率梳器件具有体积小、功耗低等优势,是构建光电集成芯片的重要器件。文中旨在对集成电光频率梳的研究现状进行综述,首先介绍光学频率梳的类型,并详细论述电光频率梳的产生机制;其次介绍产生集成电光频率梳的材料平台、相应的光梳性能指标及其应用;最后基于目前集成电光频率梳领域存在的问题,对未来的研究趋势做出展望。     

掺铒光纤飞秒光梳频率锁定研究

飞秒光梳可以直接实现光频到微波频率转换,广 泛应用于时频和计量领域,掺铒光纤 飞秒光梳因其良好的频率稳定性、鲁棒性和可搬运性而倍受科学家青睐。本文报道了对掺铒 光纤飞秒光梳载波包络相移频率和梳齿频率的锁定,通过控制腔内色散方法,利用反馈泵浦 驱动电流方法实现载波包络相移频率的锁定;利用控制光学腔长度的方法,通过反馈电光调 制晶体和压电陶瓷驱动电压实现了梳齿频率的频率锁定。最终得到载波包络相移频率和梳齿 频率的频率稳定度分别为2.3×10－16@ 1s和3. 5×10－17 @ 1s,并能长期稳定不间断锁频达到37 h。     

基于光学频率梳的可选频毫米波生成多业务分层WDM-ROF系统

针对波分复用-光纤无线通信（WDM-ROF）系统中采用的激光器阵列成本高、可扩展性与重构性差、生成的毫米波信号单一不可调、每个基站业务传输相同且可应用场合受限等问题，提出了基于光学频率梳（OFC）的可选频毫米波生成多业务分层WDM-ROF系统。在该方案中，采用光学频率梳作为系统的多载波光源，有利于系统的扩展与重构；在中心站（CS）预留部分光载波作为基站（BS）上行链路的光源，实现了基站上行传输的无光源化；在次级中心站（SCS）引入基于微机电系统（MEMS）的光开关矩阵，由MEMS光开关矩阵的不同种控制状态实现毫米波信号的可选频；构建具有分层结构的基站组（BSG），为每个基站提供多个业务的接入。建立了基于光学频率梳的WDM-ROF系统的理论模型，并进行了仿真研究。在仿真中获得了平坦度为0.58 dB、频率间隔为20 GHz的15线光学频率梳。在下行链路中，利用其中一种控制状态的MEMS光开关矩阵与光电探测器将两个不同的10 Gbit/s下行数据上变频，得到频率为35、45、65、95 GHz的4个毫米波信号，并根据不同应用场合分配给基站组中的两个基站（分层BSG），进行多个业务传输。经4...     

基于微腔光梳的低相噪微波信号产生(特邀)

低相位噪声微波信号在通信、雷达、时频计量、深空探测等领域中不可或缺,光子学微波信号产生近年来发展快速,有望在载波频率、调谐性、相噪、可集成、功耗等多个方面突破传统电子学微波信号产生瓶颈。早期的光生微波系统复杂,激光器以及相关稳定设备体积庞大,难以在实验室以外的场所应用。近年来,基于微谐振腔的光学频率梳的迅速发展,凭借其低损耗、小体积、强稳定的优势,基于微腔光梳的微波光子学应用吸引了研究者们的广泛关注,其中基于微腔光梳的光生微波系统得到深入研究。文中将综述国内外近10年来基于微腔光梳的低相噪微波信号产生发展状况,并对基于微腔光梳的光生微波系统在未来应用中的主要挑战与发展趋势作以展望。     

采用光学处理方法的被动太赫兹波综合孔径成像

综合孔径技术对于提高被动太赫(THz)成像系统的分辨率、减小系统体积有着重要的意义.研究了一种基于电光调制和空间光干涉成像的THz综合孔径成像技术.在该成像方法中,天线阵列接收目标辐射的THz信号,通过混频和电光调制将信号振幅和相位信息加栽到激光载波上,由光纤传输该激光信号并在光纤末端形成天线缩比阵列结构,最终利用光纤阵列输出光束的空间互相干在透镜焦平面上获得目标成像.分析了该成像方法的原理,以及成像中的信号变换与光学干涉处理的关键技术,并利用0.5 THz超导体一绝缘体一超导体(SIS)接收机进行了电光调制和干涉实验.结果表明:该方法能够应用于被动THz综合孔径成像.     

超宽带平坦多载波光源结构设计

为了解决波分复用系统中传统光源稳定性差、成本高、带宽小等问题,本文提出了一种超宽带平坦光源发生器结构,该结构基于级联的电吸收调制器和两个频率调制器,得到了频率间隔相同且可调的高带宽、平坦度小的多载波光源。在单波长光信号输入下,产生了大范围频率间隔可调平坦度小于0.2 dB的21个子载波的多载波光源,当驱动信号频率为8 GHz和9 GHz时,平坦度可达到0.07 dB;在多波长光信号输入下,得到了频率间隔为15 GHz,平坦度小于0.9 dB子载波数为275的超宽带平坦光源,频谱宽度可以达到THz以上。最后研究了10 GHz驱动信号下,电吸收调制器与频率调制器驱动信号的相位差、频率调制器的频率偏移以及电吸收调制器的啁啾因子对多载波光源的影响,结果表明,驱动信号的相位差在±10°上下波动时,平坦度最大改变了1.05 dB,频率调制器的频率偏移在±10 GHz范围内变化时,平坦度波动幅度仅为0.1 dB,表明该结构具有良好的稳定性和可控性。     

使用级联相位调制器和强度调制器产生平坦光学频率梳的方法

光学频率梳在光通信、光谱学等领域有广泛的应用。平坦度是光学频率梳重要的性能指标。使用级联相位调制器和强度调制器产生光学频率梳的方法，是让叠加的谐波驱动调制器，通过调节驱动电信号的幅度和相位以及强度调制器的偏置电压，可以实现平坦度好的光学频率梳。首先，建立光学频率梳的优化问题模型，通过差分进化算法得到上述各个参数，并得到在不同叠加微波驱动信号下的平坦光学频率梳。其次，固定某一微波驱动信号的相位，在同一优化问题下使用同样方法得到微波驱动信号的其他参数，并分析生成的平坦光学频率梳性能。最后，搭建实验系统，根据仿真得到的优化参数确定实验参数，并得到相应的光学频率梳。研究表明，当采用基频和三次谐波驱动相位调制器、采用四次谐波驱动强度调制器时，可以产生13根谱线的光学频率梳，仿真和实验时的平坦度分别为0.27 dB和0.83 dB。当采用基频、三次谐波和五次谐波同时驱动相位调制器和强度调制器时，可以产生19根谱线的光学频率梳，仿真显示其平坦度为0.56 dB。以上仿真和实验结果证明了所提方法的可行性和鲁棒性。     

Broadband-Frequency-Tunable Sub-Terahertz Wave Generation Using an Optical Comb, AWGs, Optical Switches, and a Uni-Traveling Carrier Photodiode for Spectroscopic Applications

We present a monochromatic sub-terahertz signal generation technique using an optical comb signal, arrayed waveguide gratings (AWGs), and a uni-traveling carrier photodiode (UTC-PD) for spectroscopic applications. This scheme offers random or continuous frequency tuning in the range between 100 GHz and up to 1 THz. In addition, since a RF synthesizer is employed as a reference signal source of the photonic frequency multiplier, frequency locking with external instruments and reliable operation are offered. Highly coherent optical comb signal for the photonic frequency multiplication provides a narrow linewidth and very low phase noise in the generated sub-terahertz signal. For 125 GHz, the phase noise is approximately $-92$ dBc/Hz at the offset frequency of 10 kHz. This is larger than that of the 25-GHz RF source by about 13 dB and agrees well with the theory regarding phase noise multiplications due to frequency multiplication. For generating monochromatic signals, unwanted spurious signals are suppressed in the optical domain over a wide range with two AWGs, and the suppression ratio is expected to be better than 46 dBc. Utilizing the implemented sub-terahertz signal generator with a J-band UTC-PD module, absorption lines of N$_{2}$O were measured in the frequency range between 240 and 360 GHz and compared with theoretical calculations.      

High Current Responsivity and Wide Modulation Bandwidth Terahertz Detector Using High-Electron-Mobility Transistor for Wireless Communication

A high-current-responsivity terahertz (THz) detector was fabricated using a broadband bow-tie antenna and an InAlAs/InGaAs high-electron-mobility transistor (HEMT) with a short gate length. High-current responsivity can be achieved by using a short gate length; the resulting high transconductance exhibited ballistic transport in the channel. We fabricated the HEMT detector with a 50-nm-long channel; the transconductance was 1.2 S/mm and the subthreshold slope was 120 mV/dec, yielding a high-current responsivity (～5 A/W) and a cutoff frequency of 460 GHz. We also measured the modulation bandwidth of the THz detector using a heterodyne mixing technique with a uni-traveling carrier photodiode (UTC-PD) for providing the radio frequency (RF) and a frequency multiplier as a local oscillator. The intensity of the intermediate signal (IF) was measured by changing the frequency of the UTC-PD; very high bandwidths of up to 26 GHz were obtained. The experimental results agree well with electromagnetic simulations, which indicate that the bandwidth is determined by the external circuit. The conversion gain from RF to IF was ?2 dB in the heterodyne mixing by using the HEMT detector.     

12-THz frequency difference measurements and noise analysis of anoptical frequency comb in optical fibers

A span up to 50 THz of optical frequency comb (OFC) has been obtained by self-phase modulation in an optical fiber. The coherent nature of the process was verified by heterodyne-detecting the sidebands offset by up to 12 THz from the carrier. The signal-to noise ratio (SNR) of the beat signal between a sideband at 12 THz offset and another single-mode laser was 32 dB in a 1-MHz bandwidth. Although the linewidth of each beat signal was maintained within a few megahertz, phase noise pedestal power increased with the offset frequency     

基于偏振复用技术的光频梳研究

为提高光频梳带宽和谱线平坦度,设计了一种基于偏振复用和电吸收调制(EAM)技术的光频梳产生方案。通过调整EAM参数产生除中心载波外的高平坦度光频梳,再结合偏振复用技术优化中心载波峰值功率,使得光频梳带宽整体提升一倍。文中讨论了相关参数对光频梳平坦度的影响,利用Optisystem软件搭建了基于该方案的微波频率可调载波重用全双工光载无线系统(RoF)。研究结果表明,在下行链路中当误码率为10^-9时,传输10 km与背靠背传输相比功率代价仅为0.42 dB。     

基于级联相位调制器和光衰减器的光频梳产生研究

提出了一种基于级联相位调制器和光衰减器的光 频梳产生方案,建立了方案的理论模型并进行了 系统验证,研究了射频(radio frequency,RF) 信号幅度和光衰减器衰减系数对光频梳平坦度的影响。结果表明数值 计算与实验 结果一致性较好,通过调整RF驱动信号幅度和光衰减器衰减系数可产生梳线数量为15条、平坦度为 0.8 dB,边模抑制比(side-mode suppression ratio,SMSR) 为5.05 dB的光频梳。方 案中引入滤波器后,在梳线数量保持不变的前 提下,其平坦度和SMSR可分别提高62.5%和61.4%。     

Wide-span optical frequency comb generator for accurate opticalfrequency difference measurement

An optical frequency comb (OFC) generator was realized for accurate optical frequency difference measurement of 1.5 μm wavelength semiconductor lasers by using a high frequency LiNbO₃ electrooptic phase modulator which was installed in a Fabry-Perot cavity. It was confirmed that the span of the OFC was wider than 4 THz. By using semiconductor lasers whose spectrum linewidths were narrowed to 1 kHz and a sensitive optical balanced-mixer-receiver for measuring beat signal between the sideband of the comb and the laser, we demonstrated a frequency difference measurement up to 0.5 THz with a signal-to-noise ratio higher than 61 dB, and a heterodyne optical phase locking with a heterodyne frequency of 0.5 THz in which the residual phase error variance was less than 0.01 rad². The maximum measurable frequency difference, which was defined as the sideband frequency with the signal-to-noise ratio of 0 dB, was estimated to be 4 THz     

一种基于DDS技术的新型宽带雷达信号源的设计

AD9858是Analog Devices公司的一款高性能DDS芯片,可产生多种形式的信号,在对DDS原理以及AD9858器件研究的基础上,介绍了一种基于AD9858的宽带雷达信号源的设计方案,可输出单点频正弦信号、基带CHIRP信号、基带BPSK信号、射频CHIRP信号、射频BPSK信号。射频CHIRP信号由基带CHIRP信号经过倍频链转换到相应频段,射频BPSK由基带BPSK经过混频转换到相应频段。输出信号形式可由上位机通过USB接口灵活控制。     

0.1～5GHz梳状谱发生器的设计与实现

梳状谱信号发生器在捷变频雷达、频标发生器等要求激励源同时输出数十个高纯频点中有着普遍的应用,同时在仪器设备中常常是扩展频带的关键器件。阶跃恢复二极管常用于梳状谱发生器及单阶高次的倍频器的设计。这里利用阶跃恢复二极管的强非线性特性,设计一个0.1到5GHz梳状谱发生器,输入信号为100MHz。首先通过理论计算和ADS辅助仿真获得初值,然后通过在真实系统上大量的实验获得最终结果。     

A new approach for a phase controlled self-oscillating mixer

The analytical and experimental demonstration of subharmonic synchronization and phase shifting of a push-pull self-oscillating mixer is presented for the first time. Inherent high mixing gain of the self-oscillating mixer circuit is exploited to generate a strong signal at the same frequency of the reference signal, which is related to the local oscillator's (LO) phase information. A phase error between this signal and the reference signal is extracted in a phase comparator before phase locking. Analytical modeling of frequency and phase stabilization of the push-pull self-oscillating mixer is presented, which is also experimentally verified for a self-oscillating mixer at 12 GHz. This self-oscillating mixer circuit demonstrates efficient phase locking, 0°-180° continuous phase shifting capability in addition to the reported large locking range (>10 MHz), low close-in to carrier phase noise (<7 dB degradation of a 6 GHz synthesized reference signal), and a high mixer conversion gain (>17 dB at 17 GHz). The demonstrated subharmonic phase locking approach replaces the need for a frequency multiplier or divider before the phase comparator. The synchronized push-pull self-oscillating mixer circuit is applicable to the millimeter-wave frequency distributed transmitters and receivers, where low-loss phase shifting and efficient subharmonic phase and frequency locking are hard to achieve