Tunable chirped microwave photonic filter employing a dispersive Mach-Zehnder structure

A Mach-Zehnder structure with modulation in one arm and dispersive time delay in the other is proposed to implement highly flexible single-bandpass chirped microwave photonic filters based on broadband optical sources. Both the amplitude response and the time delay slope can be fully reconfigured via control of the optical spectra and dispersion. The passband can also be widely tuned without changing the shape. A chirped filter with a bandwidth of ～4?GHz, a delay slope of ～-0.6?ns/GHz, and a tunability up to 40?GHz is demonstrated experimentally.     

Transmission Performance Improvement in Microwave/Millimeter-Wave Optical System Using Chirped Fiber Grating

A chirped fiber grating (CFG) written by the moving fiber/phase mask scanning beam technique with a uniform mask is used to demonstrate the dispersion compensation in the externally modulated microwave/millimeter-wave over fiber system. It is found that the use of the CFG is an efficient way to compensate for the severe RF power degradation induced by the fiber chromatic dispersion, which results in a significant improvement in the transmission performance. The signal to noise ratio is improved from 4.8 dB to 24.4 dB when 10.58 GHz RF signal carrying 5 Mbit/s QPSK format data is transmitted over 35 km single mode fiber.     

Multiple-element photonic microwave true-time-delay beamforming incorporating a tunable chirped fiber Bragg grating with symmetrical bending technique

We experimentally demonstrate a novel scheme for a multiple-element photonic microwave true-time-delay device with high tunability based on a tunable chirped fiber Bragg grating without center wavelength shift. We achieve the different true time delay by controlling the grating period of a chirped fiber Bragg grating based on the symmetrical bending technique as a multiwavelength signal source is applied to carry microwave signals. The proposed method does not require the complex structure of systems, wavelength tuning, and synchronization of optical devices such as tunable bandpass filters and optical input signals. We achieve the tunabilty of the time delay for a microwave signal carried over an optical signal in a range from 1 to 230 ps.     

Experimental study of wave propagation through a rapidly createdplasma

Frequency upconversion and converting a CW source microwave into a frequency upshifted and chirped periodic pulse have been demonstrated by two experiments. In the first one, the CW source microwave propagates through a periodically microwave-discharged plasma. The CW source microwave is converted into a periodic pulse having upshifted carrier frequency. The second one uses a high-voltage (~100-kV) DC discharge to generate a dense plasma suddenly between two parallel plates. A frequency upshifted and chirped pulse (~2 ns) converting from the CW source microwave interacting with the suddenly created plasma is observed. The central frequency (~6.4 GHz) of the pulse is upshifted from the frequency (~4.7 GHz) of the source wave by about 40%. Moreover, frequency components which are upshifted as high as 80% are also observed     

Active stabilization of a rapidly chirped laser by an optoelectronic digital servo-loop control

We propose and demonstrate a novel active stabilization scheme for wide and fast frequency chirps. The system measures the laser instantaneous frequency deviation from a perfectly linear chirp, thanks to a digital phase detection process, and provides an error signal that is used to servo-loop control the chirped laser. This way, the frequency errors affecting a laser scan over 10 GHz on the millisecond timescale are drastically reduced below 100 kHz. This active optoelectronic digital servo-loop control opens new and interesting perspectives in fields where rapidly chirped lasers are crucial.     

Millimeter-wave pulse generation based on pulse reshaping using superstructure fiber Bragg grating

A novel optical approach is proposed to generate millimeter wave (MMW) pulse signal based on the pulse reshaping of superstructure fiber Bragg grating (SSFBG). In our scheme, one input pico-second Gaussian pulse is transformed into n Gaussian pulses by the SSFBG reshaping firstly, and then the pulse train is replicated to form a required frequency modulation MMW optical pulse envelope by the linear chirped fiber Bragg grating (LCFBG) or other highly dispersive element. The high-speed photodetector (PD) and band-pass filter can transform the MMW optical pulse into an MMW pulse signal ultimately. Depending on this scheme, MMW signals with frequency up to 10 GHz can be easily generated by the completed fiber components.     

Frequency shifting of microwave signals by use of a general temporal self-imaging (Talbot) effect in optical fibers

A simple and practical microwave frequency-shifting technique based on a general temporal self-imaging (GTSI) effect in optical fiber is proposed, formulated, and experimentally demonstrated. The proposed technique can be applied to an arbitrary periodic microwave signal (e.g., a microwave tone) and provides unparalleled design flexibility to increase the frequency of the input microwave signal up to the desired value (limited only by the photodetector's bandwidth). For instance, we demonstrate frequency upshifting of microwave tones from approximately 10 to approximately 50 GHz and from approximately 40 to approximately 354 GHz. These results also represent what is to the authors' knowledge the first experimental observation of GTSI phenomena.     

Mode-locked performance of hybrid soliton pulse source utilizing fiber grating external cavity lasers

Mode-locking characteristic of hybrid soliton pulse source (HSPS) utilizing linearly chirped raised-cosine flat top apodized fiber Bragg grating (FBG) is investigated by using coupled-mode equations. It is found that the fundamental repetition frequency range of HSPS is significantly extended by using linearly chirped raised-cosine flat top apodized FBG instead of linearly chirped Gaussian apodized FBG. The range of repetition frequencies over which proper mode-locking is obtained is 2-3.3 GHz with linearly chirped raised-cosine flat top apodized grating whereas this range is 2.1-2.95 GHz with linearly chirped Gaussian apodized grating.     

用1～18GHz啁啾脉冲傅里叶变换微波光谱仪检测化学反应（英文）

傅里叶变换微波光谱仪是测量分子转动跃迁的主要工具,是研究分子转动光谱学的重要仪器。以量子力学为基础的转动光谱学对物质分子的结构分析以及破解射电望远镜所捕获的深空分子信号至关重要,这使得微波光谱仪在相关领域能发挥不可或缺的作用。目前,世界各国都在致力于研制和改进微波光谱仪以提高仪器的分辨率、灵敏度、以及应用范围,我国也正在该类仪器研制上进行积极的探索,期望为该领域做出应有的贡献。介绍了一种工作频段在1~18 GHz的宽带啁啾脉冲式傅里叶变换微波光谱仪的设计和研制。该光谱仪用于线性频率扫描的宽带啁啾脉冲信号由采样速率为1.25 GS·s^-1的任意波形发生器产生。宽带啁啾脉冲信号经混频和放大后可覆盖特定的频率范围,随即通过喇叭天线传播到样品真空室与超音速膨胀的气相样品分子束相互作用。样品分子被激发后发出的分子自由感应衰减信号由接收电路导出并放大,然后直接在高速数字示波器上数字化。该微波光谱仪的诸多电子器件均由计算机控制,利用开发的LabVIEW程序可实现仪器的自动化控制。应用气体喷嘴技术能有效降低待测样品气体束在检测室的转动温度,使仪器获得更好的检测灵敏度。应用多脉冲自由感应衰减技术能大幅度提高信号采样频率从而进一步提高仪器灵敏度。利用实验室研制的啁啾脉冲式傅里叶变换微波光谱仪对盐酸和叔丁醇的化学反应进行了监测,并成功检测到了该反应的产物叔丁基氯。通过测量天然丰度下反应产物叔丁基氯及其单取代37Cl同位素异数体的分子转动光谱数据,并利用光谱分析软件拟合这些数据后得到了叔丁基氯精准的光谱参数(转动常数,离心畸变常数,核四极耦合常数等)和分子结构信息。将以上参数和结构信息与高斯计算结果对比后证实了本实验宽带光谱仪检测到的光谱数据具有高精准度。通过对比前人所测的光谱数据进一步展示了该实验宽带光谱仪在低频范围内杰出的测试性能。     

Microwave photonic filter’s application on the microwave signal generation based on an active mode-locked fiber laser

A novel scheme which utilizes the microwave photonic filter technique for the optical generation of a microwave signal based on an active mode-locked fiber laser is proposed. A microwave signal generator using a microwave photonic filter based on a 2: 1 optical coupler with a fiber loop which can effectively suppress a low-order frequency component of the microwave signal is demonstrated and a ～10-GHz microwave signal is achieved based on an active mode-locked fiber laser with the original pulse repetition rate of ～5 GHz.     

Multiple-bipolar-tap tunable spectrum sliced microwave photonic filter

A spectrum sliced microwave photonic signal processor structure, which is all-fiber based and features simplicity, together with the ability to realize tunability, reconfigurability, bipolar taps, and multiple-tap rf filtering, is presented. It is based on thermally controlled optical slicing filters induced into two linearly chirped fiber Bragg gratings. Experimental results demonstrate the realization of versatile microwave photonic filters with frequency tunable, reconfiguration, and bipolar-tap generation capabilities.     

Direct EPR detection of transient and continuous wave signals at 2.5 GHz

Direct detection of free induction decays and electron spin echoes, and the recording of echo-detected EPR spectra and electron spin echo envelope modulation patterns at a microwave frequency of 2.5 GHz is demonstrated. This corresponds to the measurement of the transverse magnetization in the laboratory frame, rather than in the rotating frame as usually done by down-converting the signal (homodyne detection). An oscilloscope with a 6-GHz analog bandwidth, a sampling rate of 20 GigaSamples per second, and a trigger frequency of 5 GHz for the edge trigger and 750 MHz for the advanced trigger, is used in these experiments. For signal averaging a 3-GHz microwave clock divider has been developed to synchronize the oscilloscope with the frequency of the EPR signal. Moreover, direct detection of continuous wave EPR signals at 2.5 GHz is described.     

Multi-functional fibre-optic microwave links

The multi-functionality of microwave links based on remote heterodyne detection of signals from a dual-frequency laser transmitter is discussed and experimentally demonstrated in this paper. Typically, direct detection in conjunction with optical intensity modulation is used to implement fibre-optic microwave links. The resulting links are inherently transparent and mainly used for signal transmission. As opposed to direct detection links, remote heterodyne detection links can directly perform functionalities such as modulation, frequency conversion, and transparent signal recovery in addition to signal transmission. All three functionalities are presented and experimentally demonstrated with a remote heterodyne detection link based on a dual-frequency laser transmitter with two offset phase locked semiconductor lasers. In the modulating link a 1Gbit/s baseband signal is QPSK modulated onto a 9GHz RF carrier. The frequency converting link demonstrates up-conversion of a 100Mbit/s PSK signal from a 2GHz carrier to a 9GHz carrier with penalty-free transmission over 25km of optical fibre. Finally, the transparent signal recovering link transmits a standard FM video 7.6GHz radio-link signal over 25km of optical fibre without measurable distortion.     

Rotational spectrum of three conformers of 3,3-difluoropentane: Construction of a 480 MHz bandwidth chirped-pulse Fourier-transform microwave spectrometer

The rotational spectra for three conformers of 3,3-difluoropentane have been measured using both a newly constructed narrow bandwidth chirped-pulse Fourier-transform microwave spectrometer and a Balle-Flygare resonant cavity Fourier-transform microwave spectrometer. The chirped-pulse instrument produces a microwave pulse spanning up to 480 MHz bandwidth in the 7-18 GHz region by mixing a 1 μs chirped pulse (of up to 240 MHz bandwidth) from an arbitrary function generator with the output from a microwave synthesizer.Rotational spectra for the normal isotopic species and all possible ¹³C single substitutions were observed for the gauche-gauche and anti-gauche conformers, allowing a Kraitchman substitution structure and an inertial fit structure to be determined. ¹³C isotopic species and dipole moment components were not measurable for the less intense anti-anti species as a result of partially resolved fine splitting. Details of the new chirped-pulse instrument will be described and the structural results will be presented and compared with ab initio data for 3,3-difluoropentane.     

Performance limitation of chirped-fiber-Bragg-grating-based photonic microwave notch filter due to group delay and reflectivity ripples

We investigated the performance limitation of a frequency-tunable photonic microwave notch filter incorporating a chirped fiber Bragg grating (FBG) as a group delay line. In particular, we carried out theoretical and experimental studies to analyze the impact of the reflectivity ripple (RR) and group delay ripple (GDR) in the chirped FBG on the output notch performance. The results of experimental and theoretical analyses performed on a photonic microwave notch filter in which an S-bending-based linearly chirped FBG was incorporated, revealed that the notch depth and notch frequency were significantly affected by imperfections in the chirped FBG. The notch depth was found to be decreased by the RRs, whereas significant fluctuations in the notch frequency were caused by the GDRs. On the basis of the obtained results, we conclude that the RR and the GDR are the fundamental factors that degrade the performance of chirped FBG-based photonic microwave filters.     

光子型远程分布式微波信号接收码元速率估计

基于光子学技术,设计了一种针对远程分布式微波信号接收的码元速率估计方案。首先,远程终端将接收的微波信号经电光调制器对连续激光源进行载波抑制双边带调制,生成携带微波信号的两个光边带信号;此光信号经光纤链路传输至中心站在光域滤除其中一个边带;其次,进行光电探测,通过分析电频谱的谐波实现微波信号码元速率估计。针对此方案,搭建仿真及实验系统装置:仿真成功地从60 GHz微波信号中提取出0.8 GBaud和6 GBaud的二进制伪随机码(PRBS)信号码元速率、从25 GHz微波信号中提取出3GBaud的PRBS码元速率;实验成功地从25 GHz的微波信号中提取出3 GBaud和5 GBaud的PRBS码元速率。     

重复频率可调谐的超低抖动光窄脉冲源的研究

提出了一种新型的基于光电振荡器的重复频率可调谐的超低抖动光窄脉冲源. 光电振荡器系统可以产生超低相位噪声的微波信号; 被该信号调制的直调光经过两次相位调制之后, 使光脉冲的啁啾增强; 再通过一段色散补偿光纤, 光脉冲被进一步压窄. 实验中使用YIG可调滤波器, 可以得到8–12 GHz内步进为200 MHz的可调谐微波信号, 因此光脉冲的重复频率具有可调谐性. 当微波信号即脉冲重复频率为9.6 GHz时, 测得脉冲宽度为3.7 ps, 相位噪声为-130.1 dBc/Hz@10 kHz. 由此得出光脉冲的瞬时抖动为60.1 fs (100 Hz–1 MHz), 因此该方案产生的光窄脉冲源具有超低的抖动.     

Phase-locking transition in a chirped superconducting Josephson resonator

We observe a sharp threshold for dynamic phase locking in a high-Q transmission line resonator embedded with a Josephson tunnel junction, and driven with a purely ac, chirped microwave signal. When the drive amplitude is below a critical value, which depends on the chirp rate and is sensitive to the junction critical current I0, the resonator is only excited near its linear resonance frequency. For a larger amplitude, the resonator phase locks to the chirped drive and its amplitude grows until a deterministic maximum is reached. Near threshold, the oscillator evolves smoothly in one of two diverging trajectories, providing a way to discriminate small changes in I0 with a nonswitching detector, with potential applications in quantum state measurement.     

Chirped pulse Fourier transform microwave spectroscopy of 1,1,2,2-tetrafluoro-3-iodopropane

The pure rotational spectra of the two lowest energy conformers of 1,1,2,2-tetrafluoro-3-iodopropane have been investigated between the frequency limits of 7.5 and 16 GHz using chirped pulse Fourier transform microwave spectroscopy. Quantum chemical calculations have been performed to aid the spectral analyses. For the trans–trans conformer, which is calculated to be the lowest in energy, a total of 135 transitions were recorded. For the gauche–gauche conformer a total of 286 transitions were recorded. In both cases the complete iodine nuclear quadrupole coupling tensor has been determined.     

Soliton Transmission Using Actively Mode－locked Fiber Ring Laser at 2．5GHz and 5GHz

ＳｏｌｉｔｏｎＴｒａｎｓｍｉｓｓｉｏｎＵｓｉｎｇＡｃｔｉｖｅｌｙＭｏｄｅ－ｌｏｃｋｅｄＦｉｂｅｒＲｉｎｇＬａｓｅｒａｔ２．５ＧＨｚａｎｄ５ＧＨｚ￥ＺＨＯＮＧＳｈａｎ；ＬＯＵＣａｉｙｕｎ；ＬＩＵＪｕｎ；ＧＡＯＹｉｚｈｉ；ＺＨＯＵＢｉｎｇｋｕｎ（Ｄｅｐｔ...