基于双声光移频器的外差式激光多普勒测振计

分析了单声光移频器构成的外差式激光多普勒测振计中声光移频器驱动信号的频率稳定性和信号功率对待测振动信号的影响.为了降低声光移频器驱动信号频率漂移的影响,提出双声光移频器构成的外差式激光多普勒测振计,并基于直接数字频率合成技术,以相位噪音低、初始相位可控的芯片AD9912为核心器件,完成了声光移频器驱动信号生成及处理模块的设计.开展了双声光移频器组成的外差式激光多普勒测振计的振动测量实验,结果表明,驱动信号生成装置可以驱动声光移频器正常工作,且测振计的本底噪音在0~10kHz频带范围内呈现平坦分布,0~1kHz频段内噪音得到明显抑制,较单声光移频器构成的外差式激光多普勒测振计有显著改善.     

声光移频器对微多普勒效应探测的影响研究

为实现基于微多普勒效应的远距离目标探测和识别,研究了采用声光移频器的激光外差相干探测结构对目标微多普勒特征探测的影响。建立了声光移频器驱动功率与系统信噪比之间的数学模型,并进行了仿真计算,搭建了1550 nm激光外差/零差相干探测实验平台对所建模型进行了验证。研究结果表明:在移频器驱动电压限定范围内,驱动电压越高,对微多普勒效应探测的效果越好,得到的目标特征越明显,与理论分析一致。通过对比实验发现在同样条件下,外差探测得到的反映目标特征的时频分布曲线较零差的清晰,特征提取误差小,可读性更高,说明外差探测结构更有利于复杂的远距离目标探测。     

激光多普勒微振动信号的直接强度解调

在传统的激光多普勒测振方法中,频移信号的检测通常需要具有比较复杂的频率或相位解调系统。从激光多普勒频移和干涉理论出发,提出了一种测量振幅小于纳米量级的方法———直接强度解调法。分析了直接强度解调法的适用范围。实验中利用了迈克尔逊干涉仪结构,采用了直接强度解调的方法。对振幅约为1nm的振动信号来说,其信噪比为23dB。     

基于频移反馈腔的全光纤射频调制脉冲激光研究

射频调制的脉冲激光是激光雷达探测领域内的一项重要研究内容.根据声光斩波器的强度和频率调制特性,设计了基于频移反馈腔的全光纤射频调制脉冲激光.理论上,建立了基于频移反馈腔的激光外差相干理论模型,并进行了数值仿真.根据理论模型,实验上严格控制频移反馈腔的长度和声光斩波器触发信号的周期,在100 MHz的射频信号驱动下,产生了脉冲宽度110 ns、重复频率约20 kHz的具有最高700 MHz射频调制的脉冲激光(脉内调制激光);同时微调斩波周期可以实现脉冲前沿或后沿的多样性射频调制.通过改变反馈腔内光纤放大器的输出功率实现了射频调制深度的连续可调,最高达到了0.67.     

采用声光频移器反馈控制实现激光强度稳定

本文基于声光频移器,采用光电反馈方式实现了激光强度的稳定控制。根据声光频移器的布拉格衍射对激光强度的调节作用,以光电反馈得到的反馈电信号控制驱动声光频移器的射频功率大小,进而对声光频移器的输出激光强度进行稳定,激光在47 kHz以下的低频噪声实现最大抑制比为15 dB。实验结果基本满足了所要求的激光稳定度。此外还分析了整个回路的响应特性,测试了除反馈电路之外其他部分的相移特性。     

10～500 kHz水听器的激光外差干涉法原级校准

阐述了水听器在10~500 kHz频率范围的激光外差干涉法原级校准的原理和测量装置。利用激光外差干涉系统非接触测量水中反光薄膜在声波调制下引起的多普勒频移,经过零点信号解调算法得到水质点振速,准确复现水下声压量值,之后将水听器置于水中测量点完成对其自由场电压灵敏度的原级校准。对各误差因素进行了分析,详细给出了系统测量不确定度的评定方法,在所测频段的不确定度为0.6 dB (k=2)。将激光外差干涉法水听器校准结果与自由场互易法结果进行了对比,在整个测量频率范围内结果等效,且前者不确定度更小。为建立新的水声计量基准和实现水声量值的扁平化传递奠定了基础。      

一种相位调制激光多普勒频移测量方法

对相位调制拍频信号随信号光频率变化规律进行分析,发现拍频信号相位参量的频谱包含两个在值域上彼此分开的单调边缘,表明利用拍频信号的相位参量可以进行多普勒频移测量.如果利用拍频信号振幅参量对出射激光进行工作点锁定,其多普勒频移测量范围是Fabry-Perot干涉仪边缘技术的两倍.理论分析拍频信号振幅和相位参量的提取方法,表明基于此拍频信号相位参量的测量方法无需进行信号光能量检测,与Fabry-Perot边缘技术方法相比,结构更简单,且少了一条外部噪音混入的通道.为了对该多普勒频移测量方法定量分析和参量优化,利用误差合成原理以及计算机仿真,推导出其测量误差公式.根据测量原理搭建了实验系统,用频率可调光纤激光器的输出光模拟多普勒频移信号光进行测量,结果表明鉴频参量及其误差分布曲线的测量结果与理论分析相符合.     

多级复合环路光学锁相环技术研究

星间相干通信系统其多普勒频移达到了吉赫兹量级,同时受到调谐激光器线宽、相位噪声的影响,对光学锁相环路系统提出了高要求。依据科斯塔斯锁相环技术原理,将温度调谐、压电陶瓷(PZT)调谐、声光移频器(AOFS)调谐复合到一起,通过内环与外环方式对本振激光器进行调控,实现光学锁相功能。搭建实验测试系统对环路性能进行测试,结果表明:此系统可达到锁相范围为4GHz,锁相带宽为1.7 MHz,实现了信号光与本振光之间的多普勒频移跟踪、激光器线宽补偿及相位快速锁定,最终相位残余误差5.1°。     

激光微多普勒探测系统中降低相位噪音影响的方法研究

相干微多普勒激光雷达具有探测灵敏度高、探测信息量大等特点,特别适合于动目标探测、目标特征识别等应用.本文从线宽和探测距离两个方面讨论了模场相位随机起伏（相位噪音）对于测速准确度的影响,实验证实了相位噪音对激光微多普勒探测的影响,并探索出解决上述问题的方法——光纤补偿法.实验中,以输出波长为1.064 μm单块非平面环形腔激光器为光源,利用光纤补偿方法,并结合时频变换的算法,用外差探测的方式成功观测到了微多普勒频移,在传输距离为11 km时,系统最低探测速度达到了0.5 mm/s,速度分辨率达到了mm/s量级,频率分辨率达到了kHz量级,为微多普勒激光雷达的实际应用奠定了良好的实验基础.     

激光多普勒技术在固体测量方面的运用

介绍了激光多普勒测量技术的原理和后散射型固体表面测量方式。通过声光调制器的偏频后 ,能够确定物体的运动方向。对多普勒信号进行光学外差处理并对多普勒信号进行测相 ,可以提高测量的精度。用差动微分多普勒技术进行测量 ,可以消除由固体表面特性和激光光强的波动引起的误差。     

舰船辐射噪声模拟发射系统的设计研究

本文依据典型舰船噪声的频谱特性规律,设计研制了一套舰船辐射噪声发射系统实验样机,包括信号结构设计、换能器选择配置、系统构成设计等,本噪声模拟发射系统具有100Hz～16kHz频带噪声的模拟发射功能,包括线谱、连续谱成分,频谱分配和谱线形式可调可控,信号总声源级动态范围达60dB。     

TDI CCD成像系统的研究

采用IL E2TDICCD作为传感器 ,与计算机构成了成像系统 ,并在计算机CRT上显示出图像。解决了CCD的时序电路及功率驱动电路设计问题。采用相关双采样技术滤除CCD输出信号复位噪声 ,提高了视频信号的信噪比。CCD的数据传送速度达到 10MHz ,行扫描速度达到 3.5kHz。     

A W-band Frequency Source with Low Spurs and Low Phase Noise

A W-band millimeter wave frequency source is developed by frequency multiplier chain and injection locking. The referenced crystal oscillator (CO) signal 120 MHz is multiplied 400 times to output 48 GHz signal. Then, it is used as a referenced source of fundamental-wave injection-locked harmonic Gunn oscillator with output power more than 10 mW at 96 GHz and spurious output less than −65 dBc. The measured phase noise is −97 and −105 dBc/Hz at 10 kHz and 200 kHz offset, respectively. At last, the influence of the flicker noise, provided by the frequency multipliers and amplifiers, is analyzed.     

Frequency Sources in W-band Radar Front-end with Low Phase Noise

A W-band coherent stepped-frequency pulsed radar front-end is developed. It consists of a millimetre wave transmitting source, a mm-wave local source, a DDS with multi frequency points output and two microwave sources serving as local oscillators. All the sources are coherent with the 120 MHz referenced crystal oscillator. The mm-wave sources are realized by frequency multiplier chain, up-conversion and injection locking. The phase noise of fundamental-wave injection-locked W-band harmonic Gunn oscillator output signal achieves −98 dBc/Hz at 10 kHz offset and the spurious output is less than −50 dBc. The received intermediate frequency signal is also presented.     

一种铷原子频标频率综合器新方案的设计与实现

数字化和小型化是铷原子频标（RAFS）发展的重要方向．在传统铷原子频标电路中,6 840 MHz微波信号与频率综合器产生的5.312 5 MHz信号进行混频,得到用于激励铷原子跃迁的6 834.687 5 MHz微波探寻信号．早期铷频标的频率综合器大量使用了分立的模拟器件,数字化程度低、参数优化工作繁杂、电路体积较大．目前常用直接数字频率合成器（DDS）方案直接产生5.312 5 MHz信号,但这种数字电路方案通常需要对10 MHz信号进行倍频,它存在频谱纯度较低、相位噪声高等缺点．本文介绍一种产生5.312 5 MHz信号的频率综合器解决方案,这种设计方案在应用DDS器件时无需使用10 MHz倍频电路,它具有频谱纯度较高、相位噪声低、输出频率和相位可调等优点．     

Regenerative mode locking via superposition of higher-order cavity modes in composite cavity fiber lasers

We demonstrate a new method of optical pulse generation in regeneratively mode-locked fiber ring lasers (RML-FRLs). The method is based on generating dominant longitudinal modes in the fiber ring cavity by means of a composite cavity structure and their intermode beating at the photodetector incorporated in the regenerative feedback loop. The beat signal is then used as a modulation signal to generate optical pulses in a regenerative mode-locking scheme, thereby eliminating the requirement for a high-Q rf bandpass filter in a conventional RML-FRL. Optical pulses with a repetition frequency of 3.6 GHz have been generated successfully with a supermode noise suppression of more than 48 dB and a low phase noise of -85 dBc/Hz at 10 kHz offset from the carrier frequency.     

Generation of desired signals from acoustic drivers

A general but systematic procedure has been developed to control transient signal generation for the study of internal noise propagation from aircraft engines. Transform techniques are used in a simple algorithm to produce signals—pulses in this study—of any desired waveform from acoustic drivers. By a judicious input, the accurate driver response function is calculated. From the driver response function the limiting frequency characteristics are determined. The undesirable frequencies where the driver response is poor are eliminated from the analysis. The inverse of the response function is then convolved with the desired signal to produce a synthesized signal. The shape of the synthesized signal is in general quite awkward, in both the time and the frequency domain. Nevertheless, when the distorted signal is fed into the driver, the driver generates the desired signal. The driver is operated in two environments—in a free field and in a duct—and results are presented to show the impedance matching effect of the driver. A set of results with a high frequency cut-off value as a parameter is given to demonstrate the extent of the applicability of the synthesis procedure. The error in the numerical inversion is highlighted. The results show that, within the imposed guidelines, it is possible to generate desired signals through the signal synthesis procedure.     

Microwave frequency modulation in CW EPR at W-band using a loop-gap resonator

Loop-gap resonator (LGR) technology has been extended to W-band (94GHz). One output of a multiarm Q-band (35GHz) EPR bridge was translated to W-band for sample irradiation by mixing with 59 GHz; similarly, the EPR signal was translated back to Q-band for detection. A cavity resonant in the cylindrical TE011 mode suitable for use with 100 kHz field modulation has also been developed. Results using microwave frequency modulation (FM) at 50 kHz as an alternative to magnetic field modulation are described. FM was accomplished by modulating a varactor coupled to the 59 GHz oscillator. A spin-label study of sensitivity was performed under conditions of overmodulation and gamma2H1(2)T1T2<1. EPR spectra were obtained, both absorption and dispersion, by lock-in detection at the fundamental modulation frequency (50 kHz), and also at the second and third harmonics (100 and 150 kHz). Source noise was deleterious in first harmonic spectra, but was very low in second and third harmonic spectra. First harmonic microwave FM was transferred to microwave modulation at second and third harmonics by the spins, thus satisfying the "transfer of modulation" principle. The loaded Q-value of the LGR with sample was 90 (i.e., a bandwidth between 3 dB points of about 1 GHz), the resonator efficiency parameter was calculated to be 9.3 G at one W incident power, and the frequency deviation was 11.3 MHz p-p, which is equivalent to a field modulation amplitude of 4 G. W-band EPR using an LGR is a favorable configuration for microwave FM experiments.     

A novel frequency sextupling scheme for optical mm-wave generation utilizing an integrated dual-parallel Mach-Zehnder modulator

A novel scheme is proposed for frequency sextupling mm-wave generation based on a laser and an integrated dual-parallel Mach-Zehnder modulator (MZM) without optical filter. Theoretical analysis is presented to suppress the undesired optical sidebands for the high quality generation of frequency sextupling mm-wave signal. The performance of the proposed scheme is evaluated by simulations. Utilizing the integrated MZM consisted of two sub-MZMs with extinction ratio of 30 dB, the optical sideband suppression ratio (OSSR) is as high as 29.9 dB and the radio frequency spurious suppression ratio (RFSSR) exceeds 24 dB without any optical or electrical filter. The impact of the nonideal RF driven voltage and phase difference of RF driven signal applied to two sub-MZMs of the integrated MZM on OSSR and RFSSR is discussed and analyzed. After transmission over fiber, the generated optical mm-wave signal demonstrates good performance. Furthermore, the performance of two cases for the proposed scheme is also compared.