Pulse timing stabilization of a mode-locked Cr:LiSAF laser

The pulse repetition frequency of a mode-locked Cr:LiSAF laser has been stabilized to an electrical reference oscillator by use of an electrical feedback technique. The phase and frequency differences between the laser and the reference are detected by use of a digital phase detector, which overcomes the difficulties of a conventional double-balanced mixer. We obtained rms timing jitters of 20 fs (25 mHz-10 kHz) and 7 fs (25 mHz-1 kHz) relative to the reference.     

频域稀疏采样和激光成像方法

激光的单色性和自然图像频谱稀疏且集中在低频区间的特点,使图像频谱稀疏采样成像成为可能.基于小规模激光探测器,引入参考激光,本文提出了频域稀疏采样激光成像方法.介绍了频域稀疏采样激光成像的原理和成像系统结构,推导了激光回波重构复频谱的表达式,给出了重构频谱和复图像的仿真结果并分析了信号参数对重构效果的影响,同时采用相干系数、均方误差和结构相似度来评价其重构效果.规模为256×256的激光回波复图像仿真表明, 5个拼接1/4×1/4规模频域探测器组成的近似十字型稀疏采样结构,在约31.25%(5/16)的频域稀疏采样条件下,仍可获得较好的重构频谱和重构复图像.     

Wideband tunable laser phase noise reduction using single sideband modulation in an electro-optical feed-forward scheme

A wideband laser phase noise reduction scheme is introduced where the optical field of a laser is single sideband modulated with an electrical signal containing the discriminated phase noise of the laser. The proof-of-concept experiments on a commercially available 1549 nm distributed feedback laser show linewidth reduction from 7.5 MHz to 1.8 kHz without using large optical cavity resonators. This feed-forward scheme performs wideband phase noise cancellation independent of the light source and, as such, it is compatible with the original laser source tunability without requiring tunable optical components. By placing the proposed phase noise reduction system after a commercial tunable laser, a tunable coherent light source with kilohertz linewidth over a tuning range of 1530-1570 nm is demonstrated.     

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。     

基于相位调制-解调的光纤激光相位噪声检测方法研究

在主动相位控制相干合成中,常用的光纤激光主动相位控制方法主要有外差法、多抖动法和随机并行梯度下降算法等. 基于多抖动法和外差法的原理,提出了一种新型的基于相位调制-解调的相位检测与控制方法. 该方法利用周期信号对参考光进行相位调制,将调制后的参考光与待检测信号光进行相干检测,通过对相干光强信号和相位调制信号的融合处理,实现相位噪声的检测和控制. 对该方法进行了数值模拟和实验研究. 实验结果表明,对于频率为2 kHz,噪声范围为[0,2π)的正弦噪声,相位检测精度优于λ/50,控制精度可达 关键词： 光纤激光 相干合成 相位噪声检测 调制-解调     

利用锁相环和TV-Rb钟控制飞秒激光脉冲的载波包络相移

为了实现对锁模飞秒钛宝石激光器的相位控制，采用改进的相移测量装置，使载波包络频移信号的信噪比提高到了40 dB以上.在此优化测量结果的基础上，利用电子锁相环技术，通过PZT改变激光器腔内端镜的倾斜将飞秒激光脉冲的载波包络相位锁定到了微波参考源TV-Rb钟10 MHz标准信号上，同时激光脉冲重复频率也采用另一个PZT控制激光腔长锁定到了同一个TV-Rb钟10 MHz信号上.锁定后的结果显示重复频率的锁定达到了TV-Rb钟本身的稳定度，而载波包络相位锁定后比锁定前稳定度提高了三个数量级.     

变光外差为电外差的双频激光探测

演示一种双频激光位移探测系统,阐述光载波激光雷达的概念。由单块非平面环形腔固体激光器和声光调制器产生100MHz载波频率的双频激光束,作为探测光束,经过光路收发系统,探测位于电动导轨上目标的位移变化,信号处理部分采用高速光电探测器响应后信号的电子外差解调方式,位移量的获得通过高频锁相放大器解算参考光束与信号光束的相位差并计算获得。通过双频激光把光学外差探测变为了电子外差探测,系统重复误差小于3%。系统在利用无线电雷达信号处理方式的同时,保留了激光探测的优点,位移测量系统具有良好的重复性。     

Phase-noise-compensated optical frequency domain reflectometry with measurement range beyond laser coherence length realized using concatenative reference method

A novel type of optical frequency domain reflectometry with a measurement range much longer than the laser coherence length is proposed and experimentally demonstrated. To reduce the influence of laser phase noise, the measurement signal is compensated by using reference signals generated from a single auxiliary interferometer supported by a newly proposed compensation process. The compensation is accomplished numerically with a computer for each section of the delay fiber length in an auxiliary interferometer after only one data acquisition. By using the proposed technique, it is confirmed experimentally that the laser phase noise is well compensated even beyond the coherence length.     

基于双音外差的电光相位调制器半波电压自校准测量方法

电光相位调制器是光纤通信系统、微波光子系统和相干光通信系统中的关键器件之一. 作为器件本征参数, 电光相位调制器的半波电压通常利用光谱方法和电谱方法进行测量. 光谱方法受到光源线宽和光谱仪分辨率限制, 测量的分辨率较低; 电谱方法则需要光电检测之前将相位调制转换成强度调制, 电谱方法的主要困难在于需要对探测器的不平坦响应进行额外校准. 提出了利用双音外差实现电光相位调制器半波电压自校准测量新方法, 该方法利用双音电光相位调制的边带与移频光载波的外差拍频, 对外差拍频信号进行频谱分析, 获得电光相位调制器的半波电压; 通过设定双音调制信号的频率关系, 克服了探测器光电转换中的不平坦频率响应, 实现了自校准测量. 该方法可扩展探测器和频谱仪的测试频率两倍以上, 节省至少一半的带宽需求. 与光谱测量方法相比, 该方法测试分辨率大幅提高且避免了光源线宽的影响; 与传统电域测量方法相比, 该方法无须额外校准, 无驱动功率和工作波长限制, 且对测试仪器带宽需求降低一半以上. 实验证实了所提方法获得的电光相位调制器半波电压的测量结果与光谱分析法获得的结果一致, 且大幅度地提高了测量范围和分辨率. 该方法提供了非常简单的电光相位调制器微波特性化分析方法, 对其他光电子器件分析也提供了参考.     

Frequency stabilization of diode laser to 1.637μm based on the methane absorption line

The frequency of an external-cavity diode laser has been stabilized to 1.637 μm by using the reference of absorption lines of methane.The method can be applied to wavelength division multiplexed optical communication,fiber-optic sensing systems,as well as the high-sensitivity detection of methane.The derivative-like error signal yielded by frequency modulation and phase sensitivity detection technology is inputted into the PI feedback loop circuit in order to stabilize the frequency to the line center.After stabilization,the frequency fluctuation of diode laser is held within 5.6 MHz,and the root of Allan variance of error signal reaches a minimum of 1.66×10-10 for an average time of 10 s.     

基于旋转相干光谱的整形飞秒激光转动动力学调控

我们实验上发展了基于飞秒激光旋转相干光谱的整形飞秒激光转动动力学调控方法,通过脉冲整形技术调控激发脉冲的光谱相位,从而实现对飞秒激光作用下转动态相干激发过程中复原信号及转动布居数的调控. 研究了飞秒激光旋转相干光谱对激光频谱相位的响应机制,突出了飞秒激光频谱相位在气相分子转动态相干激发中的重要作用. 为飞秒激光作用下生物大分子和团簇鉴别及结构探测研究提供了新的参考.     

Accurate monitoring of an interferometric fiber-optic sensor with a multimode semiconductor laser

A technique for monitoring interferometric sensors by correlation of the optical signal from the sensor with the signal from a phase-modulated reference interferometer is described. The technique is applied to temperature measurement with a fiber Fabry-Perot sensing head. We extend the 7 degrees C unambiguous measurement range obtained with a 1.3-mum laser diode as the light source to 43 degrees C by adding a second laser diode emitting at 1.55mum . Experimentally, a rms phase-measurement error of +/-0.28rad , corresponding to a temperature error of +/-0.32 degrees C , was achieved with a low-quality multimode Fabry-Perot laser. The phase error was improved to +/-0.14rad , corresponding to a temperature error of +/-0.16 degrees C , by use of a distributed-feedback laser diode.     

高斯白噪声相位调制的激光光谱展宽

激光器是现代光学中一种常用的光源,分析其谱宽特性对于激光的研究具有重要意义.由于高性能窄线宽激光的半高全宽通常在几十M Hz以内,难以直接满足宽光谱领域的应用需求,因而无法发挥其在成本和性能方面的优势,这在一定程度上限制了激光的发展.如果在激光内部直接进行调制实现线宽展宽,又会导致频率的严重漂移,破坏稳频特性.为了在激...     

相位式激光测距全数字锁相环控制系统

针对减小相位式激光测距中的误差,介绍了一种基于现场可编程门阵列（FPGA）实现的全数字锁相环（ADPLL）控制系统的技术原理。此系统可以提高相位频率检测器的精度,同时不受温度和电压的影响,大幅降低相位式激光测距在测相过程中的频率误差。系统主要由数字鉴相器、数字滤波器和数字控制振荡器等逻辑设备组成,系统中的信号全部为数字信号。实验结果表明,当FPGA内部的参考信号为40 Hz时,采样周期为0.025 s,滤波器在300 ms达到约5 V的电压饱和状态。ADPLL系统避免了模拟电路中常常遇到的不全传输、寄生能力、温度浮动及老化等问题,并且可以在使用重置器件的情况下运行,因此很容易测试和复原。     

Signal processing method of phase correction for laser heterodyne interferometry

A novel signal processing method of movement direction identification and phase correction is presented for laser heterodyne interferometry. Based on the reference signal, four intervals with phase difference of 90° each other are set up. The real-time movement direction identification and the integer fringe counting are realized by detecting the times that the rising-edge of the measurement signal crosses the intervals. The phase correction approach is proposed in detail to solve the fraction phase compensation when the initial phase difference is not equal to the zero phase difference. Three experiments of the stability test, the nanometer and micrometer displacement tests on bi-directional movement were performed to demonstrate the usefulness and feasibility of the presented signal processing method.     

Achieving strong doubling power by optical phase-locked Ti:sapphire laser and MOPA system

We show two external cavity-enhanced second-harmonic generations of 922 nm with periodically poled potassium titanyl phosphate crystal,whose doubling cavities are locked separately with Hansch-Couillaud and intra-modulation methods.The outputs of second-harmonic generation reach 310 mW,54.8%of the conversion efficiency from the Ti:sapphire laser with the crystal length of 10 mm,and 208 mW,59% of the conversion efficiency from the MOPA system with the crystal length of 30 mm.It consists of heterodyning the Ti:sapphire laser and the MOPA system,and compares the phase of the beat frequency signal with the phase of a reference RF local oscillator.The resulting phase error is used as a feedback signal and fed back to the reference cavity of the Ti:sapphire laser to lock the two lasers in phase.A stable blue power of 520 mW is obtained,which supplies enough power for the cooling and trapping step of the strontium (Sr)optical lattice clock.Four stable isotopes of Sr, 84 Sr, 86 Sr, 87 Sr,and 88 Sr,are detected by probing the laser during a strong 460.7-nm cycling transition(5s 21 S0?5s5p 1 P1).     

用于光频传递的通信波段窄线宽激光器研制及应用

通信波段窄线宽激光器在基于光纤的光学频率传递中有着重要应用. 本文报道了1550 nm超窄线宽光纤激光器的研制及其在光学频率传递中的初步应用结果. 利用一台激光光源, 分别锁定到两个参考腔上(精细度分别为344000和296000), 锁定后经拍频比对测得单台激光线宽优于1.9 Hz, 秒级频率稳定度为1.7×10^-14, 优于国内同类报道. 将研制的超窄线宽激光器用于光纤光学频率传递, 在50 km光纤盘上实现了 7.5×10^-17/s的传递稳定度, 较采用商用光纤激光器提高了3.2倍.     

Measurement of dynamic characteristics of metal sheet under laser shock

A new approach is developed to measure the dynamic characteristics of metal sheet under laser shock,including deformation velocity,strain,and strain rate.The detecting laser beam is partially shaded by the target deformation induced by the laser action.A photodiode transforms the received beam intensity real time into an electrical signal which could record the process of the target deformation.The functional relation between the electrical signal and the deformation of the metal sheet is derived.The deformation curve of a thin aluminum and the velocity curve of its deformation are also obtained during the exper-iment.The results indicate that the average velocity of the elastic deformation of the target can reach 2.999×10 3 m/s in the central area.This new method provides an approach in the study of the effect of strain rate on deformation.     

Rare-earth-doped materials for applications in quantum information storage and signal processing

Realization of practical quantum memory and optical signal processing systems critically depends on suitable materials that offer specific combinations of properties. Solid-state materials such as rare-earth ions doped into dielectric crystals are one of the most promising candidates for several quantum information storage protocols, including quantum storage of single photons. This article provides an overview of rare-earth-doped material properties and summarizes some of the most promising materials studied in our laboratory and by other groups for applications in quantum information storage and for ultra-wide bandwidth signal processing. Understanding and controlling spectral diffusion in these materials, which ultimately limits the achievable performance of any quantum memory system, is also briefly reviewed. Applications in quantum information impose stringent requirements on laser phase and frequency stability, and employing a narrow spectral hole in the inhomogeneous absorption profile in these materials as a frequency reference can dramatically improve laser stability. We review our work on laser frequency and phase stabilization and report our recent results on using a narrow spectral hole as a passive dynamic spectral filter for laser phase noise suppression, which can dramatically narrow the laser linewidth with or without the requirement of active feedback.     

A technique for frequency stabilization of an internal mirror He-Ne laser

A technique for frequency stabilization of an internal mirror He-Ne laser using phase sensitive detection without cavity length modulation is suggested. The orthogonally plane polarized modes are separated and then convered into two photoelectric signals using two photodetectors. The photoelectric signals are switched alternately so as to generate a square wave, whose amplitude is proportional to the intensity difference between the two orthogonal polarizations. A lock-in amplifier is used to detect this square wave, with the switching frequency as reference. The phase detected signal is used for thermal stabilization of the laser. The frequency stability of 5 × 10⁻⁹ was obtained with an integration time of 1 s.