Subpicometer length measurement using heterodyne laser interferometry and all-digital rf phase meters

We present an all-digital phase meter for precision length measurements using heterodyne laser interferometry. Our phase meter has a phase sensitivity of 3 μrad/√Hz at signal frequencies of 1 Hz and above. We test the performance of our phase meter in an optical heterodyne interferometric configuration, using an active Sagnac interferometer test bed that is flexible and low noise. We demonstrate more than 70 dB of laser frequency noise suppression to achieve an optical phase sensitivity of 5 μrad/√Hz and a corresponding displacement sensitivity of 0.5 pm/√Hz at signal frequencies above 10 Hz. In addition, we demonstrate the ability of our phase meter to follow full fringe signals accurately at 100 Hz and to track large signal excursions in excess of 10(5) fringes without cycle slipping. Finally, we demonstrate a cyclic error of ≤1 pm/√Hz, above 10 Hz.     

Instantaneous frequency measurement applied to semiconductor laser relaxation oscillations

The frequency of relaxation oscillations in the output power of lasers, particularly semiconductor lasers, is an important parameter which can be used to inform other fundamental laser variables, for comparison with expected theory, and to show the effect of external influences, such as optical feedback, by a change in value. Thus, precision measurement of the relaxation frequency is important. Instantaneous frequency measurement algorithms are applied to experimental semiconductor laser relaxation-oscillation signals to determine whether reliable values can be extracted, for an extended range of injection current, as compared to direct measurement and fast Fourier transform techniques. Improvement is achieved but, more importantly, the technique clearly shows when other oscillations, such as those due to packaging, connectorization and power supply, dominate the oscillatory component of the output power, at low injection currents. The work further supports the finding that only mid-range injection currents can be used for reliable precision relaxation oscillation frequency measurement.     

相干长度可连续调谐的半导体激光器

实验利用光反馈的方法获得了相干长度连续可调的半导体激光光源.通过调节反馈强度及抽运电流,有效控制了光反馈半导体激光器的相干长度.其相干长度可由无反馈时的几米连续调至100 μm.同时,利用光反馈半导体激光器速率方程,数值模拟了反馈强度及抽运电流对半导体激光器相干长度的影响.实验及数值模拟均表明：通过调节反馈强度的大小可以有效控制半导体激光器的相干长度,光反馈半导体激光器的相干长度随反馈强度的增大而减小,而偏置电流对相干长度无明显影响.模拟结果与实验结果符合. 关键词： 光反馈半导体激光器 相干长度 反馈 混沌     

共光路移相单频激光干涉测长系统

单频激光干涉系统采用偏振光移相方法,用来解决常规单频激光干涉仪中的光强"零漂"问题。共光路设计提高了干涉系统的测量稳定性和重复性。采用光程差放大技术提高了干涉系统的分辨力。在构造了一套实验布局的基础上,分析了影响系统测长精度的主要因素,并对干涉系统的测量误差分量做了定量的分析,完成了系统的精度测试。     

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.     

利用非锁定飞秒激光实现太赫兹频率的精密测量

频率是电磁波最重要的一个基本物理量,随着THz技术的发展,在光源研制、宽带通信、超精细光谱测量等领域都对THz频率的高精度侧量提出了要求.传统的Fabry-Perot干涉法与外差探测法难以实现THz频率的高精度测量,频率梳方法虽然测量精度很高,但测量系统复杂.本文提出一种利用重复频率自由漂移的飞秒激光器实现太赫兹频率精密测量的新方法.通过对非锁定的飞秒激光器的重复频率和THz拍频频率进行同时连续采集与计算,得到被测THz频率,测量精度可以达到10~(-10)量级无需对飞秒激光重复频率进行复杂的锁定控制,测量系统大大简化.     

High-resolution measurement of fiber length by using a mode-locked fiber laser configuration

A simple method to precisely measure fiber length has been experimentally demonstrated by using a mode-locked fiber laser configuration. Since the transit time in a cavity is exactly proportional to the cavity length, it is easy to obtain the fiber length from the generation of mode-locked pulses in the fiber laser with a long-range nonlinear optical loop mirror that includes the measured fiber. Our new method has a large measurement range, over hundreds of kilometers, and a high resolution, of the order of centimeters, as well as no measurement dead zone.     

Water vapour density measurement in halogen lamps using near-infrared semiconductor laser spectrometry II Actual lamp bulb measurement

Non-destructive, quantitative measurement for the amount of water vapour included in halogen lamp bulbs has been carried out. Residual water vapour density in lamp bulbs was confirmed as several hundreds of ppm by using a working curve obtained by InGaAsP/InP semiconductor laser spectrometry in the 1.36m spectral region.     

Encoder and strain gauge using laser speckle

Applications of the electronic correlation of speckle pattern to the measurement of surface displacement and strain are described. Basic principles including speckle displacement properties and experimental results using a laser diode and line image sensors are presented.     

激光跟踪测量系统自校正方法研究

建立了测量系统运动学模型。针对以往在球坐标激光跟踪系统中参考点只能借助于外部更高精度的仪器来校正的缺点,提出了平面约束自校正方法,并对系统进行了自校正研究。仿真结果表明了该方法的有效性。     

Enhancing the relaxation oscillation frequency of a chaotic semiconductor laser transmitter using optical dual-feedback light

A method to enhance the relaxation oscillation frequency and carrier bandwidth of a delayed feedback semiconductor laser transmitter is presented using additive optical feedback light. A formula for frequency detuning of the optical dual-feedback is developed to demonstrate that frequency detuning is added with the additive optical feedback light level. The function of the relaxation oscillation frequency of the chaotic laser is theoretically determined to show that it can be broadened by including the delay time and feedback level. Numerical results demonstrate that the bandwidth with the additive optical feedback light can be enhanced 1.7 times more than the bandwidth without it and the relaxation oscillation frequency of the chaotic laser is increased to 1.8 times more than that of the laser without it. The current can enhance the relaxation oscillation frequency and bandwidth of the transmitter more efficiently.     

高测速双频激光干涉仪

现代机械工业的发展使得数控机床和三坐标测量机等的运行速度已经达到 10 0 0 mm/ s,而目前商用外差干涉仪的测量速度不能满足这一要求。为此研制了一种基于 5 MHz频差双反射膜激光器的高测速干涉仪。通过实验对干涉仪的测量速度进行了验证。实验证明 ,该种干涉仪可以对速度为 10 0 0 mm/ s的运动物体进行位移和速度测量     

半导体激光器拍摄全息图的研究

半导体激光器输出的光束为椭圆高斯光束,若直接用于全息照相非常不利.采用梯形棱镜对将半导体激光器输出光束进行整形,并且在输出光束束腰位置进行全息照相,拍摄的全息图效果非常逼真.     

Intracavity frequency doubling of a diode-pumped external-cavity surface-emitting semiconductor laser

We present a compact, robust, solid-state blue-light (490-nm) source capable of greater than 5 mW of output in a TEM(00) mode. This device is an optically pumped, vertical external-cavity surface-emitting laser with an intracavity frequency-doubling crystal.     

Bit-error rate and frequency response in superregenerative semiconductor laser receivers

A superregenerative receiver scheme developed for radio communications is translated to the scope of optical communications. Starting from application of the quasi-deterministic theory to the single-mode Langevin rate equations, closed expressions for basic parameters and features, such as bit-error rate and frequency response, are obtained. A comparison of superregenerative receivers with well-established optical receivers shows that improvements in direct-detection receiver sensitivities of more than 10 dB can be obtained; this places superregenerative receiver sensitivities closer to the shot limit. Moreover, the intrinsic frequency selectivity of the superregenerative scheme makes it especially suitable for wavelength-division multiplexed systems. Finally, appropriate devices for implementation of this receiver are suggested.     

卡尔曼滤波在激光跟踪测量系统中的应用

激光跟踪测量系统对于测量运动目标空间位置是行之有效的,但在测量过程中,各种干扰噪声的影响会降低测量精度。采用卡尔曼滤波来减小噪声的影响以提高测量精度。介绍了激光跟踪测量系统,建立了状态方程和测量方程,给出了卡尔曼滤波算法,仿真结果表明,运用卡尔曼滤波大大提高了测量系统的精度。     

Linewidth measurement of Littrow structure semiconductor laser with improved methods

In this Letter, the frequency noise spectrum is analyzed in the experiment of the laser linewidth measurement. The power spectrum of three most widely used laser linewidth measurement methods, i.e., the heterodyne measurement, the self-homodyne measurement and the self-heterodyne measurement, are restudied both theoretically and experimentally. A scheme adopting an avalanche photodetector (APD) in the delayed self-heterodyne (DSHT) method is proposed, and an indirect determined result is given.     

Frequency stability measurement of a transfer-cavity-stabilized diode laser by using an optical frequency comb

We report results of frequency stability measurements of an extended cavity diode laser (ECDL) whose frequency is stabilized by a non-evacuated scanning transfer cavity. The transfer cavity is locked to a commercial frequency stabilized helium–neon laser. Frequency stability is measured by use of an optical frequency comb. The environmental perturbations (variations of temperature, air pressure, and humidity) are also simultaneously measured. The observed frequency drift of the ECDL is well explained by environmental perturbations. An atmospheric pressure variation, which is difficult to control with a non-evacuated cavity, is mainly affected to the frequency stability. Thus we put the cavity into a simple O-ring sealed (non-evacuated) tube. With this simple O-ring sealed tube, the frequency drift is reduced by a factor of 3, and the Allan variance reaches a value of 2.4×10⁻¹⁰, corresponds to the frequency stability of 83 kHz, at the average time of 3000 s. Since the actual frequency drift is well estimated by simultaneous measurement of the ambient temperature, pressure, and humidity, a feed-forward compensation of frequency drifts is also feasible in order to achieve a higher frequency stability with a simple non-evacuated transfer cavity.