Polarization-based balanced heterodyne detection method in a Sagnac interferometer for precision phase measurement

We describe a balanced heterodyne detection method for a Sagnac interferometer that uses a polarization-dependent beam splitter. The signal and the local oscillator are orthogonally polarized components of a single laser beam, permitting the detection of the signal by subtraction of two photocurrents produced in appropriate polarization projections. Using this scheme, we experimentally demonstrate a phase measurement with a sensitivity of 9x10(-10) rad/ radicalHz. The measurement is robust in the presence of laser frequency noise, as a result of preserving the common-path nature of the Sagnac interferometer, and of laser-amplitude noise, as a result of balanced detection.     

Absolute phase measurement in heterodyne detection of transient gratings

We present a method of measuring the absolute phase in heterodyne-detected transient grating experiments. The method permits direct and sensitive characterization of the amplitude and phase of the grating parameters. We also present a convenient implementation of this technique and demonstrate its efficacy in a cuprate superconductor.     

Optical heterodyne measurement of vibration phase

An optical heterodyne system for measuring a vibration phase, which uses a frequency-shifted and phase-modulated reference beam, is proposed. This system is applicable to a rough surface. By using the light scattered by a standard vibrating point on the object surface as the reference beam (local reference beam technique), effects of the uniform displacement of the object can be eliminated, i.e. only the vibration component is detected with no sensitivity to the uniform displacement. Preliminary experiments demonstrate the validity of the theory.     

Excess-noise suppression in a fibre-optic balanced heterodyne detection system

We have investigated balanced heterodyne detection in applications where laser intensity fluctuations are the dominant noise source, as, for example, in laser Doppler velocimetry with a He-Ne laser. The suppression of excess noise in comparison with a single receiver detection system is analysed theoretically. In our heterodyne experiment we have compared two different fibre-optic Mach-Zehnder interferometers, both with single-mode polarization-preserving fibres, one in integrated form using a directional coupler, the other one with a dielectric beam-splitter as the optical mixing element. With the former we have verified the theoretical results; with the latter we have demonstrated that with a good balance the fundamental short noise detection limit can be reached.     

Experimental study of balanced optical homodyne and heterodyne detection by controlling sideband modulation

We experimentally study optical homodyne and heterodyne detections with the same setup, which is flexible to manipulate the signal sideband modulation. When the modulation only generates a single signal sideband, the light field measurement by mixing the single sideband at ω0 ±? with a strong local oscillator at the carrier frequency ω0on a beam splitter becomes balanced heterodyne detection. When two signal sidebands at ω0 ±? are generated and the relative phase of the two sidebands is locked, this measurement corresponds to optical balanced homodyne detection. With this setup, we may confirm directly that the signal-to-noise ratio with heterodyne detection is two-fold worse than that with homodyne detection. This work will have important applications in quantum state measurement and quantum information.     

光学差拍方法测量波片的相位延迟

本文提出了用双频激光器测量波片的相位延迟方法:光学差拍方法,其测量精度为激光波长的1/6000,优于其他的波片测量方法的测量精度。     

相位激光测距与外差干涉相结合的绝对距离测量研究

 为了克服一般绝对距离测量方法量程和精度不能同时满足的问题,提出一种相位激光测距与外差干涉相结合的绝对距离测量方案。该方案使用相位激光测距技术进行粗测,双纵模He-Ne激光器外差干涉测长技术进行精测,保证两者结合的单值性。建立测量系统,对方案的可行性进行了实验验证,并对影响系统稳定性的因素进行了分析。与双频激光干涉仪的比对结果表明：测量标准差优于1mm,可以满足一些大尺寸的测量精度要求。     

Phase-shifting interferometry with feedback control using heterodyne phase detection

A phase-shifting interferometer with feedback control using heterodyne phase detection was developed. A composite heterodyne phase detection method for obtaining feedback signals was proposed. Interference fringe stabilization and accurate pi/2 phase shifts under micrometer-order vibrations were successfully demonstrated using a digital high-speed lock-in amplifier.     

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.     

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.     

Quantitative amplitude and phase measurement by use of a heterodyne scanning near-field optical microscope

A coherent photon scanning tunneling microscope is presented. The setup employs heterodyne interferometry, allowing both the phase and the amplitude of the optical near field to be measured. Experimental results of measurements on a standing evanescent wave reveal the high resolution that is obtainable with such an approach. In fact we have measured the amplitude and the phase of the near field, with a resolution of 1.6 nm between sample points.     

Direct measurement of fringe amplitude and phase using a heterodyne interferometer operating in broadband light

We describe a simple heterodyne method for measuring fringe amplitude and phase difference using an interferometer operating in broadband light. A demonstration system is presented using a Michelson-type interferometer with a bandwidth of greater than 300 nm.     

Beam-splitting ratio impact on the SNR for the balanced heterodyne

Considered the beam-splitting ratio, the mathematical model of balanced heterodyne receiver is established, and the mathematical expression of the relationship between the signal-to-noise ratio and the beam-splitting ratio is obtained. Based on the experiment, we got the best range of beam-splitting ratio which is 0.159–0.5. The experiment results show that, in the framework of the best beam-splitting ratio, the balanced heterodyne receiver has better signal-to-noise ratio than the common heterodyne receiver.     

Air-dispersion measurement by second-harmonic heterodyne interferometry

Interferometers with long optical paths in air usually require knowledge and control of air dispersion. In addition, the measurements at several wavelengths and the dispersion properties of air allow errors caused by air turbulence to be compensated for. An innovative technique for air-dispersion measurement is described for long-baseline ground-based stellar interferometers. The technique combines second-harmonic interferometry and heterodyne detection to permit high-resolution measurement even for low optical powers. Experimental results show measurements of air dispersion in good agreement with the values predicted from the Edlén equation.     

压缩态光场平衡零拍探测的位相锁定

平衡零拍探测是测量量子光场的重要方法之一. 通过对相位灵敏光学参量放大器注入的信号进行位相调制, 然后利用平衡零拍探测系统测量光学参量放大器输出的压缩光. 将相位灵敏光学参量分别运转在参量放大和参量缩小, 通过观察噪声谱中的调制信号就可确定测量的量子光场是正交振幅或位相分量. 通过解调位相调制信号可获得误差信号, 实现锁定平衡零拍探测系统本底光与待测光场相对位相为零(对应于待测光场振幅噪声分量). 关键词： 平衡零拍探测 位相锁定     

Optical heterodyne measurement of in-plane vibrations

An optical heterodyne technique which detects the frequency shift of light reflected from a point in motion can be successfully used for in-plane vibration measurements. Principles and results of preliminary experiments are described.     

全息位相光栅在使用探测器列阵的激光外差探测系统中的应用

本文给出了探测器列阵和全息位相光栅在CO_2激光外差探测系统中应用的可行性实验研究结果和分析,为实现实用化提供了重要的依据。     

Full-field measurement of the phase retardation for birefringent elements by using common path heterodyne interferometry

A collimated heterodyne light passes through the tested material and an analyzer, full-field interference signals are taken by a fast CMOS camera. The series of interference intensities recorded at any pixel are the sampling points of a sinusoidal signal. From those points, the associated argument of that pixel can be derived by a least-square sine fitting algorithm on IEEE 1241 Standards. Subtracting the average argument of the reference signal, the phase retardation of that pixel can be obtained. The phase retardations of other pixels can be obtained similarly. Its validity is demonstrated.     

Selective trace detection of asymmetric rotor molecules by stark-modulated phase fluctuation optical heterodyne spectroscopy

Stark modulation of vibration-rotational absorption resonances in five asymmetric rotor molecules with hindered internal rotation allows selective detection of trace organic gas concentrations in air by means of phase fluctuation optical heterodyne spectroscopy. A parallel-beam interferometric configuration is described.     

Laser heterodyne measurement of small arbitrary displacements

One-dimensional displacements of a moving body are dectected from the phase-modulated beat signal of light, generated by two successive ultrasonic modulators. Measurements of triangular and random displacements are demonstrated using a movable reflection mirror. For a sinusoidal motion its amplitude is measured down to 2.2 Å.