Real-time surface profile measurement using a feedback type of sinusoidal phase modulating interferometer

In this paper, we propose a sinusoidal phase modulating (SPM) interferometer that is insensitive to external disturbances, and its measuring principle is analyzed theoretically. In the SPM interferometer, the interference signal is detected by a high-speed image sensor based on a low-speed CCD and a signal processing circuit is used to obtain the phase of each point on the surface. Therefore, the surface profile can be measured real-time. The experiments measuring the surface profile of a wedge-shaped optical flat show that the measurement time of the SPM interferometer is less than 10 ms, the repetitive measurement accuracy is 4.2 nm. The results show that the impacts of nonlinear distortion of the piezoelectric transducer (PZT) and part external disturbance are removed.     

Precision measurement with visual feedback using binary phase diffractive optical elements

A novel method for obtaining precision measurements by using two binary diffractive optical elements is presented. The system provides visual feedback of the measurement without the use of electronics.     

Spectral amplitude and phase measurement of ultrafast pulses using all-optical differential tomography

We demonstrate a simple, all-optical, fiber-based method for characterizing the spectral amplitude and phase of ultrafast pulses using a differential tomographic measurement realized via four-wave mixing. The technique is applied to subpicosecond pulses in the C-band of the telecommunication spectrum. Characterization of amplified pulses and propagation through dispersive media is demonstrated and compared with autocorrelation measurements and calculated predictions. We show how our approach can be extended to larger bandwidths in similar systems, extending tomographic reconstruction of coherent fields to nearly an octave of bandwidth while maintaining a robust, waveguide-based geometry.     

A new high-pressure cell for differential pressure-jump experiments using optical detection

Abstract

A differential pressure-jump autoclave with optical detection has been developed, which is capable to perform pressure-jumps of 150 bar amplitude to either. lower or higher pressures within the absolute pressure range up to 2.5 kbar. The principle of a rupture diaphragm is applied and the mechanical relaxation time of the apparatus is about 0.1 millisecond. Optical detection of light either transmitted or scattered under an angle of 90° can be utilized to follow a proceeding reaction.

The apparatus has been used to study the rate of demixing of binary liquid mixtures after performing a pressure-jump into the miscibility gap. The results of the obtained light intensity/time curves indicate no distinct cross-over behaviour between two different phase separation kinetics.     

Single-shot measurement of quantum optical phase

Although the canonical phase of light, which is defined as the complement of photon number, has been described theoretically by a variety of distinct approaches, there have been no methods proposed for its measurement. Indeed doubts have been expressed about whether or not it is measurable. Here we show how it is possible, at least in principle, to perform a single-shot measurement of the canonical phase using beam splitters, mirrors, phase shifters, and photodetectors.     

160-Gb/s polarization-multiplexing optical NRZ-DQPSK transmission using differential detection

Using differential detection,we perform polarization-multiplexing 160-Gb/s optical non-return-to-zero(NRZ) differential quadrature phase shift keying(DQPSK) signal transmission over 100-km standard single mode fiber at a bit error rate(BER) of less than 10-9.The enabling technology includes clock recovery,fine dispersion compensation,and polarization tracking for de-multiplexing.Furthermore,a hybrid clock recovery scheme is proposed.The scheme is realized with ordinary devices using an optoelectrical modula...     

Adaptive homodyne measurement of optical phase

We present an experimental demonstration of the power of feedback in quantum metrology, confirming the predicted [H. M. Wiseman, Phys. Rev. Lett. 75, 4587 (1995)]] superior performance of an adaptive homodyne technique for single-shot measurement of optical phase. For measurements performed on weak coherent states with no prior knowledge of the signal phase, adaptive homodyne estimation approaches closer to the intrinsic quantum uncertainty than any previous technique. Our results underscore the importance of real-time feedback for reaching quantum limits in measurement and control.     

Full field deformation measurement of centimeter sized objects using optical phase retrieval

Most papers in the field of optical phase retrieval either consider only the intensity (or amplitude) profile of the object under inspection (or scatterer location in the X-ray version), or a uniform tilt/rotation of the object beam. However, phase retrieval is able to recover the phase profile of the object (beam) as well, which theoretically makes the observable interference of phase retrieved object waves possible. In this paper we demonstrate this principle experimentally on centimeter sized deformable reflective objects (as large as 40 mm by 40 mm) and corresponding simulations are also presented. When the CCD camera is moved along the optical axis in the Fresnel region, the interference fringes of the displacement field have low contrast. On the other hand, when an imaging setup is built, and the camera moves near the image plane, high fringe contrast can be obtained. These fringes however suffer from some phase error. In our work the iterative modulus projection algorithm was used as a simply implementable phase retrieval method.     

用表面等离子波相位检测法测量液体折射率

表面等离子体波（ＳＰＷ） 检测技术近年来已被应用在生物传感领域。它通过探测介质的折射率变化来探测生物反应。理论分析表明,利用ＳＰＷ 相位检测的方法可以实现高分辨率的液体折射率测量。在优化测量参数的基础上,使用低频差横向塞曼激光器为光源,进行了验证实验,实验结果与理论相符合。     

Quantitative differential phase measurement and imaging in transparent and turbid media by optical coherence tomography

Differential phase-contrast optical coherence tomography allows one to measure the path-length differences of two transversally separated beams in the nanometer range. We calculate these path-length differences from the phase functions of the interferometric signals. Pure phase objects consisting of chromium layers containing steps of approximately 100-200-nm height were imaged. Phase differences can be measured with a precision of +/-2 degrees , corresponding to a path-difference resolution of 2-3 nm. To investigate the influence of scattering, we imaged the phase objects through scattering layers with increasing scattering coefficients. The limit of phase imaging through these layers was at approximately 8-9 mean free path lengths thick (single pass).     

Optical low-coherence reflectometer for differential phase measurement

A birefringent-fiber-based dual-channel optical low-coherence reflectometer capable of differential phase measurement is described. Phase noise owing to environmental perturbations that is common to both channels is canceled, resulting in accurate measurement of the phase difference between light backscattered from two spatially separated sites. Results are presented that demonstrate the accuracy and sensitivity of the system.     

Real-time detection technique for Doppler optical coherence tomography

We propose and demonstrate a novel detection technique, based on a modified electronic phase-locked loop, for Doppler optical coherence tomography. The technique permits real-time simultaneous reflectivity and continuous, bidirectional velocity mapping in turbid media over a wide velocity range with minimal sensitivity penalty compared with conventional optical coherence tomography, which is a major advance over current postprocessing and discrete parallel detection techniques.     

气溶胶单粒子粒径的实时测量方法研究

介绍了近期研制的一台实时测量大气气溶胶单粒子粒径和化学成分的仪器在如何测量气溶胶单粒子粒径方面的测量原理及特点，并结合激光解吸附电离飞行时间质谱技术，利用该仪器对木屑燃烧产生的烟气气溶胶粒子的实时测量结果. 关键词： 气溶胶粒子 空气动力学粒径测量方法 激光解吸附电离 飞行时间质谱     

Real-time phase measurement and correction of dynamic multimode beam using a single spatial light modulator

In this Letter,a novel system for adaptively correcting the phase of a dynamic multimode beam is proposed.While using merely one spatial light modulator,the phase measurement of the first-order diffraction pattern and the correction of the zeroth diffraction order are simultaneously realized.The real-time experimental result is obtained at a control rate of 10 Hz.The power-in-the-bucket value is improved from 38.5%to 61.8%,even with fundamental mode content that is consistently below 30%.To the best of our knowledge,this is the first implementation of real-time adaptive correction of the entire multimode beam.     

Spatial fringe scanning for optical phase measurement

A new method of analyzing interference fringes using a microcomputer is proposed. Interference fringes with a tilted wavefront are spatially scanned perpendicularly to the spatial carrier by a TV camera. Irradiance distribution along a raster scan is sinusoidally interpolated in each carrier interval and optical phases are calculated over the whole area under test.     

Real-time histogram generation using active optical scanning

A prototype of an optical-electronic histogram generator has been designed and tested for one-dimensional objects. In this scheme, the object to be analysed is laser scanned. The resulting optical signal is detected by a photodetector, which generates an electrical signal output that is subsequently analysed with a combination of analogue and digital electronics. The system is shown to be fairly modular in design. Various aspects of the extension of the design to two dimensions are discussed.     

Real-time polarization phase shifting technique for dynamic deformation measurement

By using a special Ronchi phase grating and polarization phase shifting method, four phase shifted patterns can be captured simultaneously, and then the dynamic deformation can be measured. The analysis and experiments are given.     

Amplitude and phase measurement of mid-infrared femtosecond pulses by using cross-correlation frequency-resolved optical gating

We describe a cross-correlation-based frequency-resolved optical gating (XFROG) technique for simultaneously measuring the amplitude and phase of two ultrashort pulses that have different wavelengths but are derived from a common mode-locked oscillator. A measurement is presented in which 4.0-mum mid-IR pulses from a synchronously pumped femtosecond optical parametric oscillator (OPO) are characterized by mixing with the 770-nm OPO pump pulses. Details of the pulse-retrieval algorithm are included, together with examples of pulse data retrieved from the experimentally measured XFROG trace.     

Wideband optical phase modulator half-wave voltage measurement technique based on phase modulation optical link

We measured the half-wave voltage V_π of LiNbO₃ phase modulators in the broadband frequency range by analyzing the gain of phase modulation interference demodulation optical link. This is a new high practical value measurement method for half-wave voltage of LiNbO₃ phase modulators in wideband frequency range, and can accurately predict the nonlinear frequency characteristics of phase modulation optical link.