Self-referenced method for optical path difference calibration in low-coherence interferometry

A simple method for the calibration of optical path difference modulation in low-coherence interferometry is presented. Spectrally filtering a part of the detected interference signal results in a high-coherence signal that encodes the scan imperfections and permits their correction. The method is self-referenced in the sense that no secondary high-coherence light source is necessary. Using a spectrometer setup for spectral filtering allows for flexibility in both the choice of calibration wavelength and the maximum scan range. To demonstrate the method's usefulness, it is combined with a recently published digital spectral shaping technique to measure the thickness of a pellicle beam splitter with a white-light source.     

Grating coupled interferometry for optical sensing

An interferometric sensor based on gratings on a planar waveguide is introduced. The device combines the advantages of known interference-based waveguide sensors with the simplicity of grating couplers. In the presented configuration, two parallel and coherent light beams, laterally separated in the direction of mode propagation, are coupled into a planar waveguide through a grating. One of the coupled beams is phase modulated using a periodically relaxing liquid crystal modulator, resulting in a time varying intensity signal at the end face of the waveguide. Refractive index changes within the waveguide section between the two coupling regions are monitored by observing characteristic changes in the intensity signal.     

Hilbert assisted wavelet transform method of optical fringe pattern phase reconstruction for optical profilometry and interferometry

A Hilbert assisted wavelet transform (HWT) method is presented for phase reconstruction of 3D profilometry and interferometry. A rigorous mathematical demonstration about this HWT method is given in this paper. An important conclusion that the phase of the optical fringe pattern is equal to the phase of its HWT coefficients on the ridge is theoretically clarified. The strict relation between the scale parameter and the phase gradient (also called the angular frequency) of the fringe pattern is also given. Computer simulations and experiments reveal the validity of the method and the correctness of the mathematical demonstration. Since the filtering process is avoided in this method, it can deal with the frequency overlapping problem to a certain extent. Applications of this method in both optical profilometry and interferometry are shown and discussed in the experiment section.     

Evaluation of a phase shifting method for vortex localization in optical vortex interferometry

The optical vortex interferometer uses a regular lattice of the optical vortices. In the previous papers we showed that changes in vortex lattice geometry can be related to physical quantities of the object being measured. The accuracy of such a measurement depends strongly on the precision of vortex point localization (vortex points are points where wavefront phase is undetermined). In this paper we compared the measurements of object wave tilt calculated from different localization methods applied to real interferograms and evaluate various localization methods.     

Reconstruction method for samples with refractive index discontinuities in optical diffraction tomography

We present a reconstruction method for samples containing localized refractive index (RI) discontinuities in optical diffraction tomography. Abrupt RI changes induce regional phase perturbations and random spikes, which will be expanded and strengthened by existing tomographic algorithms, resulting in contaminated reconstructions. This method avoids the disturbance by recognition and separation of the discontinuous regions, and recombination of individually reconstructed data. Three-dimensional RI distributions of two fusion spliced optical fibers with different typical discontinuities are demonstrated, showing distinctly detailed structures of the samples as well as the positions and estimated shapes of the discontinuities.     

Flexible interferometry for optical aspheric and free form surfaces

Optical Review - A flexible interferometry is proposed to test concave optical aspheric and free-form surfaces. It employs a flexible aberration generator (FAG) consisting of a movable reflective...     

光纤光热干涉气体检测技术研究进展

本文阐述光纤光热干涉气体检测的基本原理,从光纤光热相位调制的产生、动态过程、探测方法以及响应时间等方面出发,综述本研究组在光纤光热干涉气体检测方面的最新工作进展.光纤光热干涉技术具有灵敏度高、动态范围大、测量不受散射及其他损耗影响等优势,能够实现小型化、多点复用、组网及远程监测,在环境、医疗、安防等领域具有重要的应用.     

检测大口径光学平面镜时干涉条纹的子孔径拼接方法

提出了用Ritchey_Common法检测大口径光学平面镜时干涉条纹的子孔径拼接方法。通过确立基准点将多幅子孔径检测数据统一到全口径归一化坐标系下进行拼接,解决了在检验光路中因Ritchey角所引起的投影变形问题和如何消去因被检平面的大曲率所造成的像散。通过Zernike多项式拟合重建连续波面,可恢复全口径波面图像。     

Astronomical optical interferometry: an assessment

Optical interferometry (visible and infrared) becomes a powerful tool for astronomy, with the commissioning in 2001 of two arrays: the Very Large Telescope and the Keck. A survey of the existing interferometers is given, as well as an overview of the scientific achievements of their operation during the last decade, showing that most of the observational difficulties are now solved. Although these results mainly deal with stellar physics, the opening of new domains (extra-solar planets, active galactic nuclei) is imminent. Beyond this, new concepts are already proposed which will lead to an increase of resolution, imaging capabilities or spectral range.     

Multi-colour microscopic interferometry for optical metrology and imaging applications

Interferometry has been widely used for optical metrology and imaging applications because of their precision, reliability, and versatility. Although single-wavelength interferometery can provide high sensitivity and resolution, it has several drawbacks, namely, it fails to quantify large-discontinuities, large-deformations, and shape of unpolished surfaces. Multiple-wavelength techniques have been successfully used to overcome the drawbacks associated with single wavelength analysis. The use of colour CCD camera allows simultaneous acquisition of multiple interferograms. The advances in colour CCD cameras and image processing techniques have made the multi-colour interferometry a faster, simpler, and cost-effective tool for industrial applications. This article reviews the recent advances in multi-colour interferometric techniques and their demanding applications for characterization of micro-systems, non-destructive testing, and bio-imaging applications.     

High dynamic range imaging method for interferometry

We demonstrate a method to easily and quickly extend the dynamic range imaging capabilities of the camera in a typical interferometric approach. The camera dynamic range is usually low and limited to 256 gray levels. Also, it is well known that one may have over or under-exposed regions in the interferogram (due to non-uniform illumination) which makes these image regions not reliable. In our proposed method it is not necessary to obtain or use the non-linear camera response curve in order to extend the camera dynamic range. We obtain a sequence of differently exposed interferograms, typically five or six; after that, we compute the corresponding normalized fringe patterns and modulation maps using a typical normalization method. These normalized patterns are combined through a temporal weighted average using as weights the corresponding modulation maps. We show a set of experimental results that prove the effectiveness of the proposed method.     

船体三维角度变形的自准直干涉测量方法

以自准直原理基础,将光栅干涉原理引入,提出了一种能对船体三维变形测量的自准直干涉法。分析了测量三维角度变形的自准直干涉原理,并根据该原理设计了光学系统,系统主要包括两个主光路,自准直光路和光栅干涉光路,并且两路光部分共光路。自准直光路可以实现船体的二维测量;自准光栅的像和反射光栅干涉可测量船体的另一维变形,从而实现了船体三维变形的测量。给出了计算三维角变形的理论公式,最后进行了精度分析。试验结果表明,在±30′的视场范围内,系统精度达到2″,该方法不仅适用于船体也适用于其它物体三维角度变形的测量。     

Surface topology investigation for ancient coinage assessment using optical interferometry

In order to demonstrate the capabilities of white-light interferometry depth profiling (WLI-DP) for ancient coinage assessment, we investigated a series of notorious 1786 gold coins, bearing Louis XVIs horned effigy, and allegedly minted in Strasbourg. Scanning electron microscopy as well as WLI-DP observations unambiguously indicate that both previously differentiated single- and double-horned varieties originated from a unique minting tool. Moreover, from topological measurements, we infer that single-horned coins, rather than wearing out into double-horned coins, proceeded from the latter variety during minting by progressive failure of an already altered die. Whereas present observations do not exclude initial forgery, they suggest that protrusions resulted from progressive incidental in-service die deterioration. PACS 81.70.Fy; 07.60.Ly; 61.16.Bg; 81.40.Pq     

Electronic speckle pattern interferometry using optical fibers

Initial experiments using electronic speckle pattern interferometry with fiberoptic imaging and illumination are described.     

Quantum-circuit guide to optical and atomic interferometry

Atomic (qubit) and optical or microwave (modal) phase-estimation protocols are placed on the same footing in terms of quantum-circuit diagrams. Circuit equivalences are used to demonstrate the equivalence of protocols that achieve the Heisenberg limit by employing entangled superpositions of Fock states, such as N00N states. The key equivalences are those that disentangle a circuit so that phase information is written exclusively on a mode or modes or on a qubit. The Fock-state-superposition phase-estimation circuits are converted to use entangled coherent-state superpositions; the resulting protocols are more amenable to realization in the lab, particularly in a qubit/cavity setting at microwave frequencies.     

Variational denoising method for electronic speckle pattern interferometry

Traditional speckle fringe patterns by electronic speckle pattern interferometry (ESPI) are inherently noisy and of limited visibility, so denoising is the key problem in ESPI. We present the variational denoising method for ESPI. This method transforms the image denosing to minimizing an appropriate penalized energy function and solving a partial differential equation. We test the proposed method on computer-simulated and experimental speckle correlation fringes, respectively. The results show that this technique is capable of significantly improving the quality of fringe patterns. It works well as a pre-processing for the fringe patterns by ESPI.     

Generalized optical interferometry for modal analysis in arbitrary degrees of freedom

We generalize the traditional concept of temporal optical interferometry to any degree of freedom of a coherent optical field. By identifying the structure of a unitary optical transformation that we designate the generalized phase operator, we enable optical interferometry to be carried out in any modal basis describing a degree of freedom. The structure of the generalized phase operator is that of a fractional optical transform, thus establishing the connection between fractional transforms, optical interferometry, and modal analysis.     

A simple thermal phase stabilizer for real-time optical fibre holographic interferometry

An optical fibre interferometer can be made to phase-stabilize by simply attaching a short length of one arm of the interferometer to a straight copper track and heating the track with an electric current. This feedback thermal stabilization scheme works well even for relatively short fibre lengths and there is no need to treat or unjacket the fibre. A fibre-optic Michelson interferometer stabilized by this method successfully provided object and reference beams for real-time holographic interferometric measurements of the distortion of heated test objects.     

激光回馈效应及其传感应用研究的进展

对基于激光回馈效应的传感应用研究进展进行了综述。由于激光回馈引起激光器功率波动一个条纹对应外部反射镜移动半个光波波长,功率波动深度与传统双光束干涉系统相当,基于该现象的激光回馈干涉仪与传统的干涉仪相比具有相同的相位灵敏度。但其结构简单、紧凑、易准直的特点,引起了国内外科研者浓厚的兴趣,开发了很多全新概念、经济实用的精密测量仪器。对激光回馈效应在位移测量、速度测量、振动测量、距离测量、角度测量和形貌测量中的原理进行了介绍,同时对各传感应用系统进行了评述。     

Spectral phase interferometry for direct electric-field reconstruction of ultrashort optical pulses

We present a novel, self-referencing interferometric technique for measuring the amplitude and the phase of ultrashort optical pulses. The apparatus uses a collinear geometry that requires no moving components. The phase-retrieval procedure is noniterative and rapid and uses only two one-dimensional Fourier transforms. We apply the technique to characterize ultrashort pulses from a mode-locked Ti:sapphire oscillator.