A novel optical subdivision method for dual-frequency interferometer

The theory of optical subdivision techniques of dual-frequency laser interferometers is stated. And a novel optical subdivision technique is proposed originally to enhance resolution of a commercial interferometer by adding some corner-cubes. Then the performance of the interferometer is tested. The interferometer resolution of 1.24 nm and the average error of below 2 nm are achieved by using the technique. The most novel of the optical subdivision technique is without λ/4 plates. It is less sensitive to environmental changes, it has prodigious potential to improve resolution farther and it can reduce polarization mixing error.     

Polarization phase-shifting lateral shearing interferometer with two polarization beam splitter plates

We proposed a compact and simple polarization phase-shifting lateral shearing interferometer using two polarization beam splitter plates (PBSP). This interferometer is composed of two PBSP, a quarter-wave plate, an analyzer and a CCD camera. With the two PBSP positioned in appropriate spatial positions, optical path difference compensation is achieved, which allows for the implement of aplanatic and common-path shearing interferometer. Therefore, the system possesses significant advantages of simple structure, compact and strong anti-interference ability. The effectiveness of the interferometer is demonstrated by simulations and experiments.     

用四台阶相位板产生涡旋光束

涡旋光束的产生与应用是当前光学领域的研究热点. 利用傅里叶级数展开法分析了四台阶相位板的相位结构, 发现四台阶相位板可看作是由一系列不同拓扑荷数的螺旋相位板所组成, 用线偏振光直接照射相位板时, 将产生多级衍射光波, 各级衍射光均为不同拓扑荷数的涡旋光波, 由于多级衍射光波间的干涉导致光强分布偏离轴对称分布, 因而与涡旋光波有一定差距. 在此基础上, 提出了用四台阶相位板产生涡旋光束的新方案, 借助于Mach-Zehnder 干涉仪光路, 两块四台阶相位板产生的衍射光干涉叠加, 通过调节干涉仪光路的相位差, 使一部分衍射级干涉相消, 另一部分衍射级干涉相长, 相互加强, 从而把线偏振光转换为涡旋光束. 数值模拟计算了几种周期数不同的四台阶相位板衍射光强和角动量分布, 并与螺旋相位板进行比较, 证明用简单的四台阶相位板不仅能够获得与用螺旋相位板相同的涡旋光束, 而且可以用周期数较小的四台阶相位板产生具有大拓扑荷数的涡旋光束, 降低了制作相位板的难度.     

Diffractive interferometer for visualization and measurement of optical heterogeneities

New optical arrangements of the two beam diffractive interferometer with the inverted wave fronts and the combined optical branches based on zone plates are proposed. The special software is designed. The restitution of an interference pattern is performed; the skeleton of fringes is selected; the graphic visualization of optical heterogeneity of a sample is built in the computer-aided processing of interferograms. Proposed DI enable visualizing the optical thickness heterogeneities in the transparent sample, measuring them with accuracy ～0.05λ and can be used for research and quality surveillance of laser crystals and other optical materials.     

Symmetric Talbot bands experiment

By impinging a step phase-shifted white light beam on a grating-based interferometer, one of diffraction orders is modulated and interference bands so-called “Talbot bands” are formed. Here, classical Talbot bands set up is generalized to the symmetry configuration, in which two glass plates of the same thickness instead of one plate, are inserted halfway into the grating interferometer aperture. Formation of Talbot bands were studied theoretically and experimentally. Frequency impulse response of the new Talbot bands setup was, also presented. It was demonstrated that symmetric set-up causes modulation of both of two opposite orders, according to the theory. In this manner, their visibility is the same. As a result, this similarity of the visibility is reduced while the symmetric arrangement of the glass plates with respect to the optical axis, is broken.     

Polarization compensation: a passive approach to a reducing heterodyne interferometer nonlinearity

Cyclic errors that are due to optical leakage limit the precision of displacement measurements made with optical interferometers. A method for real-time estimation of leakage components is introduced and is used to implement a novel passive technique for suppression of cyclic nonlinearities that uses only adjustments of existing polarizers and quarter-wave plates. This approach is used to reduce the cyclic error from 3 nm to 300 pm for an interferometer operating at a wavelength of 1320 nm.     

Theory and analysis of phase sensitivity-tunable optical sensor based on total internal reflection

This study presents a theory of a phase sensitivity-tunable optical sensor based on total-internal reflection (TIR). This investigation attempts to design a phase sensitivity-tunable optical sensor consisting of an isosceles right-angle prism, some quarter- and half-wave plates, and a Mach-Zehnder interferometer. When the azimuth angles of the quarter-wave plates are chosen properly, the final phase difference of the two interference signals are associated with the azimuth angle of the fast axis of the half-wave plates, thus creating the controllable phase sensitivity. Numerical analysis demonstrates that the high phase measuring sensitivity and the small measuring range, and the low phase measuring sensitivity and the wide measuring range can be performed by selecting the suitable azimuth angle of the half-wave plates. The feasibility of the measuring method was demonstrated by the experiment results. The sensor could be applied in various fields, such as chemical, biological, biochemical sensing, and precision machinery measurement.     

Multi-directional lateral shearing interferometer based on rotatable prism pairs

The common camera lens usually includes the spherical glass/plastic lens and aspheric glass/plastic lens. However, spherical/aspheric shape measurement is still a key problem in the process of optical lens fabrication. At present, the in-process measurement of spherical/aspheric shape is conducted mainly by the probe-contacting method. But after a long time, its probe could be scratched severely and cause some big errors. Laser shearing interferometry is a good substitute to some degree. Nevertheless, it is not convenient for general shearing interferometer to carry out the in-process measurement because it is only suitable for certain kind of spherical/aspheric with respect to aperture or asperity. Here a new lateral shearing interferometer is proposed to solve the described problems. It is based on two Jamin plates and rotatable prism pairs which are used not only for shearing displacement and direction, but also for fringe period and tilt degree, in order to meet requirements of various spherical/aspheric shapes or asperities. The new interferometer features a simple optical structure and two symmetric light paths, which makes its system with minimal error. The relation between shearing displacement, fringe period and prism angle of rotation is given in this paper. And the error source is primarily from the manufacture errors of prisms and plates. The final experiments show that one can achieve good-quality fringe patterns according to the requirement of measurement, concerning the shearing direction, shearing displacement, fringe period, tilt degree, etc.     

New multiplexed system for synchronous measurement of out-of-plane deformation and two orthogonal slopes

We propose a novel system for synchronous measurement of out-of-plane deformation and two orthogonal slopes using a single camera. The linearly polarized reference beam introduced by an optical fiber interferes with the unpolarized object beam to measure the out-of-plane deformation. A modified Mach—Zehnder interferometer is used to measure the two orthogonal slopes of the out-of-plane deformation. One of the object beams of the Mach—Zehnder interferometer is an unpolarized beam, and the other object beam is split into two orthogonal linearly polarized object beams by a polarizing prism. The two beams are orthogonally polarized. Hence, they will not interfere with each other. The two polarized beams respectively interfere with the unpolarized beam to simultaneously measure the two orthogonal slopes of the out-of-plane deformation. In addition, the imaging lens and apertures are respectively placed in three optical paths to independently control the carrier frequencies and shearing amounts. The effectiveness of this method can be proved by measuring two pressure-loaded circular plates.     

Simple phase-shifting lateral shearing interferometer

A phase-shifting electronic speckle pattern shearing interferometer with a very simple shearing device is proposed. Two partially reflective glass plates are used to introduce the shear in this new interferometer. The reflection coefficients of the coatings on the two plates are 0.3 and 0.7. The distance between the two glass plates controls the size of the shear. The proposed new interferometric system is simple, flexible, and low cost.     

X-ray phase contrast imaging based on three-block multilevel zone plate interferometer

A new scheme of X-ray phase contrast imaging, based on the previously suggested three-block interferometer composed by multilevel Fresnel zone plates, is considered. Two significant features, namely, image optical magnification and low requirements on the spatial and temporal coherency of incident radiation are combined in this scheme.     

马赫-曾德尔型相移矢量剪切干涉仪

为了实现对激光波面的等光程测试,设计了一个新颖的相移矢量剪切干涉仪。该干涉仪以马赫曾德尔结构为基础,为等光程干涉仪。通过在相干的两路光束中分别插入楔角方向正交放置的楔板实现矢量剪切;其中一块楔板分成两块(平板部分和楔板部分),楔板部分沿平板部分的表面移动,通过改变光程差来实现相移,2π相移所需的移动距离为几毫米的量级,该相移方法在相移精度控制上比较简单。文中还对楔板引入的横向剪切误差和相移误差进行了分析,最后给出了实验所得的一组相移干涉图。     

Slightly dispersive white-light spectral interferometry to measure distances and displacements

A new spectral-domain interferometric technique of measuring distances and displacements is realized when the effect of low dispersion in a Michelson interferometer, which comprises two coated plates of a beam splitter and a compensator, is known and the spectral interference fringes are resolved over a wide wavelength range. First, processing the recorded spectral interferograms by an adequate method, the unmodulated spectrum, the spectral fringe visibility function and the unwrapped phase function are obtained. Then, knowing the dispersion relation for the fused-silica plates, the ambiguity of the unwrapped phase function is removed and the thickness of fused silica and the nonlinear phase function due to the effect of the coatings are determined by using a new procedure. It is based on the linear dependence of the overall optical path difference between interferometer beams on the refractive index of fused silica. Once the thickness and the nonlinear phase function are known, the positions of the interferometer mirror are determined precisely by a least-squares fitting of the theoretical spectral interferograms to the recorded ones.     

光纤连接器端面几何参量自动测量仪

报道了一种高精度测量光纤连接器端面几何参量的自动测量仪。叙述了光纤连接器的端面几何参量的测量原理。由光纤连接器端面形貌和纤芯中心坐标,可以高精度得到曲率半径、顶点偏移量、端面倾斜角和光纤高度等影响连接器性能的关键端面几何参量。该仪器体积小,自动化程度高,用户界面友好,使用方便,可测量物理接触、角度式物理接触等类型的光纤连接器端面几何参量。实际测量证明,该测量仪有很好的重复测量精度。该测量仪与美国Dorc公司ZX-1 mini PMS测量仪和Norland公司NC3000测量仪相比,测量精度水平相当。该仪器样机已通过华东国家计量测试中心的测试。     

Spatially incoherent Fourier digital holography by four-step phase-shifting rotational shearing interferometer and its image quality

Spatially incoherent Fourier digital holography using a rotational shearing interferometer for four-step phase-shifting method is proposed. The previous incoherent Fourier holography using a rotational shearing interferometer [Watanabe and Nomura (Appl. Opt. 54:A18, 2015)] employs the two-step phase-shifting method in the vertical and horizontal polarizations. The reconstructed image contains a large bias term. This paper proposes introduction of two kinds of wave plates in one path of a rotational shearing interferometer for a four-step phase-shifting method. A Fourier hologram is obtained from the four recorded holograms for eliminating the bias term and the twin image. The numerical simulation and the optical experiment demonstrate improvement of the image quality of reconstructed image by the twin image and bias level reduction. Furthermore, the effect of the size of an image sensor on the image quality in rotational shearing interferometer is also investigated by the numerical simulations.     

A high-precision optical metrology system for determining the thickness of birefringent wave plates

This study develops a non-destructive measurement system for determining the thickness and refractive indices of birefringent optical wave plates. Compared to previous methods presented in the literature, the proposed metrology system provides the ability to measure the thickness of the birefringent optical plate in high-precision. The results show that for a commercially available birefringent optical wave plate with refractive indices of n_e=1.5518, n₀=1.5427 and a thickness of 452.1428 μm, the experimentally determined value for the error in the wave plate thickness measurement is just 0.046 μm. The measurement resolution of the proposed system exceeds that of the interferometer hardware itself. The proposed method provides a simple yet highly accurate means of measuring the principal optical parameters of birefringent glass wave plates.     

Interferometry for measuring large aspherical surfaces with holographic optical elements

Interferometry for measuring the shape of large aspherical surfaces is reported. The interference fringe pattern between the parallel reference beam and the reconstructed wavefront from the master zone plate which is drawn by an electron-beam drawing machine is recorded on a hologram plate with off-axis optical arrangement. The hologram plate used as the standard element is reconstructed by the conjugate beam in a modified Twyman-Green interferometer. Insufficient parallelism of commercial hologram plates can be compensated by this method. It is also easy to make replicas. Some experimental results are also presented.     

Etude d'impulsions lumineuses breves par interferometrie a deux ondes

We have studied the evolution of the light transmitted through matter in which an optical breakdown is taking place. With a two-waves interferometer made a birefringent plate between polarizers we get informations about the time correlation function of the fields. With an interferometer made of two identical harmonic generating plates separated by a dispersion medium, we learn about the correlation function of the square of the fields. Both systems act as spectral filters with a notch cosine-shaped centered at the incident frequency. We have also observed a transient angular spreading of the beam not previously emphasized which brings a further complication in the picture.     

Interferometrische homogenitätsprüfung mit kompensation

When testing glassplates for inhomogeneities, surface deviations must be eliminated. The proposed method achieves the suppression of surface deviations by adding 2 compensating plates to the testpiece. Even unpolished plates with deviations as great as 10μm can be tested with sensitivities up to 10^-6/cm. The deviations introduced by the compensating and interferometer plates are eliminated by a compensating hologram taken of these compensating plates in the same interferometer. The resulting interferogram gives the variations of the refractive index directly.     

Step index fibre using laser interferometer

A model is suggested to describe the fringe shift which occurs due to the phase variations of cladded glass fibre introduced between the two plates of the liquid wedge interferometer illuminated with a He–Ne laser. The fringe shift of the phase object which appears in the denominator of the Airy distribution formula of the multiple beam interference is represented in the harmonic term. An experiment is conducted using liquid wedge interferometer where the step index glass fibre of a nearly quadratic thickness variation is introduced between the two plates of the interferometer. The obtained fringe shift shows a good agreement with the proposed quadratic model. The Matlab code is written to plot the interferometer fringes comprising the shift of the step index fibre. Secondly, recognition of elliptical fibres is outlined using tomographic imaging. Finally, results and concluding remarks are given.