Shearing interferometer using low-coherent light source and calcite prism

A shearing interferometer using a low-coherent light source and calcite prism is proposed in this paper. The calcite prism is the shear plate that generates sheared wavefronts with optical-path difference induced only by the contour of the specimen. Low-coherent light source is thus available while the interferometer is adopted for contour derivative determinations. The design of this interferometer is introduced, a setup constructed to realize the interferometer is described, and the experimental results from the uses of the setup are finally presented.     

Speckle shearing interferometer using a Savart plate

We describe a speckle shearing interferometer using a Savart polariscope. The purpose of this interferometer is to obtain the derivative of the out-of-plane displacement suffered by a scattering surface when put under stress. This information is useful to know the bending moments. The setup is compact, very stable, and does not require any stringent adjustment.     

Angular interferometer using calcite prism and rotating analyzer

An interferometer using a calcite prism and rotating analyzer is proposed for angular displacement determinations. The calcite prism senses the angular displacements and the rotating analyzer transfers the interference signals from dc-type into ac-type. Compact optical setup and using low-cost devices are thus the advantages of the interferometer. The theory of the interferometer is first demonstrated. A setup constructed to realize the interferometer and the results of using this setup are then presented.     

Wavelength shift determination using a dual-path heterodyne Mach-Zehnder interferometer

This paper introduces a dual-path heterodyne Mach-Zehnder interferometer adopted for wavelength shift determinations. In this interferometer, two parallel incident beams are separated into two interference pairs which are then recombined to generate two interference signals. A parallel plate is placed on the path of one wave of an interference pair, so the phase difference of the interference signals is a function of the plate and beam wavelength, and the interferometer is thus able to determine the wavelength shift of the incident beam. A setup constructed to realize the proposed interferometer is described, it shows that the interferometer has a resolution up to 1.1 × 10⁻¹⁰ (λ²/nm), and the experimental results of applying this setup not only agree the validity of the interferometer but also indicate that the interferometer has a stability of 6.5 × 10⁻¹⁰ (λ²/nm).     

新型偏振干涉成像光谱仪中Savart偏光镜透射率的研究

Savart偏光镜是自行研制的新型稳态偏振干涉成像光谱仪中的核心部件，阐述了该Savart偏光镜的分光机理.基于电磁场边值条件，分析了入射面与Savart偏光镜左板主截面重合及垂直时，光透过Savart偏光镜各界面的反射和折射，得出了各界面透射系数的表达式以及Savart偏光镜透射率的理论计算公式.采用计算机模拟，给出了Savart偏光镜透射率随视场角和波长的变化曲线，并与研制的Savart偏光镜实验测试结果进行了分析比较，两者变化规律相符. 表明该Savart偏光镜具有大视场、高通量的显著特点，适宜作为静态干涉仪和稳态偏振干涉成像光谱仪的高效横向剪切分束器. 这为新型偏振干涉成像光谱技术的研究以及仪器研制提供了重要的理论依据.     

Heterodyne angular interferometer using a square prism

An interferometer composed of a dual-frequency laser, sensing assembly, and decoding system is proposed for angular displacement determinations. The laser is a heterodyne light source. The sensing assembly generates an interference signal by the use of a square prism, and the decoding system extracts the phase difference of the interference signal. The theory, which reveals that the phase difference has a relation with the angular displacement of the square prism, of the interferometer is described. A setup constructed to realize the interferometer and the results of using this setup are then demonstrated and presented.     

Low-coherent light-source angular interferometer using a square prism and the angular-scanning technique

An interferometer based on using low-coherent light source, a square prism, and the angular-scanning technique is proposed for absolute angular-displacement determinations. An angular displacement of the square prism shifts the correlogram, which is modulated by an envelope function, of the interference signal of the beams passing through the prism. This angle can thus be discovered by detecting the shifting of the envelope peak. A setup constructed to validate the interferometer is used. The results of using this setup are then presented.     

偏振干涉成像光谱仪的视场展宽设计与分析

为了在较大视场范围内获得干涉直条纹以提高干涉数据的提取精度,设计了一种基于组合Savart板的宽场偏振干涉成像光谱仪.组合Savart板由正负晶体制作的两个Savart板组合而成.文中推出了组合Savart板的光程差和横向剪切量与入射角的理论表达式,并给出了具体设计实例.计算机模拟分析结果表明,在光谱分辨率和晶体总厚度相同的前提下,组合式Savart板获得干涉直条纹的视场是传统Savart偏光镜视场的10倍. 关键词： 偏振成像光谱仪 Savart板 光程差 视场     

A new lateral shearing interferometer for precision surface measurement

A new lateral shearing interferometer is proposed for precision surface measurement. In this shearing interferometer, a novel shear generator made of a single birefringence crystal plate is utilized. The shear adjustment is realized through the change of angle at which tested wavefront is incident into the crystal plate. By changing the orientation of the principal section of the plate, the generator can adjust the shearing direction. With the incident beam being circularly polarized, the generator can equalize the intensities of two shearing beams to make a good contrast interference pattern. The interferometer is simple and compact in terms of mechanism and has a complete common optical path structure. Phase shifting can be realized conveniently. The interferometer is insensitive to external vibrations and environmental disturbances, and hence has good stability and reliability with high measurement accuracy. To examine the performance of the proposed interferometer, experimental testing was conducted. High accuracy and repeatability are demonstrated.     

光纤Fizeau干涉仪的声发射检测研究

验证了一种基于光纤Fizeau干涉仪的声发射传感器,可用于固体表面传播的超声波的检测.这种传感器的特点是能够精确地检测由固体表面传播的超声波产生的微弱振动.当超声波信号通过光纤传感器到达探测器时,干涉仪的输出光强度受到了超声信号的调制.通过检测干涉仪的输出光强度并利用Fourier变换,测得了超声信号的振幅和频率.对传感系统的相位调制特性进行了仿真,并对实验结果进行了分析.     

Relationship between incident angle and dispersion in static large field of view polarization interference imaging spectrometer

The static large field of the view polarization interference imaging spectrometer is based on the modified Savart polariscope. There appears a dispersion between the ordinary ray and extraordinary ray when light passes through the modified Savart polariscope. The dispersion greatly influences the intensities and the results of the interferogram and target image in the static large field of the view polarization interference imaging spectrometer. At the same time, the incident angle determines the dispersion. When the light goes through the modified Savart polariscope, the dispersion occurs in the left plate, the half-wave plate and the right plate of the modified Savart polariscope. Using the extension of Snell's law, the dispersion in the crystal is theoretically calculated and numerically simulated separately. The relationship curve between incident angle and the dispersion is obtained by simulation.     

环形光纤声发射传感器的相位调制特性研究

提出了一种基于光纤Sagnac干涉仪的环形传感器,用于固体表面传播的超声波的检测.这种传感器的特点是能够精确地检测由固体表面传播的超声波产生的微弱振动.当超声波信号通过光纤传感器的两个臂到达探测器时,干涉仪的输出光强度受到了超声信号的调制.通过检测干涉仪的输出光强度并利用Fourier变换,测得了超声信号的振幅和频率.而且对传感系统的位相调制特性进行了仿真,并对实验结果进行了分析,结果表明该系统可用于固体表面传播的超声波频率特征的识别.     

稳态大视场偏振干涉成像光谱仪中视场补偿型Savart偏光镜透射率研究

论述了基于视场补偿型Savart偏光镜的稳态大视场偏振干涉成像光谱仪的分光机理.依据电磁场边值条件,分析了光在视场补偿型Savart偏光镜中各晶体分界面上的透射情况,得出了透射率的理论计算公式.采用计算机模拟,分析了在半波片为不同材料时,透射率随入射波长、视场角及半波片厚度的变化关系.研究表明,视场补偿型Savart偏光镜具有大视场、高通量、高探测灵敏度的显著特点.此研究可为新型干涉成像光谱技术的研究和新型偏振干涉成像光谱仪的设计、研制提供重要的理论指导. 关键词： 偏振干涉成像光谱仪 视场补偿型Savart偏光镜 透射率 电磁场边值条件     

Fourier-domain low-coherence interferometry for differential mode delay analysis of an optical fiber

We propose a novel mode analysis and differential mode delay measurement method for an optical fiber using Fourier-domain low-coherence interferometry. A spectral interferometer based on a Mach-Zehnder interferometer setup was used with a broadband source and an optical spectrum analyzer to detect relative temporal delays between the guided modes of a few-mode optical fiber by analyzing spectral interference signals. We have shown that experimental results of the proposed method agree well with those results obtained by using a conventional time-domain measurement method. We have demonstrated that this new mode analysis technique has high sensitivity (<60 dB) and very good resolution (<1 ps/m).     

Real time phase modulation measurements in liquid crystals

We propose real time phase measurements in liquid crystals cells using Young's interferometer constructed with a new principle with possibility to control the distance between two point sources. The optical interference optical pattern is detected by a bicell photo-detector in a back Fourier focal plane. A phase modulation controlled by a monopixel liquid crystals’ cell placed in a reference arm of interferometer is observed as a dynamic shift of the fringes’ pattern in spatial domain. Concept of signals’ demodulation in the Fourier focal plane will be described using a new approach to the demodulation signals. In this work we evaluate the demodulation condition of our setup and we present measurements of a dynamic phase response for nematic liquid crystals and antiferroelectric liquid crystals cells.     

Sinusoidal phase-modulating laser diode interferometer for real-time surface profile measurement

A sinusoidal phase-modulating (SPM) laser diode (LD) interferometer for real-time surface profile measurement is proposed and its principle is analyzed. The phase signal of the surface profile is detected from the sinusoidal phase-modulating interference signal using a real-time phase detection circuit. For 60 × 60 measurement points of the surface profile, the measuring time is 10 ms. A root mean square (RMS) measurement repeatability of 3.93 nm is realized, and the measurement resolution reaches 0.19 nm.     

偏振型干涉成像光谱仪中Savart偏光镜通光孔径的研究

论述了偏振型干涉成像光谱仪的核心部件——Savart偏光镜的结构和分光机理. 应用波法线追迹的方法, 对光在任意方位入射面内, 以任意入射角入射时Savart偏光镜中的光线传播规律及出射光孔径变化进行了理论推导, 给出了出射孔径与入射位置、入射角及入射方位角之间满足的关系, 并讨论了光线传播始终处于Savart偏光镜晶体内部, 最终从出射面射出所需满足的条件. 采用计算机模拟, 给出了光线垂直入射时, 出射孔径的表达式, 验证了推导的正确性; 在此基础上对自行设计的干涉成像光谱仪通光孔径进行了详细分析和讨论, 结果表明通光孔径精确值和近似值之间存在较大差异. 给出了孔径面积利用率随入射方位角的变化曲线, 阐明在干涉成像光谱仪的参数论证以及孔径光阑的选取中, 不能忽略由于晶体双折射现象带来的孔径变化. 研究结果可为偏振型干涉成像光谱仪的设计、研制、调试和工程化提供重要的理论依据和实践指导.     

Nulling interferometry by use of geometric phase

Nulling interferometry is a method of detecting a faint source near a bright one, in which destructive interference is realized for the light from the bright source. A nulling interferometer that makes use of geometric phase (Pancharatnam phase) is proposed. An experimental setup is constructed to simulate a stellar interferometer with geometric-phase modulation. We attained extinction of 6 x 10(-5) in white light.     

Measurement of residual wedge angle with a reversal shear interferometer

A technique for determination of residual wedge angle of high optical quality transparent parallel plate using a reversal shear interferometer-based optical system has been discussed. In this technique the parallel plate to be tested is used to introduce angular tilt in the preset two-beam interference fringes of a reversal shear interferometer. The parallelism is calculated from the angular tilt of the fringes. The technique is more sensitive compared to techniques using Fizeau interferometer and is most suitable for highly parallel transparent plate with very low residual wedge angle.     

Suppression of Multiple-Beam Interference Noise in Testing an Optical-Parallel Plate by Wavelength-Scanning Interferometry

Measurements of optical parallel plates in a Fizeau interferometer lead to problems from multiple-beam interference noise unless the back surface of the plate has an additional treatment to prevent its reflection from reaching the detector. Such internal-reflection noise can be separated from the fundamental interference signal by its modulation frequency in a wavelength-scanning interferometer. However, to completely eliminate the noise, the air-gap distance between the testing and reference surfaces of the interferometer must be adjusted to a specific value, depending on the thickness and refractive index of the plate. This adjustment requires an undesirable change in the air gap, which is related to the phase modulation rate of the interferometer, and also requires additional information regarding the testing plate, which makes the measurement laborious. We show that if we add new symmetries to the sampling functions of the phase measuring algorithm, we can obtain significantly greater tolerance for the air-gap error. A new 19-sample algorithm allows a tolerance of ±23% while keeping the systematic errors at less than λ/200. The periodicity of the new algorithm and an integrating bucket technique also provide more options for the thickness of the testing plate, which guarantees an air-gap distance more independent of this thickness.