Inscription and Visualization of Tilted Fiber Bragg Gratings

Tilted fiber Bragg gratings with different tilt angles have been inscribed in single-mode isotropic optical fiber with an increased photorefractivity using Talbot interferometer and KrF-excimer laser system. Their spectra are studied. Using a confocal laser scanning luminescent microscope the images of gratings in transmitted light were obtained. The calculated dependence of the slope angle of the grating recorded in the Talbot interferometer on the angle between the strokes of the interference pattern created in the interferometer and the transverse section of the optical fiber is experimentally verified.     

部分相干光栅衍射效应和干涉术

本文提出一种新的部分相干照明的光栅衍射干涉仪.先分析了光栅的介于Talbot和Lan效应之间的部分相干衍射效应.部分相干干涉图的特点是条纹由频率成倍的两种光栅状载波所表征.调整光源狭缝,系统在两相干性极端分别转成Talbot和Lau干涉仪.理论分析采用了模糊函数方法.最后给出了实验.     

Talbot interferometry with anisotropic gratings

An interferometer based on the Talbot effect but employing anisotropic gratings is proposed. These gratings are obtained by exposing a Weigert plate with a periodic intensity distribution of polarized light. The phase testing properties of this interferometer are discussed, and some possible extensions are proposed.     

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.     

30‐Lens interferometer for high‐energy X‐rays

A novel high‐energy multi‐lens interferometer consisting of 30 arrays of planar compound refractive lenses is reported. Under coherent illumination each lens array creates a diffraction‐limited secondary source. Overlapping such coherent beams produces an interference pattern demonstrating strong longitudinal functional dependence. The proposed multi‐lens interferometer was tested experimentally at the 100 m‐long ID11 ESRF beamline in the X‐ray energy range from 30 to 65 keV. The interference pattern generated by the interferometer was recorded at fundamental and fractional Talbot distances. An effective source size (FWHM) of the order of 15 µm was determined from the first Talbot image, proving the concept that the multi‐lens interferometer can be used as a high‐resolution tool for beam diagnostics.     

Real time out-of-plane vibration measurement/monitoring using Talbot interferometry

In the present paper, application of Talbot interferometry for real-time vibration measurement is investigated. Experiments were conducted to measure/monitor out-of-plane motion of a vibrating loudspeaker membrane. Experimental results demonstrate that by using Talbot interferometry out-of-plane vibrations as well as phase lag between driving force and membrane oscillation can be measured.     

改变写入Bragg波长的干涉条纹运动的扫描式Talbot干涉仪

一种干涉条纹运动的扫描式Talbot干涉仪被用于改变光纤Bragg光栅的写入Bragg波长。在系统中,光纤光栅是由来自相位掩模的±1级衍射光经平面镜反射后在远场形成紫外干涉条纹写入的,其中,相位掩模被用作±1级衍射光的分束器。值得注意的是通过干涉条纹的运动来扫描写入光纤光栅,有效降低了Talbot干涉仪对写入光源相干性的要求。     

Electronic talbot interferometer

This paper explains theoretically the principle of the Talbot interferometer using two ‘Fourier images’. The experimental results show that video techniques are more useful for superimposing two ‘Fourier images’ than photographic techniques.     

Collimation method using fourier imaging and moire techniques

Two techniques are proposed for beam collimation with the Talbot interferometer. One is called the mismatch method in which two gratings with slightly different periods are used. In the other method (called the grating shift method), one of two gratings of the same period is shifted in its plane in the direction perpendicular to the grating lines.     

Power-efficient Fourier domain optical coherence tomography setup for selection in the optical path difference sign using Talbot bands

A power-efficient Fourier domain optical coherence tomography fiber system is presented free of mirror terms. The object and reference beams from the interferometer are spatially separated to illuminate different parts of the diffraction grating in the spectrometer according to a method inspired from the use of Talbot bands. In this way, the system is made sensitive to only one sign of the optical path difference in the interferometer.     

Analysis of period and visibility of dual phase grating interferometer

Dual phase grating interferometer may simultaneously achieve large field of view and high x-ray dose efficiency. Here, we develop a simple theoretical method to better understand the imaging process of the dual phase grating interferometer. The derivation process of fringe period and the optimal visibility conditions of the dual phase grating interferometer are given in detail. Then, we theoretically prove that the fringe period and optimal visibility conditions of the dual phase grating interferometer include that of the Talbot interferometer. By comparing our experimental results with those of other researchers, we find that when the positions of phase gratings are far away from the positions where the fringe visibility is optimal, the fringe period of the dual π -phase grating interferometer is twice the theoretical results under the illumination of polychromatic x-ray. This conclusion may explain the contradictory research results of dual phase grating interferometer among different researchers.     

Multiple interaction bandstop filters based on the Talbot effect

We report on two tunable, bandstop spatial filters, which are based on the Talbot effect. The light interacts with more than two gratings, arranged in series. The techniques may be considered as the analogues of the Fabry-Perot interferometer and the Lyot-Öhman filter, respectively. Some experimental results are included.     

Experimental investigation of the effect of magnetic field on temperature and temperature profile of diffusion flame using circular grating Talbot interferometer

The effect of magnetic field on temperature and temperature profile of diffusion flame is investigated by using circular grating Talbot interferometer. Talbot interferometric fringes are recorded for diffusion flame generated by butane torch burner, in the absence of magnetic field, in the presence of uniform magnetic field, upward-decreasing and upward-increasing magnetic field. Analysis of recorded interferogram reveals that the temperature of the flame is increased under the influence of the upward-decreasing magnetic field and flame temperature is decreased under the influence of upward-increasing magnetic field. Uniform magnetic field has a negligible effect on temperature of the flame.     

Interferometric testing of optical aspherical surfaces

This paper explains theoretically the principle of the Talbot interferometer using two ‘Fourier images’. The experimental results show that video techniques are more useful for superimposing two ‘Fourier images’ than photographic techniques.     

Theory of an X-ray interferometer in the form of an array of planar compound refractive lenses

The results of theoretical analysis of the interference pattern created by an X-ray multilens interferometer in the case of an arbitrary number of planar compound refractive lenses are presented. The full widths at half maximum of the resonance peaks in the transverse and longitudinal directions relative to the direction of synchrotron radiation are calculated at distances corresponding to the fractional Talbot effect. A relation between the widths is shown to exist that is very close to the width relation in the case of focusing by a single lens. A difference between the fractional and full Talbot effects is discussed, and the necessary conditions for the transverse and longitudinal coherence of radiation are analyzed, the satisfaction of which guarantees that undistorted interference peaks will be observed experimentally.     

Changing photo-written Bragg wavelengths of fiber gratings via one phase mask and four mirrors

A phase mask interferometer is developed to photo-write long gratings with arbitrary Bragg wavelengths. In this system, the fiber Bragg grating is photo-written by UV interference stripes of 193 nm reflected from two rotatable mirrors and two fixed mirrors, where the phase mask is not only used as a beam splitter, but also initialized the reference quantity of Bragg wavelength; the fixed mirrors are used for reducing the incident angle; the rotatable mirrors are used for adjusting the corresponding photo-written Bragg wavelength. It is worth noting that the photo-written length is fourfold as high as the length in the Talbot interferometer with the same mirror size.     

Millimeter-wave modulated optical pulse generated by pulse repetition rate multiplication and temporal Talbot effect

A novel scheme was proposed to generate a millimeter-wave (MMW) optical pulse by combining pulserepetition rate multiplication (PRRM) technology and temporal Talbot effect (TTE). A cascaded Mach-Zehnder interferometer (MZI) lattice was used for PRRM, and a linearly chirped fiber grating (LCFG) wasused as TTE. The basic principle was analyzed by using a Gaussian input short pulse and its characteristics were discussed by numerical simulation. It is shown that the proposed scheme is feasible for MMW signal generation and has potential merits for practical application of radio over fiber (ROF) technology.     

楔块调整式Talbot干涉仪改变写入Bragg波长的调谐误差

在楔块调整式Talbot干涉仪中,光纤Bragg光栅的写入区为直接由相位模板衍射的±1级衍射光束形成的干涉条纹的近场干涉区,和由±1级衍射光束经两平面镜反射后形成的可调谐写入Bragg波长的干涉条纹的远场干涉区。在改变写入光纤光栅Bragg波长的过程中,光纤光栅的Bragg波长是由平面镜的交叉角决定的,而且,影响调谐精度的三种主要因素被控制在光纤光栅生产允许的范围内,即推动机构的位移误差系数Cd为～-0.08nm/μm,楔块的倾斜误差系数Cα为-0.15～0.23nm/(′),和转动机构的传动角误差系数Cβ为～-0.08nm/(′)。     

Variable Wavelengths Fiber Bragg Gratings Written with A Phase Mask and Four Prisms

Using only one diffractive element, the Talbot interferometer provides a robust and inherently stable method for reproducing fiber Bragg gratings with variable wavelengths, and reduces the complexity of the fiber grating fabrication system. However, the usable length of the grating is limited by the practical length of the mirrors. This paper presents a phase mask with two fixed prisms and two rotational prisms to inscribe fiber Bragg gratings with variable Bragg wavelengths. In this system, the fiber Bragg grating is inscribed by UV interference stripes of 193 nm derived from two rotational prisms and two fixed prisms, where phase mask is used as a beam splitter of ±1 order diffraction light. It is noteworthy that the tunable phase mask interferometer decreases the demand of the length of prism evidently.     

Holographic vibration measurement using a tv speckle interferometer with silicon target vidicon

A basic realization of a TV speckle interferometer applying a silicon target vidicon is described. The increased detectivity compared with other vidicons reduces the laser power requirements. This enables stroboscopic operation in a fairly straightforward manner with a He-Ne laser source. Time average- and stroboscopic fringe patterns for a vibrating test object are presented.