Interferometric phase-dispersion microscopy

We describe a new scanning microscopy technique, phase-dispersion microscopy (PDM). The technique is based on measuring the phase difference between the fundamental and the second-harmonic light in a novel interferometer. PDM is highly sensitive to subtle refractive-index differences that are due to dispersion (differential optical path sensitivity, 5 nm). We apply PDM to measure minute amounts of DNA in solution and to study biological tissue sections. We demonstrate that PDM performs better than conventional phase-contrast microscopy in imaging dispersive and weakly scattering samples.     

Phase-dispersion optical tomography

We report on phase-dispersion optical tomography, a new imaging technique based on phase measurements using low-coherence interferometry. The technique simultaneously probes the target with fundamental and second-harmonic light and interferometrically measures the relative phase shift of the backscattered light fields. This phase change can arise either from reflection at an interface within a sample or from bulk refraction. We show that this highly sensitive (~5 degrees ) phase technique can complement optical coherence tomography, which measures electric field amplitude, by revealing otherwise undetectable dispersive variations in the sample.     

光学差拍方法测量波片的相位延迟

本文提出了用双频激光器测量波片的相位延迟方法:光学差拍方法,其测量精度为激光波长的1/6000,优于其他的波片测量方法的测量精度。     

精确标定光弹调制器的新方法

针对现有光弹调制器标定方法的不足,提出了一种精确标定光弹调制器的新方法。首先利用起偏器、波片、光弹调制器和检偏器构成标定光路,通过寻找探测信号基频分量的极大值进行粗略标定,使光弹调制器的峰值延迟量处在1.841rad附近。然后撤走波片形成光弹调制器的精确标定光路,在检偏器旋转90°前后获得探测信号的直流分量和二次谐波分量。最后利用这两种探测信号的直流分量和二次谐波分量精确地计算出光弹调制器的峰值延迟量。实验验证了此光弹调制器标定方法,实验结果表明其标定误差仅为0.7%。在此光弹调制器标定方法中,光弹调制器的标定精度和入射光强、电路参量无关。同时,标定要求的峰值延迟量小,非常适合于光弹调制器在其使用波长范围长波段的标定。     

Two-dimensional mapping of electro-optic phase retardation in lithium niobate crystals by digital holography

We demonstrate accurate two-dimensional mapping of the phase retardation induced by the electro-optic effect in lithium niobate crystals. Off-axis digital holography is used to investigate congruent z-cut crystals. The spatially resolved optical path difference is interferometrically measured while a linearly rising voltage ramp is applied to the crystal. This procedure provides information on the uniformity of crystals' electro-optic properties and offers the ability to detect the presence of defects that is of fundamental importance for reliable processing of photonic devices.     

A full-field method for measuring residual stresses in optical fiber

A method for measuring the axial residual stress profile in axisymmetric optical fibers is presented. The procedure is based on integrated photoelasticity and a fringe shifting technique is used to measure the optical retardation. The radial distribution of the axial residual stress is reconstructed using the inverse Abel transform. The paper describes the operating principle, the experimental setup and the results obtained on a multimode fiber are also reported. The influence of the measurement errors is finally discussed.     

Fiber-modes and fiber-anisotropy characterization using low-coherence interferometry

An optical low-coherence interferometry technique has been used to simultaneously resolve the mode profile and to measure the intermodal dispersion of guided modes of a few-mode fiber. Measurements are performed using short samples of fiber (about 50 cm). There is no need for a complex mode-conversion technique to reach a high interference visibility. Four LP mode groups of the few-mode fiber are resolved. Experimental results and numerical simulations show that the ellipticity of the fiber core leads to a distinct splitting of the degenerate high-order modes in group index. For the first time, to the best of our knowledge, it has been demonstrated that degenerate LP11 modes are much more sensitive to core shape variations than the fundamental modes and that intermodal dispersion of high-order degenerate modes can be used for characterizing the anisotropy of an optical waveguide.     

The Local-Sampling Phase Shifting Technique for Precise Two-Dimensional Birefringence Measurement

A precise method for measurement of two-dimensional birefringence distribution is described and discussed. This method can determine the relative retardation and the azimuthal angle of the fast axis in an optical component. In order to detect relative retardation with high resolution, a local-sampling phase shifting technique is proposed. This method can measure 256 × 256 values of the birefringent phase difference and azimuthal angle in a short time with ± 0.02 deg (0.03 nm) of retardation accuracy.     

The new circular heterodyne interferometer with electro-optic modulation for measurement of the optical linear birefringence

We present a new circular heterodyne interferometer with electro-optic modulation for measurement of the optical linear birefringence. It enables the measurement of not only the phase retardation but also the principal angle. The measurement procedure is carried out in two steps. In the first step of measurements, we use the electro-optic modulated circular heterodyne interferometer and the phase-lock technique to precisely measure the principal axis angle. After rotating the analyzer in the setup, the phase retardation is determined also by the phase-lock technique. The compact configuration requires only a photodetector and two simple phase-lock extractions to determine the principal axis angle and the phase retardation. The validity of the proposed design is demonstrated by measurement of the principal axis angle and phase retardation of a quarter-wave plate sample. The root-mean-square resolutions for the principal axis angle and phase retardation are found to be 0.0396° and 0.0796°, respectively, with corresponding dynamic ranges of 0–180° and 0–180°.     

Electrically tunable generation of vectorial vortex beams with micro-patterned liquid crystal structures

We develop a new method for smooth and continuous space-variant alignment of the liquid crystal medium in micro-patterned structures, which is based on a radial micro-structured pattern of polymeric ribbons exhibiting out-of-plane orientation with respect to the ITO-coated glass plates. Thanks to the broad range of electrical tunability of the optical retardation for the micro-patterned liquid crystal structures, transformation of the fundamental Gaussian beam into different types of specific beams, including generalized cylindrical vector beams, vortex beams, and vectorial vortex beams, is efficiently demonstrated.     

Design guidelines and characteristics of beam-shaping microstructure optical fibers

Microstructure optical fibers with flat-top fundamental mode are first proposed by introducing a low-index inner core into the core of index-guiding microstructure optical fibers. The design guidelines and characteristics of beam-shaping microstructure optical fibers are demonstrated. The interrelationships of inner-core index with laser wavelength, air hole diameter and size of inner core are investigated. The influence of the relative size of inner core on the spatial profile of the fundamental mode is demonstrated. Moreover, sensitivity of the flat-top fundamental mode profile from the slight change of the optimum inner-core index value is studied. Starting from these results we deduce that it is possible to fabricate beam-shaping microstructure fibers with nowadays technique.     

Wavelength dependence of the phase retardation of a quarter-wave plate

We describe an optical heterodyne polarization interferometer that can be efficiently used for the precision measurement of the change in the state of polarization of a light wave induced by polarizing optical devices. This technique is used to measure the change with wavelength of the phase retardation of a quarter-wave plate. A theoretical derivation is presented to permit computation of the wavelength dependence of the phase shift induced by a quarter-wave plate.     

Characterization of photorefractive materials by spontaneous noncolinear frequency doubling

‘Spontaneous’ noncolinear frequency doubling (SNCFD) is a type of optical second-harmonic generation (SHG) that uses scattered light to provide additional fundamental beams in order to accomplish noncolinear phase matching. Based on a novel algorithm for the automated evaluation of the resulting ring patterns, we present an easy-to-apply, sensitive, and non-destructive method for the characterization of photorefractive materials, yielding two-dimensional spatial resolution. As applications of the technique, examples for the characterization of lithium niobate crystals are presented. Received: 30 October 1998 / Revised version: 17 December 1998 / Published online: 7 April 1999     

Design analysis of all-optical devices using second harmonic generation into a region with periodically modulated optical property

We investigate the nonlinear optical interaction through a periodic waveguide structure consisting of two alternating segments with different linear and nonlinear optical properties. A coupled equation system has been used to calculate the intensity of fundamental and second harmonic waves and the phase shift of the fundamental. The model has been experimentally tested with good results, but the effect of the phase shift has not been considered. Comparison with the quasi-phase match (QPM) technique has been presented. The novel features introduced by alternating segments with different linear and nonlinear optical properties have been discussed. The model shows a more flexible approach, which can be used in designing optical components based on coherent nonlinear interaction. Applications are straightforward for frequency doubler and all-optical switch.     

利用反馈光路的弹光调制器定标及稳定控制

为了实现弹光调制器（photoelastic modulator,PEM）精确定标和长时间稳定工作,提出了一种利用反馈光路的相位延迟幅值定标及控制方案,理论计算并仿真分析了PEM通光孔径上相位延迟幅值的空间分布。在偏离PEM中心的位置设计了集成化的定标反馈光路;结合倍频项比值的相位延迟幅值定标方法,采用数字锁相技术同时提取反馈光路调制光强信号中倍频项,求解出PEM相位延迟幅值。按照上述方案加工制作了PEM实物,并进行了定标及稳定控制实验。实验结果表明,PEM中心相位延迟幅值的定标值与实测值相对偏差不超过0.22%;利用反馈光路控制约100 min,PEM相位延迟幅值标准偏差为0.001 8 rad,最大偏差低于0.42%,实现了PEM相位延迟幅值精确、实时定标,同时实现了PEM长时间稳定控制。     

Useful way to compensate for intrinsic birefringence caused by calcium fluoride in optical lithography systems

Calcium fluoride is widely used in optical lithography lenses and causes retardation that cannot be ignored.However, few studies have been conducted to compensate for the retardation caused by calcium fluoride in optical lithography systems. In this Letter, a new index based on orientation Zernike polynomials is established to describe the value of retardation. Then, a method of retardation compensation is described. The method is implemented by clocking calcium fluoride lens elements, and the optimal rotation angles are calculated using a population-based stochastic optimization algorithm. Finally, an example is provided to validate the method.     

Wireless optical communication-based spatial pattern

We propose a novel communication technique which utilizes a set of mutually distinguishable optical patterns instead of convergent facula to transmit information. The communication capacity is increased by exploiting the optical spatial bandwidth resources. An optimum detector for this communication is proposed based on maximum-likelihood decision. The fundamental rule of designing signal spatial pattern is formulated from analysis of the probability of error decision. Finally, we present a typical electro-optical system scheme of the proposed communication.     

蜃景效应及其光热偏转光谱

本文介绍一种十分灵敏的探测固体表面、液体和薄膜材料光学和热学特性的新方法.这一方法──光热偏转光谱技术,是通过探测被加热待测样品表面的热梯度的途径进一步确定其光学和热学特性.应用这种探测技术在室温和低温条件下所作的测试结果表明,它比其它方法都显得优越.     

光束偏转信号灵敏度的分析

激光光束编转法是一种非接触的探测技术。本文从理论上分析了光速偏转信号的灵敏度的基本限制。并给出了一种提高信号对光速偏转灵敏度的方法。     

Photonic ratchet superlattices by optical multiplexing

We present a method based on incremental holographic multiplexing to create a refractive index ratchet distribution into a photorefractive crystal as an example for the generation principle of such complex multiperiodic lattices. The implemented technique follows a finite optical series expansion of the desired index modulation. To analyze the induced lattice, we determine the phase retardation of a probe beam at the back face of the crystal by digital holography analysis. Our result depicts a first example to optically explore the fascinating phenomena of ratchet resembling systems.