Measurement of the complex polarization mode dispersion vector using Jones matrix analysis

The polarization mode dispersion (PMD) of a nondepolarizing optical system is analyzed. A new method is proposed to calculate the complex PMD vector by measuring two Jones matrices at two different wavelengths.     

Submicrometer optical tomography by multiple-wavelength digital holographic microscopy

We present a method for submicrometer tomographic imaging using multiple wavelengths in digital holographic microscopy. This method is based on the recording, at different wavelengths equally separated in the k domain, in off-axis geometry, of the interference between a reference wave and an object wave reflected by a microscopic specimen and magnified by a microscope objective. A CCD camera records the holograms consecutively, which are then numerically reconstructed following the convolution formulation to obtain each corresponding complex object wavefront. Their relative phases are adjusted to be equal in a given plane of interest and the resulting complex wavefronts are summed. The result of this operation is a constructive addition of complex waves in the selected plane and destructive addition in the others. Tomography is thus obtained by the attenuation of the amplitude out of the plane of interest. Numerical variation of the plane of interest enables one to scan the object in depth. For the presented simulations and experiments, 20 wavelengths are used in the 480-700 nm range. The result is a sectioning of the object in slices 725 nm thick.     

Wavelength-multiplexing diffractive phase elements: design, fabrication, and performance evaluation

We report on the wavelength-multiplexing diffractive phase element (WMDPE) capable of generating independent spot patterns for different wavelengths. The iterative method proposed by Bengtsson [Appl. Opt. 37, 1998] for designing a kinoform that produces different patterns for two wavelengths is extended to the WMDPE for multiple wavelengths (more than two wavelengths). Effectiveness of the design algorithm is verified by design and computer simulations on the WMDPE's for four and nine wavelengths. The WMDPE for three wavelengths (441.6, 543.5, and 633 nm) is designed with five phase levels and is fabricated by electron-beam lithography. We observed that the individual spot patterns are reconstructed for the design wavelengths correctly. Performance of the WMDPE is evaluated by computer simulations on the uniformity error, the light efficiency, and the contrast. On the basis of the results, the characteristics of the WMDPE's are discussed in terms of various conditions of fabrication and usage.     

Simultaneous and continuous multiple wavelength absorption spectroscopy on nanoliter volumes based on frequency-division multiplexing fiber-loop cavity ring-down spectroscopy

We demonstrate a method for measuring optical loss simultaneously at multiple wavelengths with cavity ring-down spectroscopy (CRD). Phase-shift CRD spectroscopy is used to obtain the absorption of a sample from the phase lag of intensity modulated light that is entering and exiting an optical cavity. We performed dual-wavelength detection by using two different laser light sources and frequency-division multiplexing. Each wavelength is modulated at a separate frequency, and a broadband detector records the total signal. This signal is then demodulated by lock-in amplifiers at the corresponding two frequencies allowing us to obtain the phase-shift and therefore the optical loss at several wavelengths simultaneously without the use of a dispersive element. In applying this method to fiber-loop cavity ring-down spectroscopy, we achieve detection at low micromolar concentrations in a 100 nL liquid volume. Measurements at two wavelengths (405 and 810 nm) were performed simultaneously on two dyes each absorbing at mainly one of the wavelengths. The respective concentrations could be quantified independently in pure samples as well as in mixtures. No crosstalk between the two channels was observed, and a minimal detectable absorbance of 0.02 cm(-1) was achieved at 405 nm.     

Pulsed digital holographic interferometry with 694- and 347-nm wavelengths

A method for deformation analysis and shape measurement based on digital holography is presented. Two wavelengths, 694 and 347 nm, are used. The object is illuminated with the two wavelengths at the same time, and digital holograms are recorded on a CCD chip. The information corresponding to the two wavelengths is separated in the Fourier domain, and the phase corresponding to the wave fronts is calculated. By recording holograms with two different wavelengths at the same time, we can get measurements of deformations or shape with different sensitivities. Experimental results are presented.     

Simultaneous measurement of in-plane and out-of-plane displacement derivatives using dual-wavelength digital holographic interferometry

The paper introduces a method for simultaneously measuring the in-plane and out-of-plane displacement derivatives of a deformed object in digital holographic interferometry. In the proposed method, lasers of different wavelengths are used to simultaneously illuminate the object along various directions such that a unique wavelength is used for a given direction. The holograms formed by multiple reference-object beam pairs of different wavelengths are recorded by a 3-color CCD camera with red, green, and blue channels. Each channel stores the hologram related to the corresponding wavelength and hence for the specific direction. The complex reconstructed interference field is obtained for each wavelength by numerical reconstruction and digital processing of the recorded holograms before and after deformation. Subsequently, the phase derivative is estimated for a given wavelength using two-dimensional pseudo Wigner-Ville distribution and the in-plane and out-of-plane components are obtained from the estimated phase derivatives using the sensitivity vectors of the optical configuration.     

Simultaneous formation of four fringes by using a polarization quadrature phase-shifting interferometer with wave plates and a diffraction grating

We present a new type of quadrature phase-shifting interferometer, which utilizes wave plates, a diffraction grating, and two lasers with different wavelengths, in order to acquire two sets of two quadrature fringe patterns in each wavelength formed on a single image sensor. This method for calculating with four phase-shifted fringe patterns gives us the phase sum and difference distributions between the phases in two wavelengths. This is also substantiated by results of our experiments.     

Design of single-polarization wavelength splitter based on photonic crystal fiber

A new single-polarization wavelength splitter based on the photonic crystal fiber (PCF) has been proposed. The full-vector finite-element method (FEM) is applied to analyze the single-polarization single-mode guiding properties. Splitting of two different wavelengths is realized by adjusting the structural parameters. The semi-vector three-dimensional beam propagation method is employed to confirm the wavelength splitting characteristics of the PCF. Numerical simulations show that the wavelengths of 1.3 μm and 1.55 μm are split for a fiber length of 10.7 mm with single-polarization guiding in each core. The crosstalk between the two cores is low over appreciable optical bandwidths.     

Measurement of the complex refractive index of isotropic materials with mueller matrix polarimetry

The complex refractive index of materials at infrared wavelengths is often determined when absorption measurements are made at selected wavelengths, and then the Kramers-Kronig relationship is used to calculate the real part of the index. Because many organic materials are highly absorbing in the infrared, absorption measurements require a short path length. We report on the use of an attenuated total internal reflection (TIR) method in combination with an infrared Mueller matrix spectropolarimeter to measure the Mueller matrix spectrum of samples from 3 to 14 mum. From the elements of the Mueller matrix the complex refractive index is determined for materials whose TIR interfaces are eigenstates of s and p polarization. The calculated index for water compares well with data found in the literature.     

3D range acquisition through differential light absorption

A 3D camera based on the differential absorption of light by a colored liquid is described. The range image is obtained from two illuminance images taken at two different wavelengths. The theoretical aspects of range-from-absorption are discussed in detail. Practical considerations for the calibration and implementation of the method are also covered. The accuracy of the 3D camera is discussed, and experimental results are presented     

Analysis of the effects of bias phase and wavelength choice on the design of dual-wavelength diffractive optical elements

Diffractive optical elements (DOEs) are often used in pattern formation for display purposes. Constructing these images from two or more colors greatly enhances their visual effect. To achieve this with DOEs is not simple, as they are inherently wavelength specific. We discuss an algorithm for designing quantized elements that produce distinct intensity patterns in the far field for two wavelengths. The benefits of applying bias phase to the dual-wavelength problem are investigated. The difference between the best and the worst choice of bias phase is shown to produce a variation of up to 2% in the efficiency. The mean square error can vary by up to a factor of 2 between the best and the worst case. It is also critically important to understand how the values of the two wavelengths affect the result. We present an analysis of how choosing different pairs of wavelengths in the design process affects the quality of our results.     

用于多色光的波片的设计

在偏振光路中有时需要交替使用不同波长的光束,为使光路保持最佳状态,常需要根据不同的工作波长选用相应波长的波片。为此提出了多波长波片的概念,给出了多波长波片的设计方法,具体设计了有实用价值的双波长四边之一波片,并成功地应用于一个实际的光学系统中,从而验证了多皮长波片设计思想的正确性。虽然多波长波片不一定能完全等效于多个严格意义上的单波长波片,但在一定的误差范围内所设计的多波长波片是能满足实际需要的,从而避免了频繁更换不同波长波片的麻烦。     

Measurement of absolute distance employing a tunable CW dye laser

With a tunable CW dye laser oscillating in a single longitudinal mode, measurement of an absolute distance is demonstrated with the method of excess fractions. Five beams which have different wavelengths are emitted sequentially from the dye laser, and the interferometric phase is measured for each wavelength. An interferometric order number for a wavelength can be calculated from values of wavelengths and phases. Then a precise value of length is obtained. This method is similar to measuring distances by using group delay as used in VLBI and microwave ranging. The measured accuracy was within ±8.8 nm between 0 and 10 mm (at an absolute distance of 0.1-10.1 mm)     

Holographic interferometry using two-wavelength holography for the measurement of large deformations

Visible holographic interferometry is generally too sensitive for the measurement of large deformations. We present a holographic method that permits an increase in the range of measurable deformations. It requires the use of two different wavelengths, λ(1) and λ(2), and two holograms in series. We develop the theoretical basis of a method that permits the obtention of an interferogram as if a longer equivalent wavelength, λ(eq) = λ(1)λ(2)/|λ(1) -λ(2)|, were used. The method is experimentally tested by use of a setup that can be easily converted into a classical single-wavelength holographic interferometer, permitting comparison of the interferograms of the same deformation produced with both methods. Significant results are presented.     

Porphyrin assembly on beta-cyclodextrin for selective sensing and detection of a zinc ion based on the dual emission fluorescence ratio

In the present paper, a new cyclodextrin/porphyrin supramolecular sensitizer for zinc ion has been proposed based on the porphyrin dual fluorescence emission ratio. In aqueous solution, meso-tetraphenylporphyrin shows weak fluorescence, while in the presence of alkylated beta-cyclodextrin, it exhibits significant fluorescence enhancement by forming a cyclodextrin/porphyrin inclusion complex. Furthermore, the formation of a supramolecular complex causes a remarkable increase of the porphyrin metalation rate following the porphyrin fluorescence emission changes at two different emission wavelengths. The fluorescence emission of tetraphenylporphyrin at 656-nm bands decreases while that at 606 nm increases upon zinc ion interaction. Thus, the inclusion complex can behave as a ratiometric fluorescent sensor. Theoretically derivative equations for fluorescent ratiometry have been proposed for the first time. The feasibility of the proposed method is demonstrated by the performance of fluorometric detection of zinc ion. With the optimum conditions described, zinc ion in aqueous solution can be determined from 5.0 x 10(-7) to 2.5 x 10(-4) M. As the porphyrin electronic absorption and fluorescence emission are located in the visible range, and the fluorescence changes upon zinc ion interaction show high selectivity over biologically relevant cations, the inclusion complex could be used for biomedical application.     

Design of diffractive optical elements for multiple wavelengths

A method for producing diffractive optical elements (DOE's) for multiple wavelengths without chromatic aberration is described. These DOE's can be designed for any distinct wavelength. The DOE's are produced from two different optical materials, taking advantage of their different refractive indices and dispersions.     

Effects of phase changes on reflection and their wavelength dependence in optical profilometry

The method as well as an appropriate instrumentation for measuring phase changes of reflected light is described. The phase changes on samples of Au, Al, Ag, and Cr evaporated films are measured for five wavelengths (lambda) from 442 to 633 nm, with respect to the phase change at the glass-air interface, where it should be zero. The measured results for the Au film are in fairly good agreement with values calculated by use of optical constants from a handbook or the complex refractive index measured by an ellipsometer. The phase changes for Al and Ag films are different from calculated values by ~5 degrees or a shift length of 4.4 nm at lambda = 633 nm, while those of the Cr film show large shifts as high as 16 degrees or a shift length of 9.8 nm at lambda = 442 nm.     

Determining surface orientations of transparent objects based on polarization degrees in visible and infrared wavelengths

Techniques for modeling an object through observation are very important in object recognition and virtual reality. A wide variety of techniques have been developed for modeling objects with opaque surfaces, whereas less attention has been paid to objects with transparent surfaces. A transparent surface has only surface reflection; it has little body reflection. We present a new method for obtaining surface orientations of transparent surfaces through analysis of the degree of polarization in surface reflection and emission in visible and far-infrared wavelengths, respectively. This parameter, the polarization degree of reflected light at the visible wavelengths, is used for determining the surface orientation at a surface point. The polarization degree at visible wavelengths provides two possible solutions, and the proposed method uses the polarization degree at far-infrared wavelengths to resolve this ambiguity.     

Simple measuring technique for the diffraction efficiency of slanted volume gratings at various wavelengths

To measure diffraction efficiencies of gratings as a function of wavelength, it is necessary to have quasi-monochromatic light sources of various wavelengths. We propose a method to measure the wavelength dependence of the grating diffraction efficiency by using a quasi-monochromatic light source. This method of estimating the real diffraction characteristics of the gratings for various wavelengths is very useful and simple. First the diffraction efficiency of the grating as a function of various incident-beam angles of monochromatic light is measured, then, using these data, we can obtain the diffraction efficiencies for various wavelengths of the same incident angle of light by virtue of a mathematical-conversion method. The mathematical-conversion results for two laminated differently slanted angle gratings of the same volume grating period are in good agreement with the experimental ones.     

Two-dimensional optical wavelet decomposition with white-light illumination by wavelength multiplexing

We present a novel method for achieving in real time a two-dimensional optical wavelet decomposition with white-light illumination. The underlying idea of the suggested method is wavelength multiplexing. The information in the different wavelet components of an input object is transmitted simultaneously in different wavelengths and summed incoherently at the output plane. Experimental results show the utility of the new proposed method.