Polarization Interference Imaging Research Articles

傅立叶变换型线偏振干涉成像系统分析与设计

傅立叶变换型线偏振干涉成像系统分析与设计

Research on the optical axis of the birefringent crystal rotating in the three dimensional space

The beam splitting principle of the Gran-taylor prism as a birefringent crystal is explained. Using the ray tracing method, the angle of refraction of the extraordinary wave together with the direction of the extraordinary ray and its emitting position as a function of the incident angle θ1 and the angle θp between the optical axis and the normal are obtained in three-dimensional space. In order to analyze and discuss the influences of different parameters on the angle of refraction, the direction of the extraordinary ray and its emitting position, computers simulations are performed. If the deviation of θp is set as 5°, the biased error of the emitting position is 0.4274⁡mm in the y axis. In order to ensure that the deviation error for the emitting position is within 0.500⁡mm in the x axis, the incident angle should be controlled in a range of [0∘,1.702∘]. This study provides a theoretical and practical guidance for the industrial production of the polarization devices and the research of the polarization interference imaging spectrometer.

Novel dual channel polarization interference imaging system

The interference images with fixed spectral resolution can be obtained by using the existing static polarization-difference imaging system because the optical path of the system cannot be changed flexibly. However, for different detection targets, the spectral resolution of the system determined by the optical path difference must be appropriate. To satisfy a variety of application requirements, a novel dual channel polarization-difference interference imaging system (DPDⅡS), based on the lateral shear of the wide-field-of-view Savart polariscope (WSP) and the modulated Savart polariscope (MSP), is presented. The two-dimensional space images of a target and orthogonal interference images can be obtained by adjusting the MSP under different lateral displacements simultaneously. In addition, the remarkable characteristics of the system avoid spilling over rays and optimizing the system optical path effectively. In this paper, by using the Jones matrix, the system structure is demonstrated and the theoretical principle of DPDⅡS is analyzed in detail. The amplitudes of the four beams from the MSP and the interference intensity expressions of the coherent light are derived. Then the splitting characteristics of the Savart polariscope (SP) and WSP are presented. It is concluded that the WSP has better shear ability than SP and the WSP can optimize the optical path effectively compared with Wollaston prism in the DPDⅡS. The change ranges of the optical path difference and lateral displacement produced by the MSP for structure angles =/3, /4, /6 are analyzed in detail. The reconstructed orthogonal interferograms and the experimental interferograms under 632.8 nm monochromatic light for dMSP=1.00, 1.10, 1.20, 1.30 mm are obtained. A comparison between the experimental interference images and the simulated images proves that the interference fringes with different resolutions can be obtained simultaneously by adjusting the MSP. Meanwhile, the light intensities of the double optical paths are approximately equal and the same optical path difference is generated for the dual channel with the movement of MSP. The experimental results are consistent with the theoretical analyses. The spatial images of parallel and vertical components are detected under 632.8 nm polychromatic light. Then the total intensity image and the polarization-difference image are obtained through data processing. The conclusion that the polarization difference intensity image has a high resolution compared with the polarization intensity image is presented. The study has reference significance and practical value for the dual channel polarization interference imaging system.

Bi-dimensional empirical mode decomposition based fringe-like pattern suppression in polarization interference imaging spectrometer

Many observers using interference imaging spectrometer were plagued by the fringe-like pattern(FP) that occurs for optical wavelengths in red and near-infrared region. It brings us more difficulties in the data processing such as the spectrum calibration, information retrieval, and so on. An adaptive method based on the bi-dimensional empirical mode decomposition was developed to suppress the nonlinear FP in polarization interference imaging spectrometer. The FP and corrected interferogram were separated effectively. Meanwhile, the stripes introduced by CCD mosaic was suppressed. The nonlinear interferogram background removal and the spectrum distortion correction were implemented as well. It provides us an alternative method to adaptively suppress the nonlinear FP without prior experimental data and knowledge. This approach potentially is a powerful tool in the fields of Fourier transform spectroscopy, holographic imaging, optical measurement based on moire fringe, etc.

Linear stokes imaging spectropolarimeter based on the static polarization interference imaging spectrometer

The theoretical operation and experimental demonstration of a Fourier-transform linear imaging spectropolarimeter are presented. It is composed of a rotating Glan-Taylor prism and a Fourier-transform spectrometer based on Savart polariscope. The polarized light enters the spectrometer to create three sets of interferograms, where the spectral linear Stokes parameters can be calculated and acquired. Compared with previous instruments, the significant advantages of the described sensor are that there are no spatial aliasing in the polarized spectra and it can be used in wider spectral coverage with low cost, ultra-compact size and a simpler common-path configuration. Another static linearly Stokes imaging spectropolarimeter based on the field of view division technique and SPIIS is conceptually described. The spectral dependence of linear Stokes parameters can be recovered with Fourier transformation. Since there is no rotating or moving parts, the system is relatively robust.

Heterodyne polarization interference imaging spectroscopy

A novel heterodyne polarization interference imaging spectroscopy (HPⅡS) based on a Savart polariscope is proposed in this paper. The HPⅡS is modified by introducing a pair of parallel polarization gratings into the static polarization interference imaging spectrometer. Because of the introduced parallel polarization gratings, the lateral displacements of the two beams split by the Savart polariscope vary with wavenumber. The frequency of the interferogram obtained on the detector is related to wavenumber. Like the spatial heterodyne spectrometer where the two end mirrors in a Michelson interferometer are replaced with two matched diffraction gratings, the zero frequency of the interferogram generated in HPⅡS corresponds to a heterodyne wavenumber instead of the zero wavenumber in a non-heterodyne spectrometer. Due to the heterodyne characteristics, a high spectral resolution can be achieved using a small number of sampling points. In addition, there is no slit in HPⅡS and it is an imaging Fourier transform spectrometer that records a two-dimensional image of a scene superimposed with interference curves. It is a temporally and spatially combined modulated Fourier transform spectrometer and the interferogram of one point from the scene is generated by picking up the corresponding pixels from a sequence of images which are acquired by scanning the scene. As a true imaging spectrometer, HPⅡS also has high sensitivity and high signal-to-noise ratio. In this paper, the basic principle of HPⅡS is studied. The optical path difference produced by the Savart polariscope and the parallel polarization gratings is calculated. The interferogram expression, the spectral resolution, and the spectrum reconstruction method are elaborated. As the relationship between the frequency of the interferogram and the wavenumber of the incident light is nonlinear, the input spectrum can be recovered using Fourier transform combined with the method of stationary phase. Also, the matrix inversion method can be used to recover the input spectrum. Finally, a design example of HPⅡS is given. The interferogram is simulated, and the recovered spectrum shows good agreement with the input spectrum. In the design example, the spectral range is 16667-18182 cm-1(550-600 nm), and the number of sampling points is 500. The spectral resolution of HPⅡS is 6.06 cm-1, which is 12 times smaller than that in a non-heterodyne spectrometer with the same spectral range and sampling numbers. HPⅡS has the advantages of compact structure, high optical throughput, strong stability, and high spectral resolution. It is especially suitable for hyperspectral detection with ultra-small, high stability, and high sensitivity.

Radiometric calibration of tempospatially modulated polarization interference imaging spectrometer.

The tempospatially modulated polarization interference imaging spectrometer (TSMPIIS) nominated by the Ministry of Scence and Technology, takes part in the "Eleventh Five-Year National Science and Technology Exhibition." In order to improve the detecting precision of the TSMPIIS, its radiometric calibration scheme is proposed on the basis of the solar simulator, integrating sphere, monochromator, and spectroradiometer. Under the conditions of changing the exposure time and radiant brightness, the CCD linear responses for the TSMPIIS were first tested to validate the reliability of the radiometric calibration performed with a linear response model, and the linear errors were less than 0.15% and 1.15%, respectively. A novel method is put forward to calibrate the nonuniformity of CCD pixels, and the least squares method can commendably correct the uneven effect in the spatial direction. Besides, the absolute radiometric calibration establishes a corresponding relation between the dimensionless intensity output from the TSMPIIS and the target radiant brightness. The study lays the foundation for the engineering application of the TSMPIIS, such as remote sensing detection, and has an important significance for the development of our instrument and equipment technology with independent intellectual property rights.

Efficient background removal based on two-dimensional notch filtering for polarization interference imaging spectrometers

A background removal method based on two-dimensional notch filtering in the frequency domain for polarization interference imaging spectrometers (PIISs) is implemented. According to the relationship between the spatial domain and the frequency domain, the notch filter is designed with several parameters of PIISs, and the interferogram without a background is obtained. Both the simulated and the experimental results demonstrate that the background removal method is feasible and robust with a high processing speed. In addition, this method can reduce the noise level of the reconstructed spectrum, and it is insusceptible to a complicated background, compared with the polynomial fitting and empirical mode decomposition (EMD) methods.

Analysis on the transmittivity of a polarization interference imaging spectrometer

The intensity transmittivity of the optical system of a spectrometer based on polarization interference imaging spectroscopy for remote sensing applications is calculated. In term of the optical design of the instrument, the calculated transmittivity for its optical system are given for input unpolarized light and linearly polarized light, respectively. The factors influencing its transmittivity are analyzed for both cases. The maximal transmittivity efficiency for the polarized light is two times of that of the unpolarized light. The surface reflection ratio of the optical elements and the absorption ratio of the optical materials are two main factors to impact the transmittivity for the two kinds of incident light, and the polarization direction of the incident light is also an important factor for the polarized light. The minimum value of the light intensity of a weak target which can be detected with the imaging spectrometer can be estimated based on the transmittivity analysis in this paper.

Interference visibility of the wide-field-of-view polarization interference imaging spectrometer (WPIIS)

Wide-field-of-view polarization interference imaging spectrometer (WPIIS) is one kind of birefringent interferometers utilized for imaging and spectroscopy. WPIIS employs polarization components (the polarizer, analyzer, the field-widened Savart polariscope and an achromatic half wave plate (AHWP) sandwiched between the two Savart plates) for interferogram acquisition. To acquire excellent reconstructed spectrum, the whole system should ensure high fringe visibility. In this work, polarization deviation and retardation deviation of polarization components are considered into the interference visibility. The resultant visibility is investigated in detail. It is shown that polarization and retardation deviations would severely degrade the final spectrum estimations. The corresponding quantitative tolerances are also provided in which cases we can get attractive visibility higher than 0.97. This work would provide actual suggestions for system design, spectroscopic estimations and performance optimization of any system composed of polarization components.

偏振干涉成像光谱仪中的格兰泰勒棱镜透射比

偏振干涉成像光谱仪中的格兰泰勒棱镜透射比

Multispectral color image composition of temporally and spatially mixed modulated polarization interference imaging spectrometer

A data processing method for the color composite image of the temporally and spatially mixed modulated polarization interference imaging spectrometer (TSMPIIS) is described. In this paper, the multispectral information obtained by TSMPIIS is utilized in the color image generation. The final experimental results prove it is completely possible to produce a color image of detected targets using the multispectral data of TSMPIIS, which make the TSMPIIS not only as a spectrometer, but also as a color camera.

Optical throughput of the tempo-spatially modulated polarization interference imaging spectrometer

The basic principle of the tempo-spatially modulated polarization interference imaging spectrometer (TSMPIIS) is expounded in this paper. Using the electric vector method, the exact expression of TSMPIIS's optical throughput changing with the incident angle i, the polarized orientation angles θ and ϕ, together with the transmittances Toe and Teo is calculated. Furthermore, the effects of various parameters on the optical throughput are analyzed and discussed by computer simulations, and some important conclusions are obtained. In order to obtain a high value of the optical throughput, the incident angle is controlled in a small range, and the optimal values of the polarized orientation angles θ and ϕ are chosen as 0°. This work provides a theoretical and practical guidance for improving the optical throughput of the tempo-spatially modulated polarization interference imaging spectrometer along with its engineering realization.

Empirical mode decomposition based background removal and de-noising in polarization interference imaging spectrometer: erratum

An erratum is presented to correct an error in an equation used to determine the interferogram without background and the estimated background of the recorded interferogram based on empirical mode decomposition. (C) 2013 Optical Society of America

Image fusion of tempo-spatially modulated polarization interference imaging spectrometer

The space-based tempo-spatially modulated polarization interferometer imaging spectrometer (TSMPIIS) scans over an observed area, and acquires the image-spectrum data cubic consisting of a series of the CCD images taken at different times. Every pixel on the CCD image records interferographs with different optical path differences, corresponding to the incident angles changing from maximum, via zero, and finally to negative maximum. To improve the spatial resolution of the color comprised image acquired by TSMPIIS, the panchromatic (PAN) image of high spatial resolution is fused with the color composite image of high spectrum resolution to produce the fused image of both high spatial and spectrum resolution. Based on the characteristics of the TSMPIIS image data, the FFT (fast Fourier transform)-enhanced IHS (intensity-hue-saturation) transform method is used and compared with IHS and WT (wave transform) methods. The experimental results show that the FFT-enhanced IHS method can establish very good trade-off between spatial and spectral quality of the fused image and largely improve the spatial resolution of the color composite image. The fusion method significantly enhances the instrument performance at very low cost.

Empirical mode decomposition based background removal and de-noising in polarization interference imaging spectrometer

Based on empirical mode decomposition (EMD), the background removal and de-noising procedures of the data taken by polarization interference imaging interferometer (PIIS) are implemented. Through numerical simulation, it is discovered that the data processing methods are effective. The assumption that the noise mostly exists in the first intrinsic mode function is verified, and the parameters in the EMD thresholding de-noising methods is determined. In comparison, the wavelet and windowed Fourier transform based thresholding de-noising methods are introduced. The de-noised results are evaluated by the SNR, spectral resolution and peak value of the de-noised spectrums. All the methods are used to suppress the effect from the Gaussian and Poisson noise. The de-noising efficiency is higher for the spectrum contaminated by Gaussian noise. The interferogram obtained by the PIIS is processed by the proposed methods. Both the interferogram without background and noise free spectrum are obtained effectively. The adaptive and robust EMD based methods are effective to the background removal and de-noising in PIIS.

OPTICAL LAYOUT ANALYSIS OF POLARIZATION INTERFERENCE IMAGING SPECTROMETER BY JONES CALCULUS IN VIEW OF BOTH OPTICAL THROUGHPUT AND INTERFERENCE FRINGE VISIBILITY

A polarization interference imaging spectrometer based on Savart polariscope was presented. Its optical throughput was analyzed by Jones calculus. The throughput expression was given, and clearly showed that the optical throughput mainly depended on the intensity of incident light, transmissivity, refractive index and the layout of optical system. The simulation and analysis gave the optimum layout in view of both optical throughput and interference fringe visibility, and verified that the layout of our former design was optimum. The simulation showed that a small deviation from the optimum layout influenced interference fringe visibility little for the optimum one, but influenced severely for others, so a small deviation is admissible in the optimum, and this can mitigate the manufacture difficulty. These results pave the way for further research and engineering design.

Spectrum reconstruction based on the constrained optimal linear inverse methods

The dispersion effect of birefringent material results in spectrally varying Nyquist frequency for the Fourier transform spectrometer based on birefringent prism. Correct spectral information cannot be retrieved from the observed interferogram if the dispersion effect is not appropriately compensated. Some methods, such as nonuniform fast Fourier transforms and compensation method, were proposed to reconstruct the spectrum. In this Letter, an alternative constrained spectrum reconstruction method is suggested for the stationary polarization interference imaging spectrometer (SPIIS) based on the Savart polariscope. In the theoretical model of the interferogram, the noise and the total measurement error are included, and the spectrum reconstruction is performed by using the constrained optimal linear inverse methods. From numerical simulation, it is found that the proposed method is much more effective and robust than the nonconstrained spectrum reconstruction method proposed by Jian, and provides a useful spectrum reconstruction approach for the SPIIS.

Models for polarization detection with the modified polarization interference imaging spectrometer

The polarization interference imaging spectrometer (PIIS) developed by Zhang et al. [Opt. Commun. 203 (2002) 21] can simultaneously acquire the spectral and spatial information of targets. However, the original PIIS system can only acquire two Stokes parameters due to the fixed fore linear polarizer. The limitation for polarization detection is analyzed. To acquire three Stokes parameters, two detecting models based on a modified PIIS are proposed. The first method employs a staring model with a rotatable fore linear polarizer. After remove the fore linear polarizer temporarily, the second method employs a windowing model with phase modulation. The possible errors introduced by the misregistration of polarization elements are analyzed.

Technology of polarization interference imaging spectral based on pupil division and angle shear

With the combination of pupil division, Wollaston prism angle shear and Savart plate lateral shear interference, a new technology that can aquire the message of imaging, polarization and spectrum simultaneously is presented. The system works at the pushing mode with neither mechanical movable nor electrically tunable device, and four quarters of the single charge-coupled device can get four interferograms of different polarization states (two polarization-difference spectral imagings). The device is discussed in detail, and the relationship between azimuth of the prism principal cross section and the output light intensity is analyzed, and then system parameters are optimized. In the paper, we derive the interference fringe intensity distribution formula, use computer numerical simulation to verify the feasibility and accuracy of this method, and thus provide an important theory basis and the practice instruction for designing a new type of imaging spectrometer and its engineering applications.