Mechanism of the two-port one input mirror-symmetric all-dielectric disk array perfect absorbers is studied by temporal coupled mode theory. The perfect absorption is resulted from the degenerate critical coupling of EH111 and HE111 modes of the dielectric disks. Analytical absorption with parameters extracted from Eigen-frequency analysis matches well with that by Scattering parameter simulations, we also show that the asymmetric total field is due to the different symmetry of the two modes. The effect of the geometric parameters and material loss tangent is also investigated, which can guide the design of such all-dielectric perfect absorbers.
An integrated method is proposed for the real-time measurement of filament lamp dimension based on machine vision (FLDMV). First, an online detection platform is built, and the image is acquired by telecentric lenses and charge-coupled diode (CCD). Second, a series of image processing, including filter, edge extraction, ellipse fitting, recursive minimum bounding rectangle, and curvature restrict estimation. Finally, the actual size of lamp is obtained by system calibration. The experimental analysis and comparison show that the maximum measurement error of this method is 0.21mm, which meets the requirements of filament lamp dimension measurement. The curvature restrict estimation based on ellipse fitting are proposed to guarantee the accuracy and real time. Compared with the traditional measurement method, our method has the advantages of fast measurement speed, high accuracy, and real time. It also can be widely used in other parts of the measurement.
Grayscale camera can only obtain gray scale image of object, while the multicolor imaging technology can obtain the color information to distinguish the sample structures which have the same shapes but in different colors. In fluorescence microscopy, the current method of multicolor imaging are flawed. Problem of these method is affecting the efficiency of fluorescence imaging, reducing the sampling rate of CCD etc. In this paper, we propose a novel multiple color fluorescence microscopy imaging method which based on the Frequency division multiplexing (FDM) technology, by modulating the excitation lights and demodulating the fluorescence signal in frequency domain. This method uses periodic functions with different frequency to modulate amplitude of each excitation lights, and then combine these beams for illumination in a fluorescence microscopy imaging system. The imaging system will detect a multicolor fluorescence image by a grayscale camera. During the data processing, the signal obtained by each pixel of the camera will be processed with discrete Fourier transform, decomposed by color in the frequency domain and then used inverse discrete Fourier transform. After using this process for signals from all of the pixels, monochrome images of each color on the image plane can be obtained and multicolor image is also acquired. Based on this method, this paper has constructed and set up a two-color fluorescence microscope system with two excitation wavelengths of 488 nm and 639 nm. By using this system to observe the linearly movement of two kinds of fluorescent microspheres, after the data processing, we obtain a two-color fluorescence dynamic video which is consistent with the original image. This experiment shows that the dynamic phenomenon of multicolor fluorescent biological samples can be generally observed by this method. Compared with the current methods, this method can obtain the image signals of each color at the same time, and the color video’s frame rate is consistent with the frame rate of the camera. The optical system is simpler and does not need extra color separation element. In addition, this method has a good filtering effect on the ambient light or other light signals which are not affected by the modulation process.
Differential optical absorption spectroscopy (DOAS) has become a widely used method to measure trace gases in the atmosphere. The concentrations of trace gases can be retrieved by fitting differential absorption spectra with standard differential absorption cross-section using the linear least-square method. The basic principle of DOAS is introduced. The construction of DOAS on-line monitoring system is designed and the retrieval method of trace gases concentration based on the principle of least-squares is discussed. The properties of DOAS system are tested by experiments. The advantages of DOAS system used in atmosphere quality monitoring are shown.
White Cell is a typical multiple-path absorption cell for absorption spectroscopy. For multi-path enhanced absorption
application, we should make sure that the input light of the multiple-path cell can be output as much as possible to
enhance absorption signal. Thus the astigmatism of the White cell should be analyzed for optimization as a key factor. In
White cell, the astigmatism is difficult to be calculated as the meridian and sagittal planes of the beam would rotate with
a different angle while at each reflection. In this article, the White cell is presented by defined 4×4 optical matrices as a
nonsymmetrical system. The astigmatic difference would then be obtained from the eigenvalues of the partitioned
matrices. The numerical computation and ray-tracing simulation results presented have proved the efficiency of this
method. The astigmatism can be improved by properly choosing the distance h between the two rows of image spots on
the field mirror.
An advanced wavelength calibration process with higher wavelength accuracy is developed based on the conventional
calibration method of micro-spectrometers with multichannel detectors. The deficiencies of the conventional method in
acquiring sufficient well-spaced and adequately accurate wavelength-pixel data for calibration are analyzed. And three
steps are added to the conventional method before the final pixel-wavelength fit is carried out. First, segmented data
collection is carried out to ensure sufficient well-spaced lines for calibration. Second, sub-pixel analysis is executed to
increase sampling rate. Third, peak fit is implemented to acquire more accurate central wavelength positions. The
simulated experiment was based on a compact spectrometer with a crossed Czerny-Turner optical design. Mercury and
Argon line spectra are used as wavelength standards. A linear image sensor with 1024 pixels each 25μm in width is used
as the detector. In the new calibration process the whole spectral region was divided into two segments with different
integral time of the detector; the sampling rate was increased by 2 times by sub-pixel analysis; and log-normal function
is applied in the peak fit. The results show that by applying the new method, the wavelength accuracy improves from
above 1.0nm to around 0.6nm.
The trade-off between resolution and signal to noise ratio is a shackle to develop high performance miniature grating
spectrometers. Concentrating on breaking this shackle, freeform optics and super-resolution restoration method for
miniature grating spectrometers are proposed in this paper. Substituting a varying sagittal surface for a toroidal one, not
only aberrations along dispersive direction can be reduced, but also aberrations perpendicular to dispersive direction can
be reduced in a broad spectral range. This means both resolution and throughput would be multiplied. To reduce the
remnant imperfection of system, subpixel-deconvolution process may be supplemented. By subpixel reconstruction,
under-sampling due to finite pixel size of array detector would be got rid of. By deconvolution, blurring duo to slit and
other system imperfection would be eliminated. Consequently, resolution and throughput would be further increased.
When evaluating or designing a sampled imager, a comprehensive analysis is necessary and a trade-off among optics,
photoelectric detector and display technique is inevitable. A new method for sampled imaging system evaluation and
optimization is developed in this paper. By extension of MTF in sampled imaging system, inseparable parameters of a
detector are taken into account and relations among optics, detector and display are revealed. To measure the artifacts
of sampling, the Baseband Response Squeeze model, which will impose a penalty for undersampling, is clarified.
Taken the squeezed baseband response and its cutoff frequency for favorable criterion, the method is competent not
only for evaluating but also for optimizing sampled imaging system oriented either to single task or to multi-task. The
method is applied to optimize a typical sampled imaging system. a sensitivity analysis of various detector parameters is
performed and the resulted guidelines are given.
This paper aims at reducing the bias distortion in familiar sub-pixel analysis algorithm in miniature spectrometer. The process of sub-pixel analysis is modeled and the fallibility in reported sub-pixel analysis algorithm is discussed. The discussion suggests that an important inducement for distortion is cumulated errors. Hence, an averaged sup-pixel analysis algorithm is put forward. According to the new algorithm, the same iteration is executed twice but in opposite directions and results of the same sub-pixels are averaged. Relative simulation indicates that compare with old ones the new algorithm reduces bias distortion by several times and contributes to an enhanced resolution and wavelength accuracy.
In order to overcome the resolution limits of the detector array to the spectrometer, the super-resolution algorithms is adopted. On the basis of the study on the integral and sampling property of the detector array, the spectral line adaptability to the super-resolution algorithms was verified. The algorithms were tested respectively by three classic spectral line profiles - Gaussian, Lorentzian and Voigt, and the deviation of the reconstructed spectral line and the original one was analyzed. Consequently, the super-resolution algorithm and its optimal parameter for different spectral line profiles were deduced.