Fluorescent molecules play an important role in many fields due to their characteristic of high sensitivity and easy operation. The traditional method for detecting fluorescent molecules is Laser Scanning Confocal Microscopy, but it has light pollution and can only detect a single class of fluorescent molecules at once. Recently, Microscopic Hyperspectral Imaging(MHSI) technology has been used to the detection of fluorescent molecules due to its high spectral resolution and non-destructive detection. However, the low spatial resolution of MHSI makes it difficult to conduct high-precision molecular research. Therefore, it is important to develop an image processing method to improve it. In this work, a twostep data processing method was proposed to enhance automatic classification effect of fluorescent molecules. We used a microscopic hyperspectral system to image the mixed five kinds of fluorescent molecular samples in transmission mode. The first step is based on the difference in unit slope of spectra curve (wavelength range was chosen from 410 nm to 550 nm) between fluorescence molecule and the background, and an image segmentation method based on minimum light transmission point is proposed. The second step is to calculate the relative absorbance of each voxel according to the nearest background voxel found on the basis of image segmentation, and to take the absorbance as the final classification feature. Compared with the traditional transmittance feature on six kinds of machine learning classification models, the average classification accuracy of the new features can be improved by 2.2%, and the time consumption per classification can be reduced by 1/3 approximately. In conclusion, the proposed two-step data processing method is suitable for the classification of multi-kinds of fluorescent molecules, which has the advantages of high efficiency and accuracy, and is expected to be widely used in biology, medicine, materials and other fields.
Perovskites have been widely used in solar cells manufacturing due to their extraordinary photoelectric characteristics. The crystal quality of perovskite plays an important role in photoelectric conversion. Although conventional crystal quality detection methods, such as scanning electron microscopy(SEM) and atomic force microscope(AFM), have good performance of high spatial resolution, they are usually time-consuming, expensive, and sometimes damage the samples unavoidably. Hyperspectral imaging(HSI) technology has been utilized to monitor material growth process in recent years, due to its advantages of high spectral resolution, non-invasive and fast detection speed. Micro-hyperspectral imaging(MHSI) technology combines both HSI and microscopic technology, enabling it suitable for micro- and nanoscale material analysis. In this work, we have developed a kind of MHSI system. 3D data of perovskite monocrystals were obtained by transmission mode at room temperature. Perovskite mono-crystals were prepared by one-step solution self-assembly method. The experimental results illustrate that the specific absorption wavelength of perovskite is directly proportional to the thickness of mono-crystals. When the thickness increases, the absorption wavelength will shift red. The thickness factor is also verified by white light interference. The composition ratio of perovskite monocrystals has a certain dependence on its absorbance before 540 nm. The higher the proportion of Br atom is, the weaker the light absorption is, and auxiliary verification was carried out by energy dispersive spectrometer(EDS). In conclusion, MHSI technology can effectively monitor and analyze the preparation process and quality evaluation of micro- and nanoscale materials and structure, it shows a wide application prospect in material science and medical fields.
This study analyzes a photonic ultrawideband pulse generator by using a dual-parallel Mach-Zehnder modulator. A simple configuration capable of generating two popular types of ultrawideband pulse shape, Gaussian monocycle and doublet, is proposed. The generated ultrawideband pulses have very high quality, and the exact waveform is tunable with respect to parameter settings. By changing the time delay between two-path driving pulses applied to the upper and lower sub-Mach-Zehnder modulator of the dual-parallel Mach-Zehnder modulator, the generated ultrawideband pulses can be switched from Gaussian monocycle to doublet. The proposal is first analyzed and then validated by simulations. Results of the study demonstrate that it can offer a realistic solution to photonic ultrawideband pulse generation.
We present a prototype for optical single sideband (SSB) modulation with carrier (OSSB+C) by employing an overwritten fiber Bragg grating (FBG) is proposed and demonstrated. The grating is written using two different uniform phase masks of slight variation in the period. Then it is used in millimeter-wave SSB modulation scheme. Its operation principle can be concluded as the following two steps: (i) first, an intensity modulator double sideband (DSB) modulates the lightwave with millimeter-wave driving signals; (ii) then, the generated DSB modulation signals are reflected by the overwritten FBG. The overwritten FBG can reflect the carrier and the sideband simultaneously, resulting in two coherent subcarriers. Thus the conversion from DSB to OSSB+C can be easily achieved by using only one grating. Also, carrier-to-sideband ratio (CSR) can be optimized by using grating with different reflection depth. We demonstrate this scheme via simulation and successfully reduce signals' CSR from 14.44 to 1.25 dB.
A new method which makes use of the variable accelerated motion of servo motor is presented to fabricate the triangular
fiber Bragg grating. Considering the exponential relationship between the changes of grating refractive index and the
exposure of UV laser, this method only requires one exposure, the variable accelerated motion of servo motor is
controlled by computer program to control the increment of UV laser exposure and the linear change of grating refractive
index on the fiber axial, then the edge of triangular fiber Bragg grating can be gained. The experiment result shows that
the edge of triangular fiber Bragg grating has a good linearity, the bandwidth is 1.6nm, the linear bandwidth which can
be used is 1nm, and the maximum reflectivity is 90%. As a fiber Bragg grating sensor demodulation device, triangular
fiber Bragg grating will be more widely used in sensing fields.
A CCD fiber Bragg grating sensor demodulation system based on FPGA is proposed. The system is divided into three
units: spectral imaging unit, signal detection unit and signal acquisition and processing unit. The spectral imaging unit
uses reflective imaging system, which has few aberration, small size, simple structure and low cost. In the signal
detection unit, information of spectrum are accessed by CCD detector, the measurement of spectral line is converted into
the measurement of the pixel position of spot, multi point can be simultaneously measured, so the system's reusability,
stability and reliability are improved. In the signal acquisition and processing unit, drive circuit and signal acquisition
and processing circuit are designed by programmable logic device FPGA, fully use of programmable and high real-time
features, simplified system design, improved the system's real-time monitoring capabilities and demodulation speed.
Ion-beam etching blazed flat-field concave diffraction gratings (FFCG) to achieve high diffraction efficiency is a
difficult task. This paper presents a new method to fabricate convex holographic gratings as master gratings for making
FFCG. This method makes it convenient to fabricate blazed FFCG with corrected aberrations and uniform predetermined
blaze angle over the grating surfaces. It can also be adapted to the commercial fabrication process. This method could be
briefly described as follows: First, we make a convex grating using holographic recording method. The grooves are
determined by the interference fringes of two spherical waves, one of which is divergent coming from the back side of
the substrate, and the other is convergent coming from the front side. Leading-term aberrations can be corrected by
optimizing the center positions of the two sphere waves. Second, the exposed convex grating is etched by ion beam to
make a blazed convex grating. In this step, it is much easier to get a uniform blaze angle over the surface of a convex
grating than over the surface of a concave grating. At last, the etched convex grating is used directly as a master grating
to replicate blazed FFCG. An optimized example for a specific system structure is given in this paper. The advantages
and difficulties of the method are discussed.
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