THz transmission spectra of monosaccharide polycrystal were tested and analyzed based on terahertz time domain system and Fourier transformation infrared spectroscopy system. The characteristic absorption frequencies of of samples were acquired and their spectral results in two kinds THz systems were contrasted and discussed. Based on Density Functional Theory (DFT), Gaussian 09 molecule software and CASTEP crystal software were adopted to optimize samples structures and calculate their characteristic absorption frequencies. The simulation results are in better agreement with the experiment ones.
The absorption spectra of two kinds of important functional oligosaccharides were firstly acquired based on Fourier transform infrared spectroscopy in the range of 0.15-10THz. The simulation results of their infrared spectra were given based on Gaussian software, which were in good agreement with the experiment results. The rotation spectra and some perssad vibration spectra of these molecules were analyzed, and their absorption peaks were exactly identified. The components information was obtained by comparing the simulation results of different molecules.
As a powerful tool for the research of molecular structure, infrared absorption spectrum has been extensively studied in the field of biomedical photonics. The absorption spectrum of anhydrous glucose in terahertz region has been measured by Fourier transform infrared spectrometer (FTIR). The experimental results show that there are many characteristic absorption peaks. The origins of characteristic absorption are generally attributed to intermolecular vibrations and intramolecular torsions. CASTEP quantum chemical calculation software package was utilized to simulate the infrared spectroscopy of glucose crystal structure based on periodic boundary condition and plane wave pseudopotential method. Also, linear response approach and norm conserving pseudopotentials are essential. Besides, the performance of the generalized gradient approximation (GGA) functional has been commendably examined. The theoretical results show that the standard Perdew-Burke-Ernzerhof (PBE) approach along with its line Broyden-Fletcher-Goldfarb-Shanno (L-BFGS) algorithm tends to be superior. We analyzed the vibration mode corresponding to each characteristic absorption peak with DFT theory. The agreement between theory and experiment indicates that the crystal simulation calculation based on solid-state density functional theory can identify absorption peaks of substance and vibration attribution accurately in terahertz region.
The terahertz is an electromagnetic wave with non-ionization and low average power; therefore it is thought not to be hazardous to biological tissues. The terahertz waves can excite the vibration mode and rotation mode of macromolecules, and both amplitude and phase information of samples which are detected can be gotten and contrasted. Compared with visible and infrared light, it also has the advantage of low scattering and that the surface character and depth pattern of samples can be acquired at the same time, which makes it possible to measure tissues in vivo without any damage in the field of biomedicine. In this article, THz transmission and reflection spectra of liquid and solid samples are tested and analyzed based on THz-TDS (Terahertz time Domain Spectra system), including glucose solution and different kinds of biological tissue slices, etc. The optical parameter relations of different samples are acquired. Spectrum results are contrasted and discussed for two kinds THz systems. The results show that THz spectra of different samples are differentiable, and they can be described quantitatively.
We utilized terahertz time-domain spectroscopy (THz-TDS) to investigate the complex dielectric properties of solid polycrystalline material of anhydrous glucose (D-(+)-glucose with purity >99.9%). THz transmission spectra of samples were measured from 0.2 to 2.2 THz. The samples were prepared into tablets with thicknesses of 0.362, 0.447, 0.504, 0.522 and 0.626 mm, respectively. The imaginary part of the complex dielectric function of polycrystalline glucose showed that there were multiple characteristic absorption peaks at 1.232, 1.445, 1.522, 1.608, 1.811 and 1.987 THz, respectively. Moreover, for a given characteristic absorption peak, the real part of the complex dielectric function showed anomalous dispersion within the full width half maximum (FWHM) of the absorption peak. Both finite difference time-domain (FDTD) numerical simulations and experimental results showed that the complex dielectric function of anhydrous polycrystalline glucose fits well with the Lorentz dielectric mode. The plasma oscillation frequency was below the frequency of the light waves suggesting that the light waves passed through the polycrystalline glucose tablets. Calculations based on density functional theory (DFT) showed that the characteristic absorption peaks of polycrystalline glucose originated mainly from collective intermolecular vibrations such as hydrogen bonds and crystal phonon modes. The THz radiation can excite the vibrational or rotational energy levels of the biological macromolecules. This leads to changes in their spatial configuration or interactions. This study showed that THz-TDS has potential applications in biological and pharmaceutical research and food industry.
The optical activity of glucose molecules is important for diagnosing and monitoring blood glucose of diabetes. In order to accurately detect the diabetes at an early stage, there is an urgent need to develop innovative detection methods. By use of Mueller matrix decomposition (MMD), we have studied the optical activity of glucose molecules in three types of turbid media—polystyrene (PST) sphere suspension, chicken blood, and the vein blood of diabetic patients. The experimental setup to obtain the Mueller matrix in the forward detection geometry has been used. The experimental results show that the rotation angle has linear relationship with the concentration of the glucose when the scattering coefficient of the PST sphere suspension remains unchanged, whereas the scattering effect enlarges the rotation angle. Furthermore, optical rotation abides by Drude’s dispersion equation. The decomposition method has also been found useful applications in quantifying the optical rotations of blood glucose in diabetic patients. The diabetic severity status can be distinguished with the rotation angle of glucose and also is in accordance with the clinical diagnosis. Thus, the method of MMD has promising applications in diabetic diagnosis and monitoring.
Optical activity is the intrinsic property of chiral molecules. Investigation of optical activity is particularly important for diagnosing and monitoring blood glucose of diabetes. The experimental setup to obtain the Mueller matrix in the forward detection geometry is used. Three kinds of chiral turbid media are selected to be studied in the experiment. The first is the tissue phantom composed of an aqueous solution of glucose mixed with PST sphere suspensions. The second is the actual chicken blood mixed with glucose solution. The last is the vein blood plasma of diabetic patients. The results presented in this study demonstrate that the method of Mueller matrix decomposition can be used to quantitatively extract the optical rotation of chiral molecule in turbid medium. The rotation angle has linear relationship with the concentration of the optical activity material when the scattering coefficient of the turbid medium maintains unchanged. The scattering effect enlarges the rotation angle. Furthermore, optical rotation abides by the Drude’s dispersion equation. The decomposition method also has been found useful applications in quantifying the optical rotations due to blood glucose in diabetic patients. The diabetic severity status can be distinguished with the rotation angle of glucose by using the decomposition method and also are in accordance with the clinical diagnosis. Thus, the method of Mueller matrix decomposition has promising applications in diabetic diagnosis.
THz transmission spectrums of different glucose solution with concentration from 1% to 70% were measured on the condition of room temperature and fewer than 4% humidity in the nitrogen environment. According to the physical model of the THz optical parameters, their refractive indexes and absorption coefficients were gotten. The results showed that with the increase of glucose concentration, the THz absorption coefficients of solution decrease linearly. The fitting relations among the refractive index, the extinction coefficient, absorption coefficient and its concentration at the frequency of 0.33, 0.6 and 0.8 THz were acquired individually. Their correlation coefficients were larger than 0.95. Analysis and discussion about them were given. The THz time domain spectroscopy technologies could realize an accuracy measurement for the concentration of glucose solution. This work was meaningful to the exploration of THz spectral response of biological samples.
THz spectroscopy has recently been used to examine human disease because of its a higher sensitivity and
signal-to-noise ratio. In this work, the interaction mode between THZ radiation and biological tissue in the THz
frequency range is given. Clinical Intralipid-10% is diluted into different concentrations to use as tissue phantoms. And
they are firstly tested based on the terahertz time domain spectroscopy in the condition of room temperature. Optical
parameters of phantom solution including absorption coefficient and refractive index are gotten, and the frequency
properties of these optical parameters are analyzed. The function relations can be firstly found. The conclusions is
meaningful to make the further research of interaction between THZ radiation and human tissue, related cancers.
The optical add/drop multiplexer (OADM) is an important device to realize an auto optical exchange in optical transport
network, and tunable filters are one of its central parts. The acousto-optic tunable filter (AOTF) has not only a large
wavelength tuning range (more than 100nm), low optical loss (less than 5dB) and a narrow filter bandwidth (about
1nm), but also dynamic and reconfigurable characteristics. Thus, the acousto-optic tunable filter (AOTF) is one of
powerfully several potential candidates. In the paper, the main works are to test and analyze the sidelobes characteristics
of TeO2 AOTF with different bandwidth and its influence on the crosstalk between the neighbor channels. The new
structure of OADM based on the AOTF is suggested to lower the influence of signal crosstalk.
As an optical sensor and controller in wavelength division multiplexing (WDM) system, the acousto-optic tunable filter
(AOTF) is one of powerfully several potential sensing candidates. The AOTF can easily achieve dynamically to add/
drop arbitrary wavelength by changing the RF frequency in its range of working wavelength. In this paper, the reason of
the signal crosstalk is given and its characteristic of sidelobe is firstly analyzed on the momentum matching condition.
The coupling equations with multiple acoustic waves traveling simultaneously are presented. The analytic solution of the
diffraction efficiency for the two acoustic frequencies is given, and its impact on the device performances is discussed.
The result is correspondence with experimental results. In addition, because the TeO2 AOTF has a specific structure
based on its design principal, it is shown whether the sidelobes on the diffractive efficiency curve appear is mainly
decided by the bandwidth of the AOTF and the mismatching factors. For a definite device bandwidth, if the total
momentum mismatch is lower than a definite value, the device has no sidelobe. Then, the feasibility of the TeO2 AOTF
as an OADM in WDM system has superiority on signal crosstalk.
Estimation of camera pose is an integral part and classical problem of augmented reality (AR) system and computer
vision. Accurate pose estimation is crucial in determining the rigid transformation relating 2D images to known 3D
geometry. Therefore, the algorithm should be not only fast and accuracy, but also robust in AR system. Orthogonal
iterative (OI) algorithm is a good method, but it requires a proper initialization and cannot deal with problems of pose
ambiguity. A new method based on OI we presented before, provides a good initialization and solves a problem of pose
ambiguity introduced by coplanar markers. However, two more potential problems usually make the algorithm calculate
some wrong results, and lead to the algorithm unsteady and not robust. In this paper, we develop the method by resolving
pose ambiguities, which originate from potential problems in algorithm. Two more constraints are employed in our
method. One is camera must be located in front of the marker, while the other is camera must be oriented to the marker.
It's proved that the improved method is steady in experiments, and can calculate the pose of camera fast and correctly.
Moreover, since the method can deal with pose ambiguity, it is rather robust in AR system.
Acousto-optic tunable filter (AOTF) is one of important optical switch components in optical networks. The possibility of tellurium dioxide acousto-optic tunable filter (TeO2 AOTF) as an optical add/drop multiplexer (OADM) is studied on the basis of the theory of the anomalous acousto-optic Bragg diffraction and the design principle of non-collinear AOTF. Its main performances and structure are analyzed and discussed, and the significance of incident angles and interaction lengths for its performances is presented. The model for optimization design is built under some limitation and the transducer areas is adopted as a regulator for performance, the designed example of the TeO2 AOTF for WDM systems is given by the optimized method.
In the paper, a weighted-coupling scheme of a SiO2 film-loaded Ti:LiNbO3 quasi-collinear integrated acousto-optic mode converter is reported, in which an angular offset between the acoustic and optical waveguides is introduced to implement an optimized Hamming weighted function for realization of ultralow sidelobe level. Acoustic wave guiding properties have been investigated for films such as SiO2, ZnO on LiNbO3 firstly. SiO2 film on LiNbO3 was selected as acoustic waveguide. With the mode analysis of the acoustic wave guide and the theory of coupling mode the limit of the width, weighted coupling coefficient and the characteristics of the conversion of acousto-optic modes are obtained. As the angle between acoustical and optical waveguides is 0.45°, the worst sidelobe level is -16dB and the theoretical values of bandwidths of -3dB and -10dB is 1.37nm and 2.31nm respectively, which have excelled the domestic reported level.
Optical add/drop multiplexers(OADMs) are finding their applications in future all-optical communication networks to link the network with local transmitters and receivers. A novel fully dynamic and reconfigurable OADM based on AOTF with low crosstalk is presented. The PMD compensation issue of AOTF is addressed as well.
The Integrated acousto-optic tunable filter have the potential to perform the OADM or OXC functions, which play significant role in WDM optical network. The characteristic of the acousto-optic mode conversion is sinc2-like functions with high sidelobe intrinsic. The high sidelobe level lead to serious crosstalk in the WDM optical network. The theory of weighted coupling for IAOTF has been presented. And the filter response using four suggested weighted
functions has been calculated with the matrix methods. Significant suppression of sidelobe level has been achieved by employing the techniques of weighted coupling. It is a valid approach to reduce the sidelobe of IAOTF by choosing propriety weighted function and a realized way.
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