Contents
2020
Volume: 42 Issue 5
14 Article(s)
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APPLICATION TECHNOLOGY
Design of mode conversion between terahertz dielectric waveguide and metal waveguide
To realize the mode conversion between the terahertz(THz) dielectric waveguide and the metal waveguide, we design a low-loss, high coupling efficiency tapered waveguide coupler. We have simulated and optimized the transmission efficiency of this structure by the finite-difference time-domain(FDTD) method, and the transTo realize the mode conversion between the terahertz(THz) dielectric waveguide and the metal waveguide, we design a low-loss, high coupling efficiency tapered waveguide coupler. We have simulated and optimized the transmission efficiency of this structure by the finite-difference time-domain(FDTD) method, and the transmission loss of the fundamental mode is extremely low when the frequency is 170-220 GHz, and TM fundamental mode near lossless transmission at 190-200 GHz. This functional device can be used for coupling of integrated THz chips..
Optical Instruments
- Publication Date: Oct. 25, 2020
- Vol. 42, Issue 5, 1 (2020)
Terahertz tunable filter design
Jian SONG
In order to realize terahertz tunable filtering wave, a terahertz tunable filter based on flexible materials was designed. By twisting the Teflon waveguide to form a ring resonator, the band-stop filter function in the 160 GHz to 200 GHz frequency band is realized. Changing the length of the resonant cavity can achieveIn order to realize terahertz tunable filtering wave, a terahertz tunable filter based on flexible materials was designed. By twisting the Teflon waveguide to form a ring resonator, the band-stop filter function in the 160 GHz to 200 GHz frequency band is realized. Changing the length of the resonant cavity can achieve the tuning of the free spectral range (FSR) and the filtering frequency. In the experiment, the switching of the free spectral range between 1.9 GHz and 2.8 GHz and the corresponding filtering characteristics are tested. Research results show that when the length of the resonant cavity is fixed, the stopband can be adjusted by changing the bending radius. The terahertz ring resonator using flexible materials can be used for tunable filtering and has a higher degree of freedom..
Optical Instruments
- Publication Date: Oct. 25, 2020
- Vol. 42, Issue 5, 7 (2020)
Silicon doping impact on magnetotransport in InAs/GaSb type-II superlattices
Zhichao YING, Zhiyong SONG, Aiying CHEN, Tie LIN, and Shixiong KANG
Aiming at the characteristics of infrared detector fabrication and improving the physical properties of the materials, the magnetic transport properties of silicon-doped InAs/GaSb type II superlattice films (grown by MOCVD) at temperatures ranging from 12 K to 300 K was researched. The principle of the Hall effect was Aiming at the characteristics of infrared detector fabrication and improving the physical properties of the materials, the magnetic transport properties of silicon-doped InAs/GaSb type II superlattice films (grown by MOCVD) at temperatures ranging from 12 K to 300 K was researched. The principle of the Hall effect was used to calculate the mobility and carrier concentration of the sample at various temperatures. Electrical measurements were performed using the Vanderberg method. At low temperatures, weak localization (WL) of the thin film is observed, and it is found that the doping of silicon gave it better WL stability. The three-dimensional Kawabata model is used to fit the weak local effects to obtain the value of phase coherence length. It explains the advantage of doped n-type silicon for the quantum localization of InAs/GaSb two types of superlattices, which provides a useful reference for the development of infrared detection devices..
Optical Instruments
- Publication Date: Oct. 25, 2020
- Vol. 42, Issue 5, 12 (2020)
Generation of Bessel beam array using broadband metasurfaces
Lei CHEN, Jing LU, and Jing WEN
Bessel beam arrays can be generated by loading a phase map on a spatial light modulator (SLM) or a microaxicon-like structures fabricated by lithography. However, the pixel size of a typical SLM is more than one order of magnitude larger than the wavelength of visible light, which limits the available range of phase grBessel beam arrays can be generated by loading a phase map on a spatial light modulator (SLM) or a microaxicon-like structures fabricated by lithography. However, the pixel size of a typical SLM is more than one order of magnitude larger than the wavelength of visible light, which limits the available range of phase gradient. And the tip of the micro-axicon-like structures fabricated by lithography is not a standard cone, which affects the quality of the Bessel beam. In order to overcome these shortcomings, a device that can generate Bessel beam array (at a wavelength of 700 nm, NA = 0.3) is designed by loading a complex phase map onto the dielectric metasurface. The device can work in a broadband, the polarization conversion efficiencies of one nanopost remains higher than 57% at the wavelength range from λ=590 nm to λ=800 nm. This device (thickness of 380 nm and diameter of only 40 μm) was simulated by the three-dimensional finite difference time domain (FDTD). The array beams generated were perpendicular to the metasurface device. The proposed Bessel beam array generator has a thickness of nanometer level and a diameter of several tens of micrometers, which has great application prospects in the field of integrated optics in the future..
Optical Instruments
- Publication Date: Oct. 25, 2020
- Vol. 42, Issue 5, 20 (2020)
Terahertz spectroscopy for accurate identification of ginseng and
Tianyi KOU
Since ginsenosides contained in the two herbs have different fingerprint spectra in the terahertz band, a method based on ginsenoside terahertz spectrum was proposed for the identification of ginseng and panax quinquefolium. The terahertz spectra of ginseng and panax quinquefolium were identified by MATLAB software, anSince ginsenosides contained in the two herbs have different fingerprint spectra in the terahertz band, a method based on ginsenoside terahertz spectrum was proposed for the identification of ginseng and panax quinquefolium. The terahertz spectra of ginseng and panax quinquefolium were identified by MATLAB software, and the ginseng and panax quinquefolium were distinguished by the standard principal component analysis (PCA) according to their terahertz spectral characteristics. The results show that the principal component analysis based on terahertz spectrum can distinguish ginseng and panax quinquefolium accurately, and it can also be applied to other similar substances..
Optical Instruments
- Publication Date: Oct. 25, 2020
- Vol. 42, Issue 5, 27 (2020)
Identifying diabetic retinopathy based on deep transfer learning
Yuming YAN, Feng LI, Deming LUO, Siyuan YIN, Xiaotian FU, Zheng LIU, and Lei YAN
In order to identify diabetic retinopathy (DR) in retinal fundus images automatically, to reduce the workload of ophthalmologists, and to develop an assistant tool in detecting and diagnosing retinal diseases, automated detection of DR images which uses deep transfer learning approach based on the Inception-v3 model isIn order to identify diabetic retinopathy (DR) in retinal fundus images automatically, to reduce the workload of ophthalmologists, and to develop an assistant tool in detecting and diagnosing retinal diseases, automated detection of DR images which uses deep transfer learning approach based on the Inception-v3 model is proposed. In the Inception-v3 model trained by ImageNet datasets, the parameters of the previous layers were fixed while the last fully-connected layer of the model was retrained by fine-tuning on the dataset collected by ourselves. Experimental results manifested the performance of the proposed approach providing better predictions and highly reliable detection without specifying lesion-based features, and it could help make automated screening for early DR based on retinal fundus images in addition to assisting ophthalmologists in making a referral decision..
Optical Instruments
- Publication Date: Oct. 25, 2020
- Vol. 42, Issue 5, 33 (2020)
Near-field separated MIMO radar echo amplitude calibration method based on beam pointing adjustment
Qiliang WANG, and Ping LI
The echo amplitude of near-field separated multiple-input multiple-output （ MIMO） radar is different due to the different angle of each channel relative to the target. Therefore, a method of echo amplitude calibration based on beam pointing adjustment is proposed. By using the conversion relationship between the antennThe echo amplitude of near-field separated multiple-input multiple-output （ MIMO） radar is different due to the different angle of each channel relative to the target. Therefore, a method of echo amplitude calibration based on beam pointing adjustment is proposed. By using the conversion relationship between the antenna beam pointing and the echo amplitude change, the indirect adjustment of the antenna echo amplitude is realized by adjusting the beam pointing so that the difference of echo amplitude between channels could be calibrated. The proposed method is verified by using a conventional geometrically separated MIMO array. The results show that the imaging performance of near-field separated MIMO radar can be improved significantly after the calibration of echo amplitude difference..
Optical Instruments
- Publication Date: Oct. 25, 2020
- Vol. 42, Issue 5, 43 (2020)
DESIGN and RESEARCH
Design of near-field plasmonic vortex with shifting based on metasurface in terahertz region
Zhen LI
In this paper, a THz device based on single-layer metasurface has been designed to generate near-field plasmonic vortex with shifting functionality for increasing THz communication capacity. Based on the geometric metasurface, the shifting of near-field vortex of the device is simulated by FITD (the finite integration In this paper, a THz device based on single-layer metasurface has been designed to generate near-field plasmonic vortex with shifting functionality for increasing THz communication capacity. Based on the geometric metasurface, the shifting of near-field vortex of the device is simulated by FITD (the finite integration time domain). The corresponding results suggest that position shifting of the field distribution in the whole space can be achieved under the illumination of circularly polarized light. To a certain extent, the kind of functional devices can improve the THz communication capacity and can be used in 6G technology..
Optical Instruments
- Publication Date: Oct. 25, 2020
- Vol. 42, Issue 5, 63 (2020)
Preparation and research of perylene-doped polymer microspheres
Jiaojie HOU, and Bin CAI
Optical microsphere resonator has the advantages of high quality factor (Q), low threshold, and easy to integrate. In order to make better use of microsphere resonator, high Qlaser can be obtained.In this paper, we successfully prepared perylene doped polystyrene microspheres by solvent-nonsolvent fast injection methodOptical microsphere resonator has the advantages of high quality factor (Q), low threshold, and easy to integrate. In order to make better use of microsphere resonator, high Qlaser can be obtained.In this paper, we successfully prepared perylene doped polystyrene microspheres by solvent-nonsolvent fast injection method.By using this method the diameter of the microspheres can be easily adjusted by changing the parameters of experiments. The microspheres have a smooth surface and intact morphological features, which facilitate whispering gallery modes generation in the sphere cavities.Under the femtosecond laser pumping, we can easily obtain the laser signals from either single microsphere or aggregated microspheres, which shows promising applications..
Optical Instruments
- Publication Date: Oct. 25, 2020
- Vol. 42, Issue 5, 70 (2020)
Electromagnetically induced transparency based ontopological one-way waveguide
Qingbin YUAN
In this paper, a coupled resonant waveguide based on magnetic photonic crystal has been proposed. The resonant frequency can be controlled by tuning the position of cavities to realize the electromagnetically induced transparency in topological one-way waveguide. The corresponding characteristics are demonstrated basedIn this paper, a coupled resonant waveguide based on magnetic photonic crystal has been proposed. The resonant frequency can be controlled by tuning the position of cavities to realize the electromagnetically induced transparency in topological one-way waveguide. The corresponding characteristics are demonstrated based on the finite-difference time-domain method. Our study may provide an approach to realize optical delay and optical switches in the topological waveguide..
Optical Instruments
- Publication Date: Oct. 25, 2020
- Vol. 42, Issue 5, 77 (2020)
Terahertz signal enhancement and control based on spatial energy distribution modulation
Zhaozhao SUN
In order to effectively enhance and continuously control terahertz wave, we propose a method of modulating the spatial distribution of terahertz wave through external spatial interference. Firstly, we compare the spatial distribution when placing hollow metal waveguides with that when not placing hollow metal waveguideIn order to effectively enhance and continuously control terahertz wave, we propose a method of modulating the spatial distribution of terahertz wave through external spatial interference. Firstly, we compare the spatial distribution when placing hollow metal waveguides with that when not placing hollow metal waveguides by means of theoretical calculation. The impact on the spatial distribution of terahertz wave is exhibited when changing the propagation path of terahertz wave under external interference. At the same time, we acquire the spatial distribution of terahertz wave which can be continuously regulated by changing the relative position of hollow metal waveguide and laser filament. The results mentioned above provide a new way for continuous regulation of wideband terahertz wave. The results show that the energy intensity of the strongest point in the spatial distribution of THz wave is increased by 5.9 times, which can provide reference for the continuous regulation of broadband terahertz wave..
Optical Instruments
- Publication Date: Oct. 25, 2020
- Vol. 42, Issue 5, 83 (2020)
Terahertz radiation mechanism in laser filament with gas density control
Haicheng XIAO, and Yan PENG
In order to study the effect of gas density on the terahertz wave radiated by multi-color laser-induced air plasma filament, a theoretical model of terahertz （THz） generation from a laser-induced air plasma filament and the subsequent propagation process is established. Based on the model and simulation, the influence In order to study the effect of gas density on the terahertz wave radiated by multi-color laser-induced air plasma filament, a theoretical model of terahertz （THz） generation from a laser-induced air plasma filament and the subsequent propagation process is established. Based on the model and simulation, the influence of gas density on terahertz radiation is studied. The results show that the gas density will affect the transient current distribution of laser filament and the propagation phase of THz wave, then affect the THz radiation intensity of laser filament, and make the THz radiation energy change nonlinearly with the gas density. The theoretical study is of great significance to the cognition of the physical process of laser filamentation..
Optical Instruments
- Publication Date: Oct. 25, 2020
- Vol. 42, Issue 5, 89 (2020)
OPTICAL SYSTEM
Design of high resolution KB microscopy system based on aspherical mirror
Jingyi LEI, Jie XU, Liang CHEN, Xinye XU, Wenjie LI, and Baozhong MU
In order to break the limitation of the spherical mirror's surface shape on the spatial resolution of the traditional Kirkpatrick-Baez (KB) microscope, an optical design method for the aspherical KB microscopy imaging system was established. Elliptical cylindrical mirrors were used instead of spherical mirrors, andIn order to break the limitation of the spherical mirror's surface shape on the spatial resolution of the traditional Kirkpatrick-Baez (KB) microscope, an optical design method for the aspherical KB microscopy imaging system was established. Elliptical cylindrical mirrors were used instead of spherical mirrors, and the mathematical expressions of the mirror parameters were calculated through geometric relationships. Combining the quantitative analysis of the influence of main optical structure parameters on spatial resolution, a set of optical structure parameters of aspherical KB microscopes suitable for current high-power laser devices in China were proposed, and the imaging experiment was carried out in the lab. The experiment shows that in the central field of view, the spatial resolution is better than 2 μm, and in the field of view of 200 μm, the spatial resolution is better than 5 μm, and the geometrical solid angle can reach 1.3×10-6 sr. Aspherical KB microscope effectively improves the resolution of the central field of view of the KB microscope, which meets the needs of high-resolution diagnosis during the deceleration stage of implosion targets..
Optical Instruments
- Publication Date: Oct. 25, 2020
- Vol. 42, Issue 5, 50 (2020)
Single pixel complex amplitude imaging and experimental analysis
Yuehua ZHANG, and Guorong SUI
The imaging of light intensity information and phase information of the light field is very important for medical, optical measurement, three-dimensional imaging etc. We have designed a single-pixel imaging system that can achieve complex amplitude imaging of the light field without a reference beam. The imaging systemThe imaging of light intensity information and phase information of the light field is very important for medical, optical measurement, three-dimensional imaging etc. We have designed a single-pixel imaging system that can achieve complex amplitude imaging of the light field without a reference beam. The imaging system modulates the light field information through a phase-type optical mask, uses a non-resolution photodetector to detect the modulated light intensity information, and uses the Phaselift algorithm to recover the light intensity and phase information of the light field. We utilized the single-pixel imaging system to perform imaging experiments on diffracted light fields and transparent PDMS thin film objects. From the imaging results, light intensity information and phase difference information of the diffraction ring can be clearly observed. The phase difference is 0.053 and the width of the groove is 220 μm of the object film in the experiment, and the phase difference is 0.046 and the width of the groove is 256 μm of the image obtained by the experiment, which indicates that the imaging system is very close to the image information obtained by the traditional detection method. The imaging optical path of the system does not require a reference beam, and the system is simple and easy to integrate, which has promoted the development of portable imaging systems. It can be applied to wide-spectrum imaging and has great development potential in light field complex amplitude imaging..
Optical Instruments
- Publication Date: Oct. 25, 2020
- Vol. 42, Issue 5, 57 (2020)
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