Frontiers of Optoelectronics

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A CCD based machine vision system for real-time text detection
Shihua ZHAO, Lipeng SUN, Gang LI, Yun LIU, Binbing LIU
Front. Optoelectron.    https://doi.org/10.1007/s12200-019-0854-0
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Text detection and recognition is a hot topic in computer vision, which is considered to be the further development of the traditional optical character recognition (OCR) technology. With the rapid development of machine vision system and the wide application of deep learning algorithms, text recognition has achieved excellent performance. In contrast, detecting text block from complex natural scenes is still a challenging task. At present, many advanced natural scene text detection algorithms have been proposed, but most of them run slow due to the complexity of the detection pipeline and cannot be applied to industrial scenes. In this paper, we proposed a CCD based machine vision system for real-time text detection in invoice images. In this system, we applied optimizations from several aspects including the optical system, the hardware architecture, and the deep learning algorithm to improve the speed performance of the machine vision system. The experimental data confirms that the optimization methods can significantly improve the running speed of the machine vision system and make it meeting the real-time text detection requirements in industrial scenarios.

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Ultra-flat broadband microwave frequency comb generation based on optical frequency comb with a multiple-quantum-well electro-absorption modulator in critical state
Cong SHEN, Peili LI, Xinyuan ZHU, Yuanfang ZHANG, Yaqiao HAN
Front. Optoelectron.    https://doi.org/10.1007/s12200-019-0915-4
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In this paper, we proposed a novel ultra-flat broadband microwave frequency comb (MFC) generation based on optical frequency comb (OFC) with a multiple-quantum-well electro-absorption modulator (MQW-EAM) in critical state. The scheme is simple and easy to adjust. The performance of the MFC generation scheme is investigated using software Optisystem. The results show that the comb spacing of MFC can be adjusted from 5 to 20 GHz by changing RF signal’s frequency and the MFC is almost independent on the linewidth of the tunable laser diode. The performance of the MFC can be improved by reasonably increasing the voltage of the RF, the small-signal gain of the Erbium-doped fiber amplifier (EDFA) and the responsivity of the photodetector. The MFC generated by this scheme has 300 GHz effective bandwidth with 15 comb lines, whose power variation is 0.02 dB, when the components’ parameters in the Optisystem are set as follows: the power of tunable laser diode (TLD) is 0 dBm, the wavelength is 1552.52 nm, and linewidth is 1 MHz; RF signal’s frequency is 20 GHz and the voltage is 10 V; the reverse bias voltage of MQW-EAM is 6.92 V; the small-signal gain of the EDFA is 40 dB; the responsivity of the photodetector (PD) is 1 A/W.

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Robot visual guide with Fourier-Mellin based visual tracking
Chao PENG, Danhua CAO, Yubin WU, Qun YANG
Front. Optoelectron.    https://doi.org/10.1007/s12200-019-0862-0
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Robot vision guide is an important research area in industrial automation, and image-based target pose estimation is one of the most challenging problems. We focus on target pose estimation and present a solution based on the binocular stereo vision in this paper. To improve the robustness and speed of pose estimation, we propose a novel visual tracking algorithm based on Fourier-Mellin transform to extract the target region. We evaluate the proposed tracking algorithm on online tracking benchmark-50 (OTB-50) and the results show that it outperforms other lightweight trackers, especially when the target is rotated or scaled. The final experiment proves that the improved pose estimation approach can achieve a position accuracy of 1.84 mm and a speed of 7 FPS (frames per second). Besides, this approach is robust to the variances of illumination and can work well in the range of 250-700 lux.

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Improved offline multi-objective routing and wavelength assignment in optical networks
Harpreet KAUR, Munish RATTAN
Front. Optoelectron.    https://doi.org/10.1007/s12200-019-0850-4
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Optical networks act as a backbone for coming generation high speed applications. These applications demand a very high bandwidth which can be exploited with the use of wavelength division multiplexing (WDM) technology. The issue of setting light paths for the traffic demands is routing and wavelength assignment (RWA) problem. Based on the type of traffic patterns, it can be categorized as offline or online RWA. In this paper, an effective solution to offline (static) routing and wavelength assignment is presented considering multiple objectives simultaneously. Initially, the flower pollination (FP) technique is utilized. Then the problem is extended with the parallel hybrid technique with flower pollination and intelligent water drop algorithm (FPIWDA). Further, FPIWD is hybrid in parallel with simulated annealing (SA) algorithm to propose a parallel hybrid algorithm FPIWDSA. The results obtained through extensive simulation show the superiority of FPIWD as compared to FP. Moreover, the results in terms of blocking probability with respect to wavelengths and load of FPIWDSA are more propitious than FP and FPIWD.

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Transmission characteristics of linearly polarized light in reflection-type one-dimensional magnetophotonic crystals
Chunxiang ZENG, Zeqing WANG, Yingmao XIE
Front. Optoelectron.    https://doi.org/10.1007/s12200-019-0870-0
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The propagation properties of linearly polarized light in reflection-type one-dimensional magnetophotonic crystals are studied by using the 4×4 transmission matrix method. The structure models of reflection-type one-dimensional magnetophotonic crystals are designed, the magnetic field direction control characteristics of reflection spectrum and Kerr rotation angle are discussed, and the effect of applied magnetic field direction and strength on reflection spectrum and Kerr rotation angle are analyzed. The results show that the non-diagonal elements in the dielectric constant of magneto optical materials change when the angle ϕ between applied magnetic field and optical path changes, the reflectivity and Kerr rotation angle decrease when the angle ϕ increases; when the applied magnetic field strength changes, the reflectivity and Kerr rotation angle increase when the applied magnetic field strength increases; by adjusting the angle ϕ and strength of the applied magnetic field, the rotation angle of Kerr can be adjusted to 45°, and a more flat reflection spectrum can be obtained by designing the appropriate structure.

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Experimental and simulation assessments of underwater light propagation
Fatah ALMABOUADA, Manuel Adler ABREU, João M. P. COELHO, Kamal Eddine AIADI
Front. Optoelectron.    https://doi.org/10.1007/s12200-019-0865-x
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This paper investigates the light propagation through several types of water by experimental and simulation. The Zemax-ray tracing software allowed to simulate the propagation of light in water and to observe the receiver response by reproducing the real conditions of propagation. The underwater environment has been reproduced by a 1.2 m long water tube and 20 cm in diameter with a glass window fitted on one side. The use of tap water with different amounts of sand leads toward three types of water with different attenuation coefficients (0.133, 0.343, 0.580 m-1). The light transmission in the three types of water was experimentally evaluated using a doubled Nd:YAG laser with energy of 4.3 mJ and a pulse width of 20 ns. Comparisons were done between simulation and experimental results.

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Antimony doped Cs2SnCl6 with bright and stable emission
Jinghui LI, Zhifang TAN, Manchen HU, Chao CHEN, Jiajun LUO, Shunran LI, Liang GAO, Zewen XIAO, Guangda NIU, Jiang TANG
Front. Optoelectron.    https://doi.org/10.1007/s12200-019-0907-4
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Lead halide perovskites, with high photoluminescence efficiency and narrow-band emission, are promising materials for display and lighting. However, the lead toxicity and environmental sensitivity hinder their potential applications. Herein, a new antimony-doped lead-free inorganic perovskites variant Cs2SnCl6:xSb is designed and synthesized. The perovskite variant Cs2SnCl6:xSb exhibits a broadband orange-red emission, with a photoluminescence quantum yield (PLQY) of 37%. The photoluminescence of Cs2SnCl6:xSb is caused by the ionoluminescence of Sb3+ within Cs2SnCl6 matrix, which is verified by temperature dependent photoluminescence (PL) and PL decay measurements. In addition, the all inorganic structure renders Cs2SnCl6:xSb with excellent thermal and water stability. Finally, a white light-emitting diode (white-LED) is fabricated by assembling Cs2SnCl6:0.59%Sb, Cs2SnCl6:2.75%Bi and Ba2Sr2SiO4:Eu2+ onto the commercial UV LED chips, and the color rendering index (CRI) reaches 81.

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Chemical sensing through photonic crystal fiber: sulfuric acid detection
Etu PODDER, Md. Bellal HOSSAIN, Rayhan Habib JIBON, Abdullah Al-Mamun BULBUL, Himadri Shekhar MONDAL
Front. Optoelectron.    https://doi.org/10.1007/s12200-019-0903-8
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A photonic crystal fiber (PCF) for sensing of sulfuric acid is designed and analyzed using Comsol Multiphysics. To analyze the sensor performance, 0%, 10%, 20%, 30%, 40% H2SO4 solution is placed into the fiber separately and then relative sensitivity, confinement loss, birefringence, effective area etc. are investigated for each solution over wavelength ranging from 0.8 to 1.8 mm. The sensor structure affords moderately high relative sensitivity and around 63.4% sensitivity is achieved for the highest concentration of H2SO4 at the wavelength 1.5 mm in x polarization direction. This PCF model also shows zero confinement loss for all solutions of H2SO4 over wavelength ranging from 1 to 1.35 mm and later on approximately 1.422 × 10-17 dB/km confinement loss is found for the highest concentration of H2SO4 at 1.5 mm wavelength. Besides, higher birefringence is attained when the concentration of sulfuric acid is lower and it is achieved 7.5 × 10-4 at 1.5 mm wavelength. Moreover, higher sensing area is achieved at high concentration of sulfuric acid.

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Airy-like field under high numerical aperture optical system
Yong LIU, Zhifeng ZHANG, Cuifang KUANG
Front. Optoelectron.    https://doi.org/10.1007/s12200-019-0866-9
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The tightly focused field of an incident light beam through cubic phase modulation has been investigated by vectorial diffraction theory. For different modulation index of cubic phase and polarization states of the incident light, the focused fields have been presented. The results show that the Airy-like field can be produced by cubic phase modulation under high numerical aperture (NA) optical system. Intensity pattern and length of the main lobe are depended on modulation index for the spatial uniform polarization, and the Airy-like field is affected by polarization state for the spatial nonuniform polarization. It is helpful to structure new optical fields in optical manipulation, optical imaging, and surface plasma controlling.

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Near-infrared carbon-implanted waveguides in Tb3+-doped aluminum borosilicate glasses
Yue WANG, Jiaxin ZHAO, Qifeng ZHU, Jianping SHEN, Zhongyue WANG, Hai-Tao Guo, Chunxiao LIU
Front. Optoelectron.    https://doi.org/10.1007/s12200-019-0869-6
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Ion implantation has played a unique role in the fabrication of optical waveguide devices. Tb3+-doped aluminum borosilicate (TDAB) glass has been considered as an important magneto-optical material. In this work, near-infrared waveguides have been manufactured by the (5.5+ 6.0) MeV C3+ ion implantation with doses of (4.0+ 8.0) × 1013 ions·cm-2 in the TDAB glass. The modes propagated in the TDAB glass waveguide were recorded by a prism-coupling system. The finite-difference beam propagation method (FD-BPM) was carried out to simulate the guiding characteristics of the TDAB glass waveguide. The TDAB glass waveguide allows the light propagation with a single-mode at 1.539 mm and can serve as a potential candidate for future waveguide isolators.

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