Frontiers of Optoelectronics

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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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Edge detection on terahertz pulse imaging of dehydrated cutaneous malignant melanoma embedded in paraffin
Jiayu LI, Yijun XIE, Ping SUN
Front. Optoelectron.    https://doi.org/10.1007/s12200-019-0861-1
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Terahertz pulse imaging of cutaneous malignant melanoma dehydrated by ethanol and embedded in paraffin was carried out across a frequency range of 0.2–1.4 THz. First, the tissue images based on the time-domain electric-field amplitude information were acquired. Then the areas of normal and cancerous tissues were determined using multi-scale, multi-azimuth and multi-structural element mathematical morphology. The physical meaning of the image was analyzed by calculation of the refractive index and absorption coefficient of cutaneous malignant melanoma in different areas. The refractive index of both normal and cancerous tissues showed anomalous dispersion. The refractive index of cancerous tissues tended to vary between 0.2 and 0.7 THz, while that of normal and fat tissues remain almost unchanged. The absorption of cancerous tissues was higher, with a maximum at 0.37 THz. We concluded that both the refractive index and absorption coefficient differ considerably between normal and cancerous tissues, and the areas of normal and abnormal tissues can be identified using THz pulse imaging combined with mathematical morphology. The method for edge detection of terahertz pulse imaging of cutaneous malignant melanoma provides a reference for the safe surgical removal of malignant tumors.

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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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Reflectometric and interferometric fiber optic sensor’s principles and applications
Muhammad Noaman ZAHID, Jianliang JIANG, Saad RIZVI
Front. Optoelectron.    https://doi.org/10.1007/s12200-019-0824-6
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Fiber optic sensors have been widely used and studied in recent times. This paper presents operating principles and applications of fiber optic sensors namely reflectometric and interferometric fiber optic sensors. Majority of optical fiber sensors fall under these two broad categories. Both interferometric and reflectometric fiber optic sensors are becoming popular for their ease of use, flexibility, long distance sensing, and potentially noise free detection. Also, these sensors can easily be used in various applications such as structural health monitoring, perimeter intrusion detection, temperature monitoring, and other numerous applications. This paper broadly classifies fiber optic sensors into two subtypes. The paper further highlights different sensors based on their sensing resolution, range, spatial advantages, and applications.

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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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Screen printing process control for coating high throughput titanium dioxide films toward printable mesoscopic perovskite solar cells
Zhining WAN, Mi XU, Zhengyang FU, Da LI, Anyi MEI, Yue HU, Yaoguang RONG, Hongwei HAN
Front. Optoelectron.    https://doi.org/10.1007/s12200-019-0904-7
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Screen printing technique has been widely applied for the manufacturing of both traditional silicon solar cells and emerging photovoltaics such as dye-sensitized solar cells (DSSCs) and perovskite solar cells (PSCs). Particularly, we have developed a printable mesoscopic PSC based on a triple layer scaffold of TiO2/ZrO2/carbon. The deposition of the scaffold is entirely based on screen printing process, which provides a promising prospect for low-cost photovoltaics. However, the optimal thickness of the TiO2 layer for fabricating efficient printable PSCs is much smaller than the typical thickness of screen printed films. Here, we tune the concentration of the pastes and the printing parameters for coating TiO2 films, and successfully print TiO2 films with the thickness of 500−550 nm. The correlation between the thickness of the films and printing parameters such as the solid content and viscosity of the pastes, the printing speed and pressure, and the temperature has been investigated. Besides, the edge effect that the edge of the TiO2 films possesses a much larger thickness and printing positional accuracy have been studied. This work will significantly benefit the further development of printable mesoscopic PSCs.

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Nano-film aluminum-gold for ultra-high dynamic-range surface plasmon resonance chemical sensor
Briliant Adhi PRABOWO, I Dewa Putu HERMIDA, Robeth Viktoria MANURUNG, Agnes PURWIDYANTRI, Kou-Chen LIU
Front. Optoelectron.    https://doi.org/10.1007/s12200-019-0864-y
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An analytical and experimental study of nano-film aluminum (Al) for ultra-high dynamic range surface plasmon resonance (SPR) biosensor is presented in this article. A thin film of 16 nm Al is proposed for metallic sensing layer for SPR sensor. For the protective layer, a 10 nm of gold (Au) layer was configured on top of Al as a protection layer. This ultra-high dynamic range of SPR biosensor reached the bulk refractive index sample limit up to 1.45 RIU. For the analytical study, with the assumption of anisotropic refractive indices experiment, the dynamic range showed a refractive index value of around 1.58 RIU. The refractive index value limit achieved by the proposed sensing design is potentially implemented in various applications, such as in chemical detection and environmental monitoring study with high refractive index solution sample. The experimental results are presented as a proof-of-concept of the proposed idea.

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Design and analysis of high birefringence and nonlinearity with small confinement loss photonic crystal fiber
Rekha SAHA, Md. Mahbub HOSSAIN, Md. Ekhlasur RAHAMAN, Himadri Shekhar MONDAL
Front. Optoelectron.    https://doi.org/10.1007/s12200-018-0837-6
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High birefringence with low confinement loss photonic crystal fiber (PCF) has significant advantages in the field of sensing, dispersion compensation devices, nonlinear applications, and polarization filter. In this report, two different models of PCFs are presented and compared. Both the models contain five air holes rings with combination of circular and elliptical air holes arrangement. Moreover, the elliptical shaped air holes polarization and the third ring air holes rotational angle are varied. To examine different guiding characteristics, finite element method (FEM) with perfectly matched layer (PML) absorbing boundary condition is applied from 1.2 to 1.8 µm wavelength range. High birefringence, low confinement loss, high nonlinearity, and moderate dispersion values are successfully achieved in both the PCFs models. Numeric analysis shows that model-1 gives higher birefringence (2.75 × 102) and negative dispersion (-540.67 ps/(nm·km)) at 1.55 µm wavelength. However, model-2 gives more small confinement loss than model-1 at the same wavelength. In addition, the proposed design demonstrates the variation of rotation angle has great impact to enhance guiding properties especially the birefringence.

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Terahertz wave generation from ring-Airy beam induced plasmas and remote detection by terahertz-radiation-enhanced-emission-of-fluorescence: a review
Kang LIU, Pingjie HUANG, Xi-Cheng ZHANG
Front. Optoelectron.    https://doi.org/10.1007/s12200-018-0860-7
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With the increasing demands for remote spectroscopy in many fields ranging from homeland security to environmental monitoring, terahertz (THz) spectroscopy has drawn a significant amount of attention because of its capability to acquire chemical spectral signatures non-invasively. However, advanced THz remote sensing techniques are obstructed by quite a few factors, such as THz waves being strongly absorbed by water vapor in the ambient air, difficulty to generate intense broadband coherent THz source remotely, and hard to transmit THz waveform information remotely without losing the signal to noise ratio, etc. In this review, after introducing different THz air-photonics techniques to overcome the difficulties of THz remote sensing, we focus mainly on theoretical and experimental methods to improve THz generation and detection performance for the purpose of remote sensing through tailoring the generation and detection media, air-plasma.

For the THz generation part, auto-focusing ring-Airy beam was introduced to enhance the THz wave generation yield from two-color laser induced air plasma. By artificially modulated exotic wave packets, it is exhibited that abruptly auto-focusing beam induced air-plasma can give an up to 5.3-time-enhanced THz wave pulse energy compared to normal Gaussian beam induced plasma under the same conditions. At the same time, a red shift on the THz emission spectrum is also observed. A simulation using an interference model to qualitatively describe these behaviors has be developed.

For the THz detection part, the results of THz remote sensing at 30 m using THz-radiation-enhanced-emission-of-fluorescence (THz-REEF) technique are demonstrated, which greatly improved from the 10 m demonstration last reported. The THz-REEF technique in the counter-propagation geometry was explored, which is proved to be more practical for stand-off detections than co-propagation geometry. We found that in the counter-propagating geometry the maximum amplitude of the REEF signal is comparable to that in the co-propagating case, whereas the time resolved REEF trace significantly changes. By performing the study with different plasmas, we observed that in the counter-propagating geometry the shape of the REEF trace depends strongly on the plasma length and electron density. A new theoretical model suggesting that the densest volume of the plasma does not contribute to the fluorescence enhancement is proposed to reproduce the experimental measurements.

Our results further the understanding of the THz-plasma interaction and highlight the potential of THz-REEF technique in the plasma detection applications.

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