Li Jun   Liu Haigang   Li Yan   Wang Xianping   Sang Minghuang   Chen Xianfeng  

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Based on nonlinear wave mixing, we propose experimentally a scheme for directly generating optical orbital angular momentum (OAM) by a spirally structured fundamental wave interacting with a nonlinear medium, in which the nonlinear susceptibilities are homogenous. In the experiment, the second harmonic generation of a fundamental wave carrying positive (negative) integer and fractional OAM states was investigated. This study presents a convenient approach for dynamic control of OAM of vortex beams, which may feature their applications in optical manipulation and optical communication.

       PDF全文 (下载：0)        Chinese Optics Letters ，2021年第19卷第6期 pp.06      

Du Jiangbing   Shen Weihong   Liu Jiacheng   Chen Yufeng   Chen Xinyi   He Zuyuan  

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To overcome the capacity crunch of optical communications based on traditional single-mode fiber (SMF), different modes in few-mode fiber (FMF) can be employed for mode division multiplexing (MDM). MDM can also be extended to photonic integration for obtaining improved density and efficiency, as well as interconnection capacity. Therefore, MDM becomes the most promising method for maintaining the trend of “Moore’s law” in photonic integration and optical fiber transmission. In this tutorial, we provide a review of MDM works and cutting-edge progresses from photonic integration to optical fiber transmission, including our recent works of MDM low-noise amplification, FMF fiber design, MDM silicon photonic devices and so on. Research and application challenges of MDM for optical communications regarding long-haul transmission and short reach interconnection are discussed as well. The content is expected to be of important value for both academic researchers and industrial engineers during developing next-generation optical communication systems, from photonic chip to fiber link.

       PDF全文 (下载：1)        Chinese Optics Letters ，2021年第19卷第9期 pp.09      

Lv Renchong   Teng Hao   Zhu Jiangfeng   Yu Yang   Wei Liu   Chang Guoqing   Wei Zhiyi  

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We report a high-power fiber amplifier based on nonlinear chirped-pulse amplification (NCPA). To manage the nonlinearity, pulse shaping is introduced by the self-phase-modulation (SPM) in the fiber stretcher with the help of spectral filtering. The third-order dispersion is compensated by the nonlinear phase shift in the NCPA. With optimization, the system can output 382 fs pulse duration with 20 W average power at 1MHz repetition rate. The long-term average power fluctuation is measured to be 0.5% (RMS) in 24 hours, and the beam quality factor (M2) is 1.25.

       PDF全文 (下载：1)        Chinese Optics Letters ，2021年第19卷第9期 pp.09      

Wang Xianbin   Deng Hongchang   Yuan Libo  

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The distributed optical fiber surface plasmon resonance (SPR) sensors have been attracted wide attention in biosensing and chemical sensing applications. However, due to limitation of their sensing structure, it is difficult to adjust their resonant wavelength and sensitivity. Here a novel and flexible cascaded helical-core fiber (HCF) SPR sensors is proposed theoretically and experimentally for distributed sensing application. It is shown that the resonant wavelength and sensitivity of the sensors can be conveniently controlled by adjusting twist pitch of helical core. A high sensitivity of 11180 nm/RIU for RI measurement ranging from 1.355 to 1.365 was realized experimentally when the twist pitch of helical core is 1.5 mm. It is worth noting that the sensitivity can be further improved by reducing the twist pitch. For example, the sensor with a twist pitch of 1.4 mm can theoretically exceed to 20000 nm/RIU. This work opens up a new way to implement multi-parameter or distributed measurement, especially to establish sensing networks integrated in a single-core fiber or a multi-core fiber.

       PDF全文 (下载：2)        Chinese Optics Letters ，2021年第19卷第9期 pp.09      

Suzuki Kohei   Tao Minori   Maeda Yuki   Nakayama Hirotaka   Noguchi Ren   Oikawa Minoru   Mori Yuichiro   Kakue Takashi   Shimobaba Tomoyoshi   Ito Tomoyoshi   Takada Naoki  

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We propose a high-speed playback method for the spatiotemporal division multiplexing electroholographic 3D video stored in a solid-state drive (SSD), using a digital micromirror device. The spatiotemporal division multiplexing electroholography prevents deterioration in the reconstructed 3D video from a 3D object comprising many object points. In the proposed method, the stored data is remarkably reduced using the packing technique, and the computer-generated holograms are played back at high speed. Consequently, we successfully reconstructed a clear 3D video of a 3D object comprising approximately 1,100,000 points at 60 fps by reducing the reading time of the stored data from an SSD.

       PDF全文 (下载：1)        Chinese Optics Letters ，2021年第19卷第9期 pp.09      

Zhao Baichuan   Huang Rui-Ying   Lv Guo-Jiao  

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A micro-projection dynamic backlight for multi-view 3D display is proposed. The proposed backlight includes a light emitting diodes (LEDs) array, a lenticular lens array, and a scattering film. The LED array, the lenticular lens, and the scattering film construct a micro-projection structure. In this structure, the LEDs in the array are divided in several groups. The light from each LED groups can be projected to the scattering film by the lenticular lens and forms a series of bright stripes. The different LED groups have different horizontal positions, so these bright stripes corresponding to different LED groups also have different horizontal positions. Therefore, they can be used as a dynamic backlight. Because the distance between the LEDs array and the lenticular lens is much larger than the distance between the lenticular lens and the scattering films, the imaging progress will make the width of the bright stripes much smaller than that of the LEDs, and the pitch of the stripes is also decreased. According to the 3D display theory, the bright stripes with small width and pitch helps for increasing the number of views. So the proposed micro-projection dynamic backlight is very suitable for multi-view 3D display. An experimental prototype was developed, and the experimental results show that the micro-projection dynamic backlight can correctly complete the directional projection of the parallax images to form a 3D display.

       PDF全文 (下载：2)        Chinese Optics Letters ，2021年第19卷第9期 pp.09      

Fang Bin   Gao Shenglun   Wang Zhizhang   Zhu Shining   Li Tao  

      摘要 + 此论文可免费阅读 (可能需要登录)

We theoretically propose a hybrid lithium niobate (LN) thin-film waveguide consists of an amorphous silicon stripe and etch-free z cut LN for highly efficient wavelength conversion, circumventing the challenging etching on LN material. Profited from the spatial symmetry broken of the waveguide, the asymmetric hybrid modes can spontaneously achieve phase matching with small modal area and large spatial mode overlap, enabling enhanced second harmonic generation with a normalized conversion efficiency over 3900% W-1cm-2 (0.5-mm-long propagation distance). The choice of integrating silicon with LN alleviates the fabrication challenge, making the platform potentially compatible with silicon photonics.

       PDF全文 (下载：1)        Chinese Optics Letters ，2021年第19卷第6期 pp.06      

Xu Mengyue   He Mingbo   Zhu Yuntao   Liu Lin   Chen Lifeng   Yu Siyuan   Cai Xinlun  

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Integrated traveling-wave lithium niobate modulators need relatively long device lengths to achieve low drive voltage. To increase modulation efficiency within a compact footprint, we report an integrated Fabry-Perot-type electro-optic thin film lithium niobate on insulator modulator comprising a phase modulation region sandwich between two distributed Bragg reflectors. The device exhibits low optical loss and a high tuning efficiency of 15.7 pm/V. We also confirm the modulator’s high-speed modulation performance by non-return-to-zero modulation with a data rate up to 56 Gbit/s.

       PDF全文 (下载：1)        Chinese Optics Letters ，2021年第19卷第6期 pp.06      

Ma Bin   han jiaqi   li jing   wang ke   guan shuang   niu xinshang   li haoran   zhang jinlong   Jiao Hongfei   Xinbin Chen   Wang Zhanshan  

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The influence of nodule defects on the characteristics of femtosecond laser-induced damage has not been fully investigated. In this study, two types of 800 nm/1064 nm dual-band HfO2/SiO2 high-reflection films with different configurations were analyzed. Combined with finite-difference time-domain (FDTD) electric field simulation and focused ion beam (FIB) analysis, the initial state and growth process of femtosecond laser damage of nodules were explored. In particular, the sequence of blister damage determined by the film design and the inner damage caused by nodules were clarified. The rule of the laser-induced damage threshold (LIDT) of different nodule sizes was obtained. The difference in the damage behavior of nodules in the two types of film was elucidated.

       PDF全文 (下载：2)        Chinese Optics Letters ，2021年第19卷第8期 pp.08      

Xue Jiayun   Gao Hui   Zhang Nan   Sun Lu   Lin Lie   Liu Weiwei  

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The spatial distribution of the forward-propagating amplified spontaneous emission (ASE) of nitrogen molecular ions during femtosecond laser filamentation in air is studied via numerical simulations. The results suggest that the divergence angle and signal intensity are extremely sensitive to the external focal length. Concurrently, we show that the optical Kerr effect plays a significant role in concentrating the directivity of ASE signals, particularly in cases of loose focusing. Furthermore, the simulations demonstrate that ASE signals are enhanced for a tight focus, although the corresponding filament length is shorter. The main physical mechanism underlying this process is the competition between the plasma defocusing and optical Kerr effects. The result is important for filamentation-based lidar applying to remote sensing.

       PDF全文 (下载：3)        Chinese Optics Letters ，2021年第19卷第8期 pp.08      

Yu Zhenming   Ju Zhenyu   Zhang Xinlei   Meng Ziyi   Yin Feifei   Xu Kun  

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Multimode fiber (MMF) has great potential to transmit high-resolution images with less invasive in endoscopy due to its large number of spatial modes and small core diameter. However, spatial modes crosstalk will inevitably occur in MMF, which makes the received images become speckles. A conditional generative adversarial network (GAN) composed of generator and discriminator was utilized to reconstruct the received speckles. We conduct an MMF imaging experimental system of transmitting over one-meter MMF with 50-μm-core. Compared with the conventional method of U-net, this conditional GAN could reconstruct images with fewer training datasets to achieve the same performance, and shows higher feature extraction capability.

       PDF全文 (下载：2)        Chinese Optics Letters ，2021年第19卷第8期 pp.08      

Liu Ximei   liu mengli   Wang Yaorong   Huang Kai   Lei Ming   Liu Wenjun   Wei Zhiyi  

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Recent years have witnessed the exploration of fiber laser technology focused on numerous pivotal optoelectronic applications from laser processing, remote sensing to optical communication. Here, using the cobalt oxyfluoride (CoOF) as the nonlinear material, a 156 fs mode-locking fiber laser with strong stability is obtained. Rapid thermal annealing technique is used to fabricate the CoOF, which is subsequently transferred to the tapered region of the microfiber to form the effective pulse modulation device. CoOF interacts with pulsed laser through the evanescent field to realize the intracavity pulse shaping, and then the stable mode-locked pulse is obtained. The mode-locked operation is maintained with the pulse duration of 156 fs and repetition rate of 49 MHz. In addition, the signal-to-noise ratio (SNR) is about 90 dB. Those experimental results confirm the attractive nonlinear optical properties of CoOF, and lay a foundation for the ultrafast application of low dimensional transition metal oxides.

       PDF全文 (下载：3)        Chinese Optics Letters ，2021年第19卷第8期 pp.08      

Yu Huabin   Ren Zhongjie   Memon Muhammad   Fang Shi   Wang Danhao   Liu Zhongling   Zhang Haochen   Wu Feng   Dai Jiangnan   Chen Changqing   Sun Haiding  

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AlGaN-based deep ultraviolet light-emitting diode (DUV LED) is an alternative DUV light source to replace traditional mercury-based lamps. However, the state-of-the-art DUV LEDs currently exhibit poor wall-plug efficiency and low light output power, which seriously hinder their commercialization. In this work, we design and report a tunnel-junction-cascaded (TJC) DUV LED, which enables multiple radiative recombination within the active regions. Therefore, the light output power of the TJC-DUV LEDs is more than doubled compared to the conventional DUV LED. Correspondingly, the wall-plug efficiency of the TJC-DUV LED is also significantly boosted by 25% at 60 mA.

       PDF全文 (下载：1)        Chinese Optics Letters ，2021年第19卷第8期 pp.08      

Wu Jipeng   Tang Jie   Zeng Rongzhou   Dai Xiaoyu   xiang yuanjiang  

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Bulk Dirac semimetal (BDS), treated as three-dimensional graphene, has attracted wide attention of industry and academia because of its excellent physical and chemical characteristics. In this article, we investigate the phenomenon of coherent perfect absorption (CPA) with BDS thin film. CPA of BDS appears at the frequency of 43.89 THz with 0° phase modulation of the two coherent input lights. Meanwhile the influence of incident angle on CPA for TM and TE polarization is studied, showing the feasibility of CPA under oblique incidence circumstances for both polarizations. Moreover, the frequency of CPA can be adjusted by altering the thickness of BDS thin film, and the dynamic regulation of CPA can be realized by changing the Fermi energy via electrostatic biasing. Finally, the peak coherent absorption frequency can be controlled by changing the degeneracy factor. We believe that our work will find practical applications in adjustable detections and signal modulations.

       PDF全文 (下载：1)        Chinese Optics Letters ，2021年第19卷第8期 pp.08      

Wang Cong   Liu Bo   Luo Zhi   Ding Kaiwen   Duan Ji'an  

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In this study, an effective method is proposed for controlling titanium foil surface’s wettability. A series of microholes array is fabricated on the surface of titanium foil by femtosecond laser under different laser energy and pulse number. The changes of titanium surface’s morphology are characterized. By placing in darkroom with high-temperature treatment and immersing in alcohol under UV irradiation, respectively, the femtosecond laser treated surfaces display switchable wettability. It is demonstrated that the changing between Ti−OH and Ti−O prompts the transformation between superhydrophilic and superhydrophobic. Compared with the existing reports, the switchable wetting cycle is shorted to 1.5 h. The functional surfaces with switchable wettability have potential applications in oil-water separation and water mist collection.

       PDF全文 (下载：3)        Chinese Optics Letters ，2021年第19卷第8期 pp.08      

Sun Zhengda   Wang Feifei   Xia Haiping   Nie Hongkun   Yang Kejian   Wang Ruihua   He Jingliang   zhang baitao  

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In this paper, the absorption and fluorescence spectra of Er3+, Pr3+ co-doped LiYF4 (Er,Pr:YLF) crystal were measured and analyzed. The Pr3+ co-doping was proved to effectively enhance the Er3+: 4I11/2→4I13/2 mid-infrared (MIR) transition at the 2.7 μm with 74.1% of energy transfer efficiency from Er3+: 4I13/2 to Pr3+: 3F4. By using Judd-Ofelt (J-O) theory, the stimulated emission cross section was calculated to be 1.834×10-20 cm2 at 2685 nm and 1.359×10-20 cm2 at 2804.6 nm. Moreover, diode-end-pumped Er,Pr:YLF laser operating at 2659 nm was realized for the first time, to the best of our knowledge. The maximum output power was determined to be 258 mW with a slope efficiency of 7.4% and the corresponding beam quality factor Mx2=1.29 and My2=1.25. Our results suggest that Er,Pr:YLF should be a promising material for 2.7 μm laser generation.

       PDF全文 (下载：4)        Chinese Optics Letters ，2021年第19卷第8期 pp.08      

Guo Silin   Li Zhongpeng   Zhou Chuliang   Tian Ye  

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Ball lightning is widely concerned because it is hard to detect[1, 2], predict and reproduce[3-5]. The dependences of electromagnetic solitons, which considered as expectant ball lightning, formation on the wavelength of the incident light are investigated with two-dimensional particle-in-cell (PIC) simulations. It shows that both the long wavelength microwave and the short wavelength laser are not suitable for producing the observed ball-lightning-like electromagnetic (EM) solitons. A strong field THz wave is proposed to inject and generate EM solitons. This paper can provide some references for researchers studying ball lightning.

       PDF全文 (下载：1)        Chinese Optics Letters ，2021年第19卷第8期 pp.08      

Dai Zhicheng   Liu Yushen   Yang Guofeng   Xie Feng   Gu Yan   Lu Naiyan   Fan Qigao   Ding Yu   Li Yuhang   Yu Yingzhou   Zhang Xiumei  

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we have fabricated the AlGaN solar-blind ultraviolet metal-semiconductor-metal (MSM) photodetectors with Al composition of 0.55. The surface roughness and dislocations of the high-Al-content Al0.55Ga0.45N epitaxial layer are analyzed by atomic force microscopy (AFM) and transmission electron microscope (TEM), respectively. The device exhibits high spectral responsivity and external quantum efficiency due to the photoconductive gain effect. The current reveals a strong dependence on high temperatures in the range of 4-10 V. Moreover, the Frenkel-Poole emission model and changing space charge regions are employed to explain the carrier transport and photoconductive gain mechanisms for the AlGaN PD, respectively.

       PDF全文 (下载：3)        Chinese Optics Letters ，2021年第19卷第8期 pp.08      

Jiang Le   Luo Xi   Luo Zhongming   Zhou Dingjian   Liu Baoxing   Huang Jincheng   Zhang Jianfeng   Zhang Xulin   Xu Ping   Li Guijun  

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Halide perovskite have attracted great attentions due to their high color purity, high luminance yield, low non-radiative recombination rate, and solution processibility. Although the external quantum efficiency of light-emitting diodes (PeLEDs) is comparable with that of the organic light-emitting diodes (OLEDs) and quantum-dots light-emitting diodes (QLEDs), the brightness of which is still low compared with the traditional OLEDs and QLEDs. Herein, we demonstrate high brightness and high efficiency CsPbBr3 based PeLEDs using interface and bulk controlled nanocrystal growth of the perovskite emission layer. The interface engineering by ethanolamine and bulk engineering by polyethylene glycol led to highly crystallized and cubic-shaped perovskite nanocrystals with smooth and compact morphology. As a result, PeLEDs with a high brightness of 64756 cd/m2and an external quantum efficiency of 13.4% have been achieved.

       PDF全文 (下载：6)        Chinese Optics Letters ，2021年第19卷第3期 pp.03      

Petersen Christian   Lotz Mikkel   Markos Christos   Woyessa Getinet   Furniss David   Seddon Angela   Taboryski Rafael   Bang Ole  

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Thermal nanoimprinting is a fast and versatile method for transferring the anti-reflective properties of subwavelength nanostructures onto the surface of highly reflective substrates, such as chalcogenide glass optical fiber end faces. In this paper, the technique is explored experimentally on a range of different types of commercial and custom-drawn optical fibers to evaluate the influence of geometric design, core/cladding material, and thermo-mechanical properties. Up to 32.4 % increased transmission and 88.3 % total transmission is demonstrated in the 2-4.3 µm band using a mid-infrared supercontinuum laser.

       PDF全文 (下载：2)        Chinese Optics Letters ，2021年第19卷第3期 pp.03      

Yuan Zheng   Gao Yuan   Wang Zhuang   Sun Hanchao   Chang Chenliang   Wang Xi-Lin   Ding Jianping   Wang Huitian  

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We develop a method for completely shaping optical vector beams with controllable amplitude, phase and polarization gradient along three-dimensional freestyle trajectories. We design theoretically and demonstrate experimentally curvilinear Poincare vector beams that exhibit high intensity-gradients and accurate state of polarization prescribed along the beam trajectory.

       PDF全文 (下载：3)        Chinese Optics Letters ，2021年第19卷第3期 pp.03      

Zeng Xiahui  

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We demonstrate a configuration optimization process of an off-axis parabolic mirror to maximize the focused peak intensity based on a precise knowledge of the tight focusing properties by using a full vector-diffraction theory, and obtain an optimum configuration scaling rule which makes it possible to achieve the maximum peak intensity. In addition, we also carry out an assessment analysis of the offset and off-axis angle tolerances corresponding to a 5% drop of the maximum focused peak intensity, and present scaling laws for the tolerances of the offset and off-axis angle. Understanding these scaling laws is important to enhance the focusability of a laser beam by an off-axis parabolic mirror in the optimum configuration, in particular, which is valuable for structural design and selection of off-axis parabolic mirror in ultrashort and ultraintense laser-matter interaction experiments.

       PDF全文 (下载：1)        Chinese Optics Letters ，2021年第19卷第3期 pp.03      

Guan Yan   Wang Fang   Yang Ying   Wang De'en   Zhang Xin   Qiang Yuan   Hu Dongxia   Deng Xuewei   Ren Huaijin   Zheng Yuanlin   Chen Xianfeng  

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At the surfaces of crystals, linear susceptibility tensors would differ from their counterparts in the interior of the bulk crystal. However, this phenomenon hasn’t been shown in a visible way yet. In previous researches, numerous types of nonlinear Cherenkov radiation based on different materials have been studied, while linear Cherenkov radiation is barely reported. We experimentally prove the generation of linear Cherenkov radiation on the KDP crystal surface, and theoretically analyze its phase-matching scheme. In our study, o-polarized light and e-polarized light can mutually convert through linear Cherenkov process. According to this result, we figure out new nonzero elements at off-diagonal positions in the linear susceptibility tensor matrix at crystal surfaces, compared with the normal form of a bulk KDP. It’s the first time to probe linear susceptibility tensor at bulk crystal surface by this method.

       PDF全文 (下载：0)        Chinese Optics Letters ，2021年第19卷第3期 pp.03      

Zhuang Wei   Zhao Yang   Wang Shaokai   Fang Zhanjun   Fang Fang   Li Tianchu  

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An ultranarrow bandwidth Faraday atomic filter is realized based on cold 87Rb atoms. The atomic filter operates at 780 nm on the 52S1/2, F=2 to 52P3/2, F’=3 transition with a bandwidth of 7.1(8) MHz, which is approaching the natural linewidth of the transition. The peak transmission achieves 2.6(3)% by the multi-pass probe method. This atomic filter based on cold atoms may find potential applications in self-stabilizing lasers in future.

       PDF全文 (下载：4)        Chinese Optics Letters ，2021年第19卷第3期 pp.03      

Hussain Sajid   Raza Ahmad   Saeed Fawad   Parveen Abida   Sikhai Yan   Din Nasrud   Elemike Elias E.   Huang Qianqian   Subramanian Alagesan   Khan Qasim   Lei Wei  

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The optoelectronic applications based on the perovskites always face challenges due to the inherent chemical composition volatility of perovskite precursor. The efficiency of perovskite-based light-emitting diodes (Pe-LED) can be enhanced by improving the perovskite film via solvent engineering. A dual solvent post-treatment strategy was applied to the perovskite film which provides a synchronous effect of passivating surface imperfections and reduces exciton-quenching, as evidenced by improved surface morphology and photoluminance. Thus, the optimized Pe-LEDs reaches 17866 cd m-2 maximum-brightness, 45.8 cd A-1 current efficiency and 8.3% external quantum efficiency, and relatively low turn-on voltage (VT) of 2.0 V. Herein, we present a simple technique for the fabrication of stable and efficient Pe-LEDs.

       PDF全文 (下载：3)        Chinese Optics Letters ，2021年第19卷第3期 pp.03      

Zeng Li   Sun Xiaoyan   Chang Zikun   Hu Youwang   Duan Ji'an  

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A phase-shifted fiber Bragg grating (PS-FBG) based on microchannel was proposed and realized by combining point-by-point scanning method with chemical etching. The PS-FBG composes of a fiber Bragg grating (FBG) and a microchannel through the fiber core. The microchannel can introduce phase shift into FBG. What is more important is that it exposes the fiber core to external environment. The phase shift peak is sensitive to liquid refractive index, and it shows linear refractive index response wavelength and intensity sensitivity of 2.526 nm/RIU and -111 dB/RIU, respectively. Therefore, such gratings can be used as sensors or tunable filters.

       PDF全文 (下载：1)        Chinese Optics Letters ，2021年第19卷第3期 pp.03      

Saeed Muhammad   Khan Imad   Shah Wajid Ali   Ali Akbar   Khan Qasim   Rehman Shafiq Ur  

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Structural geometry, electronic band gaps, density of states, optical and mechanical properties of double perovskites halides Cs2InBiX6 (X = F, Cl, Br, I) are investigated using density functional functional theory (DFT). These compounds possess genuine perovskite stoichiometry, evaluated using various geometry-based indices like tolerance factor, octahedral factor and formation energy. The fundamental electronic band gaps are direct and valued in the range 2.79-0.80 eV. These compounds have narrow band gaps (except Cs2InBiF6) due strong sp coupling of the cations. The valence band maximum and conduction band minimum are confirmed to be essentially of In 5s and Bi 6p character respectively. The splitting of Bi 6p bands due to strong spin-orbit coupling causes reduction in the band gaps. These compounds have large dispersion in their bands and very low carrier effective masses. The substitution of halogen atoms have great influence on the optical properties. The mechanical properties reveal that Cs2InBiX6 (X = F, Cl, Br, I) satisfy the stability criteria in cubic structure.

       PDF全文 (下载：5)        Chinese Optics Letters ，2021年第19卷第3期 pp.03      

Zou Ningmu   Zhou Tong   Ding Zhewen   Wang Feng   Zhang Yixin   Zhang Xuping  

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A simple and effective interference fading suppression method for Φ-OTDR using optimal peak-seeking is proposed. This method can reconstruct the vibration signal with high fidelity under the premise of using only ordinary single-mode sensing fiber without changing the structure of the traditional Φ-OTDR system. Based on the data after interference suppression, we applied different machine learning models to recognize the invasive events category. The promising results show potential applications of Ф-OTDR equipment and future implementation with machine learning algorithms.

       PDF全文 (下载：0)        Chinese Optics Letters ，2021年第19卷第3期 pp.03      

Guo Bo   Guo Xin-Yu   Tang Li-Ge   Yang Wen-Lei   Chen Qiu-Mei   Ren Zhong-Yao  

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We propose and demonstrate the cascaded multi-wavelength mode-locked erbium-doped fiber laser (EDFL) based on ultra-long-period grating (ULPG) for the first time, to the best of our knowledge. Study found that, the ULPG can be used as both a mode-locker for pulse-shaping and a comb filter for multiwavelength generation simultaneously. Using the dual-function of ULPG, three-, four-, five-, six- and seven-wavelength mode-locked pulses are obtained in EDFL, seven of which are the largest number of wavelengths up to now. For the four-wavelength mode-locked pulses, its pulsewidth is about 7.8 ps. In experiment, the maximum average output power and slope efficiency of these pulses are 8.4 mW and 2.03%, respectively. Besides the conventional pulses, hybrid soliton pulses composed of four-wavelength pulse and single soliton are also observed. Finally, the effect of cavity dispersion on the multiwavelength mode-locked pulses is also discussed. Our findings indicate that apart from common sensing and filtering, the ULPG may also possess attractive nonlinear pulse-shaping property for ultrafast photonics application. © 2020 SIOM

       PDF全文 (下载：15)        Chinese Optics Letters ，2021年第19卷第7期 pp.07      

ma xiang   Zheng Shuang   Liu Jia   Chen Quanan   lu qiaoyin   Guo Weihua  

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We propose a design of single-mode orbital angular momentum (OAM) beam laser with high direct-modulation bandwidth. It’s a microcylinder/microring cavity interacted with two types of second-order gratings: the complex top grating containing the real part and the imaginary part modulation and the side grating. The side grating etched on the periphery of the microcylinder/microring cavity can select a whispering gallery mode with a specific azimuthal mode number. While the complex top gratings can scatter the lasing mode with travelling-wave pattern vertically. With the cooperation of the gratings, the laser works with a single mode and emits radially polarized OAM beams. With an asymmetrical pad metal on the top of the cavity, the OAM on-chip laser can firstly be directly modulated with electrical pumping. Due to the small active volume, the laser with low threshold current is predicted to have a high direct modulation bandwidth about 29 GHz with the bias current of ten times the threshold from the simulation. The semiconductor OAM laser can be rather easily realized at different wavelengths such as the O band, C band and L band.

       PDF全文 (下载：5)        Chinese Optics Letters ，2021年第19卷第8期 pp.08