Contents
2019
Volume: 17 Issue 12
20 Article(s)

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Research Articles
Fiber Optics and Optical Communications
Propagation characteristics of orbital angular momentum modes at 810 nm in step-index few-mode fibers
Zhouxiang Wang, Yuchen Xie, Shuangyin Huang, Han Zhou, Rui Liu, Zhifeng Liu, Min Wang, Wenrong Qi, Qianqian Tian, Lingjun Kong, Chenghou Tu, Yongnan Li, and Huitian Wang
In free-space or in optical fibers, orbital angular momentum (OAM) multiplexing for information transmission has been greatly developed. The light sources used were well coherent communication bands, and the fibers used were customized. Here, we use an 810 nm femtosecond laser to generate optical vortices carrying OAM and then feed them into two kinds of commercial step-index few-mode fibers to explore the transmission characteristics of OAM modes. We also propose a method without multiple-input multiple-output digital signal processing to identify the input OAMs. It is of great guiding significance for high-dimensional quantum information experiments via the OAMs as a degree of freedom, using the light generated by the spontaneous parametric down-conversion as the source and the commercial fibers for information transmission.
Chinese Optics Letters
  • Publication Date: Dec. 10, 2019
  • Vol. 17, Issue 12, 120601 (2019)
Investigation on temperature characteristics of weak fiber Bragg gratings in a wide range
Xiaojun Fan, Junfeng Jiang, Xuezhi Zhang, Kun Liu, Shuang Wang, and Tiegen Liu
A weak fiber Bragg grating (WFBG) is an ideal quasi-distributed optical fiber sensor. Special attention should be paid to the spectrum and sensing performance of the WFBG at extreme temperatures due to its poor reflection intensity. In this Letter, the temperature characteristics of the WFBG from 252.75°C to 200.94°C are experimentally investigated. Five WFBGs with reflectivity from ~0.25% to ~10% are used in the experiments. The reflectivity variations and wavelength shifts at different temperatures are studied. Experimental results show that the WFBG can survive and work at extreme temperatures, but the performance is affected significantly. The reflectivity is affected significantly by both cryogenic temperature and high temperature. The temperature responses of Bragg wavelengths in the wide temperature range are also obtained.
Chinese Optics Letters
  • Publication Date: Dec. 10, 2019
  • Vol. 17, Issue 12, 120603 (2019)
Package-level passive equalization technology enabling DML-based 112 Gbps/λ PAM4 transmission
Zhike Zhang, Jinye Li, Zeping Zhao, Jianguo Liu, and Xingjun Wang
We demonstrate a package-level passive equalization technology in which the wire-bonding-induced resonance effect is used to compensate for the limited gain strength within the Nyquist frequency. The corresponding gain strength under various inductance and capacitance combinations could be quantitatively determined using a numerical simulation. With the increase in the Nyquist frequency, the capacitance shows a greater effect on the gain strength than the inductance. Therefore, the parasitic capacitance should be decreased to realize the desired gain strength at a higher Nyquist frequency. With this equalization technology, gain strength of 5.8 dB is obtained at 22 GHz, which can compensate for the limited bandwidth for the 112 Gbps pulse amplitude modulation (PAM4) signal. The experimental results show that 112 Gbps/λ PAM4 transmission based on a directly modulated laser (DML) module can be realized with a bit error rate of 1 × 10 3 at a received optical power of 3 dBm.
Chinese Optics Letters
  • Publication Date: Dec. 10, 2019
  • Vol. 17, Issue 12, 120604 (2019)
A reliable sunlight communication system
Haichao Guo, Tao Shan, Li Li, Li Zhang, Xiaojun Li, and Han Gao
Chinese Optics Letters
  • Publication Date: Dec. 10, 2019
  • Vol. 17, Issue 12, 120605 (2019)
Imaging Systems
Piston sensing via a dispersed fringe sensor with a merit-function-based active scanning algorithm at low light levels
Yongfeng Zhang, and Hao Xian
Chinese Optics Letters
  • Publication Date: Dec. 10, 2019
  • Vol. 17, Issue 12, 121101 (2019)
Adaptive gradient-based source and mask co-optimization with process awareness
Yijiang Shen, Fei Peng, Xiaoyan Huang, and Zhenrong Zhang
We develop a source and mask co-optimization framework incorporating the minimization of edge placement error (EPE) and process variability band (PV Band) into the cost function to compensate simultaneously for the image distortion and the increasingly pronounced lithographic process conditions. Explicit differentiable functions of the EPE and the PV Band are presented, and adaptive gradient methods are applied to break symmetry to escape suboptimal local minima. Dependence on the initial mask conditions is also investigated. Simulation results demonstrate the efficacy of the proposed source and mask optimization approach in pattern fidelity improvement, process robustness enhancement, and almost unaffected performance with random initial masks.
Chinese Optics Letters
  • Publication Date: Dec. 10, 2019
  • Vol. 17, Issue 12, 121102 (2019)
Sidelobe suppression and axial resolution enhancement in 4pi microscopy with higher-order radially polarized Laguerre–Gaussian beams using subtractive imaging
Zhiyuan Gu, Xianghui Wang, Jianxin Wang, Fei Fan, and Shengjiang Chang
Chinese Optics Letters
  • Publication Date: Dec. 10, 2019
  • Vol. 17, Issue 12, 121103 (2019)
Lasers and Laser Optics
Direct single-mode lasing in polymer microbottle resonators through surface destruction | Editors' Pick
Saima Ubaid, Feng Liao, Tao Guo, Zhaoqi Gu, Shuangyi Linghu, Yanna Ma, Jiaxin Yu, and Fuxing Gu
Chinese Optics Letters
  • Publication Date: Dec. 10, 2019
  • Vol. 17, Issue 12, 121401 (2019)
A compact and efficient 4.25 μm BaGa4Se7 optical parametric oscillator
Minqiang Kang, Ying Deng, Xiongwei Yan, Xiaoming Zeng, Yangwu Guo, Jiyong Yao, Fa Zeng, Jiangang Zheng, Kainan Zhou, Chongbing Qu, Jingqin Su, and Qihua Zhu
Chinese Optics Letters
  • Publication Date: Dec. 10, 2019
  • Vol. 17, Issue 12, 121402 (2019)
Efficient fifth harmonic generation of Nd:glass laser in ADP crystals | Editors' Pick
Fang Wang, Xuewei Deng, Liquan Wang, Fuquan Li, Wei Han, Wei Zhou, Xiaoxia Huang, Huaiwen Guo, and Qihua Zhu
Fifth harmonic generation (5th HG) of a Nd:glass laser is an effective way to acquire high-energy coherent deep-ultraviolet radiation near 200 nm. In this work, cascade generation of the fifth harmonic of a Nd:glass laser in a 5 mm ammonium dihydrogen phosphate (ADP) crystal was investigated, and maximum conversion efficiency of 14% and large angular acceptance of 45 mrad were demonstrated at a noncritical phase-matching temperature of 75.1°C. However, as the results reveal, the temperature sensitivity and nonlinear absorption would hinder its high-energy application. As for that, based on the complementary relationship of the angle and temperature in the phase-matching condition, an upgraded focusing 5th HG design coupled with the cylindrical temperature distribution scheme was proposed. By this upgraded focusing design, more than the improvement of the conversion efficiency, the output 5ω near-field intensity distribution turns out to be insensitive to the temperature gradient. Potentially, this idea can be applied for many other frequency conversion schemes such as high-repetition frequency lasers, which have similar temperature gradient problems.
Chinese Optics Letters
  • Publication Date: Dec. 10, 2019
  • Vol. 17, Issue 12, 121403 (2019)
Enhanced nonlinear optical response of layered WSe1.4Te0.6 alloy in 1 μm passively Q-switched laser
Zhengting Du, Tianqi Zhang, Zhenda Xie, Jian Ning, Xinjie Lü, Jinlong Xu, and Shining Zhu
Due to the composition-dependent properties of two-dimensional (2D) transition metal dichalcogenides (TMDs), alloying of existing dissimilar TMDs architecture is a novel and controllable route to tailor crystal structures with superior optical and optoelectronic properties. Here, we reported the hexagonal-phase WSe1.4Te0.6 alloy can enable great promise for enhanced saturable absorption response exceeding the parent component WSe2 and WTe2, with larger modulation depth and lower saturable intensity. These advantages allowed the 1064 nm passively Q-switched lasers based on WSe1.4Te0.6 to be more efficient, with pulse duration narrowed to 45%, and slope efficiency increased by 232%. Our findings highlighted the appropriate alloying of TMDs as an effective strategy for development of saturable absorbers.
Chinese Optics Letters
  • Publication Date: Dec. 10, 2019
  • Vol. 17, Issue 12, 121404 (2019)
Mode-locked pulse generation from an all-FMF ring laser cavity
Su Chen, Weixiang Hu, Yang Xu, Yu Cai, Zhiqiang Wang, and Zuxing Zhang
Experimental generation of stable mode-locked pulses and cylindrical vector beams (CVBs), from an all few-mode fiber (FMF) ring laser is first reported, to the best of our knowledge. In this laser, a section of few-mode erbium-doped fiber (FM-EDF) is used as the gain medium. The FM-EDF is pumped by 976 nm laser with LP11 mode, which is simultaneously converted and multiplexed through a homemade hybrid device, i.e., wavelength division multiplexing-mode selection coupler (WDM-MSC). All the components in our experiment are connected using FMF. The resulted CVB pulses have a spectral width of 0.33 nm with a repetition rate of 30.58 MHz under the pump power of 340 mW. Moreover, both azimuthally and radially polarized CVBs were achieved with a high purity of >95%. This mode-locked CVB fiber laser with an all FMF configuration opens the way to manipulate the transverse mode in mode-locked fiber lasers.
Chinese Optics Letters
  • Publication Date: Dec. 10, 2019
  • Vol. 17, Issue 12, 121405 (2019)
Optical devices
On the polarization self-screening effect in multiple quantum wells for nitride-based near ultraviolet light-emitting diodes
Kangkai Tian, Chunshuang Chu, Jiamang Che, Hua Shao, Jianquan Kou, Yonghui Zhang, Zi-Hui Zhang, and Tongbo Wei
The tilted energy band in the multiple quantum wells (MQWs) arising from the polarization effect causes the quantum confined Stark effect (QCSE) for [0001] oriented III-nitride-based near ultraviolet light-emitting diodes (NUV LEDs). Here, we prove that the polarization effect in the MQWs for NUV LEDs can be self-screened once the polarization-induced bulk charges are employed by using the alloy-gradient InxGa1-xN quantum barriers. The numerical calculations demonstrate that the electric field in the quantum wells becomes weak and thereby flattens the energy band in the quantum wells, which accordingly increases the spatial overlap for the electron-hole wave functions. The polarization self-screening effect is further proven by observing the blueshift for the peak emission wavelength in the calculated and the measured emission spectra. Our results also indicate that for NUV LEDs with a small conduction band offset between the quantum well and the quantum barrier, the electron injection efficiency for the proposed structure becomes low. Therefore, we suggest doping the proposed quantum barrier structures with Mg dopants.
Chinese Optics Letters
  • Publication Date: Dec. 10, 2019
  • Vol. 17, Issue 12, 122301 (2019)
Subwavelength metal structures with tunable transmission characteristics by light
Zehua Yang, Jing Han, Wenzhi Wu, Degui Kong, and Yachen Gao
Chinese Optics Letters
  • Publication Date: Dec. 10, 2019
  • Vol. 17, Issue 12, 122302 (2019)
Optics at Surfaces
Broadband mid-IR antireflective Reuleaux-triangle-shaped hole array on germanium
Haijuan Cheng, Miao Dong, Qinwen Tan, Linghai Meng, Yi Cai, Jie Jiang, Weisheng Yang, Haizheng Zhong, and Lingxue Wang
A gradient-index Reuleaux-triangle-shaped hole array was fabricated on germanium (Ge) by nanoimprint lithography and inductively coupled plasma processing as a broadband mid-infrared (IR) antireflective surface. The interaction between the {111} planes of cubic crystalline Ge and a circular mold successfully produced an orderly and periodically distributed Reuleaux-triangle-shaped hole array. As a result, the average transmittance increased 15.67% over the waveband at 3–12 μm and remained stable at the incidence angle of up to 60°. The vertices of the Reuleaux triangle showed local enhancement of the electric field intensities due to interference of the incident and reflected radiation fields. It was also found that nonuniform hole depths acted to modulate the transmittance over the 3–12 μm waveband.
Chinese Optics Letters
  • Publication Date: Dec. 10, 2019
  • Vol. 17, Issue 12, 122401 (2019)
Spectroscopy
Miniature spectrometer based on a Fourier transform spectrometer chip and a commercial photodetector array
Xiao Ma, Jun Zou, Wenhuan Li, and Jian-Jun He
We demonstrate a novel type of miniature spectrometer based on a Fourier transform spectrometer (FTS) chip with a dense output array and a commercial photodetector (PD) array. The FTS chip has an output array cycle of 20 μm and consists of 51 Mach–Zehnder interferometers (MZIs), and the PD array is a commercial linear charged coupled device (CCD). An achromatic triplet lens is used to image the MZI output interferogram onto the CCD with a small aberration. Our experiment result shows that a free spectral range (FSR) from 489 nm to 584 nm and a retrieved spectral resolution of 3.5 nm at 532 nm are obtained. The achieved properties show that our spectrometer has the potential to outperform the best commercial compact one in terms of most performance indices.
Chinese Optics Letters
  • Publication Date: Dec. 10, 2019
  • Vol. 17, Issue 12, 123001 (2019)
Characteristics of optical emission during laser-induced damage events of fused silica
Chao Shen, Nanjing Zhao, Jaka Pribošek, Mingjun Ma, Li Fang, Xingjiu Huang, and Yujun Zhang
Chinese Optics Letters
  • Publication Date: Dec. 10, 2019
  • Vol. 17, Issue 12, 123002 (2019)
Ultrafast Optics