Contents
2020
Volume: 18 Issue 2
18 Article(s)

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Reviews
Nanophotonics
Ultrafast direct laser writing of 2D materials for multifunctional photonics devices [Invited] | On the Cover
Tieshan Yang, Han Lin, and Baohua Jia
Recently, fundamental properties and practical applications of two-dimensional (2D) materials have attracted tremendous interest. Micro/nanostructures and functional devices in 2D materials have been fabricated by various methods. Ultrafast direct laser writing (DLW) with the advantages of rich light-matter interactions; unique three-dimensional processing capability; arbitrary-shape design flexibility; and minimized thermal effect, which enables high fabrication accuracy resolution, has been widely applied in the fabrication of 2D materials for multifunctional devices. This timely review summarizes the laser interactions with 2D materials and the advances in diverse functional photonics devices by DLW. The perspectives and challenges in designing and improving laser-fabricated 2D material photonic devices are also discussed.
Chinese Optics Letters
  • Publication Date: Feb. 10, 2020
  • Vol. 18, Issue 2, 023601 (2020)
Research Articles
Fiber Optics and Optical Communications
Dual-channel microfluidic sensor based on side-hole fiber with two long-period fiber gratings
Yu Zhang, Yongzhi Li, Chao Liu, Zhihai Liu, Yaxun Zhang, Xinghua Yang, Jianzhong Zhang, Jun Yang, and Libo Yuan
We propose and demonstrate a dual-channel microfluidic sensor based on a side-hole fiber (SHF) with two long-period fiber grating (LPFG) structures. There are two air holes in the SHF, which are natural microfluidic channels. We fabricate two LPFGs (long-period gratings LPG-A and LPG-B) in the SHF with the resonance wavelengths of 1268.7 nm and 1385.8 nm, respectively. Results show that the refractive index sensitivities of LPG-A and LPG-B are ?76.0 nm/RIU and ?71.1 nm/RIU, respectively. One can measure the refractive index of liquid samples in two channels simultaneously. The proposed dual-channel microfluidic sensor has advantages of good linearity response, fluidic technology compatibility, and easy light input/output coupling and system integration, which helps the sensor to have a potential application in environmental detection and food safety detection.
Chinese Optics Letters
  • Publication Date: Feb. 10, 2020
  • Vol. 18, Issue 2, 020601 (2020)
Highly efficient excitation of LP01 mode in ring-core fibers by tapering for optimizing OAM generation
Chunxiang Zhang, Fufei Pang, Huanhuan Liu, Lifei Chen, Junfeng Yang, Jianxiang Wen, and Tingyun Wang
We have demonstrated the highly efficient excitation of the linearly polarized mode (LP01) in ring-core fibers (RCFs) by tapering the spliced point between the RCF and the standard single-mode fiber (SMF) to optimize all-fiber orbital angular momentum (OAM) generation. The tapering technique has been investigated theoretically and experimentally. Before tapering, only 50% of light can be coupled from SMFs to RCFs. The modal interference spectrum with an extinction ratio (ER) of ~9 dB is observed, showing that higher-order modes are excited in RCF. By tapering the spliced point, 90% of light is coupled, and the ER is minimized to be ~2 dB, indicating that the higher-order modes are effectively suppressed by tapering. Such tapered spliced points of RCF–SMF are further applied for all-fiber OAM generation. The efficiencies of OAM+1 and OAM?1 generation are found to be enhanced by approximately 11.66% and 12.41%, respectively, showing that the tapered spliced point of the RCF–SMF is a feasible way to optimize OAM generation.
Chinese Optics Letters
  • Publication Date: Feb. 10, 2020
  • Vol. 18, Issue 2, 020602 (2020)
Stable RF transfer over a fiber-optic ring with DSBCS modulation and a DSB RF signal
Pingyang Shi, Guiling Wu, Liang Hu, Qi Li, and Jianping Chen
Chinese Optics Letters
  • Publication Date: Feb. 10, 2020
  • Vol. 18, Issue 2, 020603 (2020)
Analysis of detection error for spot position in fiber nutation model
Xueqiang Zhao, Yunpeng Zhang, Minjie Huang, Peipei Hou, Ren Zhu, Jianfeng Sun, Xia Hou, and Weibiao Chen
Chinese Optics Letters
  • Publication Date: Feb. 10, 2020
  • Vol. 18, Issue 2, 020604 (2020)
Holography
Multi-reference lens-less Fourier-transform holography with a Greek-ladder sieve array
Jing Xie, Junyong Zhang, Xue Pan, Shenlei Zhou, and Weixin Ma
Lens-less Fourier-transform holography has been actively studied because of its simple optical structure and its single-shot recording. However, a low-contrast interferogram between the reference and object waves limits its signal to noise ratio. Here, multi-reference lens-less Fourier-transform holography with a Greek-ladder sieve array is proposed in the experiment and demonstrated effectively to improve the signal to noise ratio. The key technique in our proposed method is a Greek-ladder sieve array, which acts as not only a wave-front modulator but also a beam splitter. With advantages of the common path, single shot, and no need for a lens, this system has enormous potential in imaging and especially in extreme ultraviolet and soft X-ray holography.
Chinese Optics Letters
  • Publication Date: Feb. 10, 2020
  • Vol. 18, Issue 2, 020901 (2020)
Real-time electroholography using a single spatial light modulator and a cluster of graphics-processing units connected by a gigabit Ethernet network
Hiromi Sannomiya, Naoki Takada, Tomoya Sakaguchi, Hirotaka Nakayama, Minoru Oikawa, Yuichiro Mori, Takashi Kakue, Tomoyoshi Shimobaba, and Tomoyoshi Ito
Chinese Optics Letters
  • Publication Date: Feb. 10, 2020
  • Vol. 18, Issue 2, 020902 (2020)
Lasers and Laser Optics
Alignment and efficiency-monitoring method of high-power fiber-to-fiber coupling
Qingqing Kong, Yiqiu Jing, Hua Shen, Shiwei Deng, Zhigang Han, and Rihong Zhu
Chinese Optics Letters
  • Publication Date: Feb. 10, 2020
  • Vol. 18, Issue 2, 021402 (2020)
Laser-induced damage and periodic stripe structures of a CaF2 single crystal by an ArF excimer laser
Jingzhen Shao, Xu Liang, Libing You, Ning Pan, Ying Lin, Shimao Wang, Zanhong Deng, Xiaodong Fang, and Xi Wang
Chinese Optics Letters
  • Publication Date: Feb. 10, 2020
  • Vol. 18, Issue 2, 021403 (2020)
Nonlinear Optics
Dynamic relaxation process of a 3D super crystal structure in a Cu:KTN crystal | Editors' Pick
Quanxin Yang, Xin Zhang, Hongliang Liu, Xuping Wang, Yingying Ren, Shan He, Xiaojin Li, and Pengfei Wu
In this Letter, we report the existence and relaxation properties of a critical phenomenon on called a 3D super crystal that emerges at T = TC ? 3.5°C, that is, in the proximity of the Curie temperature of a Cu:KTN sample. The dynamics processes of a 3D super crystal manifest in its formation containing polarized nanometric regions and/or polarized clusters. However, with strong coupling and interaction of microcomponents, the characteristic relaxation time measured by dynamic light scattering demonstrates a fully new relaxation mechanism with a much longer relaxation time. As the relaxation mechanism of a relaxator is so-far undetermined, this research provides a novel perspective. These results can help structure a fundamental theory of ferroelectric relaxation.
Chinese Optics Letters
  • Publication Date: Feb. 10, 2020
  • Vol. 18, Issue 2, 021901 (2020)
Ultra-broadband enhanced nonlinear saturable absorption for Mo0.53W0.47Te2 nanosheets
Zhengting Du, Hui Wu, Tianqi Zhang, Zhenda Xie, Yangyang Lü, Xinjie Lü, Jinlong Xu, Gang Zhao, and Shining Zhu
Alloying in two-dimension has been a hot spot in the development of new, versatile systems of optics and electronics. Alloys have been demonstrated to be a fascinating strategy to modulate the chemical and electronic properties of two-dimensional nanosheets. We firstly reported ultra-broadband enhanced nonlinear saturable absorption of Mo0.53W0.47Te2 alloy at 0.6, 1.0, and 2.0 μm. The nonlinear saturable absorption of Mo0.53W0.47Te2 saturable absorber (SA) was measured by the open aperture Z-scan technique. Compared to MoTe2 and WTe2 SAs, the Mo0.53W0.47Te2 SA showed five times deeper modulation depth, 8.6% lower saturable intensity, and one order larger figure of merit. Thus, our research provides a method of alloys to find novel materials with more outstanding properties for optics and optoelectronic applications.
Chinese Optics Letters
  • Publication Date: Feb. 10, 2020
  • Vol. 18, Issue 2, 021902 (2020)
Optical Sensing, Measurements, and Metrology
Simultaneous measurement of SO2 and NO2 concentration using an optical fiber-based LP-DOAS system
Jieshu Zou, and Fei Wang
SO2 and NO2 are the most important pollution in atmosphere. An optimized long path (LP) differential optical absorption spectroscopy (DOAS) system of high light intensity at an ultraviolet (UV) wavelength is proposed and used to measure the concentration of SO2 and NO2 simultaneously. In contrast to the traditional DOAS, the system adopted a Y-type optical fiber structure instead of a combination of mirrors in the telescope. The UV light intensity test shows that the light intensity of UV can arrive to above 80% of the max measuring range when the light path reaches 135 m, and the integral time of the spectrograph is only 15 ms. The system is proved to be efficacious through laboratory calibration. The maximum error of SO2 calibration is 4.19%, and is 5.22% for NO2. The error of the SO2 and NO2 mixture calibration is within 10%. Field measurement is implemented in a wastewater treatment plant in winter. The measurement light path is 738 m. The concentration of SO2 varies from 6 μg/m3 (2.26 ppb) to 20 μg/m3 (7.52 ppb), and the concentration of NO2 varies from 100 μg/m3 (53.2 ppb) to 200 μg/m3 (106.4 ppb) approximately. The results are in accordance with the data from a monitoring station nearby in magnitude order and variation tendency mostly.
Chinese Optics Letters
  • Publication Date: Feb. 10, 2020
  • Vol. 18, Issue 2, 021201 (2020)
All-reflective self-referenced spectral interferometry for single-shot measurement of few-cycle femtosecond pulses in a broadband spectral range | Editors' Pick
Zhe Si, Xiong Shen, Jingxin Zhu, Lei Lin, Lihua Bai, and Jun Liu
Chinese Optics Letters
  • Publication Date: Feb. 10, 2020
  • Vol. 18, Issue 2, 021202 (2020)
A new phase-shifted long-period fiber grating for simultaneous measurement of torsion and temperature
Cuiting Sun, Ran Wang, Xiren Jin, Zemin Wang, Weiliang Liu, Shuo Zhang, Yiwei Ma, Jingyu Lin, Yue Li, Tao Geng, Weimin Sun, Zhongquan Qu, and Libo Yuan
A novel phase-shifted long-period fiber grating (PS-LPFG) for the simultaneous measurement of torsion and temperature is described and experimentally demonstrated. The PS-LPFG is fabricated by inserting a pre-twisted structure into the long-period fiber grating (LPFG) written in single-mode fiber (SMF). Experimental results show that the torsion sensitivities of the two dips are ?0.114 nm/(rad/m) and ?0.069 nm/(rad/m) in the clockwise direction, and ?0.087 nm/(rad/m) and ?0.048 nm/(rad/m) in the counterclockwise direction, respectively. The temperature sensitivities of the two dips are 0.057 nm/°C and 0.051 nm/°C, respectively. The two dips of the PS-LPFG exhibit different responses to torsion and temperature. Simultaneous measurement of torsion and temperature can be implemented using a sensor. The feasibility and stabilization of simultaneous torsion and temperature measurement have been confirmed, and hence this novel PS-LPFG demonstrates potential for fiber sensing and engineering applications.
Chinese Optics Letters
  • Publication Date: Feb. 10, 2020
  • Vol. 18, Issue 2, 021203 (2020)
Non-intrusive flow measurement based on a distributed feedback fiber laser
Jiasheng Ni, Ying Shang, Chen Wang, Wenan Zhao, Chang Li, Bing Cao, Sheng Huang, Chang Wang, and Gangding Peng
We propose a new non-intrusive flow measurement method using the distributed feedback fiber laser (DFB-FL) as a sensor to monitor flow in the pipe. The relationship between the wavelength of the DFB-FL and the liquid flow rate in the pipeline is derived. Under the guidance of this theory, the design and test of the flow sensor is completed. The response curve is relatively flat in the frequency range of 10 Hz to 500 Hz, and the response of the flow sensor has high linearity. The flow from 0.6 m3/h to 25.5 m3/h is accurately measured under the energy analysis method in different frequency intervals. A minimum flow rate of 0.046 m/s is achieved. The experimental results demonstrate the feasibility of the new non-intrusive flow measurement method based on the DFB-FL and accurate measurement of small flow rates.
Chinese Optics Letters
  • Publication Date: Feb. 10, 2020
  • Vol. 18, Issue 2, 021204 (2020)
Ultrafast Optics
Time-resolved study of the lasing emission from high vibrational levels of N2+ pumped with circularly polarized femtosecond pulses
Dongjie Zhou, Xiang Zhang, Qi Lu, Qingqing Liang, and Yi Liu
We experimentally investigated the forward 353.8 nm radiation from plasma filaments in pure nitrogen gas pumped by intense circularly polarized 800 nm femtosecond laser pulses. This emission line corresponds to the B2Σu+(v′=4)-X2Σg+(v=3) transition of nitrogen ions. In the presence of an external seeding pulse, the 353.8 nm signal was amplified by 3 orders of magnitude. Thanks to the much enhanced intensity, we performed time-resolved measurement of the amplified 353.8 nm emission based on the sum-frequency generation technique. It was revealed that the built-up time and duration of these emissions are both inversely proportional to the gas pressure, while the radiation peak power grows up nearly quadratically with pressure, indicating that the 353.8 nm radiation is of the nature of superradiance.
Chinese Optics Letters
  • Publication Date: Feb. 10, 2020
  • Vol. 18, Issue 2, 023201 (2020)
Terahertz wave emission from water lines
Shijia Feng, Liquan Dong, Tong Wu, Yong Tan, Rui Zhang, Liangliang Zhang, Cunlin Zhang, and Yuejin Zhao
Chinese Optics Letters
  • Publication Date: Feb. 10, 2020
  • Vol. 18, Issue 2, 023202 (2020)

About the Cover

The device separates light with different spins, the left-handed component is coupled into the left waveguide, and the right-handed component is coupled into the right waveguide.