Contents
2019
Volume: 17 Issue 10
22 Article(s)

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UNDERWATER WIRELESS OPTICAL COMMUNICATION
Hybrid LD and LED-based underwater optical communication: state-of-the-art, opportunities, challenges, and trends [Invited]
Xuan Huang, Fang Yang, and Jian Song
Chinese Optics Letters
  • Publication Date: Oct. 10, 2019
  • Vol. 17, Issue 10, 100002 (2019)
Simulation and verification of pulsed laser beam propagation underwater using Markov chains [Invited]
Tianhua Zhou, Jian Ma, Tingting Lu, Guyu Hu, Tingwei Fan, Xiaopeng Zhu, Xiaolei Zhu, and Weibiao Chen
Chinese Optics Letters
  • Publication Date: Oct. 10, 2019
  • Vol. 17, Issue 10, 100003 (2019)
50 Gb/s PAM4 underwater wireless optical communication systems across the water–air–water interface [Invited]
Chung-Yi Li, Hai-Han Lu, Yong-Cheng Huang, Qi-Ping Huang, Jing-Yan Xie, and Song-En Tsai
A 50 Gb/s four-level pulse amplitude modulation (PAM4) underwater wireless optical communication (UWOC) system across the water–air–water interface is demonstrated in practice. In practical scenarios, laser beam misalignment due to oceanic turbulence degrades performance in UWOC systems. With the adoption of a reflective spatial light modulator (SLM) with an electrical controller, not only can the laser be arbitrarily adjusted to attain a water–air–water scenario, but oceanic engineering problems can also be resolved to establish a reliable UWOC link. Brilliant bit error rate performance and clear PAM4 eye diagrams are attained by adopting a Keplerian beam expander and a reflective SLM with an electrical controller. This proposed PAM4 UWOC system presents a feasible state that outperforms existing UWOC systems due to its feature providing a high-speed water–air–water link.
Chinese Optics Letters
  • Publication Date: Oct. 10, 2019
  • Vol. 17, Issue 10, 100004 (2019)
Performance characterization of two-way multi-hop underwater networks in turbulent channels [Invited]
Fangyuan Xing, Hongxi Yin, and Lianyou Jing
Chinese Optics Letters
  • Publication Date: Oct. 10, 2019
  • Vol. 17, Issue 10, 100005 (2019)
Robust UOWC systems against bubble-induced impairments via transmit/receive diversities [Invited]
Lian-Kuan Chen, Yingjie Shao, and Rui Deng
Chinese Optics Letters
  • Publication Date: Oct. 10, 2019
  • Vol. 17, Issue 10, 100006 (2019)
Recent achievements on underwater optical wireless communication [Invited]
Giulio Cossu
Chinese Optics Letters
  • Publication Date: Oct. 10, 2019
  • Vol. 17, Issue 10, 100009 (2019)
Absorption and scattering effects of Maalox, chlorophyll, and sea salt on a micro-LED-based underwater wireless optical communication [Invited]
Pengfei Tian, Honglan Chen, Peiyao Wang, Xiaoyan Liu, Xinwei Chen, Gufan Zhou, Shuailong Zhang, Jie Lu, Pengjiang Qiu, Zeyuan Qian, Xiaolin Zhou, Zhilai Fang, Lirong Zheng, Ran Liu, and Xugao Cui
In this work, a blue gallium nitride (GaN) micro-light-emitting-diode (micro-LED)-based underwater wireless optical communication (UWOC) system was built, and UWOCs with varied Maalox, chlorophyll, and sea salt concentrations were studied. Data transmission performance of the UWOC and the influence of light attenuation were investigated systematically. Maximum data transmission rates at the distance of 2.3 m were 933, 800, 910, and 790 Mbps for experimental conditions with no impurity, 200.48 mg/m3 Maalox, 12.07 mg/m3 chlorophyll, and 5 kg/m3 sea salt, respectively, much higher than previously reported systems with commercial LEDs. It was found that increasing chlorophyll, Maalox, and sea salt concentrations in water resulted in an increase of light attenuation, which led to the performance degradation of the UWOC. Further analysis suggests two light attenuation mechanisms, e.g., absorption by chlorophyll and scattering by Maalox, are responsible for the decrease of maximum data rates and the increase of bit error rates. Based on the absorption and scattering models, excellent fitting to the experimental attenuation coefficient can be achieved, and light attenuation by absorption and scattering at different wavelengths was also investigated. We believe this work is instructive apply UWOC for practical applications.
Chinese Optics Letters
  • Publication Date: Oct. 10, 2019
  • Vol. 17, Issue 10, 100010 (2019)
Nonlinear adaptive filters for high-speed LED based underwater visible light communication [Invited]
Nan Chi, and Fangchen Hu
Underwater visible light communication (UVLC) is expected to act as an alternative candidate in next-generation underwater 5G wireless optical communications. To realize high-speed UVLC, the challenge is the absorption, scattering, and turbulence of a water medium and the nonlinear response from imperfect optoelectronic devices that can bring large attenuations and a nonlinearity penalty. Nonlinear adaptive filters are commonly used in optical communication to compensate for nonlinearity. In this paper, we compare a recursive least square (RLS)-based Volterra filter, a least mean square (LMS)-based digital polynomial filter, and an LMS-based Volterra filter in terms of performance and computational complexity in underwater visible light communication. We experimentally demonstrate 2.325 Gb/s transmission through 1.2 m of water with a commercial blue light-emitting diode. Our goal is to assist the readers in refining the motivation, structure, performance, and cost of powerful nonlinear adaptive filters in the context of future underwater visible light communication in order to tap into hitherto unexplored applications and services.
Chinese Optics Letters
  • Publication Date: Oct. 10, 2019
  • Vol. 17, Issue 10, 100011 (2019)
High-speed underwater wireless optical communications: from a perspective of advanced modulation formats [Invited]
Chao Fei, Xiaojian Hong, Ji Du, Guowu Zhang, Yuan Wang, Xiaoman Shen, Yuefeng Lu, Yang Guo, and Sailing He
In this paper, recent advances in underwater wireless optical communication (UWOC) are reviewed for both LED- and LD-based systems, mainly from a perspective of advanced modulation formats. Volterra series-based nonlinear equalizers, which can effectively counteract the nonlinear impairments induced by the UWOC system components, are discussed and experimentally demonstrated. Both the effectiveness and robustness of the proposed Volterra nonlinear equalizer in UWOC systems under different water turbidities are validated. To further approach the Shannon capacity limit of the UWOC system, the probabilistic constellation shaping technique is introduced, which can overcome the inherent gap between a conventional regular quadrature amplitude modulation (QAM) format and the Shannon capacity of the channel. The experimental results have shown a significant system capacity improvement compared to the cases using a regular QAM.
Chinese Optics Letters
  • Publication Date: Oct. 10, 2019
  • Vol. 17, Issue 10, 100012 (2019)
The effect of turbulence on NLOS underwater wireless optical communication channels [Invited]
Mohammed Sait, Xiaobin Sun, Omar Alkhazragi, Nasir Alfaraj, Meiwei Kong, Tien Khee Ng, and Boon S. Ooi
Conventional line-of-sight underwater wireless optical communication (UWOC) links suffer from huge signal fading in the presence of oceanic turbulence due to misalignment, which is caused by variations in the refractive index in the water. Non-line-of-sight (NLOS) communication, a novel underwater communication configuration, which has eased the requirements on the alignment, is supposed to enhance the robustness of the UWOC links in the presence of such turbulence. This Letter experimentally and statistically studies the impact of turbulence that arises from temperature gradient variations and the presence of different air bubble populations on NLOS optical channels. The results suggest that temperature gradient-induced turbulence causes negligible signal fading to the NLOS link. Furthermore, the presence of air bubbles with different populations and sizes can enhance the received signal power by seizing the scattering phenomena from an ultraviolet 377 nm laser diode.
Chinese Optics Letters
  • Publication Date: Oct. 10, 2019
  • Vol. 17, Issue 10, 100013 (2019)
Research Articles
Atomic and Molecular Physics
Micro-fabrication and hermeticity measurement of alkali-atom vapor cells based on anodic bonding
Lu Zhang, Wendong Zhang, Shougang Zhang, and Shubin Yan
A vapor cell provides a well-controlled and stable inner atmosphere for atomic sensors, such as atomic gyroscopes, atomic magnetometers, and atomic clocks, and its hermeticity affects the stability and aging of atomic sensors. We present the micro-fabrication of a micro-electromechanical system wafer-level hermit vapor cell based on deep reactive ion etching and vacuum anodic-bonding technology. The anodic-bonding process with the voltage increasing in steps of 200 V had a critical influence on vapor cell hermeticity. Further, the silicon–glass bonding surface was experimentally investigated by a scanning electron microscope, which illustrated that there were no visual cracks and defects in the bonding surface. The leak rate was measured using a helium leak detector. The result shows that the vapor cells with different optical cavity lengths comply with the MIL-STD-883E standard (5 × 10 8 mbar·L/s). Moreover, D2 absorption spectroscopy was characterized via optical absorption. The bonding strength was determined to be 13 MPa, which further verified the quality of the vapor cells.
Chinese Optics Letters
  • Publication Date: Oct. 10, 2019
  • Vol. 17, Issue 10, 100201 (2019)
Detectors
Impulse response of Ge2Sb2Te5-based ultrafast photodetector integrated with SOI waveguide
Vibhu Srivastava, Prateek Mishra, and Sunny
Chinese Optics Letters
  • Publication Date: Oct. 10, 2019
  • Vol. 17, Issue 10, 100401 (2019)
Fiber Optics and Optical Communications
OFDM-based visible light communication with rotated polarity modulation aided complex color shift keying
Jianxun Xu, Ming Jiang, and Yufa Chen
Chinese Optics Letters
  • Publication Date: Oct. 10, 2019
  • Vol. 17, Issue 10, 100602 (2019)
Analyzing OAM mode purity in optical fibers with CNN-based deep learning
Tianying Lin, Ang Liu, Xiaopei Zhang, He Li, Liping Wang, Hailong Han, Ze Chen, Xiaoping Liu, and Haibin Lü
Inspired by recent rapid deep learning development, we present a convolutional-neural-network (CNN)-based algorithm to predict orbital angular momentum (OAM) mode purity in optical fibers using far-field patterns. It is found that this image-processing-based technique has an excellent ability in predicting the OAM mode purity, potentially eliminating the need of using bulk optic devices to project light into different polarization states in traditional methods. The excellent performance of our algorithm can be characterized by a prediction accuracy of 99.8% and correlation coefficient of 0.99994. Furthermore, the robustness of this technique against different sizes of testing sets and different phases between different fiber modes is also verified. Hence, such a technique has a great potential in simplifying the measuring process of OAM purity.
Chinese Optics Letters
  • Publication Date: Oct. 10, 2019
  • Vol. 17, Issue 10, 100603 (2019)
Lasers and Laser Optics
Temperature dependence of spectral and laser properties of Er3+/Al3+ co-doped aluminosilicate fiber
Qiang He, Fan Wang, Zhiquan Lin, Chongyun Shao, Meng Wang, Shikai Wang, Chunlei Yu, and Lili Hu
Chinese Optics Letters
  • Publication Date: Oct. 10, 2019
  • Vol. 17, Issue 10, 101401 (2019)
Dynamic image acquisition and particle recognition of laser-induced exit surface particle ejection in fused silica
Yangliang Li, Chao Shen, Li Shao, and Yujun Zhang
Particle ejection is an important process during laser-induced exit surface damage in fused silica. Huge quantities of ejected particles, large ejection velocity, and long ejection duration make this phenomenon difficult to be directly observed. An in situ two-frame shadowgraphy system combined with a digital particle recognition algorithm was employed to capture the transient ejecting images and obtain the particle parameters. The experimental system is based on the principle of polarization splitting and can capture two images at each damage event. By combining multiple similar damage events at different time delays, the timeline of ejecting evolution can be obtained. Particle recognition is achieved by an adaptively regularized kernel-based fuzzy C-means algorithm based on a grey wolf optimizer. This algorithm overcomes the shortcoming of the adaptively regularized kernel-based fuzzy C-means algorithm easily falling into the local optimum and can resist strong image noises, including diffraction pattern, laser speckle, and motion artifact. This system is able to capture particles ejected after 600 ns with a time resolution of 6 ns and spatial resolution better than 5 μm under the particle recognition accuracy of 100%.
Chinese Optics Letters
  • Publication Date: Oct. 10, 2019
  • Vol. 17, Issue 10, 101402 (2019)
Materials
Effect of reduction co-sintering on the photoluminescence properties of phosphor in glass in boro-bismuthate glass
Qiaoyu Zheng, Yang Li, Wenjuan Wu, Jun Zou, Bobo Yang, and Mingming Shi
Chinese Optics Letters
  • Publication Date: Oct. 10, 2019
  • Vol. 17, Issue 10, 101601 (2019)
Underwater Wireless Optical Communication
Editorial for Special Issue on Underwater Wireless Optical Communication
Jing Xu, Boon S. Ooi, and Gong-Ru Lin
Underwater wireless optical communication (UWOC) has gained increasing research interest worldwide from both academic and industrial communities, because of its high bandwidth, compact antennas, low latency, cost-effectiveness, and low power consumption. In the underwater world, the wireless optical links can be complementary to or even more competitive than its acoustic counterpart. Nevertheless, the hostile underwater environment sets up natural obstacles to most information carriers, including the lightwave, even at the right wavelength. Much attention has been recently paid to this interesting and challenging area, leading to impressive progresses. Hence, we launched this focus issue to discuss recent advances and progress in UWOC, and aimed to further stimulate future advancements in this emerging field.
Chinese Optics Letters
  • Publication Date: Nov. 08, 2019
  • Vol. 17, Issue 10, 100001 (2019)