Table of Content

31 July 2020, Volume 38 Issue 4

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Optical Fiber Communication Technology

Progress in High-Speed Classical Physical Key Distribution Techniques

GAO Hua, WANG Anbang, WANG Yuncai

2020, 38(4):  507-519.  doi:10.3969/j.issn.0255-8297.2020.04.001

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Information encryption transmission is a critical problem of cyberspace security. According to Shannon's “one-time-pad” theory, secure encryption requires the secret distribution of random keys. With the increase of optical communication rate, high-speed key distribution techniques are urgently needed for information encryption transmission. In recent years, researchers continue to explore the key distribution based on classical physical methods, expecting to achieve high-speed key distribution which is compatible with current communication networks. The main methods include random selection of fiber laser parameters, physical unclonable function, fiber channel noise, and chaotic laser synchronization. This paper introduces the basic principle and main research progress of these classical physical key distribution schemes. Among which, the key distribution based on laser chaos synchronization with high potential in high-speed distribution is emphasized, and its corresponding problems need to be solved are analyzed as well.

Progress in Near Infrared Ultra-Broadband Fiber Amplification

JIAO Yan, SHAO Chongyun, HU Lili

2020, 38(4):  520-541.  doi:10.3969/j.issn.0255-8297.2020.04.002

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With the rapid development of optical communications, expanding the gain bandwidth of fiber amplifiers has become an urgent problem to be solved. However, the present gain bandwidth of conventional fiber amplifiers cannot meet the needs of communication capacity, thus bringing serious challenges to the speed and capacity of optical communication. This study briefly introduces the latest research achievements of broadband amplifiers based on Bi-doped fiber, Bi/Er co-doped fiber and quantum dot-doped fiber. And the future researches of ultra-broadband amplifying materials are prospected as well.

Performance Monitoring for Multi-dimensional Optical Fiber Communication System

JIANG Lin, YI Anlin, PAN Yan, YAN Lianshan, PAN Wei, LUO Bin

2020, 38(4):  542-558.  doi:10.3969/j.issn.0255-8297.2020.04.003

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Optical fiber communication system is rapidly developing towards the direction of ultra-high speed, large capacity, and dynamic aspects. New dimensions and multiplexing methods, as well as more complex architecture will be introduced to meet these requirements. However, they also pose a huge challenge to the reliable and safe operation and management of transmission networks. The physical layer parameter monitoring technique which can monitor and warn the impairments of optical fiber transmission networks would provide information source and management basis for adaptive compensation, quality of transmission (QoT) and network resource optimization. Therefore, it would be valuable, in both scientific and social point of view, to enhance the reliability and safety of operation and management. Research highlights of chromatic dispersion monitoring, nonlinearity monitoring and modulation format monitoring are first reviewed, then followed by the discussion about the trends of performance monitoring technology for multi-dimensional optical fiber communication systems. It is concluded that the future performance monitoring will be characterized as precise measurement, functionality integration, intelligent processing and simultaneous multi-parameter monitoring.

Progress in Vortex-Multiplexed Communications Based on Conventional Fibers

WANG Jian, CHEN Shi

2020, 38(4):  559-578.  doi:10.3969/j.issn.0255-8297.2020.04.004

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The rapid development in big data era brings tremendous pressure and challenge to optical communication system. High-speed and large-capacity optical communication has become an inevitable trend of development. Besides the extensive exploitation of traditional physical dimensions of optical waves, vortex mode multiplexing technique based on the transverse spatial dimension has attracted great attention for the improvement of transmission capacity. Except for specially designed ring-core fibers, the widely deployed conventional fibers are also capable of supporting vortex mode multiplexing communication. This paper reviews the research progress of vortex-multiplexed communications based on conventional fibers. First, the characteristics and performance for mode-division multiplexing (MDM) transmission of different mode bases in conventional fibers are introduced. Second, vortex mode properties in conventional single-mode fiber (SMF) and multi-mode fiber (MMF) are comprehensively investigated, and the research progress of vortex-multiplexed communications based both on MMF and on other mode bases are reviewed and discussed. Finally, the future of vortex-multiplexed communication is prospected.

Progress in Radiation-Resistant Erbium-Doped and Erbium-Ytterbium Co-doped Fibers for Space Optical Communication

SHE Shengfei, MEI Lin, ZHOU Zhenyu, HOU Chaoqi, GUO Haitao

2020, 38(4):  579-594.  doi:10.3969/j.issn.0255-8297.2020.04.005

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Erbium-doped and erbium-ytterbium co-doped fiber amplifiers play an important role in space optical communication systems because of their advantages of anti-electromagnetic interference, high efficiency of electro-optic conversion, size compactness and lightness, and free debugging and maintenance. However, when exposed to the harsh radiation environment of the earth's space orbit for long time, fiber amplifiers will be affected by charged particles and high-energy electromagnetic radiation in the space. In particular, the radiation will damage gain fiber and cause the failure of optical amplification, accordingly, seriously restricting the application of fiber amplifiers in the field of space optical communication. This study first briefly introduces the phenomena and problems of space radiation-induced deterioration of fiber amplifiers, then elaborates the research progress of radiation-resistant erbium-doped and erbium ytterbium co-doped fiber on three aspects: radiation mechanism, radiation-resistant factors in fibers, and methods of radiation reinforcement, and finally prospects the future research trend of radiation-resistant fiber amplifiers.

Progress in Chaotic Semiconductor Lasers

QIAO Lijun, YANG Qiang, CHAI Mengmeng, WEI Xiaojing, ZHANG Jianzhong, XU Hongchun, ZHANG Mingjiang

2020, 38(4):  595-611.  doi:10.3969/j.issn.0255-8297.2020.04.006

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Chaotic laser, known for the wide-spectrum and noise-like characteristics, has been widely used in various fields such as communication, sensing and lidar. Due to the advantages of small size, stable performance and low cost, semiconductor lasers have become the main light source for the generation of chaotic laser. The traditional chaotic semiconductor lasers with optical feedback have the problems of narrow signal bandwidth, with time-delay signature, and low integration with discrete devices. For these problems, the research progress in recent years of researchers on the bandwidth enhancement, time-delay signature suppression and integrated chaotic lasers is introduced comprehensively in this paper. And the development trend and potential applications of chaotic semiconductor lasers are also prospected.

Progress in Key Technologies of Physical Layer in Next Generation Optical Access Networks

LUO Siyu, XU Yan, LI Zhengxuan, SONG Yingxiong, WANG Min

2020, 38(4):  612-629.  doi:10.3969/j.issn.0255-8297.2020.04.007

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The rapid growth of 5G and data-intensive applications poses new challenges to the capacity of next-generation optical access networks. As the most mature broadband fiber access technology, passive optical networks (PON) has drawn widespread attention. In order to achieve a higher transmission rate under the premise of meeting the power budget, the key technology to improve the performance of the physical layer has always been a research hotspot in this field. Meanwhile, it is of great significance to reduce the system cost as much as possible for the large-scale deployment of PON. In this paper, we describe and summarize the research progress of key physical layer technologies in optical access network. We introduce the evolution and current status of the PON standards, analyze the challenges and causes in the next-generation PON, and focus on the key technologies such as digital equalization technology, high-order modulation formats, optical amplification, forward error correction, experimental analysis of nonlinear crosstalk, and low-cost coherent detection and their research progress. We also review the current research achievements of relevant works.

Self-Calibrated High-Frequency Analysis of High-Speed Optoelectronic Devices by Frequency-Shifted Heterodyne

ZHANG Shangjian, WANG Mengke, ZHANG Yali, ZHANG Zhiyao, LIU Yong

2020, 38(4):  630-639.  doi:10.3969/j.issn.0255-8297.2020.04.008

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High-speed optoelectronic devices are key elements for large-capacity optical fiber communication systems and wideband microwave photonic systems, in which the high-frequency characterization of optoelectronic devices is of importance for the precise signal conversion between optical domain and electrical domain. In this paper, we proposed a frequency-shifted heterodyne method based on optical heterodyne theory for mapping signal spectrum from optical domain to electrical domain, in order to obtain the joint analysis of optical spectrum and electrical spectrum in electrical domain. In experiments, we have successfully conducted self-calibrated high-frequency measurements with three devices including Mach-Zehnder modulators, phase modulators and photodetectors by carefully choosing the frequency relationship between the desired mapped electrical spectrum lines. The main characteristic of the devices, such as modulation index,half-wave voltages, chirp and responsivity are extracted. Experimental results indicate that our method is helpful for the wideband, high-resolution, multiparameter, self-calibration measurement of high-speed optoelectronic devices.

Multi-band Linearly Frequency Modulated Fourier Domain Mode-Locked Optoelectronic Oscillator

HAO Tengfei, SHI Nuannuan, LI Wei, ZHU Ninghua, LI Ming

2020, 38(4):  640-646.  doi:10.3969/j.issn.0255-8297.2020.04.009

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A photonic approach to generating reconfigurable multi-band linearly frequency modulated microwave waveform is proposed and experimentally demonstrated based on a Fourier domain mode-locked optoelectronic oscillator (FDML OEO). In the proposed system, a frequency scanning multi-passband microwave photonic filter (MPF) consisting of a frequency scanning multi-wavelength laser, a phase modulator and an optical notch filter is incorporated into the FDML OEO cavity. Multi-band linearly frequency modulated microwave waveform is generated at the output of the FDML OEO by synchronizing the scanning period of the MPF to the cavity round-trip time to achieve Fourier domain modelocking operation. The key significance of the approach is that it allows the generation of multi-band linearly frequency modulated microwave waveforms without using a highspeed baseband single-chirped microwave source. In addition, the central frequency and bandwidth of the generated waveforms can be easily reconfigured. The proposed approach has great potential in applications such as modern multi-band radar and multiple radio access wireless communication networks.

Anti-nonlinear Support Vector Machine Based Geometrically Shaping Visible Light Communication System

CHI Nan, NIU Wenqing, JIA Junlian, HA Yinaer

2020, 38(4):  647-658.  doi:10.3969/j.issn.0255-8297.2020.04.010

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Nonlinear effect has been becoming a major bottleneck in high speed visible light communication (VLC) system. In this paper, we propose a supervised learning algorithm, support vector machine (SVM) for improving constellation classification in geometrically shaping (GS) VLC system. By taking the in-phase and quadrature components of the signal as feature vectors, an optimal classification plane can be built, and the symbol error introduced by nonlinearity could be therefore reduced. The performances of several GS designs are conducted and compared. Simulation and experimental results show that SVM could significantly reduce the error rate, compared with conventional classification scheme based on Euclidean distance. Among all simulations with SVM, the system with the data rate of 1.2 Gbit/s, circle169 GS-16QAM performs the lowest symbol error rate.