From the industry and technology point of view,the development status of optical communication devices is summarized. The current development level of China's optical communication devices is introduced in detail, and the gap with the international leading level is described. Photonic integration circuit (PIC) is the mainstream direction of future development of optical devices, and Ⅲ-Ⅴ group material and silicon-based material are more widely seen as the two camps in terms of the future optical integration technology by the industry, and they will change the design and future of the optical devices.

This paper reviews the development and latest research progress of large-capacity optical transmission systems. Theoretical and experimental studies have shown that due to the limitations of the fiber nonlinear effect and the amplifier bandwidth, communication capacity is close to the limit of single-mode fiber transmission. Therefore, on the one hand, the development of optical fiber communication needs to overcome the bottleneck of high-speed electrical devices in single carrier transmission. So this paper investigates the multi-carrier generation schemes like orthogonal frequency division multiplexing (OFDM) technology or Nyquist wavelength division multiplexing (Nyquist-WDM) technology, which can improve spectrum efficiency and increase channel capacity to achieve Pbit/s rate or even higher. On the other hand,we study from the perspective of the optical fiber itself how to take full advantage of the spatial dimension of the fiber in consideration of cost-effectiveness and energy efficiency. It is shown that space division multiplexing (multi-mode, multi-core) and angular momentum multiplexing (OAM) will be the focus of future research to overcome the limit of the capacity of single-mode fiber and greatly improve optical transmission capacity.

Broadband communication networks include both high-speed optical fiber transmission backbone networks and broadband access networks (BAN), but developments of the two kinds of networks are very uneven. Particularly, several challenges of BAN such as speed and bandwidth, security and privacy, cost-effectiveness, energy consumption and integration need to be addressed. In this paper, according to the international research reports, a brief overview of the research progress of BAN is presented, and the trend in technology development and key issues of BAN are indicated. At last, the security and privacy enhancement, the cost reduction, the integration and compatibility improvement of BAN are summarized and discussed.

RoF(radio-over-fiber) technology combines microwave radiofrequency technology with photonics technology, and simultaneously embodies the technical features of "high speed" of optical communication and "mobility" of wireless communication. It greatly reduces the energy consumption of wireless network, representing the future development direction of optical networks and wireless networks. This paper begins with the domestic and foreign state of the RoF technology research and application, then focuses on the challenges that the ROF technology currently faces, and finally gives its future R/D direction on the basis of investigation of ROF key technologies.

Mode division multiplexing(MDM)is becoming a hot topic in the field of optical fiber communication. It can increase the capacity of optical fiber communication exponentially by using the limited and orthogonal spatial modes of few-mode fiber to transmit information in parallel. In this paper, we present a thorough review of recent progress in MDM in terms of system modeling, equalization, and development of system experiment. Firstly, we give a detailed description of the equalization method used for demultiplexing and analyze its computational complexity. Then, we summarize some recent experimental demonstrations of MDM, including the particular structure of the system and main results. Finally, we give some possible research directions for MDM.

The growing Internet traffic has imposed strong demands on current fiber optical communications. Mode division multiplexing (MDM) transmission based on few mode fiber (FMF) has attracted worldwide research interests, due to the potential for overcoming the capacity crunch of standard single mode fiber (SSMF). It is expected that N spatial modes in the FMF can achieve a capacity N times higher than that of the SSMF. We review the recent progress of MDM techniques including mode division multiplexer/demultiplexer, FMF design and fabrication, few-mode fiber amplifiers for long-haul transmission, and the latest outstanding transmission demonstrations. Finally, we outline the prospects and future challenges in this research topic.

To meet the fast-growing bandwidth requirement of end users, a time and wavelength division multiplexing technique is proposed to extend the network capacity. Meanwhile, the data rate of each wavelength should also be increased. In this paper, the feasibility of using DML in TWDM-PON systems is investigated, with an emphasis on chirp management and power budget improving techniques. Besides, the Raman crosstalks between the new-added and the traditional channels are analyzed with a proposed crosstalk mitigation solution based on Dicode coding.

Space information network (SIN) is a heterogeneous network that has multiple platforms including GEO/MEO/LEO satellites, stratosphere balloons, unmanned aerial vehicles in the backbone, and terrestrial terminals (e.g., ground stations) functioning as access nodes. The appearance of SIN realizes efficient resource sharing and utilization of distributed information within a large-scale space. Due to the diversity of network nodes, the condition of communication links in SINs is very complicated. Specifically, there are six types of SIN links:inter-satellite link, inter-aircraft link, terrestrial link, satellite-aircraft link, satellite-ground link, and aircraft-ground link. In this paper, we extensively investigate the recent advances in the field of communication links in the SIN, and analyze the research findings, especially the studies on radio frequency (RF), free space optics (FSO) and FSO/RF hybrid communication in the SIN. The analysis demonstrates that, compared with the traditional RF communication, FSO technology has high bandwidth, large capacity, and negligibly small requirement of spectral examination, at the additional cost of narrow spread, slow motion tracking, and vulnerability to bad weather. We further show that FSO is most suitable for inter-satellite links, while for the other links over atmosphere influence or rapid positioning, the FSO/RF hybrid communication has more obvious advantages. Since there have been minor efforts on the FSO/RF hybrid communication, we propose an adaptive switching mechanism for FSO/RF hybrid communication based on big data prediction.

Visible light communication (VLC) technology, which provides green lighting and data communication functions, is one of the most vibrant research topics in optical wireless communications. Since the popularity of smartphones, imaging sensor-based VLC (or optical camera communication, OCC) is receiving more and more attention and investigation. Such OCC technology has the ability to separate light signals coming from the different angles of incidence, thus shows an extensive application prospect in many areas. The OCC has lots of differences from the traditional single photodiode-based VLC system, not only in signal processing filed but also in modulation and other domains. Therefore, we have to develop dedicated techniques to support the OCC. This paper reviews some key techniques in OCC system, and discusses the application scenarios of this system.

Optical interconnect on printed circuit boards (OPCBs) is a research focus in the field of communication due to its unique advantages of high transmission rate, low power consumption, low cost, no electromagnetic interference, etc. In this article, firstly the schematic diagrams of optical waveguide and the preparation process of OPCBs are introduced in brief. Then, the progresses of the transmission characteristics, coupling method, environmental reliability, system application, etc. about OPCBs are discussed in detail. Finally, the outlook of its development direction is prospected.

Ultra-long haul high-precision fiber-optic two-way time transfer is demonstrated by adopting the proposed scheme called bidirectional time division multiplexing transmission over single fiber with the same wavelength (BTDM-SFSW), which can effectively eliminate the impact of Rayleigh backscattering and reach the maximum bidirectional symmetry at the same time. The inter-range instrumentation group (IRIG-B) time code is modified by increasing bit rate and defining new fields for the proposed BTDM-SFSW time transfer scheme. A dedicated codec (encoder and decoder) with low delay fluctuation and self-synchronization is developed by using a mask technique and combinational logic circuit. A BTDM-SFSW based time transfer testbed is built with the employment of loop configuration in laboratory to evaluate the performance of fiber-optic time transfer over thousands of kilometers. Stabilities of less than 89 ps/s and 23 ps/10⁵ s are achieved for the time transfer over a 2000 km fiber link with single fiber bidirectional amplifiers (SFBA). In order to overcome the issues of using the SFBA including the impact of Rayleigh backscattering and incompatibility with commercial fiber links, a novel time transfer scheme of single-fiber bidirectional-transmission with unidirectional optical amplifiers (SFBT-UOA) is proposed. Transmission over 6000 km is experimentally demonstrated with the time deviations of 190 ps/s and 61 ps/10⁵ s, respectively. A full uncertainty budget for the BTDM-SFSW based time transfer is provided, which considers the contributions of different factors, including the precision and stability of transmitted wavelengths, power dependence of transceivers'receiving delays, Sagnac effect, etc. The calculated theoretic combined uncertainty is not beyond 70 ps without the requirement of fiber link calibration, which well agrees with the experimental verification over different lengths of non-calibrated fiber link.

A single-longitudinal-mode thulium-doped fiber laser using Fabry-Perot (F-P) filter and saturable absorber is proposed and experimentally demonstrated at the 2 μm band. In the structure, the combination of a narrowband F-P filter and a section of unpumped thulium-doped fiber ensures the single-longitudinal-mode lasing operation. A stable lasing operation is obtained at room temperature, with the central wavelength of 1941.6 nm and the optical signal-to-noise ratio of 32 dB. For an experimental period of 100 min, the output power fluctuates less than 1.5 dB and the center wavelength shifts less than 0.04 nm, indicating that the single-longitudinal-mode thuliumdoped fiber laser possesses good long-term stability.

The quality of transmitted signal is easy to be impacted due to the fiber Kerr nonlinearity, which results in the difficulty in increasing transmission capacity and speed of single mode fiber (SMF) based optical fiber communication systems. However, a new research by University of California at San Diego (UCSD) has shown that the technology based on optical frequency comb (OFC) combined with digital signal processing can improve the transmission performance significantly. This manifests that this OFC-based technology can be treated as a breakthrough of the nonlinear Shannon limit. This paper mainly relates to the topic of OFC, including the definition, generation methods, typical applications in information and communication systems, and the OFC-based crossed applications in other related physical scientific fields. Meanwhile, the trends of OFC technology have also been discussed.

Optical frequency comb, consisting of many coherent lines spaced with equal frequency separation, is a new type of light source. This paper presents the optical frequency comb generation techniques including electro-optic modulation and nonlinear microresonator, and demonstrates its application and prospects in microwave photonic signal generation, conversion and receiving.

Near-infrared (NIR) electro-optic (EO) modulator will play a key role in future optical signal processing and communication systems. Graphene-silicon hybrid EO modulators have attracted much attention due to the merits regarding device footprints, modulation speeds, modulation bandwidth, and mass-productivity. In this paper, we firstly introduce the electro-optical properties of graphene and light modulation mechanism in EO modulators. Then based on the application of the graphene in EO modulators, this paper reviews current research progress of various types of NIR EO modulators based on graphene-silicon hybrid structure, and describes their operation principles and performances, including silicon waveguide graphene-based modulator, silicon micro-ring modulator based on graphene, and EO modulator based on graphene-silicon hybrid 1D photonic crystal nanobeam cavity. Finally, some future research directions are predicted.

A demo system at 105.1 Tbit/s over 14350 km was reported in the OFC'2016, and ultra high bit rate transmission and all optical switch have been the most keypoint of the optical fiber telecommunications and all optical networking. High speed optical signal processing, including all optical logic gates, wavelength convertor, all optical buffer, optical computations, etc., are employed at the switching node in the all optical network. In this article, some technologies about the high speed all optical digital signal processing for high speed optical fiber systems are presented with our related research works.

Fractional Fourier transformation (FrFT) is an extension form of the Fourier transformation (FT). It can analyze the fractional signal between time and frequency domains. Thanks to its unique properties, the FrFT has found multiple applications such as solving differential equations, quantum mechanics, optical image processing and signal processing. This paper gives a brief introduction to FrFT and reviews the current research progress of FrFT in several fields such as filtering, neural network, image processing and wireless communication. In addition, some typical applications in optical communication are depicted in detail. Some research directions of FrFT in optical communication field are suggested.

Visible light communication (VLC) is an emerging wireless optical communication technology, which combines illumination and communication. So it has a broad application prospect that makes it a research hotspot in recent years. The main challenge of VLC's development is the limited modulation bandwidth of LED, which leads to a limited transmission rate of the VLC system. To solve this problem, hardware pre-equalization circuit is used in the VLC system. We design and use single and cascaded bridged-T amplitude equalizers. By combining the orthogonal frequency division multiplexing (OFDM) technology, the VLC system's modulation bandwidth and transmission rate can be improved efficiently.

A method of real-time dispersion equalization for optical OFDM system based on FPGA is researched in this paper. According to the principle of dispersion equalization, a simulation platform for the OFDM-PON system is setup. The results show that the dispersion equalization module based on FPGA can effectively compensate for the dispersion damage, and that the performance of OSNR can be improved by about 0.5~1 dB and the requirement for real-time processing system can be met.

Single channel rate for optical fiber communication has been up to 100 Gbit or even higher, thus a higher and higher bandwidth of the measuring instrument is required. Due to the limitation of electronic bottleneck, the bandwidth limit is 70~90 GHz. At present, difficulty and cost for an electric oscilloscope to be able to measure 100 Gbit/s optical communication signals are increasing. In order to break through the limitation of electronic bottleneck, some new sampling mechanism is needed to measure the ultra high speed optical communication signal or the ultra wide band optical signal. This paper introduces the basic principle of optical field sampling and the corresponding optical sampling oscilloscope that has the advantages of high time precision and ultra wide band measurement. Also introduced are the development progresses of optical sampling oscilloscope made by the authors' research group and foriegn counterparts. In addition, with continuous improvement on channel rate, the influence of physical damage of optical fiber link on signal is becoming more significant. Therefore, how to monitor physical damage turns to be a problem in the ultra high speed optical communication network. A method of measuring the dispersion and nonlinear effect of optical fiber link based on fractional Fourier transform is presented. In the end, the development of measurement technology for high speed optical fiber communication link is prospected.