Aiming at the influence of matched filter (e.g. root raised cosine filter) on the coherent optical fiber communication system, the effect of roll-off factor (Rf) are studied under different value of optical bandwidth, residual dispersion and nonlinearity. Simulations are carried out for 256 Gbit/s Polarization Division Multiplexing-16 Quadrature Amplitude Modulation (PDM-16QAM) signals when the optical bandwidth are 33, 50 and 100 GHz, the residual dispersion ranging from -300 to 300 ps/nm and launched power ranging from -3 to 4 dBm in a 1 200 km optical fiber link. The simulations show that a good transmission performance can be achieved for limited optical bandwidth system when Rf is set to the value of (1+Rf) B (B is the Baud rate of the signal) that similar to the system optical bandwidth. When optical bandwidth near or exceed 2 times Baud rate of signals, Rf should be set between 0.2 and 0.5 to achieve a better transmission performance.

As a kind of non-periodic, random-like, and initial sensitive nonlinear dynamic phenomenon, chaos is an important transmission carrier for secure communication. Aiming at the problem of complex structure and difficult realization of the traditional chaos synchronization method, this paper proposes a neural network method based on Field Programmable Gate Array (FPGA) to synchronize chaos. At the transmitter side, FPGA is used to generate a chaotic signal according to the Lorenz state equation, and the transmission signal is encrypted in real-time mode. The neural network is used to model the chaotic transmitter precisely, and the signal is decrypted by the trained neural network at the receiver side, which is verified on FPGA. Finally, the real-time encryption and decryption of a 10 Mbit/s signal are realized successfully. This method greatly simplifies the synchronization structure of a chaotic secure communication system and makes it possible for point to multipoint real-time chaotic communication.

In view of the complex structure and high cost of traditional chaotic lidar systems, this paper proposes two transmission schemes using Field Programmable Gate Array (FPGA) and Arbitrary Waveform Generator (AWG), based on the improved Logistic mapping formula to dynamically generate digital chaotic signals in real time. The digital signal generated on the electrical domain is modulated to a direct-modulated laser to generate a chaotic signal in the optical domain. Then the chaotic optical signal is used as a lidar transmission signal. Therefore, a complete lidar detection system is built on the optical transceiver system. To measure the distance of an object with a reflectivity of 50%, accurate distance measurement at the centimeter level can be achieved without complicated optical structures. We conduct experiments to compare the ranging effects of continuous and binarized chaotic signals. It is found that the ranging accuracy of binarized chaotic signals is at least doubled than that of continuous chaotic signals. For square wave, sine wave and chaotic interference signals at different frequencies, it has stronger anti-interference ability and shows greater application advantages.

There is a problem of waste of resources in the dedicated path 1+1 protection strategy in the traditional optical network. In this paper, a priority shared link protection strategy is proposed. After detecting the link failure, the flexible optical transponder switches to the shared protection link, and rearranges the service weight according to the priority of the service and the requested frequency, and provides differentiated spectrum slot allocation according to the service weight. In addition, this paper proposes an optimal routing and spectrum allocation method that considering the physical network topology, the set of service requirements, and the proportion of high-quality services as constraints, and considering the minimization of the utilization of spectrum slots as the goal. The theoretical analysis and simulation results show that compared with the traditional 1+1 protection method, the proposed protection strategy can save up to 38% of the spectrum resources while reducing the network congestion rate, and maximizing the sharing of backup spectrum resources.

Aiming at the problem of how edge computing and Content Delivery Network (CDN)edge nodes implementing the resource coordination, the technology and method of CDN cache software adapting to virtual machines and containers are proposed. By comparing and analyzing the performance test data of CDN in three deployment modes of physical machine, container and virtual machine, the performance loss caused by CDN virtualization is evaluated. The performance loss of the container mode is small, and its performance is comparable to the physical machine. The performance loss of the virtual machine mode is large, and its performance is equivalent to about 75% of the physical machine. According to the nominal value of performance, the virtualized CDN edge node can release most of the central processing unit, memory and disk resources, and achieve resource sharing with edge computing.

Aiming at the application of ultra-long-distance monitoring in scenarios such as power transmission lines, this article uses Raman amplification and heterodyne detection based on a distributed optical fiber phase sensitive Optical Time Domain Reflectometer (OTDR) to design a photoelectric signal segmented detection collected optical fiber sensing system. According to the length of the optical fiber, the optical fiber is divided into two sections for signal processing and acquisition, and the corresponding signal processing and acquisition parameters are adapted to different strength signals to solve the problems of insufficient dynamic range and poor signal-to-noise ratio of the ultra-long-distance monitoring system. After testing and analysis, a single-end ultra-long-distance distributed optical fiber monitoring system with a distance of more than 124 km is realized. The signal-to-noise ratio at the end of the system is larger than 10.5 dB.

With the continuous improvement of single carrier transmission rate, it is great challenging to increase the transmission distance in unrepeatered link. This paper demonstrates a unrepeatered transmission of single-carrier 400 Gbit/s over 501.18 km with 78.68 dB span loss using single fiber for the first time. The technology of high-order pumps, forward and backward remote optically pumped amplifier, sub-carrier frequency-division multiplexing and ultra-low & large effective area fiber are used in this experiment. The transmission wavelength, the power of the high-order pump and the location of the remote gain unit are also optimized in this work.

Traditional high-order stepped spiral phase plate that is difficult to fabricate on the fiber end face and easy to damage during the application. In order to solve these issues, a design scheme of flat spiral phase plate fabricated on the fiber end face is proposed. This kind of phase plate has the same height at different azimuth angles, and different topological charges are obtained by controlling the refractive index at different azimuth angles. The Fresnel diffraction theory is used to conduct a detailed theoretical analysis of the vortex electric field distribution and light intensity distribution generated by this scheme. The finite difference time domain method is used to simulate the propagation process of the fundamental mode Gaussian beam in the fiber after passing through the flat spiral phase plate with different topological charge. The results show that this kind of flat phase plate on fiber end face can generate high-quality vortex beams for both high-order and low-order modes, which effectively overcomes the shortcomings of traditional stepped spiral phase plate.

It is difficult to prepare Fiber Bragg Grating (FBG) with integrated structure of core-and-cladding. This paper first analyzes the structure characteristics of FBG with integrated structure. Based on the optical fiber coupled-mode theory, Rsoft and Matlab are used to simulate the reflection spectra of fiber cores, cladding gratings and integrated gratings respectively. The reflection spectrum characteristics of FBG with integrated structure are analyzed in the simulation with different grating period, grating length and modulation depth. The simulation results show that when the grating period is 541 nm and other parameters are fixed, the central reflection wavelength of the separate fiber core and cladding grating is 1 563.4 and 1 558.0 nm respectively, and the integrated grating can obtain the bimodal reflection spectrum with the same central wavelength. The grating period, grating length and modulation depth of the integrated grating have regular effects on the central wavelength, intensity and half high width of the reflection spectrum. The results can provide reference and theoretical support for grating writing and application.

With the demand of data center traffic soaring, many service providers are already working on 400 Gbit/s Ethernet communication systems. Compared with the 100 Gbit/s optical module, the 400 Gbit/s optical module can provide higher transmission bandwidth with lower power consumption and cost. Aiming at the above requirements, this paper proposes a design scheme of 400 Gbit/s optical transceiver module for data center optical communication network system. We first introduce the 400 Gbit/s optical module related protocols and standards. Then we present the general design of the module framework, mainly from the rate of conversion, launch, receive and monitoring 4 parts. Finally, we conduct a performance test and the test results show that the module in accordance with the agreement and the provisions of the standard, which is a good solution to realize data center 400 Gbit/s Ethernet transmission.

In order to solve the signal integrity problem caused by gold bonding wire or flexible printed circuit interconnection between components in optical module, the electromagnetic characteristics of gold bonding wire and flexible printed circuit are analyzed by three-dimensional electromagnetic simulation software HFSS, and the corresponding compensation structure is designed. The electromagnetic simulation results show that the return loss (within 0~20 GHz frequency range) of gold bonding wire interconnects with compensation structure is increased by about 18 dB, and the insertion loss is reduced by 0.10~0.25 dB. The return loss (within 0~20 GHz frequency range) of the flexible printed circuit with compensation structure is increased by about 17 dB, and the insertion loss is reduced by 0.10 dB. The test results show that the optical module with compensation structure has good transmission performance, and the compensation structure can be effectively applied to the design of interconnection structure in optical module.

In current heterogeneous network, the multi-decision attribute vertical handover algorithm is difficult to dynamically adjust the weight value of the network attributes, and thus cannot meet the user’s Quality of Service (QoS) requirements. To solve this issue, this paper aims at accessing the optimal heterogeneous wireless network and guaranteeing the user’s QoS, and proposes an adaptive vertical handover algorithm based on the fuzzy hierarchy-entropy weight method. First, according to user experience, a model of network attribute optimization is constructed by combining subjective fuzzy hierarchical weighting and objective entropy weights. Then, an adaptive mechanism is used to dynamically adjust the weight value of each network attribute according to user experience. Finally, the cost function is used to predict the state of the heterogeneous network to select the optimal wireless network. Simulation experiments verify that the proposed algorithm can effectively reduce the network switching rate, better ensuring the load balancing between heterogeneous wireless networks, and increase the endurance of mobile terminals.

In order to improve the wireless communication capability of large-scale marine unmanned aerial vehicle, the domestic and international development status of airborne wireless laser communication technology and the experimental situation and trend are summarized and analyzed. The application scenarios of the wireless laser communication of large-scale marine unmanned aerial vehicles are planned and conceived and the performance indicators, key technologies and opportunities and challenges of wireless laser communication for large-scale marine unmanned aerial vehicle are analyzed. It provides a reference for the application and development of wireless laser communication for large-scale marine unmanned aerial vehicle in China.

As a beneficial supplement to radio frequency communication, Visible Light Communication (VLC) can provide high-speed, ultra-low delay, green, low-cost, safe and reliable communication services. However, limited coverage range has become the bottleneck of long distance and reliable communication in VLC system. Since the coverage range of VLC is limited, an effective method is proposed to use relay technology in VLC system. The paper starts from the functional characteristics of relay technology, and analyzes the relay system model. Then we give a review on several key technologies of relay-assisted VLC, including the application scenario, network mode, transfer agreement, modulation mode, working mode and non-orthogonal multiple access. The reliable performance, safety and energy efficiency with the corresponding key technologies are analyzed. Finally, we point out a research emphasis and direction in VLC by adopting the heterogeneous network, non-orthogonal multiple access, multi-input and multi-output, full-duplex mode multiple and relays collaboration for the next generation communication network.

The 4th Generation Mobile Communication Technology (4G) Long Term Evolution (LTE) is restricted by the frequency band of 1 785 ~ 1 805 MHz private network in China. Rail transit must ensure stable minimum bandwidth requirements for dual network redundancy configuration and special services, which greatly limits the service capacity of LTE-M integrated bearing system. In view of the above problems, we propose to upgrade the 4G base station, core network and vehicle mounted Terminal Adapter Unit (TAU). and add the 5th Generation Mobile Communication Technology (5G) public network Non-Standalone (NSA) base station. Therefore, 4G private network can be used as the main network of Communication Based Train Control (CBTC) system service, and 5G network is used as the auxiliary network to carry CBTC system. The 5G base station can also be used to carry large bandwidth service of rail transit private network. Our propose solution realizes the integration of 4G private network and 5G public network to carry the large bandwidth requirements of the communication system.