Yongjun Li

Scheduling algorithm for data relay satellite optical communication based on artificial intelligent optimization

Optical satellite communication with the advantages of broadband, large capacity and low power consuming broke the bottleneck of the traditional microwave satellite communication. The formation of the Space-based Information System with the technology of high performance optical inter-satellite communication and the realization of global seamless coverage and mobile terminal accessing are the necessary trend of the development of optical satellite communication. Considering the resources, missions and restraints of Data Relay Satellite Optical Communication System, a model of optical communication resources scheduling is established and a scheduling algorithm based on artificial intelligent optimization is put forwarded. According to the multi-relay-satellite, multi-user-satellite, multi-optical-antenna and multi-mission with several priority weights, the resources are scheduled reasonable by the operation: “Ascertain Current Mission Scheduling Time” and “Refresh Latter Mission Time-Window”. The priority weight is considered as the parameter of the fitness function and the scheduling project is optimized by the Genetic Algorithm. The simulation scenarios including 3 relay satellites with 6 optical antennas, 12 user satellites and 30 missions, the simulation result reveals that the algorithm obtain satisfactory results in both efficiency and performance and resources scheduling model and the optimization algorithm are suitable in multi-relay-satellite, multi-user-satellite, and multi-optical-antenna recourses scheduling problem.

Markov process based reliability model for laser diodes in space radiation environment

Abstract The reliability of laser diodes is a prerequisite for use in satellite optical communication systems, which is significant influenced by both displacement damage effect and annealing effect. A reliability model was proposed to evaluate the reliability and lifetime for laser diodes in space radiation environment. Degradation process is separated into discrete states, and reliability model is subsequently established based on Markov process. The Markov process consists of a Poisson process and an exponential process, representing the displacement damage effect and annealing effect, respectively. Reliability characteristics of a given laser diode are simulated over 100,000xa0h, and applicability of this reliability model is demonstrated by analyzing the variety trend of probability density of performance states.

High power high brightness laser source for material processing through incoherent beam combination

With the continuous increase of output power of double cladding fiber lasers, more effort is put into the researches of the technique of fiber laser beam combination, especially for incoherent laser beam combination because it is easier and with better system stability. Once high power output laser beam is achieved, there would be broad applications in industry, especially for manufacturing and material processing. The combination systems coupling efficiency plays an important role in determining the output power. Through theoretical analysis and numerical simulations, it has been proved that lower lateral off-set and higher grating period would be favorable, also an optimum spot radius exists which corresponds to a maximum value of coupling efficiency. Although lower focal length is helpful in improving the coupling efficiency, there is a contradiction that it makes a narrower fiber array width, which would limits the number of fiber lasers that could be utilized. Thus a moderate value of 20cm is chosen. Based on such optimized parameters, the beam quality M2 is around 2, also a method of two parallel gratings is introduced, which ensures the M2 factor to be around 1. Such combined fiber laser would be of great potential applications in manufacturing and material processing.

Performance research of multiple access of satellite formation flying laser communication in atmospheric turbulence

A novel multiple access model of satellite formation flying is brought forward, which has the advantages of shared signal bandwidth, asynchronous access etc, at the same time it overcomes the problems of difficulty of constructing the addressing codes in the optical code division multiple access and that of hardware implementing in wavelength division multiple access. The model makes use of delay difference between two arms of Mach-Zender interferometer (MZI) to encode and decode at the end of transmitter and receiver respectively, thats to say when the delay difference of receiving end is close to that of transmitting end, the received optical power would be maximum. Frequency shift keying modulation is adopted to achieve the coherent multiplexing multiple access. Then when the micro-satellite beam is transmitted in atmosphere condition of weak turbulence, the receiving optical field is described by the Rytov model based on the premise of independent optical field interference, the formula of SNR and BER is deduced. The simulation results show that given the turbulence amplitude, 1/SNR ascends along with increasing of satellite number, furthermore the larger turbulence amplitude, the more quickly 1/SNR rises, this proves number of satellites and turbulence amplitude are the dominating parameters which affect the system performance.

The optimization of incoherent fiber laser beam combination

With the continuous increase of output power of double cladding fiber lasers, the researches of the techniques of fiber laser beam combination have become a new focus. With the inherent characters of small volume, light weight, good beam quality and system stability. Once the high power output laser was achieved, there would be broad applications in industry, scientific researches and military field. Incoherent beam combination is much easier to be realized compared with coherent beam combination, and with better system stability, thus it became an promising technique to achieve small volume and high power laser source. In an incoherent fiber laser beam combination system, the transform lens and diffractive grating play an important role in determining the coupling efficiency. Through theoretic analysis and numerical simulations, it has been proved that the optimum focal length of transform lens should be around 20cm in order to ensure a high system coupling efficiency under some selected simulation parameters. Also the lower frequency of diffractive grating is preferred, and a contradiction is present that is the higher frequency of diffractive grating is favorable in the consideration of maximum fiber array width, thus a moderate value was chosen as 200mm-1 with comprehensive consideration. The lower grating thickness is helpful in improving the diffractive efficiency, while it faced the problem of heat resistance and manufacturing difficulty, therefore the grating thickness between 2mm and 4mm is preferred. Under such optimized parameters, the coupling efficiency would be 70% or even higher with small deviation angle and wavelength. An example of effective jamming distance of combined fiber laser to visible light silicon CCD has been given, whose results had proved the application foreground of combined fiber laser.