针对机间光通信中的附面层效应问题,通过对附面层结构的分析,将飞机舱壁外侧附面层视为负透镜,在飞机高速机动和高空大气条件下,对其在机载光通信光束传播中的聚焦效应进行了仿真研究.结果表明:保持飞行高度不变,随着飞行马赫数的增加,附面层的聚焦效应增强.位于海平面高度,马赫数为2以上的飞行平台,附面层焦距和平台曲率半径的比值-F/Rs下降到8以下;当海拔升高到10 km和15 km,该比值可分别达到16和25;当-F/Rs达到6.3以上,则可满足通信误码率条件.

Performance of optical inter-satellite communication system is influenced by the harsh space radiation environment. Gamma radiation effects on main devices of communication system are analyzed and on the basis of existing experimental data, performance degradation of on off keying (OOK), differential phase shift keying (DPSK) and homodyne binary phase shift keying (BPSK) based system under 1kGy gamma irradiation is simulated. Variation of Q factors and bit error ratio of these systems with different radiation position are achieved and discussed. The result shows that it is more urgent to improve the radiation hardness of transmitter, and the introduction of local laser is a considerable method to reduce gamma radiation impact on system performance.

Aiming at the characteristics of dynamic routing and limitation on power in satellite optical network, a wavelength-shift-free regenerative scheme based on two-stage offset filter is put forward. Making use of the property that the signs of chirp induced by self-phase modulation are opposite in semiconductor optical amplifier (SOA) and high nonlinear fiber (HNLF), the scheme imposes a red-shifted filter and a blue-shifted filter respectively on the signals after SOA and HNLF, which not only realizes a two-stage regeneration for signals, but also compensates the frequency offset and keeps the wavelength unchanging before and after the regenerator. The results show that the Q factor of signals can be improved 6 dB, and the timing jitter caused by one-stage offset filter can be suppressed effectively.

According the defects that genetic algorithm easily falling into local optimum and ant colony optimization is little initial pheromone information, the fusion algorithm of genetic and ant colony was proposed for the resources scheduling problem. The definition of ant colony optimization pheromone was improved. The idea of coding based on the serial number of time windows was used. The restrictive condition and the objective function of the resources scheduling was given and the mathematical model was established. The optimization characteristics of fusion algorithm, standard genetic algorithm and modified ant colony algorithm were analyzed by simulation. The result shows that it is quite good to solve the relay satellite scheduling problem by using the fusion algorithm.

A generalized intersatellite microwave photonics links model to study the influence of the modulation index of Mach–Zehnder modulator on the receiver sensitivity with multiple radio frequency (RF) signals is presented. An exact analytical solution of signal-to-noise and distortion ratio (SNDR) for optical double-sideband (ODSB) and optical single-sideband (OSSB) modulation is deduced with Bessel expansion and Graf's addition theorem. Numerical results show that the receiver sensitivity increases and then decreases as the increase in modulation index, there is an optimum modulation index that maximizes the receiver sensitivity and the larger channel numbers lead to lower receiver sensitivity for maintaining the SNDR at the desired level. In addition, ODSB modulation can be more attractive than OSSB modulation in intersatellite microwave photonics links, since the maximum receiver sensitivity for ODSB modulation is better than that for OSSB modulation.

The intersatellite microwave photonics link with an optical preamplifier is affected by third-order inter-modulation distortion under dual-tone modulation and pointing errors due to beam wander, which would greatly degrade the link performance. An exact analytical expression for signal-to-noise and distortion ratio (SNDR) is derived considering the signal fade caused by the pointing errors of transceiver. It is shown that, given the desired SNDR and the rms random pointing jitter, an optimum modulation index of Mach-Zehnder modulator exists that minimizes laser output power. Moreover, an optimized model for laser output power and modulation index is established. The effects of the optical preamplifier gain and noise figure on the optimum link performance are also examined. Numerical results show that the minimum laser output power required to achieve the desired SNDR is more sensitive to the preamplifier noise figure. For an SNDR of 20 dB, doubling the preamplifier noise figure results in an 8.95 dB increase in minimum laser output power at the rms pointing jitter of 0.5 mu rad. (C) 2013 Optical Society of America

考虑到星间微波光子链路传输损耗大且多路微波信号之间交调干扰严重,利用前置光放大来提高链路的信号噪声失真比RSNDR.建立了两路输入前置光放大星间微波光子链路模型,推导出了RSNDR的解析表达式.通过优化马赫-曾德尔调制器的直流偏置相移,使得在给定输入射频信号功率条件下RSNDR最大,并进一步分析了前置光放大器参数对最优直流偏置相移和RSNDR的影响.仿真结果表明,前置光放大改变了影响RSNDR的主要因素,使信号放大的倍数大于噪声和三阶交调(IM3)放大的倍数,从而提高了链路的RSNDR.当前置光放大器增益为20 dB、噪声系数为3 dB时,最优的RSNDR比不加前置光放大器时提高24 dB.前置光放大器增益和噪声系数对最优的RSNDR影响很大,而对最优的直流偏置相移几乎无影响.

A dual-tone modulation inters atellite microwave photonics link model was presented including optical source,Mach-Zehnder modulator,erbium-doped fiber amplifier and photodiode.An exact analytical solution for any harmonic and intermodulation components at the output of the detector was deduced with the method of bessel expansion,fourier transform/inverse fourier transform and graf addition theory,thus,the expression of SNDR was derived considering the effects of third-order intermodulation distortion(IM3).The SNDR,fundamental and IM3 power varies with the radio frequency(RF) input power under different modulation modes was analyzed.Numerical results indicate that the SNDR, fundamental and IM3 power increases and decreases as the increase of RF input power,there is an optimum RF input power that maximize the SNDR.The SNDR of double sideband modulation is larger than single sideband modulation under the same RF input power and it is suitable for the application of intersatellite microwave photonics link.

The charge coupled device (CCD) is the key component of beacon light subsystem in optical satellite communication system. The influences of the space radiation environment on the CCD's charge transfer efficiency (CTE) and its dark current are theoretically analysed. Based on the analysis the induced CTE and dark current degradations under some typical operation temperatures and particle fluences are numerically calculated. Its further influences on the system bit error ratio (BER) are also discussed. The calculation results have proved that adding shielding layers and a temperature controlling unit are both efficient ways to improve the radiation hardness of an optical satellite communication system.

The choice of station's address,interval and number of stations in ground station's space diversity technology is investigated by modeling optical link for satellite-to-ground optical communication.The result of research shows,reasonable choice of station's address can improve the availability of satellite-to-ground optical communication link;the interval of stations should ensure the weathers at different stations are uncorrelated but not too long;the attenuation resulted from zenith angle is more than 10 dB when the ratio of interval and altitude of satellite is larger than 1;the necessary amount of stations is smaller if the availability of single ground station is higher;only 3 stations are needed with equivalent availability of microwave link when the availability of single station is 0.6.

The light emitting diode(LED) is one of the key components in the optical satellite communication system,whose performance determines the reliability of the communication system.The theoretical analysis of the minority carrier′s lifetime and output power of LED device under particle radiation is made.The numerical simulation is also done based on the theoretical analysis.The calculation results prove that the increase of the doped Zn density in the active area of LED can effectively decrease the radiative lifetime of the minority carrier and it also can improves the LED′s anti-radiation performance while heightening its output power.

We propose a novel optical carrier suppression (OCS) millimeter-wave generation scheme with data carried only by one sideband using a dual-drive Mach–Zehnder modulator (MZM) in radio-over-fiber system, and the transmission performance is also investigated. As the signal is transmitted along the fiber, there is no time shifting of the codes caused by chromatic dispersion. Simulation results show that the eye diagram keeps open and clear even when the optical millimeter-waves are transmitted over 110km and the power penalty is about 1.9dB after fiber transmission distance of 60km. Furthermore, due to the +1 order sideband carrying no data, a full duplex radio-over-fiber link based on wavelength reuse is also built to simplify the base station. The bidirectional 2.5Gbit/s data is successfully transmitted over a 40km standard single mode fiber with less than 0.8dB power penalty in the simulation. Both theoretical analysis and simulation results show that our scheme is feasible and we can obtain a simple cost-efficient configuration and good performance over long-distance transmission.

As the key terminal,the performance of PIN detector affects the stability and reliability of the optical satellite communication system.The properties of γ radiation and particle radiation of PIN detector under space radiation environment were researched.The results show that both radiation mechanisms impose effects on PIN detector,expressing as the increase of dark current noise and decrease of both responsivity and response bandwidth.It is indicated that the influence of space radiation on dark current noise should be the first factor to be considered in the design of optical satellite communication system.

An exact analytical expression of the signal-to-noise ratio (SNR) for an intersatellite microwave photonics link with an optical preamplifier is derived considering the signal fade caused by the pointing errors of the transceiver, and an optimized model for laser output power and direct current (DC) bias phase shift of the Mach-Zehnder modulator is established. It is shown that, given the desired SNR and the root mean square (rms) random pointing jitter, an optimal DC bias phase shift exists that minimizes laser output power. The effects of the optical preamplifier parameters on the minimum laser output power and optimal DC bias phase shift are also examined. Numerical results show that the preamplifier noise figure determines the minimum laser output power needed to achieve the desired SNR but affects the optimal DC bias phase shift little. For a SNR of 20 dB, doubling the preamplifier noise figure results in a 6.36 dB increase in minimum laser output power for rms pointing jitter of 0.4 μrad.

To improve the space anti-radiation performance of the optical satellite communication system, the research of the influence on its system bit error ratio(BER) under space radiation environment was developed. The radiation-induced BER model was established, based on which the BER numerical calculations after the radiation damage of either optical source or optical detector were developed. The calculation results have proved that both γ and proton radiations can degrade the system BER by several levels, some suitable radiation shielding equipments are further needed.

Wideband and reliable satellite communication systems will mix microwave and optical links in the future.The microwave photonics technology,which integrates the flexibility of microwave communication and low loss and wide band of optical transmission,could be used to solve the problem of information fusion brought by existence of both microwave and optical communication types.The basic concept of on board microwave photonics technology is introduced.The new research progress of microwave photonics key techniques applied to satellites such as optical generation of microwave signals,microwave photonics repeater,high-throughput optical interconnect,intra-satellite optical wireless links and optical amplification of microwave signals are reviewed,and the research expectations to be further focused on are also presented.

The laser source is the key terminal in optical satellite communication system,whose performance affects the stability and reliability of the communication system.The theoretical research of the threshold current density for GaAs and InP laser source under space radiation environment was made.The numerical calculation results show that the change of the threshold current density is proportional to the irradiated particle flux,and the InP laser source is better than GaAs′s in the aspect of anti-space radiation.Further study was extended for vacuum environment.It shows that the influence is not obvious under this condition.The main influence is the shift of the central wavelength.

To verify the potential space radiation-induced degradation of optical satellite communication system, the γ ray radiation experiments of its key components have been developed. No obvious performance degradations of the DFB laser and photo detector module were found at the total dose less than 150krad. The EDFA seems to be the most radiation sensitive, and it comes to its malfunction through the radiation of 16.2krad. It is believed that the high energy particles’ radiation effect should be first considered when it refers to the optical terminals’ applications in the space.

The charge coupled device（CCD） is the key component of the beacon subsystem in optical satellite communication system,so its efficiency determines the performance of the communication system.The capture time constant and emission time constant affecting the charge transfer efficiency under three typical bulk traps were determined.The variations of charge transfer inefficiency with temperature,traps energy,read-out frequency,particle fluence and signal charge density were achieved,which could be the foundation for the further researches of space radiation characteristics of the optical satellite communication system.

To improve the space anti-radiation performance of the optical satellite communication system,the research on the space radiation environment′s influence on system bit error ratio(BER)is carried out.The radiation-induced BER model is established,based on which the BER numerical calculations after the radiation damage of either optical source or optical detector are developed.The calculation results have proven that both γ radiation and proton radiation can degrade the system BER by several order of magnitude.It points out that some suitable radiation shielding measures or homodyne BPSK mode are needed.