Quantum access network can't guarantee the absolute security of multi-user detector and eavesdropper can get access to key information through time-shift attack and other ways. Measurement-device-independent quantum key distribution is immune from all the detection attacks, and accomplishes the safe sharing of quantum key. In this paper, that Measurement-device-independent quantum key distribution is used in the application of multi-user quantum access to the network is on the research. By adopting time-division multiplexing technology to achieve the sharing of multiuser detector, the system structure is simplified and the security of quantum key sharing is acquired.
The bit error rate is raised by the presence of the noise when the quantum key transmits in practice. So both sides of communication can not judge the presence of eavesdropping. For this issue, an improved scheme based on BB84 protocol is proposed by a paper of Luanxin that a matrix transformation is carried out for every quantum of both sides. The advantage of the transformation is that the eavesdropper can be found easily. But the disadvantage is that it leads to a low key generation rate. In this paper, an improvement that a matrix transformation is carried out randomly for the quantum of both sides based on the scheme of Luanxin is proposed. The result shows that not only the presence of eavesdropping can be judged easily, but also the key generation rate is increased significantly.
Based on non-regenerative relays, the bit error probability expressions of CSI-assisted relay and
fixed-gain relays for high altitude platform multi-hop optical communication is given. The effect of the factors, including
atmospheric turbulence pointing error and relay node position, on the performance of multi-hop optical links is analyzed.
The simulation results show that the influence of atmospheric turbulence on optical links is greater than that of pointing
error. The improvement of average SNR per hop and transmit power on multi-hop optical communications may be
restricted by pointing error. Compared to CSI-assisted relay, fixed-gain relay is suited to more hops links with the
condition of high average SNR per hop.
Based on Navier-Stokes equations, numerical simulations of air-breathing mode laser propulsion by nanosecond laser
pulse are carried out. An analytical model of the thruster's inner flow involving the simple processing of the ignition
zone is established. The evolvement of the laser sustained plasma shockwaves is systemic analyzed; also the effects of
pulse energy and thruster's structure such as focal length, scale and open angle on propulsion performance are
researched. The simulated results show that the focal length dominates among the structural factors of thruster in the
propulsion by nanosecond laser pulse. The larger focal length leads to better propulsion performance. It is also evident
that for single pulse propulsion, nanosecond laser pulse is better than microsecond laser pulse, the momentum coupling
efficient achieved by the former is 2~5 times of the latter's, which is highly agree with the existing experimental results.
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 system's 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.
Based on the rate equations and light propagation equations, a novel theoretical model of double-cladding erbium-ytterbium co-doped superfluorescent fiber source (SFS) in double-pass forward (DPF) configuration has been presented. By optimum choosing the fiber length and pump power, the characteristics including mean wavelength stability, threshold, output power, and bandwidth of the SFS are theoretically analyzed in details. The effects of the variation in pump wavelength on the system performance are also been investigated. The analysis results show that a double-cladding erbium-ytterbium co-doped SFS in DPF configuration may serve as light source for the navigation-grade fiber-optic gyroscope applications.
In this paper, the operation principle of the broadband Er-Tm co-doped silica fiber amplifier when pumped at 980nm is presented. Numerical analysis of this broadband Er-Tm co-doped silica fiber amplifier has been performed based on the rate and propagation equations. The signal amplification gain as functions of the fiber length, the input pump power, the erbium-thulium concentration, as well as the pumping ways is described. The results show that the erbium- thulium co-doped silica fiber amplifier could provide more than 80 nm effective gain bandwidth, which is twice larger than the conventional singly erbium-doped fiber amplifier. The minimum gain value exceeds 9 dB when the launched pump power is higher than 400 mW. These results could be useful for the optimized design of DWDM amplifier in the near future.
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