Eavesdropping Receiver Performance With Bandwidth Limitation In Optical Coherent Communication Systems

With the rapid development and widespread application of optical fiber communications, it has become an important task for eavesdropper to intercept information from fiber. In addition to the current technology about optical tapping and decryption, an important aspect is to improve the performance of eavesdropping receiver in optical fiber communication system. As the continuous increase of transmission bandwidth in optical networks, available electronic devices cannot meet the bandwidth requirements of high speed transmission system. Therefore, it’s indispensable to improve the performance of eavesdropping receivers in the presence of bandwidth limitation which can reduce additive noise power but also induce ISI. Thus it’s necessary to study the effect of bandwidth limitation on received signals.Firstly, this paper introduces the development of eavesdropping technologies in optical fiber communication, and analyzes the significance of eavesdropping combining with the advantages of optical coherent communication. The eavesdropping system is set up and noises are discussed in the process of intercept. In addition, DAML phase estimation algorithm is introduced and analyzed in this paper.Secondly, optical coherent eavesdropping receiver model with limited bandwidth is established and equivalent filter model about bandwidth limitation is given. The interferences of other symbols on current symbol are analyzed. The symbol SNR is redefined and BER of DAML phase estimation receiver is derived in the case of bandwidth limitation. Meanwhile, the optimum sampling timing offset and bandwidth are also derived.Finally, simulations are performed to analyze the performance of DAML eavesdropping receiver. We find that the maximum SNRs per bit we defined correspond to the minimum BER under different bandwidth. And the influence of different emulate filter types on receiver performance is discussed. Simulation results show that the optimum sampling timing offset and bandwidth are different with different type of filter, and the linewidth of laser has no effect on the optimum sampling timing offset and bandwidth. In addition, the BERs obtained from simulation in QPSK system is compared with theory ones. Results show that we can use the approximate analysis BER to analyze the optimum performance of eavesdropping receiver.