Based on periodically poled lithium niobate, a scheme for optical signal temporal cloak and encryption in the optical physical layer is proposed and numerically studied, in which the amplitude and phase information of the symbols to be sent are detected and transmitted while that of all other symbols will be hidden from the receiver. Meanwhile, the phase and amplitude of the symbols that are not hidden can be encrypted according to arbitrary encryption rules in the optical physical layer. The simulation results show that there is almost no ripple in the cloak time window, which makes the performance of temporal cloak quite well. The output signals with high Q factor can be obtained when the linewidths of the tunable lasers are <300 kHz. Two simple encryption rules are designed, 43.75% of binary codes will be misinterpreted by eavesdropper if the signal is encrypted with such two rules in the demonstration.
Internal wave is a dominant source of ocean uncertainties in shallow waters. The ability of passive source localization may be degraded due to mismatch between model predictions and measurements caused by the activities of internal waves. Using ocean environment measurements from an experiment, the effects of Garrett-Munk and solitary internal waves on the temporal correlation of matched-field processing (MFP) in shallow water for sources with different frequencies and different depths are numerically investigated. It is shown that the temporal correlation of MFP decreases as the amplitude of solitons or the average energy density of linear internal waves increased. For a source with lower frequency or located below the thermocline, the temporal correlation of MFP is less affected by internal waves, and the length of which is longer. Moreover, the effects of the range between solitons and source on the temporal correlation of MFP are relatively small.
Relationships among the signal coherence-time of matched-field processing (MFP), the acoustic frequency, the source-receiver range, and the sound speed standard deviation (STD) caused by internal waves in shallow water, are numerically investigated based on oceanographic data from two shallow water experiments. It is found that the coherence-time can be fitted with an inverse square-root power of range, a near inverse 1 power of frequency, and inverse 1.3 power of sound speed STD.
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