A triple-wavelength erbium-doped fiber laser based on seven-core fiber (SCF) interferometer is proposed and successfully implemented. In the structure of the laser, a special structure of single-seven-single core is used to realize laser interference, which is composed of a 6 cm SCF and ordinary fiber optic patch cables fused by convex cone. In the laser with simple structure, triple-wavelength output with central wavelengths of 1530 nm, 1544 nm and 1558 nm are obtained by adjusting the polarization controller, and the optical signal-to-noise ratio (OSNR) of the triple-wavelengths is approximately 60 dB. The laser has high stability in terms of both wavelength and power. In the stability test of 150 min, the frequency drift of three wavelengths is approximately 0.4 nm, and the output wavelength peak power jitter is approximately 1.6 dB. The laser has the characteristics of simple structure and high stability, and has broad application prospects in the fields of optical fiber sensing, wavelength division multiplexing (WDM) optical communication system and microwave photonics.
The scheme of optical digital-to-analog conversion based on weighted fiber coupler is proposed. The simulation results show that when the output signal without filter, the time domain waveform is interfered by beat noise, and the function of optical digital-to-analog conversion cannot be realized. Fortunately, the beat noise is concentrated in the high frequency region which is more than 100GHz by setting the wavelength interval of the directly modulated laser array, and it can be removed effectively by the low-pass filter. However, some peak interference will appear at the time of signal alternation. When the filtering processing matching with the bandwidth of the transform signal, the peak interference can be suppressed. Finally, the optical digital-to-analog conversion with signal rate of 10Gbps and quantization accuracy of 5 bits can be realized.
The statistical characteristics of quantum noise stream cipher system is investigated. Simulation results shows that with the variance of the noise σ2 is changed from 0 to 0.3, the statistical parameter of signals decreases to the floor. When the variance of the noise is more than noise masking threshold, the statistical characteristic of signals is completely submerged in noise. Moreover, when the variance of the noise is equal to {0.001, 0.01}, PB =1 is unchanged with the increase of modulation order. Furthermore, when the variance of the noise is equal to {0.1, 0.2}, the correct probability for Bob PB decreases to a fixed value which is 0.99 and 0.79, respectively. Correspondingly, the correct probability for Eve PE decreases to 0 with the modulation order increasing. And the channel advantage for main channel over wiretap channel can be formed by combining proper modulation order with noise.
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