Transmission Characteristics Of Partially Coherent Optical Carrier In The Atmosphere

Compared with microwave communication,free space optical(FSO)communication has the advantages of higher modulation rate,wider bandwidth,and does not occupy spectrum resources;compared with optical fiber communication,it has short construction period,low cost,flexible installation,etc.advantage.However,the biggest disadvantage of free-space optical(FSO)communication is that it is more severely affected by atmospheric channels,causing problems such as power attenuation,beam drift,beam expansion,and light intensity flicker.For a long time,due to the influence of atmospheric turbulence,the development of long-distance FSO communication has encountered obstacles.Many studies from theoretical analysis and numerical simulation have shown that some coherent beams are less affected by turbulence than coherent beams.There are many methods to generate partially coherent light,mainly including extended light sources,spatial light modulators,and rotating random phase screens.However,the partially coherent light source produced by the above-mentioned means cannot easily achieve Gbps-level high-speed modulation,and therefore cannot be applied to FSO communication systems with higher modulation rates.The supercontinuum light source generated by using the ultrashort pulse fiber laser to pump the nonlinear fiber can not only exert its partial coherence advantages to resist the influence of the atmospheric channel on the FSO communication system,but also use its high repetition frequency to achieve High-speed modulation of the carrier light source.This paper mainly proposes a high-repetition frequency partially coherent optical carrier and studies its transmission characteristics in simulated atmospheric channels.This article mainly completed the following work:1.According to the principle of supercontinuum light source generation,an active mode-locked fiber laser with a repetition frequency of 4 GHz was experimentally studied as a supercontinuum pump light source.After Raman soliton compression,the pulse width is changed from 38 ps to 4.2 ps.This ultrashort pulse is used to pump the highly nonlinear fiber to obtain a supercontinuum broadening.2.Based on the measurement principle of the coherence of the supercontinuum light source,the Mach-Zehnder interferometer and the Michelson interferometer were experimentally studied respectively.The coherence degree was calculated to be 0.352 through the interference pattern of the supercontinuum light source,which confirmed the obtained The supercontinuum light source has partial coherence and is a typical partially coherent light source.3.A method for generating a partially coherent light source with a repetition frequency of 10 GHz is proposed.Through experiments,a partially coherent optical carrier based on spectral nonlinear broadening has been realized.The transmission rate of a single channel in the turbulence simulation system is as high as 10 Gbit/s,and its flicker factor,eye signalto-noise ratio and bit error rate in the turbulence simulation system Research on transmission characteristics.When the temperature difference between the upper and lower boards of the atmospheric turbulence simulation system is "?T=230 ?",the signal-tonoise ratios of the coherent optical carrier and the partially coherent light source carrier are reduced by 12.52 d B and 6.19 d B,respectively,and the sensitivity of the partially coherent optical carrier link at this time Improved by 1.6 d B.