Wavefront Difference And Correction Of Gaussian Beams With Different Wavelengths In Atmospheric Turbulence

Wireless optical coherence detection can improve the ability of optical signal to suppress atmospheric turbulence,and adaptive optical technology can improve the efficiency of optical mixing at the receiving end of the system.The wavefront distortion caused by atmospheric turbulence can be detected directly by signal light or by optical signal with different wavelength from signal light.In this paper,the statistical differences of wavefront of different wavelengths which are affected by atmospheric turbulence are studied in detail.The main contents are:1.The global variance of wave front fluctuation corresponding to different wavelengths is derived when the light wave propagates along the horizontal link near the ground in the atmospheric turbulence environment.In kolomogorov turbulence,based on the atmospheric coherence length related to the optical wavelength in the turbulence,the relationship between the variance of wave front overall fluctuation and atmospheric temperature,pressure,optical wavelength and other parameters is derived.In a certain distance near the ground level link,the variation of ambient temperature and pressure is small,and the variance of wave front overall variation corresponding to different optical wavelength is different.The wavefront fluctuation of short wavelength beam is greater than that of long wavelength beam.2.Using Hankel transform and trigonometric function series approximation,the spatial correlation function,the spatial correlation coefficient and the fluctuation variance of the two wavefronts corresponding to different wavelengths in the aperture of the receiving end are derived when two Gaussian beams with different wavelengths from the same transmitting aperture travel horizontally near the ground and pass through the atmospheric turbulence.The results show that the correlation degree of wavefront corresponding to the two wavelengths decreases with the increase of transmission distance,and the influence of turbulence internal scale on the correlation degree of wavefront corresponding to the two wavelengths is the main factor,while the influence of turbulence external scale is relatively small.The variance between the wavefront corresponding to the two wavelengths decreases with the approaching of the two wavelengths,and increases with the increasing of the wave front transmission distance.3.The influence of the adaptive optical system on the wavefront correction of different wavelengths is analyzed after the beam is transmitted horizontally near the ground.Theoretically,the centroid deviation of the spot caused by the dispersive effect of microlens array on different wavelengths in the wavefront sensor is analyzed,which makes the corresponding wavefront slope of different wavelengths different.At the same time,the limitation of the correction resolution of deformable mirror to the correction of wavefront is analyzed,and the correction residual variance of deformable mirror size to the correction of wavefront corresponding to one wavelength and another wavelength is derived.Finally,the limitation of Greenwood frequency to adaptive optics is analyzed.The system should meet the Greenwood frequency corresponding to the larger of the two wavelengths to make the system work continuously and normally.4.In order to improve the correction effect of the adaptive optical system in two wavelengths theoretically,when the wavelength of the target light and the wavelength of the beacon light are different,the ratio of the fluctuation variance of the target correction wave front to the fluctuation variance of the beacon light front is proposed as the correction feedback information of the adaptive optical system to drive the deformable mirror to correct the correction system of the target light front Number.The correction coefficient obtained from the parameters such as the size of the deformable mirror is loaded into the deformable mirror type control.Compared with the state of direct correction,the Strehl ratio after the correction coefficient is gradually rising and finally tends to the ideal state of complete correction,which improves the correction efficiency of self-adaptive optical dual wavelength operation in theory and improves the performance of the receiver of free space optical communication system Space fiber coupling power has further optimization and promotion.The results show that the variation of distorted wavefront corresponding to different wavelengths in horizontal transmission is small,and the fluctuation of wavefront corresponding to long wavelength is less than that corresponding to short wavelength.When the wavefront corresponding to two wavelengths is transmitted in atmospheric turbulence,the influence of inner scale of turbulence is far greater than that of outer scale of turbulence;when the two wavelengths are similar,one wavelength is used The effect of wave front correction before and after the wave corresponding to another wavelength is better.The wave front correction distance has an important influence on the wave front correction corresponding to different wavelengths.The closer the wave front correction is to the ideal situation,the more obvious the effect of turbulence internal scale on the correction of wave front with this different wavelength is affected by turbulence internal scale;the fluctuation variance and exploration of corrected wave front are adopted As a correction coefficient,the ratio of the variance of the wavefront fluctuation can improve the correction efficiency in theory.