CN102289076B - Method for designing light source for restraining turbulence influence in atmospheric channel - Google Patents

Abstract

The invention provides a novel method for designing a light source and belongs to the field of space laser communication. By the method, the aim of restraining influence of atmospheric turbulence on communication quality can be fulfilled. In the invention, the light source of a transmitting end adopts a radial light beam array, and after a laser of the transmitting end is transmitted through an atmospheric channel, the root-mean-square light beam width of a receiving end is obtained according to a light transmission principle and called light beam width for short. By analysis of the light beam width, the optimum light beam array parameter which corresponds to the minimal value of the light beam width is obtained, and the transmitting end finishes optimization of the light beam array. Moreover, our research also shows that: when the number of light beams is large enough, the optimum radial light beam array is equal to a hollow light beam, so that the hollow light beam which realizes the optimum light beam array function is required to meet the situation that the radius of a bright ring is unchanged; and another important research result of the invention is adjustability of the radius of a hollow area. The method for designing the light source has an important significance for improving the quality of the space laser communication.

Description

The light source design method that suppresses Turbulent Flow Effects in a kind of atmospheric channel

One, technical field

The invention belongs to the laser space communication field, particularly a kind of light source design method that in atmospheric channel, suppresses Turbulent Flow Effects by regulating the annular radii of beam array radially, and the experimental provision of realizing described beam array.

Two, background technology

Since the laser appearance of the sixties in last century, laser is in monochromaticity, directivity, the advantage of coherence and brightness aspect has determined that laser space communication and Radio Frequency (RE) communication compares with the obvious advantagely, and high such as transmission code rate, antijamming capability is strong, safe, frequency is not subjected to control, and equipment volume is little, and energy consumption is low.People have begun star ground, the laser link such as absolutely empty are carried out theoretical simulation, have meanwhile also carried out the research work such as gordian technique and lecture experiment.Atmospheric turbulence is a kind of random medium heterogeneous, usually regard the set that comprises various yardstick vortexs as, when laser passes through atmospheric turbulence, wave front and vortex interact, cause light wave to produce the turbulence effects such as arrival angle fluctuation, drift, expansion and light intensity fluctuation, all will exert an influence to speed, bandwidth and the bit error rate etc. of laser space communication system.

Therefore, the Atmospheric propagating effects of laser (Li Xiaofeng, Jiang Dagang, Deng Ke, Hu Wei, 201010115486.5) and atmospheric turbulence parameter measurement (Zhang Bin, but have complete a kind of method of testing of lightwave transmission characteristics in atmospheric channel, number of patent application:, Pan Pingping, Qi Na is based on M ²The factor and light scintillation index are determined atmospheric turbulence parametric technique and device, number of patent application: 201010533777.6) more and more be subject to people's attention, become the focus of FreeSpace Laser Communications Technique area research.Simultaneously, the beam array that is widely used in high power system and the inertial confinement fusion also is introduced in the propagation in atmosphere research, has mainly studied linear and radially beam broadening and the beam quality (M of beam array ²-the factor and Rayleigh distance) etc., such as document P.Zhou, Y.Ma, X.Wang, H.Zhao, and Z.Liu, Opt.Lett.35,1043-1045,2010 and X.Li, X.Ji, and F.Yang, Optics﹠amp; Laser Technology 42,604-609,2010.Therefore, if can work out a kind of simply and accurately method of definite optimum beam array parameter, and the experimental provision of realizing described method, so to improving the laser space communication quality with significant, this is task of the present invention place just.

Three, summary of the invention

1, purpose

The objective of the invention is to study the light source design method that suppresses Turbulent Flow Effects in a kind of atmospheric channel, and the experimental provision of realizing described method, the design of this light source can suppress atmospheric turbulence to the impact of light transmission, significant to improving the laser space communication quality, the simultaneously design of this light source is adjustable.

2, technical scheme

Basic thought of the present invention is the basic theories from light transmission, adopts non-Andrei Kolmogorov atmospheric turbulence model and Gaussian beam array radially, as shown in Figure 1, studies the root mean square width of light beam of receiving end.In the situation that relevant synthetic, the cross-spectral density function of transmitting terminal is:

$w^{\left(0\right)}(x_1,y_1,x_2,y_2,z=0)=\underset{m=0}{\overset{N-1}{\mathrm{\Σ}}}\underset{n=0}{\overset{N-1}{\mathrm{\Σ}}}\exp [-\frac{{(x_1-r_0\cos {\mathrm{\θ}}_m)}^2+{(y_1-r_0\sin {\mathrm{\θ}}_m)}^2}{w_0^2}]$

$\×\exp [-\frac{{(x_2-r_0\cos {\mathrm{\θ}}_n)}^2+{(y_2-r_0\sin {\mathrm{\θ}}_n)}^2}{w_0^2}],---\left(1\right)$

Wherein, w ₀The waist width of Gaussian beam, r ₀The annular radii of beam array radially,

J=0,1,2 ..., N-1, N 〉=2,

Be the angle between adjacent two light beams.

According to the Huygens-Frensel principle of broad sense, the root mean square width of light beam of receiving end is:

$<I(x,y,z)>={\left(\frac{k}{2\mathrm{\&pi;z}}\right)}^2{\&Integral;}_{-\&infin;}^{\&infin;}{\&Integral;}_{-\&infin;}^{\&infin;}{\&Integral;}_{-\&infin;}^{\&infin;}{\&Integral;}_{-\&infin;}^{\&infin;}{w}^{\left(0\right)}(x_1,y_1,x_2,y_2,z=0)$

$\&times;\exp \left\{\frac{\mathrm{ik}}{2z}\right[{\left({x-x}_1\right)}^2+{\left({y-y}_1\right)}^2-{\left({x-x}_2\right)}^2-{\left({y-y}_2\right)}^2\left]\right\}$

$\&times;<\mathrm{ex}[\mathrm{p\&psi;}(x,y,x_1,y_1)+{\mathrm{\&psi;}}^{*}(x,y,x_2,y_2)]>{\mathrm{dx}}_1{\mathrm{dx}}_2{\mathrm{dy}}_1{\mathrm{dy}}_2,---\left(2\right)$

Wherein, ψ is the random partial of the spherical wave complex phase position that causes of turbulent flow, the ensemble average item in the formula

$<\mathrm{ex}[\mathrm{p\&psi;}(x,y,x_1,y_1)+{\mathrm{\&psi;}}^{*}(x,y,x_2,y_2)]>=$

$\exp \{-4{\mathrm{\&pi;}}^2{k}^{2}z{\&Integral;}_0^1{\&Integral;}_0^{\&infin;}\mathrm{\&kappa;}{\mathrm{\&phi;}}_n(\mathrm{\&kappa;},\mathrm{\&alpha;})[1-J_0\left(\mathrm{\&kappa;\&xi;}\sqrt{{(x_1-x_2)}^2+{(y_1-y_2)}^2}\right)\left]\mathrm{d\&kappa;d\&xi;}\right\}.---\left(3\right)$

Definition according to the root mean square width of light beam

$w_{\mathrm{turb}}={[{\&Integral;}_{-\&infin;}^{\&infin;}{\&Integral;}_{-\&infin;}^{\&infin;}(x^2+y^2)<I(x,y,z)>\mathrm{dxdy}/{\&Integral;}_{-\&infin;}^{\&infin;}{\&Integral;}_{-\&infin;}^{\&infin;}<I(x,y,z)>\mathrm{dxdy}]}^{1/2},---\left(4\right)$

As can be known, the relation of the root mean square width of light beam at transmission range z place and atmospheric turbulence parameter and beam array parameter is as follows

$w_{\mathrm{turb}}=f(w_0,N,r_0,{\tilde{C}}_n^2,L_0,l_0,z,\mathrm{\&alpha;}),---\left(5\right)$

In the formula, The broad sense refractive index structure parameter, L ₀The turbulent flow external measurement, l ₀Be yardstick in the turbulent flow, α is the descriptor index of the spectrum of turbulence.By the research to width of light beam, draw for given light beam and count N, there is the annular radii r of an optimum _0m, so that the width of light beam of receiving end reaches minimal value, and along with the increase of N, r _0mIncrease gradually, finally trend towards asymptotic value.In addition, when N was enough large, optimum radially beam array was equivalent to hollow beam, therefore, produced the hollow beam of realizing above-mentioned functions and should satisfy in the situation that the bright ring radius is constant, and the hollow area radius is adjustable.Generation satisfy above-mentioned requirements hollow beam experimental provision as shown in Figure 2, experimental provision is comprised of frosted glass plate, lens, Lens Coupling device, multimode optical fiber, collimation lens, charge coupled device ccd and the PC of laser instrument, rotation.Laser instrument emission beam of laser, through having changed its degree of coherence after the frosted glass plate that rotates, then this partially coherent light is coupled into multimode optical fiber by the Lens Coupling device through lens focus.At the output terminal output hollow beam of multimode optical fiber, the intensity distributions of the hollow beam of output behind the collimation lens collimation is presented on the CCD, and CCD links to each other with computing machine, the experimental data that obtains is transferred to computing machine carries out analyzing and processing.We can obtain the hollow beam that we need by changing incidence angle θ and side-play amount, and namely in the constant situation of the bright ring radius of hollow beam, the hollow area radius is adjustable.

3, advantage and effect

1, radially the annular radii of beam array is adjustable, and the beamlet of beam array is completely coherent light or is partially coherent light;

2, there is optimum annular radii r _0mSo that the width of light beam of receiving end reaches minimal value;

3, count N when enough large when light beam, optimum beam array is equivalent to hollow beam.This hollow beam requires to satisfy in the situation that the bright ring radius is constant, and the hollow area radius is adjustable;

4, in the experimental provision that produces hollow beam, hollow beam is produced by multimode optical fiber, changes the degree of coherence of hollow beam by the frosted glass plate of rotation, improves the quality of the hollow beam of generation by the length that increases multimode optical fiber;

5, along with the increase of incident angle and side-play amount, the hollow area radius of hollow beam increases, and the bright ring radius is substantially constant, therefore satisfy the requirement of the hollow beam of our needs;

6, because this hollow beam is equivalent to the radially beam array of the optimum that we obtain by research, so hollow beam can suppress atmospheric turbulence well on the impact of light transmission, significant to the quality that improves laser space communication.

Four, description of drawings

Fig. 1 is the schematic diagram of beam array radially.

Fig. 2 is the Experimental equipment that hollow beam produces.

Symbol description is as follows among the figure:

LS: light source (helium-neon laser), RGGD: the frosted glass plate of rotation, L: lens, LC: Lens Coupling device, MMF: multimode optical fiber, OPP: output terminal, CL: collimation lens, CCD: charge-coupled image sensor, PC: personal computer.

Fig. 3 is the process flow diagram of light source design.

Five, embodiment

The process flow diagram of light source design as shown in Figure 3, the implementation step is as follows:

1, the transmitting terminal light source is beam array radially, and the annular radii r of beam array radially ₀Adjustable, each beamlet of beam array is completely coherent light or is partially coherent light;

2, according to the Huygens-Frensel principle of broad sense, obtained the average intensity of receiving end by the cross-spectral density function of transmitting terminal;

3, according to the definition of root mean square width of light beam, obtained the width of light beam of receiving end by the average intensity of receiving end;

4, by the analysis of width of light beam that receiving end is obtained, draw the beam array parameter that exists corresponding to the minimizing optimum of width of light beam, i.e. optimum annular radii r _0mCount N with light beam;

The beam array parameter feedback of the optimum that 5, will obtain is to transmitting terminal, and transmitting terminal is finished the design to light source accordingly;

6, further achievement in research shows, when light beam is counted N when enough large, optimum radially beam array is equivalent to hollow beam, therefore, function for the beam array of realizing above-mentioned optimum, the hollow beam that we produce need to satisfy in the situation that the bright ring radius is constant, and the hollow area radius is adjustable;

7, the experimental provision of generation hollow beam as shown in Figure 2, laser instrument emission beam of laser, changed its degree of coherence after the frosted glass plate through rotation, this partially coherent light is by lens focus, then be coupled into multimode optical fiber by the Lens Coupling device, at the output terminal output hollow beam of multimode optical fiber, the intensity distributions of the hollow beam of output behind the collimation lens collimation is presented on the CCD, CCD links to each other with PC, the experimental data that obtains is transferred to PC carries out analyzing and processing.In addition, we can obtain the hollow beam that we need by changing incidence angle θ and side-play amount, namely in the constant situation of the bright ring radius of hollow beam, the hollow area radius is adjustable, can also improve by the length that increases multimode optical fiber simultaneously the quality of the hollow beam of generation.

Claims (3)

1. suppress the light source design method of Turbulent Flow Effects in the atmospheric channel, mainly may further comprise the steps:

1) the transmitting terminal light source is beam array radially, and radially the annular radii of beam array is adjustable, and each beamlet of beam array is Gaussian beam or Gaussian Schell-model beams;

2) transmitting terminal laser according to generalized Huygens-Fresnel principle, obtains the average intensity of receiving end after the atmospheric channel transmission;

3) according to the definition of root mean square width of light beam, obtained the root mean square width of light beam of receiving end by the average intensity of receiving end, there is the beam array parameter corresponding to the minimizing optimum of described root mean square width of light beam;

4) by the analysis to described root mean square width of light beam, obtain optimum beam array parameter, when the light beam number is enough large, optimum beam array is equivalent to hollow beam, therefore, the hollow beam that produces the beam array function that realizes above-mentioned optimum need to satisfy in the situation that the bright ring radius is constant, the hollow area radius is adjustable, the experimental provision that wherein produces hollow beam comprises: laser instrument emission beam of laser, changed its degree of coherence after the frosted glass plate through rotation, this partially coherent light is by lens focus, then be coupled into multimode optical fiber by the Lens Coupling device, at the output terminal output hollow beam of multimode optical fiber, the intensity distributions of the hollow beam of output behind the collimation lens collimation is presented on the CCD, CCD links to each other with PC, the experimental data that obtains is transferred to PC carries out analyzing and processing;

5) transmitting terminal is finished design to light source according to the beam array parameter of the optimum that obtains.

2. a light source design method according to claim 1 is characterized in that: in the process that produces hollow beam, can improve by the length that increases multimode optical fiber the quality of hollow beam.

3. a light source design method according to claim 1 is characterized in that: in the process that produces hollow beam, can produce by changing incidence angle θ and side-play amount the hollow beam of the beam array function that realizes above-mentioned optimum.

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