CN102519607B - Satellite-borne atmospheric coherent length testing method and satellite-to-ground coherent optical communication method - Google Patents

Abstract

The invention discloses a satellite-borne atmospheric coherent length testing method and a satellite-to-ground coherent optical communication method, which comprise the following steps that: (1), atmospheric turbulence parameters of a random channel are tested and received according to ground testing equipment; (2), according to the atmospheric turbulence parameters tested on the ground, the ground receives light beam emitted by a satellite in the process of establishing acquisition and tracking, and a self-adaptive optical system can invert for atmospheric pre-distortion compensation in an uplink; (3), satellite-borne optical communication receiving equipment is used for testing an optical wave surface according to the method; and (4), by means of the test of the optical wave surface, whether the uplink for satellite-to-ground optical communication is established can be judged, thus, the purpose of establishing self-adaptive communication is achieved. By adopting the satellite-borne atmospheric coherent length testing method and the satellite-to-ground coherent optical communication method disclosed by the invention, self-adaptive communication can be established on the uplink carrying out satellite-to-ground coherent optical communication anytime and anywhere; furthermore, whether communication is carried out can be effectively judged in the process of establishing acquisition and tracking of a laser communication link, thus, the reliability and the feasibility of the uplink for satellite-to-ground optical communication are realized.

Description

A kind of spaceborne atmospheric coherence length method of testing and star ground coherent light communication method

Technical field

The present invention relates to a kind of spaceborne atmospheric coherence length method of testing and star ground coherent light communication method.

Background technology

The wave front that laser is propagated in uniform dielectric is uniform, if transmission medium be turbulent atmosphere since in the beam cross section air index of different piece rise and fall, cause the different piece of light beam wave front to produce different phase shifts, therefore the wave front of light beam is the curved surface of random fluctuation in turbulent atmosphere, this phase place deformation causes the arrival angle fluctuation of Beam Wave-Front, makes that finally picture point is shaken in accepting the aperture.

The laser communication of the relevant system in the star ground accidental channel, not only intensity is subjected to the decay of atmosphere, and its phase bit integrity is also destroyed.Atmospheric coherence length is the wavefront important parameter of describing after laser is subjected to atmospheric interference.Atmospheric coherence length r ₀Be called Freed (Fried) constant again, it be r that its physical significance its resolution that is optical system to through the light wave imaging of atmospheric turbulence disturbance the time can not surpass bore ₀The diffraction limit resolution of optical system be that the spatial coherence yardstick of light wave its phase perturbation after atmospheric turbulence is propagated is r to the maximum ₀So r ₀It is more good to be worth more big expression atmospheric conditions.

The ground survey atmospheric coherence length detects, and adopts Differential Image motion measurement method (DIMM) to measure atmospheric coherence length as shown in Figure 1.Be provided with two small-bore receiving elements in the heavy caliber, can test the atmospheric turbulence yardstick; The light intensity flash detection can adopt PIN unit or high frame rate CCD unit to survey, and obtains light intensity time domain test data respectively, and it is carried out statistical study, can obtain light intensity shake variance and light intensity probability density distribution; By the variation to the relative distance of two hot spots, can obtain the atmospheric coherence length of channel.

Present coherent optical communication system realization aspect, star ground, coherent light communication terminal and the ground of the TerraSAR satellite of TeSAT company communicate test, ADAPTIVE OPTICS SYSTEMS compensation corrugated is not adopted in its test, and the movement station of setting up is near terrestrial observatory, according to astronomical observatory's measurement of Atmospheric Turbulence situation, determine whether to carry out the coherent light communication of star ground according to the ground atmospheric coherence length, it does not have the coherent length detection method on the star.

In the star ground coherent light communication at present, the precondition that up-link is set up is: select for use the plateau of weak atmospheric turbulence to build land station, perhaps set up adaptive optics wavefront modification system at star, the adaptive optics wavefront modification precision on existing ground is pi/4, and the device that adaptive system is applied on the satellite is immature.So just limit the development of the up-link of star ground coherent light communication.

As shown in Figure 2, be adaptive optics compensation process schematic diagram.Behind the light beam process star ground atmospheric turbulence that optical sender sends, the ground wave front sensor carries out wavefront measurement, reconstruct wavefront information by the wave front restoration algorithm then, the signal that the wavefront controller detects Wavefront sensor is converted into the control signal of wave-front corrector through control algolithm, drive wave-front corrector and change wavefront shape, thereby proofread and correct various disturbances effectively to the influence of laser beam quality, obtain the output laser beam near diffraction limit, send into communication system receiver finally by the light beam of crossing the ADAPTIVE OPTICS SYSTEMS correction, carry out opto-electronic conversion, thereby obtain source signal.

In the star flash of light preceding an earthquake communication system down link link, light beam is propagated through the vacuum of long distance, when arriving the atmospheric envelope top. its diameter has been expanded greatlyyer than atmospheric turbulence external measurement, so the scintillation effect that atmospheric turbulence has only beam spread and small scale to cause to the influence of light signal basically, this moment, drift effect can be ignored; And for the up-link under the equal conditions, beam drift, expansion and scintillation effect are of equal importance.For the up-link that receives on ground surface launching and the star, adopt pre-wavefront correction, its correcting value derives from the wavefront sensing tolerance of the adaptive optics that the ground of downlink receives, because up-link and downlink is asymmetric, so the measurement that wavefront precorrection can not very complete compensation goes out up-line system.So be necessary the receiving unit on the star, do atmospheric coherence length and detect, thereby reach system communication assessment and to the signal feedback of ground predistortion.

Summary of the invention

Technical matters to be solved by this invention is: the method and the star ground coherent light communication method that provide a kind of spaceborne atmospheric coherence length to measure, and to improve the reliability of star ground communication.

The present invention includes following technical scheme:

A kind of spaceborne atmospheric coherence length method of testing comprises the steps:

(1) for the coherent light communication of star ground, setting up in the process of acquisition and tracking, the light beam that the optical antenna of satellite borne laser communication terminal receives, be transferred in the optical mixing phase shifter through optical channel, enter the visual field of optical mixing phase shifter when light beam after, after the mixing phase shift through the mixing phase shifter, in 270 degree phase shifts or at 90 degree phase shift path punishment light;

(2) light beam of telling is realized being transformed into angle pencil of ray by arrow beam of light through the extender lens group, focuses on through two aperture diaphragm lens again, is imaged on two 4 quadrant detectors;

(3) the hot spot signal that two 4 quadrant detectors are obtained calculates hot spot centre of gravity place coordinate respectively;

The centre of gravity place coordinate of the hot spot that one of them 4 quadrant detector obtains is (δ x, δ y), and the centre of gravity place coordinate of the hot spot that another 4 quadrant detector obtains is (δ x ', δ y ');

(4) calculate atmospheric coherence length r by following formula ₀,

$r_0={\left\{\frac{2f^2[0.36{(\mathrm{\&lambda;}/D)}^{1/3}-0.242{(\mathrm{\&lambda;}/d)}^{1/3}]{\mathrm{\&lambda;}}^{5/3}}{<{\mathrm{\&Delta;\&rho;}}_{\mathrm{<figure-callout\; id="2"\; label="c"\; filenames="HSA00000624370600013.png"\; state="\{\{state\}\}">c</figure-callout>}}^2>-{<{\mathrm{\&Delta;\&rho;}}_c>}^2}\right\}}^{3/5},$

Wherein D and d are respectively the centre distance of beam diameter and two 4 quadrant detectors of extender lens group; F is extender lens group system focal length; Δ ρ _cBe the polar coordinates alternate position spike of two hot spots,

Δ ρ _cCalculate acquisition by following formula: ${\mathrm{\&Delta;\&rho;}}_c=\sqrt{{(d-\mathrm{\&delta;x}+{\mathrm{\&delta;x}}^{\&prime;})}^2+{(\mathrm{\&delta;y}-{\mathrm{\&delta;y}}^{\&prime;})}^2}.$

By the centre of gravity place coordinate of following normalization computing formula calculating hot spot,

$\mathrm{\&delta;y}=\frac{(A+B)-(C+D)}{A+B+C+D},$

$\mathrm{\&delta;x}=\frac{(A+D)-(B+C)}{A+B+C+D},$

A wherein, B, C and D represent the light spot energy that I, II, III and IV quadrant are surveyed respectively; δ x and δ v are the centre of gravity place coordinates of the hot spot that obtains in the 4 quadrant detector.

The adaptive communication method of a kind of star ground coherent light communication is characterized in that realizing by following steps:

(1) the atmospheric turbulence parameter by ground checkout equipment test receiving cable; According to the atmospheric turbulence parameter of ground test, in the process that acquisition and tracking is set up, ground based terminal application self-adapting method measuring optical corrugated situation is used the corrugated pre-distortion that the pre-distortion compensated method is carried out up-link;

(2) adopt said method to test spaceborne atmospheric coherence length r ₀

(3) the reception bore of satellite borne laser communication terminal is r ₁, as the atmospheric coherence length r that measures ₀Greater than r ₁, the satellite borne laser communication terminal sends instruction to ground, and communication is normally carried out; Otherwise do not send instruction, modulate emission is not carried out on ground, and communication is ended.

Method of the present invention compared with prior art has following advantage:

1, for star ground coherent optical communication system, under the situation of coherent reception, when adopting heterodyne tracking, can measure the atmospheric coherence length of up-link on the star of up-link.

2, the method can be caught with during setting up in the optical communication of star ground, to the pre-correction of the optical wave-front on ground, can measure assessment to correction result, and can be used as the foundation that whether begins the communicate optical signal transmission.

3, adopt the method can realize independently catching with communication, do not rely on task equipment and measure atmospheric coherence length, and can remedy the inaccuracy of the atmospheric coherence length of ground test.

4, propose to carry out atmospheric coherence length at star and detect, whole technique method integrated level is subjected to other factors of space to disturb little than higher.

5, in the coherent light communication of star ground, adopt atmospheric coherence length measuring method on the star of the present invention, catching with establishment stage, can judge whether and to communicate; Thereby improved the reliability that communication link is set up.

Description of drawings

Fig. 1 is the process flow diagram of Differential Image motion (DIMM) measurement of Atmospheric Turbulence;

Fig. 2 is adaptive optics compensation process schematic diagram;

Fig. 3 is the schematic diagram that atmospheric coherence length is measured on the star;

Fig. 4 is four-quadrant position transducer position measurement schematic diagram;

Fig. 5 is normalized 4 quadrant detector modulate circuit schematic diagram;

Fig. 6 is the process flow diagram of star of the present invention ground coherent light communication method.

Embodiment

The invention will be described further below in conjunction with accompanying drawing:

As shown in Figure 6, star ground coherent light communication method of the present invention comprises the steps:

1, tests the atmospheric turbulence parameter of receiving cable by ground checkout equipment; According to the atmospheric turbulence parameter of ground test, in the process that acquisition and tracking is set up, ground based terminal application self-adapting method measuring optical corrugated situation is used the corrugated pre-distortion that the pre-distortion compensated method is carried out up-link.

The scintillation index σ of downlink _IdScintillation index σ with up-link _In:

${\mathrm{\&sigma;}}_{\mathrm{<figure-callout\; id="2"\; label="Id"\; filenames="HSA00000624370600013.png"\; state="\{\{state\}\}">Id</figure-callout>}}^2=\exp [\frac{{0.49\mathrm{\&sigma;}}_0^2}{{(1+1.11{\mathrm{\&sigma;}}_0^{12/5})}^{7/6}}+\frac{{0.51\mathrm{\&sigma;}}_0^2}{{(1+0.69{\mathrm{\&sigma;}}_0^{12/5})}^{5/6}}]-1$

${\mathrm{\&sigma;}}_{\mathrm{<figure-callout\; id="2"\; label="Iu"\; filenames="HSA00000624370600013.png"\; state="\{\{state\}\}">Iu</figure-callout>}}^2=\exp [\frac{{0.49\mathrm{\&sigma;}}_0^2}{{(1+0.55{\mathrm{\&sigma;}}_0^{12/5})}^{7/6}}+\frac{{0.51\mathrm{\&sigma;}}_0^2}{{(1+0.69{\mathrm{\&sigma;}}_0^{12/5})}^{5/6}}]-1$

σ ₀Be the Rytov variance of not adaptive equalization, according to down link self adaption correction corrugated σ ₁, can sum up the correction corrugated of downlink according to Andrews:

The up-link corrugated should be:

K is wave number, Be the air index textural constant, κ is spatial frequency, and L is the light transmission range, and D is the bore of receiver lens, and z is sea level elevation, F _i(κ, D, Be the adaptive optics transition function.This revises corrugated σ ₁Be by the adaptive optics closed-loop control.Wave front restoration information according in the ADAPTIVE OPTICS SYSTEMS in the downlink makes the up-link corrugated

Reach optimum, so just realized the pre-distortion compensated of wavefront.

2, spaceborne atmospheric coherence length measuring method

In the coherent light communication of star ground, setting up in the process of acquisition and tracking, the light beam that spaceborne coherent light communication terminal optical antenna receives is transferred in the optical mixing phase shifter through optical channel, carries out atmospheric coherence length at the optical mixing phase shifter and measures.

In the coherent light communication terminal, the optical mixing phase shifter is optical passive component, local oscillator light E _L0, flashlight E _SBetween carry out the relevant and phase shift of light field.As shown in Figure 3, comprise quarter-wave plate 1, polarization beam combiner 2, half-wave plate 3, polarization beam apparatus 4.Light carrier and the local oscillator light of input all are linearly polarized light, and wherein local oscillator light becomes rotatory polarization behind quarter-wave plate 1.Through polarization spectro repeatedly with change the polarization direction, make the light of output obtain interference pattern at test surface.Realize the mixing of flashlights and local oscillator light at polarization beam combiner 2, all orthogonal from the polarization direction of the I branch road of polarization beam combiner output and the two-way light field the Q branch road.In order to obtain flashlight and local oscillator interference of light pattern, need to change the polarization direction of I branch road and Q branch road, this function is realized by half-wave plate 3.Behind polarization beam apparatus 4, obtain 4 tunnel output coherent light signals from the light field of half-wave plate output, obtain interference pattern.In order to realize the phase shift of 180 degree, the rotation angle of half-wave plate 3 must be 45 °.Compensating glass 10 is used for optical path compensation, to reach phase place output accurately.

In the acquisition and tracking process, enter the visual field of optical mixing phase shifter when light beam after, owing to adopt the coherent tracking mode, so the visual field of mixing phase shifter is tracking field of view, so the tracking phase light beam enters the mixing phase shift, measure in order to realize atmospheric coherence length, to satisfy the purpose of star ground adaptive communications, so tell 1: 9 ratio light beam at the branch road of 270 degree phase shift outputs or at 90 degree phase shift output branch roads, wherein the light intensity of small part is measured for atmospheric coherence length.

For the polarizing beam splitter mirror 4 of 90,270 degree phase shift outputs place, must consider the light beam power unanimity of 90,270 degree phase shift outputs, the light splitting ratio of polarization spectroscope 4 is 5.5: 4.5.Wherein, the light beam of 5.5 correspondences is again through spectroscope 9 light splitting, and the light splitting ratio is 1: 9, and wherein the small part light beam is as the atmospheric coherence length measuring beam.So just obtaining 90,270 degree phase shift Output optical power ratios is 4.95: 5.

This method is based on the DIMM ultimate principle, so need reach sub-aperture focal imaging to beam expander.The light beam of telling is realized being transformed into angle pencil of ray by arrow beam of light through Cassegrain formula extender lens group, light beam is earlier through 6 emissions of Cassegrain secondary mirror, and beam divergence obtains angle pencil of ray through primary mirror 7 reflections to primary mirror 7, through two aperture diaphragm lens 8 focused beams, be imaged on the 4 quadrant detector again.Survey the imaging signal as shown in Figure 4 because the imaging area of CCD is limited, and for near-infrared wavelength insensitive and frame frequency speed can not well detect the atmospheric turbulence response.The 4 quadrant detector index request is as follows:

Diameter 0.5mm is surveyed in the effective coverage

Raceway groove: 13um

Equivalent noise: 2.8E-15w/Hz

Dark current: 0.01nA

Rise time: 3ns (10V biasing)

Corresponding rate: 0.65A/W (970nm)

Working temperature :-40 ℃-100 ℃

The signal that 4 quadrant detector records carries out position calculation respectively, by the normalization computing formula

With

Calculate the modulate circuit of four-quadrant hot spot as shown in Figure 5, A wherein, B, C and D represent the light spot energy that I, II, III and IV quadrant are surveyed respectively.δ x and δ y are respectively the position coordinateses of the hot spot center of gravity calculated in a 4 quadrant detector.Because DIMM need adopt two 4 quadrant detectors, the facula position coordinate that another 4 quadrant detector obtains is (δ x ', δ y ').

Calculate atmospheric coherence length r by following formula ₀ $r_0={\left\{\frac{2f^2[0.36{(\mathrm{\&lambda;}/D)}^{1/3}-0.242{(\mathrm{\&lambda;}/d)}^{1/3}]{\mathrm{\&lambda;}}^{5/3}}{<{\mathrm{\&Delta;\&rho;}}_{\mathrm{<figure-callout\; id="2"\; label="c"\; filenames="HSA00000624370600013.png"\; state="\{\{state\}\}">c</figure-callout>}}^2>-{<{\mathrm{\&Delta;\&rho;}}_c>}^2}\right\}}^{3/5},$ D in this formula and d are respectively the centre distance of beam diameter and two 4 quadrant detectors of extender lens group, and f is extender lens group system focal length, and λ is optical wavelength, Δ ρ _cBe two four-quadrant hot spot polar coordinates alternate position spikes, wherein

One of them four-quadrant facula position information, can be used as the position quantity of the tracking hot spot of coherent light communication, because what adopt is that the DIMM principle is calculated coherent length, so for following the tracks of reasons such as compensation, satellite vibration interference, the variation of the facula position that causes can not have influence on the calculating accuracy of atmospheric coherence length.

3, adaptive communications

It is that the spatial coherence yardstick of diffraction limit resolution light wave its phase perturbation after atmospheric turbulence is propagated of the optical system of r is r to the maximum that optical system its resolution to through the light wave imaging of atmospheric turbulence disturbance the time can not surpass bore.Therefore the more big expression atmospheric conditions of r value are more good.The reception bore of satellite borne laser communication terminal is r ₁, can obtain atmospheric coherence length according to top method of testing is r ₀, as the r that measures ₀Greater than r ₁The time, the satellite borne laser communication terminal sends instruction and shows that communication can normally carry out, otherwise does not send instruction, and modulate emission is not carried out on ground, and communication is ended.

The unspecified part of the present invention belongs to general knowledge as well known to those skilled in the art.

Claims (3)

1. a spaceborne atmospheric coherence length method of testing comprises the steps:

(1) for the coherent light communication of star ground, setting up in the process of acquisition and tracking, the light beam that the optical antenna of satellite borne laser communication terminal receives, be transferred in the optical mixing phase shifter through optical channel, enter the visual field of optical mixing phase shifter when light beam after, after the mixing phase shift through the mixing phase shifter, in 270 degree phase shifts or at 90 degree phase shift path punishment light;

(2) light beam of telling is realized being transformed into angle pencil of ray by arrow beam of light through the extender lens group, focuses on through two aperture diaphragm lens again, is imaged on two 4 quadrant detectors;

(3) the hot spot signal that two 4 quadrant detectors are obtained calculates hot spot centre of gravity place coordinate respectively;

The centre of gravity place coordinate of the hot spot that one of them 4 quadrant detector obtains is (δ x, δ y), and the centre of gravity place coordinate of the hot spot that another 4 quadrant detector obtains is (δ x ', δ y ');

(4) calculate atmospheric coherence length r by following formula ₀,

$r_0={\left\{\frac{2f^2[0.36{(\mathrm{\&lambda;}/D)}^{1/3}-0.242{(\mathrm{\&lambda;}/d)}^{1/3}]{\mathrm{\&lambda;}}^{5/3}}{<{\mathrm{\&Delta;\&rho;}}_c^2>-{<\mathrm{\&Delta;}{\mathrm{\&rho;}}_c>}^2}\right\}}^{3/5},$

Wherein D and d are respectively the centre distance of beam diameter and two 4 quadrant detectors of extender lens group; F is extender lens group system focal length; Δ ρ _cBe the polar coordinates alternate position spike of two hot spots,

Δ ρ _cCalculate acquisition by following formula: $\mathrm{\&Delta;}{\mathrm{\&rho;}}_c=\sqrt{{(d-\mathrm{\&delta;x}+\mathrm{\&delta;}{x}^{\&prime;})}^2+{(\mathrm{\&delta;y}-\mathrm{\&delta;}{y}^{\&prime;})}^2}.$

2. spaceborne atmospheric coherence length method of testing as claimed in claim 1 is characterized in that: calculate the centre of gravity place coordinate of hot spot by following normalization computing formula,

$\mathrm{\&delta;y}=\frac{(A+B)-(C+D)}{A+B+C+D},$

$\mathrm{\&delta;x}=\frac{(A+D)-(B+C)}{A+B+C+D},$

A wherein, B, C and D represent the light spot energy that I, II, III and IV quadrant are surveyed respectively; δ x and δ y are the centre of gravity place coordinates of the hot spot that obtains in the 4 quadrant detector.

3. the adaptive communication method of a star ground coherent light communication is characterized in that realizing by following steps:

(1) the atmospheric turbulence parameter by ground checkout equipment test receiving cable; According to the atmospheric turbulence parameter of ground test, in the process that acquisition and tracking is set up, ground based terminal application self-adapting method measuring optical corrugated situation is used the corrugated pre-distortion that the pre-distortion compensated method is carried out up-link;

(2) adopt the described method of claim 1 to test spaceborne atmospheric coherence length r ₀

(3) the reception bore of satellite borne laser communication terminal is r ₁, as the atmospheric coherence length r that measures ₀Greater than r ₁, the satellite borne laser communication terminal sends instruction to ground, and communication is normally carried out; Otherwise do not send instruction, modulate emission is not carried out on ground, and communication is ended.

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