CN115276801B

CN115276801B - Satellite laser communication link light spot tracking compensation method and signal transmission method

Info

Publication number: CN115276801B
Application number: CN202211133761.5A
Authority: CN
Inventors: 李军; 张文睿; 周颖; 姜承志; 张若凡; 张锦龙; 张睿奇
Original assignee: Xian Institute of Space Radio Technology
Current assignee: Xian Institute of Space Radio Technology
Priority date: 2022-09-19
Filing date: 2022-09-19
Publication date: 2022-12-23
Anticipated expiration: 2042-09-19
Also published as: CN115276801A

Abstract

The application relates to a satellite laser communication link light spot tracking compensation and signal transmission method, which comprises the following steps: in a satellite laser communication receiver, splitting the received signal light and local oscillator light, and respectively inputting the split signal light and local oscillator light to a plurality of quadrant detectors; the detection units corresponding to the quadrant detectors realize balanced detection, the obtained multiple photocurrents are calculated, the centroid offset of the received signal light spots in the X direction and the Y direction of the detectors is determined, and accordingly closed-loop tracking compensation is carried out on the light spots. Meanwhile, the signals after balanced detection can be used for demodulation and decoding, so that signal transmission is realized while stable tracking is realized. The method has at least one of the following beneficial technical effects: the unit balance detection corresponding to the plurality of quadrant detectors is utilized to filter the noise of the rabdosia background light superposed in the signal light, the problem that the existing laser link cannot continuously work when the sunlight is normally incident is solved, and the satellite laser link has the capability of rabdosia resistant stable tracking and communication.

Description

Satellite laser communication link light spot tracking compensation method and signal transmission method

Technical Field

The application relates to the field of communication transmission, in particular to a satellite laser communication link light spot tracking compensation method and a signal transmission method.

Background

When a satellite laser communication link tracks a target, a light spot centroid tracking mode is generally adopted, and the method belongs to an incoherent energy detection type tracking mode. The satellite laser terminal usually uses a CCD detector or a QD detector as a tracking detector, calculates the gray value of a target light spot received by the detector to obtain the centroid position of the target light spot, and feeds the centroid position back to a closed-loop control system for compensation in real time. The tracking mode has the advantages of high tracking bandwidth, simple control loop, good device availability and the like, and is widely applied to the field of satellite laser communication.

However, due to the principle of energy detection, the above tracking method is vulnerable to interference of stray light from the background in space applications, such as the background of the sun, the background of the stars such as the earth, the background of the solar reflected sunlight, the meteors, and the background of the stars, where the intensity of the background light from the sun is the highest. Although the improvement can be achieved by adding a narrow-band filter, an optical window and the like, background stray light in a band-pass frequency range of a terminal cannot be filtered all the time, so that a satellite laser communication link cannot be stably maintained under the condition of the sun. Based on the reasons, the laser terminal product usually adopts a sun-ice avoidance strategy on track, the laser communication link is actively disconnected and the pointing mechanism is biased to avoid the sun-ice by calculating the sunlight irradiation time, and the transmission link is reestablished after the sun-ice is finished. Therefore, the satellite laser communication link is difficult to work stably in orbit for a long time, and needs to frequently execute chain breakage avoidance and link reconstruction, and the usability is not high.

Disclosure of Invention

In order to overcome at least one of the deficiencies in the prior art, embodiments of the present application provide a method for tracking and compensating a light spot of a satellite laser communication link and a method for transmitting a signal.

In a first aspect, an embodiment of the present application provides a method for compensating for tracking of a light spot in a satellite laser communication link, including:

splitting the signal light and the local oscillator light to obtain a plurality of beams of split signal light and a plurality of beams of split local oscillator light; a plurality of beams of beam splitting signal light and a plurality of beams of beam splitting local oscillator light are respectively input into a plurality of detectors, and each detector comprises a plurality of quadrant detection units;

determining the photocurrent detected by each quadrant detection unit in each detector according to the split-beam signal light and the split-beam local oscillator light input into each detector;

and determining the centroid offset of the light spot along the X direction and the centroid offset of the light spot along the Y direction according to the photocurrent detected by each quadrant detection unit, wherein the centroid offset of the light spot along the X direction and the centroid offset of the light spot along the Y direction are used for tracking and compensating the light spot.

In one embodiment, determining the centroid displacement amount of the light spot along the X direction and the centroid displacement amount of the light spot along the Y direction according to the photocurrent detected by each quadrant detection unit comprises:

determining a plurality of quadrant detection unit pairs, wherein two quadrant detection units in each quadrant detection unit pair form balanced detection; two quadrant detection units in each quadrant detection unit pair are quadrant detection units of corresponding quadrants in two different detectors;

calculating the difference value of the photocurrents detected by the two quadrant detection units in each quadrant detection unit pair;

determining the difference value of the corresponding optical power of each quadrant detection unit pair according to the difference value of the photocurrent calculated by each quadrant detection unit pair;

and determining the centroid offset of the light spot along the X direction and the centroid offset of the light spot along the Y direction according to the difference value of each quadrant detection unit to the corresponding light power.

In one embodiment, determining the centroid shift amount of the light spot in the X direction and the centroid shift amount of the light spot in the Y direction according to the difference of the corresponding optical power of each quadrant detection unit pair comprises:

the number of the detectors is 2, each detector comprises 4 quadrant detection units, and quadrant detection units of corresponding quadrants in the 2 detectors form 4 quadrant detection unit pairs;

the difference values of the corresponding optical powers of the 4 quadrant detection units are respectively recorded as:P _A ，P _B ，P _C andP _D and then:

centroid offset of light spot in X direction

：

Centroid offset of light spot in Y direction

：

。

the number of the detectors is 4, namely a detector PD1, a detector PD2, a detector PD3 and a detector PD4, and each detector comprises 2 quadrant detection units;

quadrant detection units of corresponding quadrants in the detector PD1 and the detector PD2 form 2 quadrant detection unit pairs, and the difference values of the corresponding optical powers are respectively recorded as:

and

the quadrant detection units of the corresponding quadrants in the detector PD3 and the detector PD4 form 2 quadrant detection unit pairs, and the difference values of the corresponding optical powers are respectively recorded as:

and

then:

centroid offset of light spot in X direction

：

Centroid offset of light spot in Y direction

：

。

In one embodiment, the method further comprises:

controlling the inconsistency coefficients of the two quadrant detection units in each quadrant detection unit pair:

in the formula (I), the compound is shown in the specification,

the inconsistency coefficients of the two quadrant detection units in the ith quadrant detection unit pair,qis the amount of electricity of the electron,

the optical power of the split local oscillator light of the quadrant detection unit in the ith quadrant detection unit pair,

for the sunset background light power received by the quadrant detection unit in the ith quadrant detection unit pair,RINfor the local oscillator light relative intensity noise figure,Rin order to convert the coefficients of the image data,

is the coherent filter bandwidth.

In a second aspect, an embodiment of the present application provides a method for transmitting a satellite laser communication link signal, including:

determining the photocurrent detected by each quadrant detection unit in each detector according to the split-beam signal light and the split-beam local oscillator light which are input into each detector;

and determining a communication signal according to the photocurrent detected by each quadrant detection unit, wherein the communication signal is used for communication transmission.

In one embodiment, determining the communication signal based on the photocurrent detected by each quadrant detection unit comprises:

and determining a communication signal according to the difference value of the corresponding optical power of each quadrant detection unit.

In one embodiment, determining the communication signal according to the difference of the corresponding optical power of each quadrant detection unit pair comprises:

the difference values of the corresponding optical powers of the 4 quadrant detection units are respectively recorded as:P _A ，P _B ，P _C andP _D then:

the communication signal M comprises a first signal component M1 and a second signal component M2, wherein the first signal component M1= isP _A +P _B + P _C +P _D Second signal component M2=P _A +P _D -（P _B +P _C ）Or M2=P _A +P _B -（P _C +P _D ）。

and

and

and then:

communication signal

Comprising a first signal component

And a second signal component

Wherein the first signal component

Second signal component

Or

。

In one embodiment, the method further comprises:

in the formula (I), the compound is shown in the specification,

for the power of the rabdosia background light received by the quadrant detection unit in the ith quadrant detection unit pair,RINis the relative intensity noise figure of the local oscillator light,Rin order to convert the coefficients of the image,

is the coherent filter bandwidth.

In a third aspect, an embodiment of the present application provides a satellite laser communication link light spot tracking compensation apparatus, including:

the optical splitting unit is used for splitting the signal light and the local oscillator light to obtain a plurality of beams of split signal light and a plurality of beams of split local oscillator light;

the detector unit is used for receiving the multiple beams of beam splitting signal light and the multiple beams of beam splitting local oscillator light, the detector unit comprises a plurality of detectors, and each detector comprises a plurality of quadrant detection units;

the photocurrent calculating unit is used for determining the photocurrent detected by each quadrant detecting unit in each detector according to the split beam signal light and the split beam local oscillator light which are input into each detector;

and the centroid offset determining unit is used for determining the centroid offset of the light spot along the X direction and the centroid offset of the light spot along the Y direction according to the photocurrent detected by each quadrant detecting unit, wherein the centroid offset of the light spot along the X direction and the centroid offset of the light spot along the Y direction are used for tracking compensation of the light spot.

In one embodiment, the centroid offset determination unit is further configured to:

In a fourth aspect, an embodiment of the present application provides a satellite laser communication link signal transmission apparatus, including:

and the communication signal determining unit is used for determining a communication signal according to the photocurrent detected by each quadrant detection unit, and the communication signal is used for communication transmission.

In one embodiment, the communication signal determination unit is further configured to:

In a fifth aspect, an embodiment of the present application provides a satellite laser communication link light spot tracking compensation and communication system, including:

the photocurrent calculation unit is used for determining the photocurrent detected by each quadrant detection unit in each detector according to the split-beam signal light and the split-beam local oscillator light which are input into each detector;

the mass center offset determining unit is used for determining the mass center offset of the light spot along the X direction and the mass center offset of the light spot along the Y direction according to the photocurrent detected by each quadrant detecting unit, wherein the mass center offset of the light spot along the X direction and the mass center offset of the light spot along the Y direction are used for tracking compensation of the light spot;

Compared with the prior art, the method has the following beneficial effects: after a target light signal and local oscillator light are split, the target light signal and the local oscillator light are transmitted to a multi-quadrant detector with multiple consistent performance parameters, multi-path balanced detection is achieved by using a multi-quadrant detector corresponding to a detection unit, multi-path light current is obtained, and by using a balanced detection principle in coherent detection, rabdosia background light noise and local oscillator light intensity noise superposed in the target signal light are filtered, so that a satellite laser link has the capability of anti-rabdosia stable tracking and communication.

Drawings

The present application may be better understood by reference to the following description taken in conjunction with the accompanying drawings, which are incorporated in and form a part of this specification, along with the detailed description below. In the drawings:

FIG. 1 is a schematic diagram illustrating a satellite laser communication link transceiver system model according to an embodiment of the application;

FIG. 2 illustrates a schematic diagram of a satellite laser communication link speckle tracking compensation method using two four-quadrant detectors according to an embodiment of the present application;

FIG. 3 is a schematic diagram illustrating simulation results of signal-to-noise ratios under different local oscillator light intensities;

FIG. 4 shows a schematic diagram of a satellite laser communication link tracking communication integrated structure according to an embodiment of the application;

FIG. 5 illustrates a schematic diagram of a satellite laser communication link speckle tracking compensation method using four two-quadrant detectors according to an embodiment of the present application;

FIG. 6 is a block flow diagram illustrating a method for spot tracking compensation in a satellite laser communication link according to an embodiment of the present disclosure;

FIG. 7 is a block flow diagram illustrating a method for satellite laser communication link signal transmission according to an embodiment of the application;

fig. 8 shows a block diagram of a satellite laser communication link spot tracking compensation device according to an embodiment of the present application;

fig. 9 is a block diagram illustrating a structure of a satellite laser communication link signal transmission apparatus according to an embodiment of the present application;

FIG. 10 shows a graph (X-axis) comparing laser termination performance for single frequency microvibration tracking at an amplitude of 40 μ rad and a frequency of 1 Hz;

FIG. 11 shows a graph comparing laser termination performance for single frequency microvibration tracking at 40 μ rad amplitude and 1Hz frequency (Y-axis);

FIG. 12 shows a comparison of laser termination versus single frequency microvibration tracking performance at 40 μ rad amplitude and 1Hz frequency (centroid coordinates);

FIG. 13 shows a comparative plot (X-axis) of laser terminal versus single frequency micro-vibration tracking performance at 30 μ rad and 5 Hz;

FIG. 14 shows a comparative plot (Y-axis) of laser terminal versus single frequency micro-vibration tracking performance at 30 μ rad and 5 Hz;

FIG. 15 shows a comparison of laser termination versus single frequency microvibration tracking performance at 30 μ rad amplitude and 5Hz frequency (centroid coordinate);

FIG. 16 shows a graph (X-axis) comparing laser termination performance for single frequency microvibration tracking at 20 μ rad amplitude and 10Hz frequency;

FIG. 17 shows a graph comparing laser termination performance for single frequency microvibration tracking at 20 μ rad amplitude and 10Hz frequency (Y-axis);

FIG. 18 shows a comparison of laser termination versus single frequency microvibration tracking performance at 20 μ rad amplitude and 10Hz frequency (centroid coordinates);

FIG. 19 shows a graph comparing laser termination performance for single frequency microvibration tracking at 10 μ rad amplitude and 30Hz frequency (X-axis);

FIG. 20 shows a comparative plot (Y-axis) of laser termination versus single frequency micro-vibration tracking performance at 10 μ rad amplitude and 30 Hz;

FIG. 21 shows a comparison of laser termination versus single frequency microvibration tracking performance at 10 μ rad amplitude and 30Hz frequency (centroid coordinate);

FIG. 22 shows a composite microvibration power spectrum before closed loop tracking;

FIG. 23 shows a spot centroid residual power spectrum after closed loop tracking;

fig. 24 is a communication performance test result diagram illustrating a satellite laser communication link signal transmission method according to an embodiment of the present application.

Detailed Description

Exemplary embodiments of the present application will be described hereinafter with reference to the accompanying drawings. In the interest of clarity and conciseness, not all features of an actual embodiment are described in the specification. It will of course be appreciated that in the development of any such actual embodiment, numerous implementation-specific decisions may be made to achieve the developers' specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another.

Here, it should be further noted that, in order to avoid obscuring the present application with unnecessary details, only the device structure closely related to the solution according to the present application is shown in the drawings, and other details not so related to the present application are omitted.

It is to be understood that the application is not limited to the described embodiments, since the description proceeds with reference to the drawings. In this context, embodiments may be combined with each other, features may be replaced or borrowed between different embodiments, one or more features may be omitted in one embodiment, where feasible.

Fig. 1 shows a schematic diagram of a satellite laser communication link transceiving system model according to an embodiment of the present application. Referring to FIG. 1, assume that the boresight of the transmitting laser terminal deviates from the theoretical boresight of the pointing receiving laser terminal by

The deviation between the visual axis of the receiving laser terminal and the theoretical visual axis of the pointing transmitting laser terminal is

And both sides have translation

. Laser output optical field distribution

After being transmitted by long-distance space channel, the signal light electric field reaches the receiver at the receiving end

. Because the laser communication light field transmission accords with the far field distribution characteristics of Fraunhofer, the signal light electric field in front of the receiver

And

、

、

、

and (6) correlating. According to the on-orbit dynamic working characteristics of the satellite,

the intensity of the signal light is changed along with the jitter of the position of the received signal light, and the receiver needs to compensate the jitter of the signal light in real time and realize the data recovery of the communication signal.

Fig. 2 shows a schematic diagram of a satellite laser communication link spot tracking compensation method using two four-quadrant detectors according to an embodiment of the present application. Referring to fig. 2, after the signal light is received by the receiver, the signal light is split into two split signal lights by the splitting module, and the two split signal lights are respectively sent to the two four-quadrant detectors QD1 and QD2, where the splitting module may include a first splitter for splitting the signal light into two split signal lights; similarly, after the local oscillator light with the same frequency as the signal light passes through the beam splitting module, the local oscillator light is split into two beams of beam splitting local oscillator light, one beam is collimated and then sent to the four-quadrant detector QD1, and the other beam is collimated and then sent to the four-quadrant detector QD2 through the 180-degree frequency mixing phase shifter, wherein the beam splitting module comprises the 180-degree frequency mixing phase shifter and is used for carrying out 180-degree phase shift on one beam of the beam splitting local oscillator light. The beam splitting module also comprises a second beam splitter which is used for splitting the local oscillation light into two beams of split local oscillation light.

The four-quadrant detectors QD1 and QD2 each include four quadrants, which are a first quadrant detection unit, a second quadrant detection unit, a third quadrant detection unit, and a fourth quadrant detection unit, respectively, wherein the first quadrant detection unit in QD1 and the first quadrant detection unit in QD2 constitute a quadrant detection unit pair, the second quadrant detection unit in QD1 and the second quadrant detection unit in QD2 constitute a quadrant detection unit pair, the third quadrant detection unit in QD1 and the third quadrant detection unit in QD2 constitute a quadrant detection unit pair, the fourth quadrant detection unit in QD1 and the fourth quadrant detection unit in QD2 constitute a quadrant detection unit pair, and here, two quadrant detection units in the quadrant detection unit pair constitute balanced detection.

The following describes a process of detecting a difference in optical power by using a quadrant detection unit pair of each quadrant as an example.

Signal optical electric field

And local oscillator photoelectric field

The simplified expression of (c) is:

wherein, the first and the second end of the pipe are connected with each other,

representThe optical power of the signal received by the receiver,

indicating the signal light phase;

which is indicative of the optical power of the local oscillator,

representing the local oscillator optical phase;

the switching matrix S of the 180 ° hybrid phase shifter is:

accordingly, the photocurrent detected by the first quadrant detection cells of the detectors QD1 and QD2

And

respectively as follows:

wherein the content of the first and second substances,

representing the optical power of the split signal light of the first quadrant-detection unit,

the optical power of the beam splitting local oscillator light of the first quadrant detection unit is represented;

representing the noise of the first quadrant detection cells of the detector QD1,

representing the noise of the first quadrant detection cells of the detector QD2,Rrepresenting the conversion coefficient.

Based on the balance detection principle, the photocurrents detected by the first quadrant detection units of the two detectors QD1 and QD2 are differenced to obtain the difference value of the photocurrents detected by the two first quadrant detection units

：

Wherein the content of the first and second substances,

residual intensity noise.

Similarly, the difference value of the photocurrents detected by the two second quadrant detection units can be obtained

The difference value of the light currents detected by the two third quadrant detection units

The difference value of the photocurrents detected by the two fourth quadrant detection units

。

Here, the

、

、

And

can be regarded as four-quadrant detection energy values of an equivalent new composite four-quadrant detector, and each quadrant detection unit is used for corresponding difference value of optical powerP _A 、P _B 、P _C 、P _D Representation for calculating the centroid offset of the spot in the X-direction

And centroid displacement in the Y direction

Namely error output of the light spot along the X direction and error output of the light spot along the Y direction:

in this embodiment, the obtained centroid offset of the light spot along the X direction and the centroid offset along the Y direction are input into the fine tracking mechanism for tracking compensation of the centroid of the light spot.

Residual intensity noise

Can be expressed as:

wherein the content of the first and second substances,RINrepresenting the local oscillator light relative intensity noise figure,

which represents the bandwidth of the coherent filtering,

representing the inconsistency coefficients of the two first quadrant detection units,Bwhich represents the bandwidth of reception of the data,

indicating the power of the background daylight received by the first quadrant detector unit,

representing the optical power of the split local oscillator light of the first quadrant detector unit,Rrepresenting the conversion coefficient.

Inconsistency coefficient of two first quadrant detection units

Detecting responsivity of unit from two first quadrants

And

and calculating to obtain:

the signal-to-noise ratio can then be calculated according to the following formula:

wherein the content of the first and second substances,qthe amount of the electric charge is represented,Bwhich represents the bandwidth of reception of the data,Rrepresenting the conversion coefficient.

When the coefficient of inconsistency is

The highest signal-to-noise ratio can be obtained at this time, i.e. the responsivities of the first quadrant detection units of the two detectors are completely identical. Through the calculation, the method has the advantages that,the signal-to-noise ratio which can be realized by the method is larger than 40dB, a schematic diagram of simulation results of the signal-to-noise ratio under different local oscillator light intensities is shown in FIG. 3, the local oscillator light intensities corresponding to 10 curves in the FIG. 3 from bottom to top are 1mW to 10mW in sequence, the abscissa in the FIG. 3 is solar background light power (dBm), and the ordinate is a tracking signal-to-noise ratio (dB).

Then, in the practical application process, the inconsistency coefficient

The method is in an ideal state and cannot be achieved, and the embodiment of the application needs to control the inconsistency coefficient of the first quadrant detection unit in the two detectors

To obtain a higher signal-to-noise ratio,

the constraint conditions of (1) are:

wherein the content of the first and second substances,qthe amount of the electric charge is represented,Rthe number of the conversion coefficients is represented,

representing the optical power of the split local oscillator light of the first quadrant detector unit,

indicating the power of the background daylight received by the first quadrant detector unit.

Obtained in the examples of the present applicationP _A ，P _B ，P _C AndP _D and may also be used to determine communication signals, fig. 4 shows a schematic diagram of a satellite laser communication link tracking communication integrated structure according to an embodiment of the present application; here, the communication signal M may include a first signal component M1 and a second signal component M2Wherein the first signal component M1=P _A +P _B +P _C +P _D Second signal component M2=P _A +P _D -（P _B +P _C ）Or M2=P _A +P _B -（P _C +P _D ）。

Fig. 5 shows a schematic diagram of a satellite laser communication link spot tracking compensation method using 4 2-quadrant detectors according to an embodiment of the present application. Referring to fig. 5, after the receiver receives the signal light, the signal light is divided into 4 beams of split signal light after passing through the splitting module, and the split signal light is respectively sent to 4 2-quadrant detectors PD1, PD2, PD3, and PD4, where the splitting module may include 3 first beam splitters for splitting the signal light into 4 beams of split signal light; similarly, after the local oscillation light with the same frequency as the signal light passes through 3 second beam splitters of the beam splitting module, the local oscillation light is split into 4 beams of beam splitting local oscillation light, one beam is collimated and then directly sent to the 2-quadrant detector PD1, the second beam is collimated and then sent to the 2-quadrant detector PD2 through the 180-degree frequency mixing phase shifter, the third beam is collimated and then sent to the 2-quadrant detector PD3 through the 90-degree frequency mixing phase shifter, and the fourth beam is collimated and then sent to the 2-quadrant detector PD4 through the 270-degree frequency mixing phase shifter.

The 2-quadrant detectors PD1, PD2, PD3 and PD4 respectively comprise 2 quadrants which are respectively a first quadrant and a second quadrant, a first quadrant detection unit and a second quadrant detection unit are respectively arranged, the first quadrant detection unit in the PD1 and the first quadrant detection unit in the PD2 form a quadrant detection unit pair, the second quadrant detection unit in the PD1 and the second quadrant detection unit in the PD2 form a quadrant detection unit pair, the first quadrant detection unit in the PD3 and the first quadrant detection unit in the PD4 form a quadrant detection unit pair, the second quadrant detection unit in the PD3 and the second quadrant detection unit in the PD4 form a quadrant detection unit pair, and here, two quadrant detection units in the quadrant detection unit pair form balanced detection.

The process of detecting the photocurrent by the quadrant detection unit in this embodiment is identical to that of the previous embodiment and will not be described in detail here.

The present embodiment can also obtain the difference between the corresponding photocurrents of the 4 quadrant detection units, wherein the difference between the detected optical powers of the first quadrant detection unit in PD1 and the first quadrant detection unit in PD2 is recorded as

The difference between the optical powers detected by the second quadrant detection unit in PD1 and the second quadrant detection unit in PD2 is recorded as

The difference between the optical powers detected by the first quadrant detection unit in PD3 and the first quadrant detection unit in PD4 is recorded as

The difference between the optical powers detected by the second quadrant detection unit in PD3 and the second quadrant detection unit in PD4 is recorded as

。

Based on

、

、

And

calculating the offset of the centroid of the light spot along the X direction

And centroid displacement in the Y direction

：

。

In this embodiment of the present invention,

、

、

and

and may also be used to determine the communication signal, where the communication signal

Comprising a first signal component

And a second signal component

Wherein the first signal component

Second signal component

Or

。

Fig. 6 shows a block flow diagram of a method for compensating spot tracking of a satellite laser communication link according to an embodiment of the present application. The method starts with step S610, splitting beams of signal light and local oscillator light to obtain a plurality of beams of split signal light and a plurality of beams of split local oscillator light; the multiple beams of beam splitting signal light and the multiple beams of beam splitting local oscillator light are respectively input into a plurality of detectors, each detector comprises a plurality of quadrant detection units, and the signal light can comprise the noise of the sun-and-rain background light. Here, the number of the split signal light and the split local oscillator light obtained by splitting the signal light and the local oscillator light is the same, and is the same as the number of the detectors.

Then, in step S620, the photocurrent detected by each quadrant detection unit in each detector is determined according to the split signal light and the split local oscillator light input into each detector. Here, one quadrant detection unit is arranged per quadrant in each detector.

Then, in step S630, a centroid offset amount of the light spot in the X direction and a centroid offset amount of the light spot in the Y direction are determined according to the photocurrent detected by each quadrant detection unit, wherein the centroid offset amount of the light spot in the X direction and the centroid offset amount of the light spot in the Y direction are used for tracking compensation of the light spot.

According to the embodiment of the application, after the signal light and the local oscillator light are split, the signal light and the local oscillator light are transmitted to the multi-quadrant detector with multiple consistent performance parameters, the multi-quadrant detector is used for corresponding to the detection unit to realize multi-path balanced detection, multi-path light current is obtained, and superimposed sunset background light noise and local oscillator light intensity noise in the signal light are filtered by using a balanced detection principle in coherent detection, so that a satellite laser link has the capability of resisting sunset stable tracking and communication.

In one embodiment, determining the centroid shift amount of the light spot in the X direction and the centroid shift amount of the light spot in the Y direction according to the photocurrent detected by each quadrant detection unit may include:

In one implementation mode, the number of the detectors is 2, each detector comprises 4 quadrant detection units, and quadrant detection units of corresponding quadrants in the 2 detectors form 4 quadrant detection unit pairs;

centroid offset of light spot in X direction

：

Centroid offset of light spot in Y direction

：

。

In other implementation manners, 4 detectors are provided, namely a detector PD1, a detector PD2, a detector PD3 and a detector PD4, and each detector comprises 2 quadrant detection units;

the quadrant detection units of the corresponding quadrants in the detectors PD1 and PD2 form 2 quadrant detection unitsFor each, the corresponding optical power difference is respectively recorded as:

，

and

and then:

centroid offset of light spot in X direction

：

Centroid offset of light spot in Y direction

：

。

In summary, the embodiment of the present application adopts the two detection arrangement manners, so as to achieve four-way balanced detection, and by using the balanced detection principle in coherent detection, the noise of the rabdosia background light and the noise of the local oscillator light intensity superimposed in the target signal light can be effectively filtered.

In an embodiment, in order to ensure that the satellite laser communication link light spot tracking compensation method of the embodiment of the present application has a higher signal-to-noise ratio, it is necessary to further control the inconsistency coefficients of two quadrant detection units in each quadrant detection unit pair:

in the formula (I), the compound is shown in the specification,

the inconsistency coefficients of the two quadrant detection units in the ith quadrant detection unit pair,qis the amount of the electric charge of the electron,

for the sunset background light power received by the quadrant detection unit in the ith quadrant detection unit pair,RINis the relative intensity noise figure of the local oscillator light,Rin order to convert the coefficients of the image,

is the coherent filter bandwidth.

Fig. 7 is a block flow diagram illustrating a method for transmitting signals of a satellite laser communication link according to an embodiment of the application. The method starts with step S710, splitting the signal light and the local oscillator light to obtain a plurality of beam split signal lights and a plurality of beam split local oscillator lights; a plurality of beams of beam splitting signal light and a plurality of beams of beam splitting local oscillator light are respectively input into a plurality of detectors, each detector comprises a plurality of quadrant detection units, and the signal light comprises the noise of a rabdosia background light; here, the number of the split signal light and the split local oscillator light obtained by splitting the signal light and the local oscillator light is the same, and is the same as the number of the detectors.

Then, in step S720, determining the photocurrent detected by each quadrant detection unit in each detector according to the split-beam signal light and the split-beam local oscillator light input into each detector; here, one quadrant detection unit is arranged per quadrant in each detector.

Then, in step S730, a communication signal is determined according to the photocurrent detected by each quadrant detection unit, and the communication signal is used for communication transmission.

In this embodiment, based on the photocurrent detected by the balanced detector, a signal for communication transmission is output, thereby realizing integration of tracking and communication. The optical signal after the balance detection of the corresponding unit of the balance detector can be directly used for demodulation and data recovery, the anti-rabdosia stable tracking and communication of the laser link are realized, the single-machine integration level is high, the miniaturization and the light weight are easy to realize, and the method is suitable for the inter-satellite and inter-satellite laser link transmission scene.

In one embodiment, determining a communication signal based on the photocurrent detected by each quadrant detection unit, the communication signal for communication transmission comprises:

In one implementation mode, the number of the detectors is 2, each detector comprises 4 quadrant detection units, and quadrant detection units of corresponding quadrants in the 2 detectors form 4 quadrant detection unit pairs; the difference values of the corresponding optical powers of the 4 quadrant detection units are respectively recorded as:P _A ，P _B ，P _C andP _D and then: the communication signal M comprises a first signal component M1 and a second signal component M2, wherein the first signal component M1= isP _A +P _B +P _C +P _D Second signal component M2=P _A +P _D -（P _B +P _C ）Or M2=P _A +P _B -（P _C +P _D ）。

In other implementation manners, 4 detectors are provided, namely a detector PD1, a detector PD2, a detector PD3 and a detector PD4, and each detector includes 2 quadrant detection units; quadrant detection units of corresponding quadrants in the detector PD1 and the detector PD2 form 2 quadrant detection unit pairs, and the difference values of the corresponding optical powers are respectively recorded as:

and

quadrant detection units of corresponding quadrants in the detector PD3 and the detector PD4 form 2 quadrant detection unit pairs, and the difference values of corresponding optical powers are respectively recorded as:

and

and then: communication signal

Comprising a first signal component

And a second signal component

Wherein the first signal component is the first signal component

Second signal component

Or

。

In order to ensure that the satellite laser communication link signal transmission method of the embodiment of the present application has a higher signal-to-noise ratio, it is necessary to further control the inconsistency coefficients of the two quadrant detection units in each quadrant detection unit pair:

in the formula (I), the compound is shown in the specification,

for the disparity coefficients of the two quadrant detection units in the ith quadrant detection unit pair,qis the amount of electricity of the electron,

is the coherent filter bandwidth.

Based on the same inventive concept as the satellite laser communication link light spot tracking compensation method, this embodiment further provides a satellite laser communication link light spot tracking compensation device corresponding to this embodiment, and fig. 8 shows a structural block diagram of the satellite laser communication link light spot tracking compensation device according to the embodiment of the present application, including:

an optical splitting unit 810, configured to split the signal light and the local oscillator light to obtain multiple beam split signal light and multiple beam split local oscillator light, where the signal light may include a background noise of a sun-ray;

a detector unit 820 configured to receive the plurality of split-beam signal lights and the plurality of split-beam local oscillator lights, wherein the detector unit includes a plurality of detectors, and each detector includes a plurality of quadrant detection units;

a photocurrent calculating unit 830, configured to determine a photocurrent detected by each quadrant detecting unit in each detector according to the split-beam signal light and the split-beam local oscillator light input to each detector;

and the centroid offset determining unit 840 is configured to determine a centroid offset of the light spot along the X direction and a centroid offset of the light spot along the Y direction according to the photocurrent detected by each quadrant detecting unit, where the centroid offset of the light spot along the X direction and the centroid offset of the light spot along the Y direction are used for tracking compensation of the light spot.

and determining the centroid offset of the light spot along the X direction and the centroid offset of the light spot along the Y direction according to the difference of the light power calculated by each quadrant detection unit pair.

Based on the same inventive concept as the satellite laser communication link signal transmission method, the present embodiment further provides a satellite laser communication link signal transmission apparatus corresponding thereto, and fig. 9 shows a block diagram of a structure of the satellite laser communication link signal transmission apparatus according to the embodiment of the present application, including:

an optical splitting unit 910, configured to split the signal light and the local oscillator light to obtain a plurality of split signal lights and a plurality of split local oscillator light, where the signal light includes a rabdosia background light noise;

a detector unit 920, configured to receive the multiple beams of split-beam signal light and the multiple beams of split-beam local oscillator light, where the detector unit includes multiple detectors, and each detector includes multiple quadrant detection units;

a photocurrent calculating unit 930, configured to determine, according to the split-beam signal light and the split-beam local oscillator light input into each detector, a photocurrent detected by each quadrant detecting unit in each detector;

and a communication signal determining unit 940 for determining a communication signal according to the photocurrent detected by each quadrant detecting unit, wherein the communication signal is used for communication transmission.

The embodiment of the present application further provides a satellite laser communication link light spot tracking compensation and communication system, including:

the light splitting unit is used for splitting the signal light and the local oscillator light to obtain a plurality of beams of split signal light and a plurality of beams of split local oscillator light, and the signal light comprises the noise of the daylight background light;

In this embodiment, in order to effectively utilize the received optical signal and simplify the optical design, a design integrating communication and fine tracking is adopted, and referring to fig. 4, after the signals after balanced detection by the multi-quadrant detector are subjected to photoelectric conversion, data signals obtained by adding in a digital domain need to be subjected to processing such as equalization, clock recovery, soft decision, decoding and the like. Based on the digital data demodulation module, the received signals are converted into digital signals through high-speed A/D and transmitted to the FPGA for digital demodulation. In FPGA, firstly, data signals are equalized through a digital filter, and factors such as intersymbol interference caused by a channel and a preceding stage receiving circuit are eliminated; the equalized signal is subjected to clock recovery through a digital algorithm, and the signal is resampled, so that a received signal clock is synchronous with a clock of a signal processor; and finally, performing data recovery on the signal in a soft decision mode, and performing other data processing such as subsequent decoding.

The satellite laser communication link light spot tracking compensation method based on the embodiment of the application verifies and analyzes the light spot tracking compensation effect.

Under the condition of providing sun constant sunlight strong illumination and different magnitudes of micro-vibration interference, closed-loop tracking verification is performed by adopting the method of the embodiment of the application. Table 1 shows the tracking accuracy of two axes of the receiving laser terminal under different simulation conditions. The closed loop tracking test results for the conditions corresponding to table 1 are given in fig. 10-23, respectively.

TABLE 1 tracking accuracy of two shafts of receiving laser terminal under different simulation conditions

Serial number	Analog quantity of micro-vibration of platform	X-axis tracking precision (μ rad)	Y-axis tracking accuracy (μ rad)
				1	40μrad、1Hz	0.10	0.12
2	30μrad、5Hz	0.12	0.15
				3	20μrad、10Hz	0.12	0.15
4	10μrad、30Hz	0.12	0.15
				6	0 to 100Hz composite vibration	0.14	0.16

10-12 show graphs comparing the single frequency micro-vibration tracking performance of a laser terminal pair with an amplitude of 40 μ rad and a frequency of 1Hz, wherein the left graph shows the 1Hz single frequency micro-vibration interference intensity and the right graph shows the tracking performance after tracking the closed loop; FIGS. 13-15 are graphs showing the comparison of the single-frequency microvibration tracking performance of a laser terminal at an amplitude of 30 μ rad and a frequency of 5Hz, wherein the left graph shows the 5Hz single-frequency microvibration interference intensity performance and the right graph shows the tracking performance after tracking the closed loop; 16-18 are graphs showing the comparison of single frequency microvibration tracking performance of a laser termination at 20 μ rad amplitude and 10Hz frequency, wherein the left graph shows the 10Hz single frequency microvibration interference strength and the right graph shows the tracking performance after tracking the closed loop; fig. 19-21 are graphs showing the comparison of single-frequency microvibration tracking performance of a laser termination at an amplitude of 10 μ rad and a frequency of 30Hz, wherein the left graph shows the 30Hz single-frequency microvibration interference intensity and the right graph shows the tracking performance after tracking the closed loop. According to the results in the figure, the light spot tracking compensation method (namely after tracking the closed loop) of the embodiment of the application has good tracking compensation capability on single-frequency micro-vibration, and the tracking precision is superior to 0.15 mu rad.

Fig. 22 shows a composite micro-vibration power spectrum before closed-loop tracking, fig. 23 shows a spot centroid residual power spectrum after closed-loop tracking, fig. 23 is a power spectrum distribution after closed-loop tracking is adopted for the composite micro-vibration spectrum shown in fig. 22, and it can be known from the results in the figure that closed-loop tracking has a significant effect on suppressing micro-vibration in the range of 0 to 100hz, and the tracking accuracy is better than 0.16 μ rad.

While the composite micro-vibration closed-loop tracking test is performed, a communication performance test is performed, fig. 24 shows a communication performance test result diagram of the satellite laser communication link signal transmission method according to the embodiment of the present application, where the abscissa is detection sensitivity (dBm), the ordinate is Bit Error probability (Bit Error Ratio, BER), and from left to right, four curves respectively represent a theoretical value at 0.5Gbps, a test value at 0.5Gbps, a theoretical value at 1Gbps, and a test value at 1Gbps, and it can be known from fig. 24 that by using the signal transmission method of the present application, stable communication at 1Gbps is achieved, and the communication performance test value is close to the theoretical value.

In summary, the present application has the following technical effects:

(1) By utilizing a balanced detection principle in coherent detection, the method effectively filters the noise of the rabdosia background light superposed in the signal, solves the problem that the traditional incoherent energy detector cannot stably work under the interference of strong background light noise such as rabdosia and the like, can realize stable tracking and communication against rabdosia and greatly improves the on-orbit availability of a laser link; (2) By utilizing heterodyne coherent detection, the optical frequency of a target signal does not need to be accurately captured, doppler frequency shift does not need to be compensated, an additional execution mechanism does not need to be introduced, and a processing algorithm is simplified; (3) Tracking and communication integration is realized by using a multi-quadrant detector; the optical signals after the balance detection of the corresponding units of the balance detector can be directly used for demodulation and data recovery, the anti-rabdosian stable tracking and communication of the laser link are realized, the single-machine integration level is high, the miniaturization and the light weight are easy to realize, and the method is suitable for the inter-satellite and inter-satellite laser link transmission scene.

In the embodiments provided in the present application, it should be understood that the disclosed apparatus and method may be implemented in other manners. The apparatus embodiments described above are merely illustrative, and for example, the flowchart and block diagrams in the figures illustrate the architecture, functionality, and operation of possible implementations of apparatus, methods and computer program products according to various embodiments of the present application. In this regard, each block in the flowchart or block diagrams may represent a module, segment, or portion of code, which comprises one or more executable instructions for implementing the specified logical function(s). It should also be noted that, in some alternative implementations, the functions noted in the block may occur out of the order noted in the figures. For example, two blocks shown in succession may, in fact, be executed substantially concurrently, or the blocks may sometimes be executed in the reverse order, depending upon the functionality involved. It will also be noted that each block of the block diagrams and/or flowchart illustration, and combinations of blocks in the block diagrams and/or flowchart illustration, can be implemented by special purpose hardware-based systems which perform the specified functions or acts, or combinations of special purpose hardware and computer instructions.

In addition, functional modules in the embodiments of the present application may be integrated together to form an independent part, or each module may exist separately, or two or more modules may be integrated to form an independent part.

The functions, if implemented in the form of software functional modules and sold or used as a stand-alone product, may be stored in a computer readable storage medium. Based on such understanding, the technical solutions of the present application or portions thereof that substantially contribute to the prior art may be embodied in the form of a software product, which is stored in a storage medium and includes several instructions for causing a computer device (which may be a personal computer, a server, or a network device) to execute all or part of the steps of the methods described in the embodiments of the present application. And the aforementioned storage medium includes: a U-disk, a removable hard disk, a Read-Only Memory (ROM), a Random Access Memory (RAM), a magnetic disk or an optical disk, and other various media capable of storing program codes.

The above description is only for various embodiments of the present application, but the scope of the present application is not limited thereto, and any person skilled in the art can easily think of the changes or substitutions within the technical scope of the present application, and shall be covered by the scope of the present application. Therefore, the protection scope of the present application shall be subject to the protection scope of the claims.

Claims

1. A method for compensating spot tracking of a satellite laser communication link is characterized by comprising the following steps:

splitting the signal light and the local oscillator light to obtain a plurality of beams of split signal light and a plurality of beams of split local oscillator light; the plurality of beams of beam splitting signal light and the plurality of beams of beam splitting local oscillator light are respectively input into a plurality of detectors, and each detector comprises a plurality of quadrant detection units;

determining the photocurrent detected by each quadrant detection unit in each detector according to the beam splitting signal light and the beam splitting local oscillator light input into each detector;

determining the centroid offset of the light spot along the X direction and the centroid offset of the light spot along the Y direction according to the photocurrent detected by each quadrant detection unit, wherein the centroid offset of the light spot along the X direction and the centroid offset of the light spot along the Y direction are used for tracking compensation of the light spot;

after phase shifting is carried out on part of the beam splitting local oscillator light in the plurality of beams of beam splitting local oscillator light, the phase shifted partial beam splitting local oscillator light is input into the detector;

determining a plurality of quadrant detection unit pairs, wherein two quadrant detection units in each quadrant detection unit pair form balanced detection; the two quadrant detection units in each quadrant detection unit pair are quadrant detection units of corresponding quadrants in two different detectors.

2. The method of claim 1, wherein determining the centroid displacement amount of the optical spot in the X direction and the centroid displacement amount in the Y direction based on the photocurrent detected by each quadrant detection unit comprises:

and determining the centroid offset of the light spot along the X direction and the centroid offset of the light spot along the Y direction according to the difference value of the corresponding optical power of each quadrant detection unit.

3. The method of claim 2, wherein determining the centroid shift amount of the light spot in the X direction and the centroid shift amount of the light spot in the Y direction based on the difference between the corresponding optical powers of the each quadrant detection unit pair comprises:

centroid offset of light spot in X direction

：

Centroid offset of light spot in Y direction

：

。

4. The method of claim 2, wherein determining the centroid shift amount of the light spot in the X direction and the centroid shift amount of the light spot in the Y direction based on the difference between the corresponding optical powers of the each quadrant detection unit pair comprises:

and

and

then:

centroid offset of light spot in X direction

：

Centroid offset of light spot in Y direction

：

。

5. The method of claim 2, wherein the method further comprises:

controlling the inconsistency coefficients of the two quadrant detection units in each of the quadrant detection unit pairs:

in the formula (I), the compound is shown in the specification,

is the coherent filter bandwidth.

6. A method for transmitting signals over a satellite laser communication link, comprising:

splitting the signal light and the local oscillator light to obtain a plurality of beams of split signal light and a plurality of beams of split local oscillator light; the multiple beams of beam splitting signal light and the multiple beams of beam splitting local oscillator light are respectively input into a plurality of detectors, and each detector comprises a plurality of quadrant detection units;

determining a communication signal according to the photocurrent detected by each quadrant detection unit, wherein the communication signal is used for communication transmission;

7. The method of claim 6, wherein determining a communication signal based on the photocurrent detected by each quadrant detection unit comprises:

8. The method of claim 7, wherein determining a communication signal based on the difference in optical power corresponding to each of the quadrant detection unit pairs comprises:

the communication signal M comprises a first signal component M1 and a second signal component M2, wherein the first signal component M1= isP _A +P _B +P _C +P _D The second signal component M2= i =P _A +P _D -（P _B +P _C ）Or M2=P _A +P _B -（P _C +P _D ）。

9. The method of claim 7, wherein determining a communication signal based on the difference in optical power corresponding to each of the quadrant detection unit pairs comprises:

quadrant detection units of corresponding quadrants in the detector PD1 and the detector PD2 form 2 quadrant detectorsAnd the difference values of the corresponding optical powers of the measuring unit pairs are respectively recorded as:

and

and

and then:

the communication signal

Comprising a first signal component

And a second signal component

Wherein the first signal component

The second signal component

Or

。

10. The method of claim 7, wherein the method further comprises:

in the formula (I), the compound is shown in the specification,

for the power of the rabdosia background light received by the quadrant detection unit in the ith quadrant detection unit pair,RINfor the local oscillator light relative intensity noise figure,Rin order to convert the coefficients of the image,

is the coherent filter bandwidth.

11. A satellite laser communication link facula tracking compensation arrangement, characterized by that, including:

the optical splitting unit is used for splitting the signal light and the local oscillator light to obtain a plurality of beams of split signal light and a plurality of beams of split local oscillator light; phase shifting is carried out on part of the beam splitting local oscillator light in the plurality of beams of beam splitting local oscillator light;

a detector unit, configured to receive the multiple beams of split-beam signal light and the multiple beams of split-beam local oscillator light, where the detector unit includes multiple detectors, and each of the detectors includes multiple quadrant detection units;

the photocurrent calculating unit is used for determining the photocurrent detected by each quadrant detecting unit in each detector according to the beam splitting signal light and the beam splitting local oscillator light which are input into each detector;

the centroid offset determining unit is used for determining the centroid offset of the light spot along the X direction and the centroid offset of the light spot along the Y direction according to the photocurrent detected by each quadrant detecting unit, wherein the centroid offset of the light spot along the X direction and the centroid offset of the light spot along the Y direction are used for tracking compensation of the light spot;

the centroid offset determining unit is further configured to determine a plurality of quadrant detecting unit pairs, where two quadrant detecting units in each quadrant detecting unit pair form a balanced detection; the two quadrant detection units in each quadrant detection unit pair are quadrant detection units of corresponding quadrants in two different detectors.

12. The apparatus of claim 11, wherein the centroid offset determination unit is further configured to:

13. A satellite laser communication link signal transmission apparatus, comprising:

the optical splitting unit is used for splitting the signal light and the local oscillator light to obtain a plurality of beams of split signal light and a plurality of beams of split local oscillator light; performing phase shift on partial beam splitting local oscillator light in the plurality of beams of beam splitting local oscillator light;

a detector unit for receiving the plurality of beams of split-beam signal light and the plurality of beams of split-beam local oscillator light, wherein the detector unit includes a plurality of detectors, and each of the detectors includes a plurality of quadrant detection units;

a communication signal determining unit, configured to determine a communication signal according to the photocurrent detected by each quadrant detection unit, where the communication signal is used for communication transmission;

the communication signal determination unit is further configured to determine a plurality of quadrant detection unit pairs, wherein two quadrant detection units in each quadrant detection unit pair form balanced detection; and the two quadrant detection units in each quadrant detection unit pair are quadrant detection units of corresponding quadrants in two different detectors.

14. The apparatus of claim 13, wherein the communication signal determination unit is further configured to:

15. A satellite laser communication link facula tracking compensation and communication system is characterized by comprising:

the centroid offset determining unit is further used for determining a plurality of quadrant detecting unit pairs, wherein two quadrant detecting units in each quadrant detecting unit pair form balanced detection; two quadrant detection units in each quadrant detection unit pair are quadrant detection units of corresponding quadrants in two different detectors;