CN114326102A - Static aberration correction method for space optical communication miniaturized terminal - Google Patents

Abstract

A static aberration correction method for a miniaturized terminal of space optical communication relates to the technical field of communication terminals. In view of the poor initial aberration of the common optical path and the beacon light receiving optical path in the prior art, the quality of the light spot of the beacon light received by the CCD is relatively poor. Poor, it is not conducive to the realization of the tracking function. This application can solve the problem of poor initial aberration in the common optical path and the beacon light receiving optical path. By controlling the deformable mirror to generate a specific initial compensation surface, the common optical path and the signal can be effectively eliminated. The static aberration of the light receiving path of the target light improves the spot quality of the beacon light received by the CCD, which is beneficial to the realization of tracking.

Description

Static aberration correction method for miniaturized terminal of space optical communication

technical field

The invention relates to the technical field of communication terminals, in particular to a static aberration correction method for a miniaturized terminal of spatial optical communication.

Background technique

In the space optical communication terminal with the same optical path for receiving and transmitting, adaptive optics is used to correct the wavefront aberration of the transmitted and received signals and beacon light. At this time, the communication terminal has one common optical path and five non-common optical paths. Among them, the wavefront detection optical path only plays the role of detecting wavefront aberration, and can calibrate its own initial aberration, so the communication terminal requires its aberration is relatively low, while the requirements for other non-common path aberrations are relatively high. However, the conventional adaptive optics system detects wavefront aberrations in the wavefront detection optical path through the Shack-Hartmann wavefront detector (SH-WFS), thereby controlling the deformable mirror (DM) to generate specific surface compensation This aberration can only ensure that the received signal quality of the wavefront detection optical path is good, and cannot guarantee that the aberrations of other non-common optical paths are also corrected. At the same time, there may be a large static aberration in the optical path of the entire system. Although this aberration can be measured in the laboratory, during the operation of the communication terminal, there will be special situations such as temperature change and dust adhesion. Static aberration will change. When the initial aberration of the common optical path and the beacon light receiving optical path is poor, the quality of the spot of the CCD receiving the beacon light is poor, which is not conducive to the realization of the tracking function.

SUMMARY OF THE INVENTION

The purpose of the present invention is: in view of the problem that the initial aberration of the common optical path and the beacon light receiving optical path in the prior art is poor, the quality of the light spot of the CCD receiving beacon light is poor, which is not conducive to the realization of the tracking function. A static aberration correction method for the common optical path and the beacon light receiving optical path in a miniaturized terminal of space optical communication.

The technical scheme that the present invention takes in order to solve the above-mentioned technical problems is:

A static aberration correction method for a miniaturized terminal of spatial optical communication, the method comprising:

Step 1: Build an all-optical path module, the all-optical path system includes three optical paths:

Optical path 1: The incident light passes through the telescope, the tracking system and the piezoelectric deformable mirror in sequence, and the beacon light after passing through the piezoelectric deformable mirror passes through the first beam splitter for beam reduction, and then enters the Shack-Hartmann wave after beam reduction front detector;

Optical path 2: The incident light passes through the telescope, the tracking system and the piezoelectric deformation mirror in sequence, and the beacon light after passing through the piezoelectric deformation mirror passes through the first beam splitter and then enters the second beam splitter. The target light enters CCD2 after being output by the focusing lens;

Optical path 3: The incident light passes through the telescope, the tracking system and the piezoelectric deformable mirror in sequence, and the beacon light after passing through the piezoelectric deformable mirror passes through the first beam splitter and then enters the second beam splitter, and then enters the signal of the second beam splitter. The target light enters the avalanche photodiode through the third beam splitter, the focusing lens, and the multimode fiber in sequence;

Step 2: According to the constructed all-optical path module, solve the control voltage of the compensation surface shape of the piezoelectric deformation mirror of the spot on the CCD2;

Step 3: Control the deformed mirror to generate a specific surface shape to compensate for aberration according to the control voltage, and record the deformed mirror surface shape at this time as the initial surface shape, that is, to complete the aberration correction.

The beneficial effects of the present invention are:

The present application can solve the situation that the initial aberration of the common optical path and the beacon light receiving optical path is poor. By controlling the deformable mirror to generate a specific initial compensation surface, the static aberration of the common optical path and the beacon light receiving optical path can be effectively eliminated, and the CCD can be improved. The spot quality of the received beacon light is beneficial to the realization of tracking.

Description of drawings

1 is a schematic structural diagram of an all-optical path system of the present application;

Fig. 2 is a schematic diagram of PSF evaluation function definition;

FIG. 3 is a schematic diagram of the RMS improvement of the random wavefront wavefront of the 100 groups of the optical path 2. FIG.

Detailed ways

It should be noted that, in the case of no conflict, the various embodiments disclosed in the present application may be combined with each other.

Embodiment 1: This embodiment is described in detail with reference to FIG. 1. The method for correcting static aberrations of a miniaturized terminal for spatial optical communication described in this embodiment includes:

Step 1: Build an all-optical path module, the all-optical path system includes three light paths:

Optical path 1: The incident beacon light passes through the telescope, the tracking system and the piezoelectric deformation mirror in sequence. The beacon light after passing through the piezoelectric deformation mirror passes through the first beam splitter for beam reduction, and then enters the Shack-Hart after beam reduction. Man wavefront detector;

Optical path 2: The incident light passes through the telescope, the tracking system and the piezoelectric deformation mirror in sequence, and the beacon light after passing through the piezoelectric deformation mirror passes through the first beam splitter and then enters the second beam splitter. The target light enters CCD2 after being output by the focusing lens;

Optical path 3: The incident light passes through the telescope, the tracking system and the piezoelectric deformable mirror in sequence, and the beacon light after passing through the piezoelectric deformable mirror passes through the first beam splitter and then enters the second beam splitter, and then enters the signal of the second beam splitter. The target light enters the avalanche photodiode through the third beam splitter, the focusing lens, and the multimode fiber in sequence;

Step 2: According to the constructed all-optical path module, solve the control voltage of the compensation surface shape of the piezoelectric deformation mirror of the spot on the CCD2;

Step 3: Control the deformed mirror to generate a specific surface shape to compensate for aberration according to the control voltage, and record the deformed mirror surface shape at this time as the initial surface shape, that is, to complete the aberration correction.

Embodiment 2: This embodiment is a further description of Embodiment 1. The difference between this embodiment and Embodiment 1 is that the specific steps of Step 2 are:

Step 21: Turn on the telescope, and the telescope receives opposite incident light;

Step 22: apply an initial voltage u ⁰ ={0,0,...0} to the piezoelectric deformation mirror electrodes;

Step 2 and 3: Calculate the evaluation function J ^k (u ^k ) by using the pixels on the CCD2, wherein,

I_i为CCD2圆盘中心，I_i直径为

λ为信标光波长，λ为808nm，f为CCD2前透镜焦距，f为20mm，D为透镜孔径，D为10mm，I_o为CCD2中去掉圆盘中心I_i的圆环，I_o直径为

J为评价函数，k表示第k次迭代结果，u表示压电变形镜控制电压向量；

I _i is the center of the CCD2 disc, and the diameter of I _i is

λ is the wavelength of the beacon light, λ is 808 nm, f is the focal length of the front lens of CCD2, f is 20 mm, D is the lens aperture, D is 10 mm, I _o is the ring in CCD2 that removes the center I _i of the disk, and the diameter of I _o is

J is the evaluation function, k is the result of the k-th iteration, and u is the control voltage vector of the piezoelectric deformable mirror;

Step 24: Randomly generate a disturbance vector δu ^k that satisfies the Bernoulli distribution;

和

Step 25: Apply the positive half perturbation vector δu ^k and the negative half perturbation vector δu ^k to the piezoelectric deformable mirror electrodes respectively, and then read the received power P of the avalanche photodiode respectively, and use the formula J= -P computes the merit function

and

和

得到评价函数的变化δJ^k：Step 26: According to

and

The change δJ ^k of the evaluation function is obtained:

Step 27: obtain u ^k+1 according to the disturbance vector δu ^k and the change δJ ^k of the evaluation function;

Step 28: Judging the value of k, if k>500, output the final optimized voltage u ^* , if k<=500, set u ^k = u ^{k +1} , repeat steps 22 to 27;

Step 29: Set the voltage of the deformable mirror to u ^* to complete the aberration correction.

Embodiment 3: This embodiment is a further description of Embodiment 2. The difference between this embodiment and Embodiment 2 is that the change δJ ^k of the evaluation function is expressed as:

Embodiment 4: This embodiment is a further description of Embodiment 3. The difference between this embodiment and Embodiment 3 is that the u ^k+1 is expressed as:

u ^k+1 =u ^k -γδJ ^k δu ^k

Among them, γ is the gain coefficient.

Embodiment 5: This embodiment is a further description of Embodiment 4. The difference between this embodiment and Embodiment 4 is that the piezoelectric deformable mirror includes 43 electrodes, including 40 electrodes on the main reflector and 3 independent pitch/tilt electrodes.

Embodiment 6: This embodiment is a further description of Embodiment 5. The difference between this embodiment and Embodiment 5 is that the working wavelength band of the piezoelectric deformable mirror is 450 nm-20 μm.

Embodiment 7: This embodiment is a further description of Embodiment 6. The difference between this embodiment and Embodiment 6 is that the piezoelectric deformation mirror has a maximum refresh rate of 4 kHz.

Embodiment 8: This embodiment is a further description of Embodiment 7. The difference between this embodiment and Embodiment 7 is that the detection band of the Shack-Hartmann wavefront detector is 400-900 nm, and the aperture is 4.5mm, the number of microlenses is ≤700, the size is 150μm, and the focal length is 10mm.

Embodiment 9: This embodiment is a further description of Embodiment 8. The difference between this embodiment and Embodiment 8 is that the detection band of the avalanche photodiode is 850-1650 nm.

Embodiment 10: This embodiment is a further description of Embodiment 9. The difference between this embodiment and Embodiment 9 is that the incident light is a laser diode.

The optical path diagram of the static aberration correction principle of the common optical path and the beacon light receiving optical path of the miniaturized terminal of space optical communication is shown in Figure 1. Assuming that the incident light is a plane wave, the light beam received by the CCD2 just contains both the static aberration information of the common optical path and the static aberration information of the optical path (2). The opposite incident beacon light is received by the telescope, enters the BS1 through the tracking system and the deformable mirror, and is divided into two beams. CCD2 receives. If the wavefront aberration is known through the light spot on the CCD2, and then the deformable mirror is controlled to generate a specific surface shape to compensate for this aberration, and the deformed mirror surface shape at this time is recorded as the initial surface shape, the common optical path and beacon light reception can be corrected. Static aberrations of the optical path. However, due to the limitations of the miniaturized communication terminal such as volume, quality, power consumption, etc., the communication terminal cannot additionally provide a reference plane wave. The present invention considers that when the weather conditions are good, the oppositely incident beacon light has only a small aberration, so the oppositely incident beacon light can be used as a reference light wave.

In this process, how to calculate the control voltage of the compensation surface of the deformable mirror through the light spot on the CCD2 is the key issue. It is generally considered to be an optimization problem, and the stochastic parallel gradient descent method is used to solve iteratively, and the specific iterative expression is shown in formula (1).

u ^k+1 =u ^k -γδJ ^k δu ^k (1)

where the superscripts k and k+1 represent the k-th iteration result and the k+1-th iteration result respectively, u={u ₁ , u ₂ ,...u _N } is the control voltage vector of the deformable mirror, and N is the number of actuators number, J is the evaluation function, and γ is the gain coefficient. δu={δu ₁ ,δu ₂ ,...δu _N } is the applied random disturbance vector, the evaluation function change value is δJ,

δJ=J ₊ -J _- =J(u+δu/2)-J(u-δu/2) (2)

The selection of the evaluation function is also very important in the algorithm. Since the plane wave incident imaging is equivalent to the imaging of a point light source, the point spread function can be selected as the evaluation function. The point spread function is the light field distribution of the output image when the input object is a point light source. A perfect PSF consists of a bright Airy disk with minimal diffraction fringes around the disk. If wavefront aberration occurs, more intensity energy will be pushed into the diffraction fringes, thereby reducing the energy in the Airy disk, so we give the expression of the evaluation function J as follows,

Among them, I _i is the light intensity of each pixel in the Airy disk, and I ₀ is the light intensity of each pixel of the diffraction fringes around the disk, as shown in Figure 2,

The present invention corrects the static aberration of the common optical path and the beacon light receiving optical path as follows:

Turn on the telescope so that the communication terminal can receive the opposite incident light, the communication terminal stops other work, starts to perform static aberration correction, and uses the computer to complete steps (2) to (8);

The initial voltage u ⁰ ={0,0,...0} is applied to the 43 electrodes of the deformable piezoelectric deformable mirror, u[1:40] is the control voltage of the 40 actuators on the main mirror, u[41: 43] are the control voltages for the 3 independent pitch/tilt actuator arms;

λ为信标光波长805nm，f为CCD2前透镜焦距20mm，D为透镜孔径10mm，I_o为直径为

中心为CCD中心、去掉I_i部分的圆环；Using the pixels on CCD2, the evaluation function J ^k (u ^k ) is calculated according to formula (3) and Fig. 2, the center of the I _i disk is the center of the CCD, and the diameter is

λ is the wavelength of the beacon light 805nm, _f is the focal length of the CCD2 front lens 20mm, D is the lens aperture 10mm, Io is the diameter of

The center is the CCD center, and the ring with the I _i part removed;

Randomly generate random disturbance vectors that satisfy Bernoulli distribution δu ^k ={δu ₁ ,δu ₂ ,...δu ₄₃ };

和

Using the pixels on CCD2, the evaluation function is calculated according to formula (3)

and

Calculate δJ ^k by formula (2);

Calculate u ^k+1 by formula (1);

Judging the value of k, if k>500, output the final optimized voltage u ^* , if k<=500, then set u ^k =u ^k+1 , repeat the process of (2) to (7);

Save the optimized voltage u ^* in the computer hard disk;

Set the voltage of the deformable mirror to u ^* , and the communication terminal resumes normal operation.

The specific implementation scheme of the static aberration correction device for the common optical path and the beacon light receiving optical path in the miniaturized terminal of space optical communication is as follows:

光瞳，具有大行程，最高刷新率为4kHz，43个致动器(主反射镜上的40个致动器和3个独立的俯仰/倾斜致动器臂)。The deformable mirror is a deformable piezoelectric deformable mirror of Thorlab's model DMH40-P01, a silver film with a protective layer, and the working band is 450nm-20μm.

Pupil, with large travel, maximum refresh rate of 4kHz, 43 actuators (40 actuators on the primary mirror and 3 separate pitch/tilt actuator arms).

SH-WFS selects the wavefront detector of OKO company model UI-2210M, the detection type is CCD detection, the detection band is 400-900nm, the aperture is 4.5mm, the number of microlenses is ≤700, the size is 150μm, and the focal length is 10mm.

The test computer is a computer server, the CPU is i7 4630K (6x3.4Ghz avec 12Mo LLC, 2MoL2total), the motherboard is ASUS X79-DELUXE, the hard disk is SAMSUNG SSD 840PRO 256GB, the graphics card is GAINWARDGEFORCE GT730 2GB DDR3 SILENT FX, and the memory is GSKILL 16GB (4X4) QUAD CHANNEL F3-14900CL9Q-16GBZL.

The beacon light source uses a laser diode model ML620G40, the wavelength is 808nm, the output optical power is 150mw, the typical driving current is 180mA, the maximum is 220mA, and the size is

The detector uses an avalanche photodiode model APD310, the detection band is 850-1650nm, the 3dB bandwidth is 5-1000MHz, and the responsivity at 1550nm wavelength is 0.9A/W.

It should be noted that the specific embodiments are only explanations and descriptions of the technical solutions of the present invention, and cannot be used to limit the protection scope of the rights. Any changes made according to the claims and description of the present invention are only partial changes, which should still fall within the protection scope of the present invention.

Claims (10)

1. The method for correcting the static aberration of the space optical communication miniaturized terminal is characterized by comprising the following steps:

the method comprises the following steps: constructing an all-optical-path module, wherein the all-optical-path system comprises three optical paths:

a first optical path: the incident light sequentially passes through the telescope, the tracking and aiming system and the piezoelectric deformable mirror, the beacon light passing through the piezoelectric deformable mirror is contracted after passing through the first beam splitter, and the contracted light enters the summer-Hartmann wavefront detector;

and a second light path: the incident light sequentially passes through the telescope, the tracking and aiming system and the piezoelectric deformable mirror, the beacon light passing through the piezoelectric deformable mirror enters the second beam splitter after passing through the first beam splitter, and the beacon light output by the second beam splitter enters the CCD2 after being output by the focusing lens;

and (3) an optical path III: the incident light sequentially passes through the telescope, the tracking and aiming system and the piezoelectric deformable mirror, the beacon light passing through the piezoelectric deformable mirror enters the second beam splitter after passing through the first beam splitter, and the beacon light entering the second beam splitter enters the avalanche photodiode after sequentially passing through the third beam splitter, the focusing lens and the multimode fiber;

step two: according to the constructed full light path module, the control voltage of the light spot piezoelectric deformable mirror compensation surface type on the CCD2 is calculated;

step three: and controlling the deformable mirror to generate a specific surface type compensation aberration according to the control voltage, and recording the deformed mirror surface type as an initial surface type at the moment, namely completing aberration correction.

2. The method for correcting the static aberration of the space optical communication miniaturized terminal according to claim 1, wherein the second step comprises the following specific steps:

step two, firstly: opening the telescope, and receiving the opposite incident light by the telescope;

step two: applying an initial voltage u to the piezoelectric deformable mirror electrode⁰＝{0，0，...0}；

Step two and step three: calculating evaluation function J by using pixel points on CCD2^k(u^k) Wherein, in the step (A),

I_iis the center of the disk of CCD2, I_iDiameter of

λ is the wavelength of the beacon light, λ is 808nm, f is the focal length of the front lens of the CCD2, f is 20mm, D is the aperture of the lens, D is 10mm, I_oRemoving the disc center I from CCD2_iCircular ring of (I)_oDiameter of

J is an evaluation function, k represents a kth iteration result, and u represents a control voltage vector of the piezoelectric deformable mirror;

step two, four: randomly generating disturbance vector delta u satisfying Bernoulli distribution^k；

Step two and step five: respectively applying positive one-half disturbance vector delta u to the electrodes of the piezoelectric deformable mirror^kAnd negative one-half disturbance vector delta u^kThen, the received power P of the avalanche photodiodes is read, and an evaluation function is calculated by the formula J-P

And

step two, step six: according to

And

obtaining the change delta J of the evaluation function^k：

Step two, seven: according to the disturbance vector delta u^kAnd the change δ J of the evaluation function^kTo obtain u^k+1；

Step two eight: judging the value of k, if k is more than 500, outputting the finally optimized voltage u^*If k is less than 500, let u be^k＝u^k+1Repeating the second step to the seventh step;

step two nine: setting the deformable mirror voltage to u^*And completing aberration correction.

3. The method for correcting the static aberration of the space optical communication miniaturized terminal as claimed in claim 2, wherein the variation δ J of the evaluation function^kExpressed as:

4. the static aberration correction method for space optical communication miniaturized terminal according to claim 3, wherein said u is^{k +1}Expressed as:

u^k+1＝u^k-γδJ^kδu^k

where γ is a gain factor.

5. The spatial optical communication miniaturization terminal static aberration correction method as defined in claim 4, wherein said piezoelectric deformable mirror comprises 43 electrodes, including 40 electrodes on the main mirror and 3 independent pitch/tilt electrodes.

6. The static aberration correction method for space optical communication miniaturized terminal according to claim 5, characterized in that the working wavelength band of said piezoelectric deformable mirror is 450nm-20 μm.

7. The static aberration correction method for space optical communication miniaturization terminal according to claim 6, characterized in that the maximum refresh rate of said piezoelectric deformable mirror is 4 kHz.

8. The method for correcting the static aberration of the space optical communication miniaturized terminal according to claim 7, wherein the detection waveband of the shack-Hartmann wavefront detector is 400-900 nm, the caliber is 4.5mm, the number of the micro-lenses is less than or equal to 700, the size is 150 μm, and the focal length is 10 mm.

9. The method as claimed in claim 8, wherein the detection band of the avalanche photodiode is 850-1650 nm.

10. The static aberration correction method for space optical communication miniaturized terminal according to claim 9, wherein said incident light is a laser diode.

Images