SU1712934A1 - Adaptive optical focusing system - Google Patents

Abstract

The invention relates to radio engineering. The purpose of the invention is to improve the quality of focusing on a long object with a uniformly reflecting surface. This is achieved by those. that, in the plane of the receiving aperture, the distribution of the intensity of the field reflected from the extended object is analyzed and the complex functional that takes into account not only the magnetic ones is maximized. but also the spatial information (entropy) characteristics of this gender. For this purpose, M processing devices, a matrix of M photodetectors, a DC source, an adder, and the relations between them are introduced into the adaptive optical focusing system with time division channels. 2 il. • h * ^^

Description

The invention relates to radio engineering and can be used both in optical location systems and in optical information and clearing systems operating on the reflected signal in adaptive modes of selection, search and tracking.

Adaptive focusing optical systems are known that operate on the principle of phase conjugation and aperture sounding, in which, in order to improve the energy characteristics of the radar system channels under the conditions of different phase disturbances of the medium, a diffraction-limited beam is obtained, i.e. focus it on a dot or extended

object using the methods and means of adaptive optics. In this case, focusing on a long object is achieved due to the effect of convergence of the beam on the most intense point.

However, for uniformly reflecting objects of specular or diffuse types, it is not possible to obtain a diffraction limited beam in the Fraunhofer zone.

Adaptive optical systems focusing on an extended object are also known, using the method of aperture sounding and based on the analysis of the interference field generated by the emitted and reflected waves.

However, these devices only partially improve the quality of adaptive focusing.

The closest in technical essence to the present invention is an adaptive optical system operating according to the method of aperture sounding with time division channels and analyzing the intensity of the field reflected by an optical intensity receiver. The system (Fig. 1) consists of successively optically coupled coherent light source 1, a corrector 2 of N phase-shifting elements with transmitting optics, a turbulent medium 3 reflecting the light of an extended object 4, a telescope and receiving optics 5 and an optical intensity receiver 6, and also a digital device 7 generating control signals, comprising electrically connected analog-to-digital converter 7-1, processor 7-2, digital-to-analog converter 7-3, decoder 7-4 addresses, as well as N circuits 7-5 tension Moreover, the output of the telescope and receiving optics 5 is connected to the input of the optical receiver 6, the output of which is connected to the input of analog-digital converter 7-1, and the output of which is connected to the input of processor 7-2, the output of the latter is simultaneously connected to the inputs of the decoder 7-4 addresses and digital-to-analog converter 7-3, the outputs of which are connected to the corresponding inputs of N voltage storage circuits 7-5, and their outputs are connected to the inputs of N phase-shifting elements of the corrector 2.

The transmitting aperture is divided into N sub-apertures by the number of phase-shifting elements, and is also divided into equal parts by the number of sub-apertures (sub-aperture ensembles) called orthogonal spatial planes that can be constructed using Walsh functions.

The known adaptive optical focusing system works as follows.

In the initial state, due to random distortions of the phase front by the turbulent medium 3 or the intrinsic aberrations of the optics in the far zone (in the object plane), a defocused beam with a certain number of local maxima and minima is formed. The width of such a beam depends on the nature and statistical characteristics of the phase distortions and the initial distribution of the phases on the subapertures. The laser radiation 1 is directed to the equalizer 2, in which the beam splits into N rays.

The beams are directed to the corresponding phase-shifting elements, which sequentially in time, in accordance with the processor operation algorithm, change them.

phase in small limits D - 20.

Then all the rays are combined into a beam and directed through the turbulent medium 3 to the object 4, and the signal reflected from it is directed to the receiving telescope 5 and the optical receiver 6.

The photocurrent of the received signal is proportional to its intensity (AND Ti when the beam phase changes by + A. (p BI moment of time ti and la T2 when changing

 the phases of the beam are at –A at time t2), from the output of the photoreceiver 6 is fed to the input of the analog-digital converter 7-1, then the signal in digital form is fed to the input of the processor 7-2. The processor (computer) calculates the difference A ii And - 1o and A12 12 - io. where 1o is the photocurrent from the photodetector output at time point to. corresponding to the initial position of the photo-shifting elements on a given control step. On

 The processor output produces a digital code proportional to a positive Al value, which corresponds to an increase in the intensity of the received beam. It also contains the address code of the voltage memory circuits, which operate at this step of the algorithm and control the corresponding ensemble of sub-apertures. The address code decoding device reads the address code and, with its output signal at a given control cycle, includes the appropriate voltage memory circuitry. The digital error signal from the processor output is fed to a digital-to-analog converter and then to the input of voltage memory circuits, from the output of which the control signal is fed to the input of phase-shifting elements. In such a sequence, the phase-shifting elements of the ensemble of sub-apertures are controlled until they reach the position when the condition А И О, А 1 о is fulfilled, which corresponds to the maximum intensity of the reflected radiation received by the photoreceiver. Then, following a signal from processor 7-2, the next set of voltage storage circuits 7-5 corresponding to the next ensemble of sub-apertures begins to work.

Thus, all elements of the corrector are sequentially controlled in time until the compensation of phase raids is achieved, which leads to

maximize the intensity reflected from the object gender.

However, such a system does not achieve full focusing on an extensive object with a uniformly reflecting surface, i.e. It does not form (5ts diffraction limited spot on an object located in the far diffraction zone. This is due to the fact that the intensity of the field reflected from the object, which forms a certain interference pattern (speckle pattern), is analyzed in the aperture plane. As a result, the intensity at the point is maximized the receiving aperture, as a rule, is achieved by increasing the intensity of one of the speckles of the interference pattern. The size of this speckle is equal to

gz

where I am the wavelength;

P is the distance to the object;

R is the linear size of the object, which on the object corresponds to the disintegration of the laser beam into several rays.

The purpose of the invention is to improve the quality of focusing, for example, to obtain a diffraction orpaHj / i4eHHpro beam or the maximum possible intensity on an object with a uniformly reflecting surface. .

The goal is achieved by the fact that in the process of adaptation both energy and information characteristics of the reflected floor in the aperture plane are taken into account, i.e. Entropy type criteria are used. The physical essence of obtaining diffraction-limited beams while maximizing the intensity and entropy of the reflected field is as follows. A beam focused in the plane of the object in the far zone (in the plane of the aperture) gives a reflected field with a uniform directivity characteristic within the aperture size. Such a uniform field has a maximum entropy, written as m

(MI17

1; 5, -TG (H

where Im are the intensity counts in the aperture plane at the m-th point of the analysis;

M is the total number of analysis points;

00

In 2 f is full intensity in

aperture plane ..

To achieve maximum intensity within the facility, it is also necessary to maximize the received

intensity. Then for a spectacular focus on a uniformly reflecting object, it is necessary to choose criteria that maximize both the intensity and the entropy field, for example, the functional;

Rl Slm-Ilm (En (), (1)

m 1 tch

which can be converted to mind

R2 lm (A-fnlm), (2)

m 1

where A is a constant that is selected from

conditions A 1 + Enln based on the forecast.

To achieve this goal in

an adaptive optical focusing system introduced M processing devices, an array of photodetectors of M elements, a DC source and an adder, and the outputs of photodetectors are connected to

the first inputs of processing devices, the second inputs of which are connected to the output of a direct current source, and the outputs are connected to the inputs of an adder whose output is connected to the input of a digital device

generating control signals.

Fig, 2 shows a structural diagram of an adaptive optical focusing system.

The circuit consists of optically coupled

coherent light source 1, corrector 2 of N phase-shifting elements, turbulent medium 3, reflecting light of extended object 4, telescope and receiving optics 5, matrix 6 intensity photodetectors, as well as M processing devices 7, DC 8 source, adder 9 digital device 10 generation of control signals. The output of the telescope and receiving optics 5 optical

connected to the input of the matrix 6 photodetectors, and their outputs are connected to the inputs of processing devices 7, a separate input of which is connected to the output of a DC source 8, and the outputs are connected to

the inputs of the adder 9. The output of the latter is connected to the input of the digital device 10 of the formation of control signals, the outputs of which are connected to the corresponding electrical inputs

phase shifter corrector 2.

Each of the M processing devices 7 is configured as a series-connected logarithmic amplifier 11 with a gain factor KEnI, a subtractive device 12 and a multiplier device 13, as well as a direct current amplifier 14 with a gain factor K. Such a device in cooperation with an adder 9 and a source 11 constant current

performs the transformation (which corresponds to the functional Rz):

n} -1

KIm (lc-ftiKlm).

t 1

where 1c is the direct current from the output of the source 8 of the direct current, playing the role of a constant A in the relation (2).

The system works as follows.

The beam reflected from the extended object 4 is fed to the input of the telescope with receiving optics 5 and to the matrix b of photodetectors consisting of M elements.

From the output of each photo / detector to the input of the corresponding processing device 7, an electrical signal is proportional to the received intensity, and is processed in a certain way. Next, the signals from the outputs of the processing devices are fed to the inputs of the adder 9, and from its output the resulting signal is fed to the input of the digital device 10 for generating control signals, from the outputs of which the signals go to the corresponding electrical inputs of the equalizer 2.

Fo rumula and 3 a b op i Adaptive optical radiation focusing system with modal control and time division of channels, consisting of consecutively optically coupled coherent light source.

gtjue.i

a corrector consisting of N phase-shifting elements, a telescope and receiving optics, an optical receiver and a digital control shaping device

signals, and the N outputs of the digital device for generating control signals are connected to the corresponding electrical inputs of the corrector, characterized in that, in order to increase

the quality of focusing the radiation on the object, the optical receiver is made in the form of an array of photodetectors of M elements, the dimensions of this matrix are matched with the dimensions of the aperture of the corrector, M processing devices are entered into the system, each of which consists of a DC amplifier and serially connected logarithmic amplifier subtracting devices and

multiplication devices, with the input of the current amplifier connected to the input of the logarith-. power amplifier, and the output is connected to the second input of the ground device. the DC source and the adder, the photodetector outputs are connected to the inputs of logarithmic amplifiers, the output of the DC source is connected to the second inputs of the subtractors, and the outputs of the multiplication devices are connected to the digital input of the control signals.

Claims (1)

Claim Adaptive optical radiation focusing system with modal control ₃ and time division of channels, consisting of sequentially optically connected coherent light source, corrector, consisting of N phase-shifting elements, telescope and receiving optics, optical receiver and digital device for generating control signals, with N outputs a digital device for generating control signals connected to the corresponding electrical inputs of the corrector, characterized in that, in order to improve the quality and focusing radiation on an extended object, the optical receiver is made in the form of a matrix of photodetectors of M elements, the dimensions of this matrix being consistent with the size of the corrector aperture, M processing devices are introduced into the system, each of which consists of a direct current amplifier and a logarithmic amplifier connected in series subtracting devices and multiplication devices, and the input of the current amplifier is connected to the input of the logarithm. of the amplifier, and the output is connected to the second input of the multiplying device, as well as a DC source and adder, the outputs of the photodetectors are connected to the inputs of the logarithmic amplifiers, the output of the DC source is connected to the second inputs of the subtracting devices, and the outputs of the multiplying devices are connected to the inputs of the adder, the output of which connected to the input of a digital control signal generation device.