RU1793219C - Aperture sounding adaptive optical system - Google Patents

Abstract

Usage: in information and measuring systems. SUMMARY OF THE INVENTION: the device comprises a coherence radiation source 1 with a phase shifter 2, a detector 3 connected to an amplitude detector 5 and connected in series with a voltage limiter 4, a synchronous detector 6, a low-pass filter 9, a character determination unit 10, the output of which is connected to the input multiplier 11, and the output of the latter with the input of the adder 12, the second input of which is connected to the output of the modulating generator 7. and the output with the control input of the phase shifter 2. The modulating generator is connected to the control input oh delay line 8. the output of the detector is connected to the input of the second bandpass filter of combinational frequency connected in series, the amplifier is a limiter 14 and the phase detector 17, the second input of which is connected to the output of the first bandpass filter 15, 1-2-3-16-14-17- 8-6-9-10-11-12 1-2-3-5-11-12-13-15-17 1-2-3-4-6-9-10-11-12. 1 ill. ate with

Description

The invention relates to laser technology and can be used in information and measurement systems.

Various devices of adaptive optical systems for aperture sounding are known in which the phase of the coherent radiators is adjusted according to the reflected signal.

These devices propose the introduction of a time delay in the reference signal equal to the propagation time of the radiation to the target and vice versa. A disadvantage of these devices is that an error in the value of the distance to the object leads to errors in the phasing of the system as a whole.

Closest to the technical nature is an adaptive optical system comprising a coherent radiation source with a phaser, a detector; synchronous detector, low-pass filter, adder, modulating oscillator, amplitude detector, voltage limiter, controlled delay line, sign detection unit; multiplier. During operation, the signal of the coherent radiation source passes through a phase shifter, while the phase modulation of the reflected radiation is received by the detector. This signal is simultaneously applied to a voltage limiter and an amplitude detector. Preliminarily, a delay value is set in the delay lines corresponding to the time the signal travels to the target and vice versa. At the output of the synchronous detector, the signal is proportional to the phase difference of the signal from the output of the limiter and the delay line. Depending on the sign of the output voltage of the synchronous detector, a corresponding phase correction signal is generated, which is summed in the adder with a modulating signal to control the phase shifter. This ensures a decrease in the dependence of the phase correction signal on range measurement errors / leads to an increase in the accuracy of focusing the laser radiation of the source on the target:

The disadvantage of this device is the need for preliminary measurement of the distance from the object, which requires the presence of an additional measuring range of the system, while the measurement channels of the optical system and the additional rangefinder system require accurate angular alignment, which leads to a significant decrease in the reliability of the adaptive system as a whole.

The aim of the invention is to improve the accuracy,

This goal is achieved by using the phase modulation Raman frequencies to measure the distance to the target. For this, a limiter amplifier, mixer, two bandpass filters and a phase comparator are additionally introduced into the prototype device. In this case, the first input of the mixer is connected to the output of one of the modulating generators, and the second input

- with the output of another modulating generator, the output is with the input of the first bandpass filter, the input of the second bandpass filter is connected to the output of the optical detector, and the output is connected to the input of the amplifier-limiter,

the output of which is connected to the second input of the phase comparator, the first input of which is connected to the output of the first band-pass filter, and the output to the input of the controlled delay line .;

The invention is as follows.

We expand in the Bessel-Fourier series the expression for: the intensity of the signal reflected from a point target

lf Xvi cos (% t sin QJ t) 2, (1)

where vi is the sex field created by the i-th subaperture at the object;

Sho is the frequency of optical radiation; p is the intrinsic phase of the radiation of the i-th subaperture at the object, comprising the intrinsic phase of the generator and the geometric phase incursion from the I-th subaperture to the object; $ is the phase modulation index in the i-th channel;

QI - phase modulation frequency in the i-th channel,,

When transforming expression (1), we take into account only low-frequency components of the form

 + t / (Sinfii t- sin Qit) (2) where Ap y - fi; ip $ Щ. After transformations, expression (2) can easily be rewritten in the form (taking into account the third and fourth harmonics of the frequencies of the phase modulation)

A | j COS + 2l0l2COS2 Qi t +

+ 2l0l2cos 2 Qjt + 2 I0 Ts cos 4 Qjt +

+ 4 l22 cos 2 Qi t cos 2 ujj t + 4 la Ucos 2 x

xQj t cos 4 QI t 4 -...) + sin (2 I0 li sin

Qj t. + 2 h 12 sin Qj t) cos 2 Qi t +2 ttU sin

xQjt cos 4 Qit +2 0 lasin 3 Qjt + 4I2I3X

Sin3 Qjt cos2 Qi t. + 2 ioH sin Qit + 2 Irl2 sin Qi t cos 2 Qjt + ...),

where li is the Bessel function of the ith order of the phase modulation index.

By analyzing expression (3), we can distinguish terms of the form., Sin Apij 2 h 12 sin Qi tcos2 Qj t (4.1),

sin 2 H 2 sin QJ t cos 2.Qi t (4.4)

co: s 4

I22cos2 Q; t cos 2 Qit (4.3).

| cos 4 h 2 sin QI t sin QJ t (4.4), etc.

 In the spectrum of signals (4) there are Raman frequencies, for example, for expression (4.4)

1 cos Apij 2 (Q | -Qj) (Qi + Qj) t (5) When the radiation propagates from the emitting aperture to the object and vice versa, each frequency component due to the signal delay in the channel will receive an additional phase shift proportional to the distance to the object. Low difference frequencies allow you to unambiguously measure the distance to the object.

The drawing shows a structural diagram of the proposed device.

The device comprises a coherent radiation source 1, a phase shifter 2, de-3, a voltage limiter 4, an amplitude detector 5, a synchronous detector 6, a modulating generator 7, a controlled delay line 8, a low-pass filter 9, a sign determination unit 10, a multiplier 11, adder 12, mixer 13 amplifier-limiter 14, first combinational frequency field filter 15), second combinational frequency bandpass filter 16, phase detector 17.-. Description of the device in statics. The coherent radiation source 1 is optically connected to the input of the phase shifter 2, the output of which is optically connected through the object to the input of the detector 3, the output of which is simultaneously connected to the inputs of the amplitude detector 5, the voltage limiter 4 and the input of the second Raman bandpass filter 16. The output of the voltage limiter Jack 4 is connected to the input of the synchronous detector 6, the second input of which is connected to the output of the controlled delay line 8, and the output to the input of the low-pass filter 9, the output of which is connected to the input of the unit tim plate 10, whose output is connected to a first vhbdom multiplier 11, a second input coupled to an output of the amplitude detector 5, the output of multiplier 11 is connected to a first input of an adder 12, a second input coupled to an output of the modulating oscillator 7, and an output. - with

the control input of the phase shifter 2, the first and second inputs of the mixer 13 are connected to the outputs of the modulating generators 7 of two different channels of the device, and the 5 output is connected to the input of the first bandpass filter of combinational frequency 15, the output of which is connected to the first input of the phase detector 17, the second input of which is connected -. nen with amplifier output limiter 14,

0, the input of which is connected to the output of the second bandpass filter of combinational frequency 16, the output of the phase detector 17 is connected to the inputs of the controlled delay line 8 of all channels.

5 The device operates as follows. -:

The optical radiation of the coherent radiation source 1 passes through a phase shifter 2, where it acquires in each

In channel 0, an additional phase shift consisting of a control phase and a phase shift at the modulation frequency in the channel. The radiation of individual channels reaches the object where the interference

5 is a radiation pattern of the entire apparatus. The radiation reflected from the target is received by the detector 3, the output of which is fed to the input of the voltage limiter 4 and the amplitude detector 3, and

0 to the input of the second bandpass filter 16 of the Raman frequency. The voltage limiter 4 eliminates the dependence of the procedure for determining the sign of the signal on its amplitude, which is performed by units 6, 9, and 10. The signal from the output of the voltage limiter 4 is fed to the input of a synchronous detector 6, to the second input of which a signal is output modulating generator 7 through a controllable line

0 of the hold 8. The signal from the output of the synchronous detector is fed to a low-pass filter 9, where a low-frequency signal is allocated, which is proportional to the phase difference of the received and modulating oscillations at the frequency of this channel. The amplitude detector 5 detects the phase deviation of a given channel from the reference phase, since it is proportional to the amplitude of the oscillations. in the reflected signal at the frequency of a given channel, as

0 this is known from the theory of adaptive aperture sounding systems (see Adaptive Optics of the collection of articles edited by Weirichenko). The character determining unit 10 determines the sign of the voltage at the output of the low frequency filter.

The signal from the output of the sign-determining unit 10 is multiplied in the multiplier 12, with the signal from the output of the amplitude detector 5. As a result, the output signal is a phase correction signal in this channel.

The signal from the output of the multiplier 11 is added with modulating oscillation from the output of the modulating generator 7 in the adder 12, the output signal of which is the control for the phase shifter 2.

We can assume that the channel for determining the sign of the correction signal, containing the voltage limiter 4, a synchronous detector 6, a low-pass filter 9, and a sign determination unit 10, implements an accurate measurement of the distance to the object in this channel. In order to implement a coarse scale, the measurement range must be carried out at a low frequency to ensure that measurements are unambiguous in the range of maximum ranges and to introduce roughly time delay values into the controlled delay line 8 in all channels simultaneously. For this, two channels are selected in the device so that the condition

C / (Qi-Qj) DMax. (6) where C is the speed of light;

Qi, QJ - modulating frequencies;

Omaha - the maximum range of the adaptive optical system.

Signals from the outputs of modulating generators 7 of two channels satisfying

condition (6), are fed to the inputs of the mixer 13. The signal from the output of the mixer 13 is fed to the input of the first band-pass filter 15 of the combination frequency tuned to the differential frequency. The signal from the output of the detector 3 is fed to the input of the second band-pass filter 16 of the combination frequency tuned to the same frequency as the first, from the output of which the signal is fed to the input

a limiter amplifier 14, which amplifies and limits the difference frequency signal to eliminate the dependence of the output signal of the phase detector 17 on the amplitude of the combination frequency signal. At the output of the phase detector 17, the signal is proportional to the phase difference of the oscillations of the Raman frequencies generated by the mixer 13 and extracted from the reflected signal, which is proportional to the distance to the object. The signal from the output of the phase detector 17 is fed to the control inputs of the controlled delay lines 8 of all channels.

Thus, in a controlled line

range information is inputted, where the time delay in the radiation propagation channel is compensated.

Claims (1)

SUMMARY OF THE INVENTION Adaptive optical aperture sensing system comprising a coherent radiation source with a phase shifter, a detector whose output is connected to an input of an amplitude detector and a series-connected voltage limiter, a synchronous detector, a low-pass filter, a sign-determining unit, the output of which is connected to the second the input of the multiplier, the first input of which is connected to the input of the controlled delay line, the input of which is connected to the second input of the synchronous detector and the first input an ora, the second input of which is connected to the output of the switch, and the output is connected to the control input of the phase shifter, which requires that, in order to increase the accuracy of the device, an additional limiter, mixer, first and second bandpass filters are introduced combination frequency, phase detector, the output of the detector connected to the input of the second band-pass filter of combination frequency, the output of which is connected to the second input of the phase detector, the first input of the mixer is connected to the output of the modulating generator of the 1st channel a, and the second input - to the output of the modulating oscillator j-ro channel mixer output coupled to an input of the first bandpass filter matching the frequency, the output of which is connected to a first input of the phase detector, the output of which is connected with the control inputs of controlled delay lines;