SU1355939A1 - Acoustical spectrum analyser - Google Patents

Abstract

The invention relates to optical information processing and can be used in radar systems, plasma diagnostics, radio astronomy for analyzing the spectra of rapidly changing signals. The aim of the invention is to increase the speed of an acousto-optical spectrum analyzer. The device contains a source of coherent light 1 — a laser, a beam shaper 2, an acousto-optic modulator 3, an amplifier 4, an integrating lens 5, a multi-element photodetector 6 on devices with charge coupling, an analog processing unit 7, an opaque screen c (L d

Description

8, having an aperture, optical, shutter 9, high-frequency key 10, unit 11 of the same type ring recorders, unit 12 of the same type timers, unified main line 13 of the computer, ring registers 14-16, generator 17 clock pulses, timer modules 18-20, converter 21 levels .

The invention relates to optical information processing and can be applied in radar systems, plasma diagnostics, radio astronomy for the analysis of rapidly changing spectra from signals.

The aim of the invention is to improve the speed of the acousto-optic spectrum analyzer.

FIG. 1 shows a functional diagram of the spectrum analyzer; Fig. 2 shows timing diagrams explaining the control of the electric key and the optical shutter; in fig. 3 is a block diagram of a timer module; in fig. 4 is a block diagram of a ring register; in fig. 5 is a schematic diagram of a control frame time structure.

The functional diagram of the spectrum analyzer (Fig. 1) contains a source of coherent light 1 — a laser, a beam shaper 2, an acousto-optic modulator (AOM) 3, a pulse (U) 4, an integrating lens (1Sh) 5, a multi-lane photodetector 6 on devices with charge coupling (CCD), block 7 analog processing (BAO), opaque screen 8 with a hole (D) optical shutter (3) 9, high-frequency key (CS) 10, block 14 of the same type of registers (BKR), block 12 of the same type of timer modules (BTM), unified main line of computer 13, ring registers (CR) 14-16, g generator of clock pulses 17 (HHP), timer modules 18-20 (TM), the inverter 21 levels (PU).

Laser 1 is the light source in the optical system. Shaper

mk niy

1355939

The beamformer 2 is used to align the geometric dimensions of the laser beam and the acoustic duct of the acousto-optical modulator 3. The algorithm of the operation of the device and timing diagrams explaining its operation are given in the description of the invention, 2 hp, f- ly, 5 Il.

beam 2 serves to match the geometrical dimensions of the laser beam and the AOM 3 lumen. The IL 5 performs the Fourier transform of the light distribution incident on it. The AOM 3 is a signal input device to the optical system. An IL 5 matrix is placed in the output plane of the IL 5. It serves as a device for outputting signals from the optical system. Close to it is placed the diaphragm D 8, leaving only one row of the matrix open. The shutter 9 and the key 10 serve for gating the light and electric signals, respectively. The elements of the device 1, 9, 2, 3, 58 and 6 are interconnected optically and are arranged in series. The AOM 3 input is electrically connected to an amplifier 4, which increases the power of the electrical signals. The analog output of the CCD of the photodetector 6 is electrically connected to the BAO 7, which is necessary to amplify the amplitude of the signals. The electrical inputs of the CCD of the photodetector 6 through the level converter are connected to the outputs of the control unit, which consists of two parts: the operating unit 11 and the control BTM 12. The TBC generates the pulse sequences necessary for the operation of the CCD array 6, the optical quantum generator 9 (laser) key 10 at the input of the amplifier 4. The BTI 12 forms a predetermined, intraframe structure of control pulses Φ supplied to the RBB 11, and counts the number of phase II pulses at the CDR counting outputs. Both units are connected to the unified computer main line 13 by information and address inputs.

BTM 12 is a homogeneous structure of q of the same type of timer modules (Tlfj-TMa) 18–20, with the output of the start of the UE; The i-ro TI is connected to the i-th inputs of the start-lock of all TM blocks.

BKR 11 consists of p modules of the same type annular registers (CU - KPC) 14-16, and the phase outputs through the level converter 21 are connected to the electrodes of the phases of the CCD 6, gate 9 of laser 1, key 10, synchronization inputs K are connected to the output of the GTH 17 Counting output P .; j-ro To the ring register unit 11 is connected to all the j-counting inputs of the BTM timer modules, and the i-ro Til control output of the BTM 12 is connected to all the i-M control inputs of the BKR ring registers 11 ..

The device works as follows.

The analyzed signal is amplified by the amplifier 4 and fed to the AOM 3, illuminated by a coherent light beam of the laser 1 formed by the shaping unit 2. The integrating lens 5 performs the Fourier transform in two coordinates. In the output plane of the device, the distribution of the amplitude of the optical field along a direction parallel to the direction of propagation of ultrasound in the flux tube of the AOM is proportional to the instantaneous spectrum of the input signal. This optical signal is converted into an electrical one by accumulating charges for the time t in one row of the CCD 6 matrix, which is located behind the hole in the screen 8. To accumulate the charges only in one row of the matrix, geometrically. The dimensions of the aperture and the opaque screen B must coincide with the geometrical dimensions of the row of the matrix 6 In addition, the parameters of the AOM and the CCD matrix determine the focal distance of the integrating lens in the optical axis plane — the direction of propagation of ultrasound in the AOM sump. The size of the working field L in the output plane along the direction of propagation of ultrasound is equal to

T - i.F

L - -g- F ,,

where A is the wavelength of the light laser; st - frequency band AOMj

F is the focal distance of the integrating lens in this plane; , S - the speed of sound in the material

zvukoprovod.

In order to optimally use the elements of the row of the CCD matrix, it is necessary that

L Ma,

where M is the number of elements in the maritsa line;

and - the size of one element matresses along the line.

Line items are optimally used when

L (0.9 ... 1) Ma,

where 0.9 ... 1 is the utilization factor. Consequently, the focal distance 1W 5 in the plane of the optical axis — the direction of propagation — of ultrasound in the AOM duct must satisfy the relation

() Mag. T.

(one)

The size G of the intensity distribution of light in the output plane along a direction perpendicular to the direction of ultrasound propagation is determined from the expression

 .

where d is the width of the sound pole in

AOM sound conduit; Fj is the focal length of the lens 5

in a plane, perpendicular

direction of distribution

ultrasound.

In order for G not to exceed the size of a single element of the matrix in the direction perpendicular to the direction of ultrasound propagation, it is necessary that the condition

bd

2 (1 ... 2)

(2)

Where. 1 ... 2 - proportionality factor;

b - the size of one element of the matrix across the line. From formulas (1) and (2) it is easy to obtain that, with real values of the width of the sound column F, P.

As IL 5 it is convenient to use an anamorphic system with F, V.

After accumulating charges in one row of the matrix for a period of time IT, the charge relief proportional to the power of the spectrum of the input signal is transferred to the next row. The spectral characteristic of the input signal is again recorded during the next time interval 1. After that, the charging relief of the CCD matrix is shifted by another row, and so on. Thus, it is possible to break down the spectral characteristics of k time intervals of duration G, where k is the total number of rows in the matrix.

Neighboring intervals are analyzed and are separated by a time interval o, necessary for transferring charges to one element along the column. The minimum value of "that interval is determined by the read clock frequency f and is equal to

 1 / f.

The accumulation time of Zr can be made any small. In fact, it is limited from below by the required frequency resolution min

 b

If € „f

one

 V-, i.e. the accumulation time is equal to the transfer time, then in the rows of the matrix will accumulate the charge-relief, corresponding to the spectral characteristics of the parts of the signal that are spaced apart by the reciprocal of the clock frequency. Moreover, the information about the input signal spectrum is averaged over the same time, equal to 1 / f. Characterizing the speed of the prototype, the averaging time T N / f, where N is the number of readable elements in the linear photodetector of the prototype, i.e. in this device, the averaging time is N times less than the averaging time T in the prototype device. Therefore, the speed of this device is higher than the speed of the prototype with the same sampling clock frequencies equal to the number of elements in the linear photodetector of the prototype device.

After filling a specified number of rows of the matrix with charge packets containing information about the energy spectra of the input signal segments, they are output through the shift register. Time (Mk) / / f is spent on the output of all information, after which the device is ready for

new measurement cycle. From this it follows that the device is able to analyze the spectrum of the input signal with high speed for a certain period of time equal to

 sg +) k, followed by a pause equal to (Mk) /.

Sometimes it is necessary to conduct a spectral analysis with a ".

FIG. , and the power level of the output signal is shown, and hatching marks the time intervals at which the spectrum of the input signal is to be measured. Signal or noise components arriving at the photodetector in the gaps T ,, cause

reduce the dynamic range of the device. To eliminate noise components over the radio channel, an electrical switch 10 is installed in the input information circuit, disconnecting the Ug from the AOM for a time T. To eliminate the noise component via the optical channel, an optical shutter 9 (for example, electro-optical) is installed between the laser and the beamformer. Moreover, the optical shutter 9 should open simultaneously with the electric key 10 and close after the electric key for a while.

-g: 2

0 5

where D is the AOM aperture.

Such a delay is necessary in order

g so that the spectral components are accumulated in the photodetector as long as the analyzed signal is in the AOM aperture. Impulses control electric key Unnp

And the optical shutter Uapp are shown in FIG. 26, respectively. Opens the device high level. The maximum speed of the spectroanalyzer is achieved with c Ti 1 / f.

5 The acousto-optic spectrum analyzer control unit performs the following functions: it forms a programmable intraframe pulse sequence of phase voltages.

element 26 (LE2;) in accordance with

| its exit function

 V.

J

 TO

CCD; software controls the laser radiation | controls the electron with a high-frequency key at the input of the spectrum analyzer.

The control unit is made in the form of two blocks: the block of 11 ring registers and the block of 12 timer modules.

BTM 12 is a uniform-10 structure from q of the same type of timer modules 18-20. The internal structure of the i-ro timer module (TM) is disclosed in FIG. 3, where a programmable counter (PS;) 22 counts 15 by the main line 13. Thus

where t - block control pulses

timer modules; - a set of q logical software-defined at the information outputs of the constants control register.

By information-address inputs PC;

and RU2; associated with unified

pulses at the output of M; logic element (LEG;) 23 at the resolving signal level at the control output F; LE1, Logic Element 23 i-ro TTl implements the following logic functions from the signals at the counting inputs P ,, .. Pr, start inputs (blocking UE, ... UPL) and information inputs oi, j6, y:

-GGPk ":.,

- (zivn.pvy (, r) /

where p is the number of ring modules

registers in BKR 11; q is the number of timer modules in BTM 12; values of logical constants

.Mfv

software control of the ring register is provided.

The control frame structure is necessary for the operation of acoustics

20 optical spectrum analysis in the mode of analysis of the energy spectra of radio signals (segments of radio signals) with a high time resolution is schematically presented in FIG. five

25 and can be conditionally divided into three cycles: I - the accumulation of spectral information about the analyzed input signals; II - information output through the shift register; III - cleaning mat

30 wits before the next frame.

FIG. 5 shows the pulse sequences of the phases of the accumulation (F) and storage (F) sections, the phases of the shift register (Фр) and the drop pulses.

on the information output of the re-35 (), formed by the BKR 11, except

control hub 24 (RU1r.

Switching on the logic element 23 together with the control register 24 allows realizing the controlled start-blocking of the i-ro TM and switching an arbitrary counting output to the RBM with an arbitrary counting input BTM, which is necessary for the operative reorganization of the functioning mode of the spectrum analyzer. To implement software control of the timer module RU1 24 and PS; 22 information and address inputs are connected with a unified computer line 13

WRC 11 consists of p modules of the same type, which also form the homogeneous structure of ring registers 14-16. : The internal structure of the j-ro KR is shown in FIG. 4, where the shift register 25 (PC) generates a sequence of overlapping phase voltages at the inputs of the level converter 21. Start-lock PC; implemented using a logical

40

In addition, an impulse sequence of pauses (D) is shown, which establishes a temporary resolution of the device. Since in the CCDs, the three-phase control, F, F, F control is a combination of three phase-shifted voltages each.

At the beginning of the first cycle, the control device generates voltages transferring jg charges along the columns with a frequency of 1 / (T + Tj). In this part of the frame, the sequences Fz, Fh, o "are formed. In addition, Uupp.Kft and Uunp.-ij are shown here.

gQ in FIG. 2, where only this part of the frame is shown. In cycle II, the charges accumulated in the rows are successively shifted to the shift register and output from it. This requires the formation of FC, Fo, PvES. And the last F,

gg

X f

a single pulse F, F are produced by a sequence of M pulses FR and RES. In the third cycle in the final part of the frame, the continuous production of the element 26 (LE2;) in

| its exit function

 V.

mainline computer 13. Thus

where t - block control pulses

timer modules; - a set of q logical software defined by the information outputs of the register of control constants.

By information-address inputs PC;

and RU2; associated with unified

mainline computer 13. Thus

software control of the ring register is provided.

The structure of the control frame, which is necessary for the operation of acousto-optic spectroanalysis in the mode of analyzing the energy spectra of radio signals (segments of radio signals) with a high time resolution, is schematically represented in FIG. five

and it can be conditionally divided into three cycles: I - accumulation of spectral information about the analyzed input signals; II - information output through the shift register; III - cleaning the matrix before the next frame.

FIG. 5 shows the pulse sequences of the phases of the accumulation (F) and storage (F) sections, the phases of the shift register (FR) and the harsh () pulses generated by the BKR 11, except

In addition, an impulse sequence of pauses (D) is shown, which establishes a temporary resolution of the device. Since, in a CCD, the three-phase control, F, F, F is a combination of three phase-shifted voltages each.

At the beginning of the first cycle, the device up. This formula generates voltages that move charges along columns with a frequency of 1 / (T + Tj). In this part of the frame, the sequences Fz, Fh, o "are formed. In addition, Uupp.Kft and Uunp.-ij are shown here.

in fig. 2, where only this part of the frame is shown. In cycle II, the charges accumulated in the rows are successively shifted to the shift register and output from it. This requires Form-FC, Fo, PvES. And after f,

FSC,

X f

a single pulse F, F are produced by a sequence of M pulses FR and RES. In the third cycle in the final part of the frame, the sequences F, F, Fr and RES are continuously generated to eliminate the saturation of the photodetector dark current before receiving the next frame. This cycle is necessary if the time intervals between successive acquisition frames exceed the memory time of the CCD. As can be seen from the structure of the control frame shown in FIG. 5, & according to the proposed construction principle of the control device, three ring registers and nine timer modules are required.

The operation algorithm of the control device, acousto-optic spectrum analyzer in the mode of super-operational recording of the energy spectra of the input radio signal segments, is as follows.

. A computer through the unified highway 13 through information and address buses of all BKR modules 11 and BTM 12 records constants, into the control registers RU1 and RU2, the internal states of all AND 14-16 and that 18-20 are set.

At the end of the program setting of the BKR and BTM computer parameters, a start pulse of the first timer module is generated, after which the control unit operates in the autonomous mode in accordance with the timing diagram in FIG. 5 before the arrival of either a reset signal from the computer, or until the terminal value in the timer module reaches the number of full frames.

An analog signal from the output of the CCD matrix, reflecting the results of super-operative recording and buffering in the analog storage device of the energy spectra of the analyzed input radio signals (segments of radio signals), is fed to the input of the analog processing unit 7, where amplification, filtering and double correlated sampling are detected. Further, it can be displayed on the screen of the video monitor and

after digitization is introduced into the EHF for further analysis.

Claims (3)

1. Acousto-optic spectrum analyzer, containing successively located optically coupled laser, light beam shaper, an acousto-optic modulator, electrically connected to an amplifier, whose input is an information input of a spectrum analyzer, an integrating lens and a multi-element photo-receiver based on charge-coupled devices, electrically connected via a level converter to a control unit containing a clock generator of an analog processing unit, the output of which is an information output of the spectrum analyzer, characterized in that, in order to improve speed, the multi-element photodetector is en in the form of a matrix optically connected with the integrating lens with one of its lines closest to the upper register of the matrix, for which an opaque screen with an aperture close to it is placed in front of the matrix photoreceiver and the integrating lens is anamorphic the system with a focal distance F in the plane of the optical axis is the direction of propagation of ultrasound in the modulator sound field equal to  th where M is the number of photosensitive elements in the row of the matrix; a is the size of one matrix element in the direction of sound propagation in the sound duct of the modulator; S - the speed of sound in the material zvukoprovod; L is the laser wavelength; - band analysis of the spectrum analyzer, with a focal distance F, equal to  2 in ORTOGOF. Y (H2) i where b d 5 the size of one element of the matrix; the size of the sound column in the sound pipe in the direction perpendicular to the direction of propagation of ultrasound, with the multi-element photo-receiver located in the output plane of the anamorphic system. 2, The spectrum analyzer of claim 1, wherein the control device contains a uniform stackable structure of uniform ring registers and a uniform stackable CTpyKfypy of the same type timer modules electrically connected to it, and the trigger output of each timer module is connected to the corresponding trigger inputs - blocking of all timer modules, the counting output of each ring register is connected to the corresponding counting inputs of all timer modules, and the control output of each timer module is connected to the control inputs of all ring registers, each timer module consists of a programmable counter, a control register and a logic element whose inputs are counting inputs and start-lock inputs of the timer module, the logic level M (at the first output of the logic element i- second timer module is defined by M; ZZnK- i, L number of ring registers; logic level at the k-m counting input of the logic element; logical level on set and the output of the logic element is connected to the control input of the shift register, the outputs of which are the outputs of the control device and connected to the converter inputs of the information input logic input 35 Who is the element of the 1st timer module, and the logic level F at the second output of the logic element i-ro timer module is determined by the expression 40 register, and the input of the shift register synchronization is connected to the output of the clock pulse generator, the logic element is connected to the control register via information inputs, and the information address inputs of the control register and shift register are connected to a unified computer mainline. R; (. / з;) (Ye K-1 where q is the number of timer modules;  logical level at input start-lock logic element; Ri is the logical level on (p + k) -m g ,, information input of the logic element of the i-ro timer module; X is the logic level on the (p + q + +1) -th information input of the logic element of the i-ro timer module. the first output of the logic element is connected to the counting input of the programmable counter, and the second output of the logic element is the control output of the timer module and is additionally connected to the control input of the programmable counter, the output of which is the start output of the timer module, the logic element of the information inputs connected with the control register, and the information address inputs of the control register and the programmable counter are connected to a unified computer main line, each ring register p is composed of a shift register, a control register and a logic element whose inputs are the control inputs of the register ring, logic level Y; at the output of the logical element j-ro of the ring register is determined by the expression CHY 11. J where - the logic level at the i-th information input of the logical element j-ro of the ring register, moreover, the output of the logic element is connected to the control input of the shift register, the outputs of which are the outputs of the control device and are connected to the inputs of the transducer or- to the counting output of the ring 40 45 m g ,, register, and the input of the shift register synchronization is connected to the output of the clock pulse generator, the logic element is connected to the control register via information inputs, and the information address inputs of the control register and shift register are connected. .Cheny to the unified computer mainline. 3. Spectrum analyzer on PP. 1 and 2, characterized in that, in order to broaden the dynamic range, an optical shutter is placed between the laser and the light beam shaper, and an electric key is installed in the information circuit of the spectrum analyzer, both of which are electrically connected to the control device. % / 7f / 7 2 fJp i y / 7f / 7 / U 7 / J fivZ ::