SU1250978A1 - Acoustical-optical spectrum analyzer - Google Patents

Abstract

The invention relates to a radio measuring technique and can be used to obtain signal spectra in real time. The purpose of the invention is to increase the range of frequency analysis. The device contains a source of coherent light 1, a collimator 2, a cylindrical lens 15, acousto-optic modulators 9, 11, 4 and 6 with the corresponding converters 10, 12, 5 and 7, a focal diaphragm 14, a generator of 17 chirp signal. Using a two-dimensional photodetector 16, having a significantly larger number of resolution elements, in combination with the corresponding two-dimensional organization of the device structure, requiring the introduction of a cylindrical lens 3, spherical lenses 8 and 13, and a sinusoidal signal generator 18, as well as ensuring a special position and orientation of acousto-optic generators with a certain ratio the lengths of the sound ducts of the last. allow to increase the number of frequency resolution elements by several times and, respectively, analyzed frequency spectrum analyzer and to bring it to a value determined by the algorithm of the device. 1 il. i SL 9 12 4 75 „ie

Description

This invention relates to a radio metering technique and can be used to obtain real-time signal spectra.

The purpose of the invention is to increase the range of frequencies by frequency by converting the light distribution in the plane of the photodetector from one-dimensional to two-dimensional, in the form of a raster, which allows the use of a large number of resolving elements of a two-dimensional photodetector.

The drawing shows a structural diagram of the proposed anapizator.

The analyzer contains optically coupled coherent light source 1, for example, an optical quantum oscillator of nonferging action, a collimator 2, a cylindrical lens.

3, acousto-optic modulator (AS)

4, the piezoelectric transducer 5 of which is the input of the spectrum analyzer, the ACL 6, the piezoelectric transducer 7 of which is located on the suction line on the same side as the piezoelectric transducer 5 4. Next comes a spherical lens 8. The AOM 9 with the piezoelectric transducer 10 and the AOM 11c follows Step 8; piezoelectric transducer 12 and 10 and 12 are located on the opposite faces of the acoustic conductors AOM | 9 and 11. With this, the AOM 9 and 11 are rotated 90 ° around the optical axis relative to the AOM 4 and 6 and displaced along the axis, perpendicular to the piezo plane formers 5 and 7, opposite to the optical axis, respectively

X.

where f, and f. - the average frequencies of the spectra of the analyzed signal and the chirp signal, respectively, J F - the focal length of the first spherical lens {

 L is the light wavelength; V is the propagation velocity of acoustic waves in the third and fourth AOM.

These sides are determined by the position of the respectively -1th light diffraction order after AOM 4 and -1-1th order after A (F 6, Next

there is a spherical lens 13, a focal diaphragm 14, a transmissive fl-th diffraction order after AOM 9 and 11, a cylindrical lens 15,

a two-dimensional photodetector 16, for which the CCD matrix can be used, the ratio of the length of the AOM 9 and 11 sound circuits to the length of the AOM 4 and 6 sound circuits is equal to

rows of photodetector 16. The output of photodetector 16 is the output of the spectrum analyzer. In addition, the spectrum analyzer contains a 17 chirp signal generator, the output of which is connected to piezo transducers 7 and 12, as well as a sinusoidal signal generator 18, the output of which is connected to piezotransducer 10. The frequency of the sinusoidal signal of the generator

18 is selected to compensate for the spatial carrier along the y coordinate.

The device works as follows.

|

The light beam from the source 1 is expanded by the collimator 2 and focused by the lens 3 on the aperture of the AOM 4 and 6. The signal being analyzed

on the piezoelectric transducer 5 and is converted last into an acoustic wave in the AOM 4. The chirp signal from the output of the generator 17 is fed to the piezoelectric transducer and 7 and 12, which

convert it to acoustic waves in AC 6 and 11. A sinusoidal signal is fed from the output of generator 18 to a piezo transducer 10, which is converted into an acoustic wave

in ASH 9. The light beam diffracts on acoustic waves in AOM 4 and 6. Lens 8 performs a spatial Fourier transform over the luminous distribution S of the output plane of the AOM 6 and focuses the light beams of the -1st diffraction order after the AOM 4 on the AOM aperture 9 and + 1 diffraction order after AOM 6 on the AOM 11 aperture. Further

Light diffracts on acoustic waves in AC 9 and 11. Lens 13 performs Fourier transform on the light distribution in the output plane AOM 9 and 11, focal

the diaphragm 14 allows only –I diffraction order to pass, which ensures the collinearity of the propagation along the

A lens that passes to the photodetector 16. Lens 5 reconstructs the output planes of the modulators in the plane of the photoreceiver t6. To increase the accuracy of matching the structure of the light distribution and the topology of the two-dimensional photodetector 16, the lens 15 can be replaced by an astigmatic pair, i.e. a pair of cylindrical and spherical lenses. Photodetector 16, which can be used as, for example. measures, the CCD array, accumulates a charge in proportion to the intensity of the light distribution incident on it. As a result of accumulation on the photodetector 16, a two-dimensional charge distribution is formed, having a raster shape, the lines in which are oriented along the X axis, and their number is equal to the ratio of the lengths of the AOM 9 and i1 sound conductors to the AOM 4 and 6. The mathematical analysis of the device operation shows that the charge distribution structure represents the spatial carrier along the X coordinate, i.e. along the lines of the raster, amplified in amplitude by the amplitude spectrum, and in phase - by the phase spectrum of the analyzed signal. As a result of the reading, the charge distribution is converted into an electrical signal at the output of the photodetector 16.

Thus, the use of a two-dimensional photodetector, having a significantly larger number of resolution elements as compared to one-dimensional, in combination with a corresponding two-dimensional organization of the structure of an acousto-optic spectrum analyzer, requiring the introduction of additional lenses and a sinusoidal signal generator, as well as providing a special position and orientation of the AOM at a certain the ratio of the lengths of the conduits of the latter makes it possible to increase in several times the number of elements of the frequency resolution Actually, the range of analyzed frequencies of the spectrum analyzer and bring them to the value determined by the device operation algorithm. In the proposed analyzer, the number of frequency resolution elements is numerically equal to the base of the AOM. Base sovre978. four

variable AOM reaches fO value - 340

Thus, in the analyzer according to the invention, the number of frequency resolution elements is 3-5 times greater than in the prototype analyzer. Since the frequency resolution is achievable for the proposed analyzer and the prototype analyzer is the same and

is determined by the accumulation time of the photodetector, then the gain in the number of frequency resolution elements leads to a gain of the same number (i.e., 3-5 times) in the magnitude of the analyzed frequency range.

Claims (1)

Invention Formula An acousto-optical spectrum analyzer containing a source of coherent light located on one optical axis, a collimator, a pair of modulators consisting of first and second acousto-optical modulators, which are displaced along an axis, perpendicular to the plane, formed by the optical axis and the axis of the sound conductors of the first and second acousto-optic modulators, in opposite from the optical axis of the side, the diaphragm, the first cylindrical lens, the photodetector, and the third and fourth acousto-optic modulators, whose piezotransducers are located on the same edges of the acoustic ducts, and a signal generator with linear frequency modulation, the output of which is connected to the second and second piezoelectric transducers of the fourth acousto-optic modulators, which is due to the fact that, in order to increase the range of analyzed frequencies, a second cylindrical lens, first and second spherical lenses, a sinusoidal signal generator, the second cylindrical lens, the third acousto-optic modulator, the fourth acousto-optic modulator, the first spherical lens are arranged in series on the same optical axis between the collimator and a pair of modulators consisting of the first and second acousto-optic modulators, and the second spherical lens is located on the optical axis between a pair of modulators consisting of the first and second acousto-optic $ 1 modulators, and the diaphragm, while the third and fourth acousto-optic modulators are rotated 90 around the optical axis relative to the first and second acousto-optic modulators, and the first and second acousto-optical modulators are shifted with li.  V from the optical axis where responsibly at distance x, f And v 2tt a p f | and fj are the average frequencies of the spectra of the signal being analyzed and the LMCH signal, respectively; F is the focal distance of the first spherical lens} T (is the wavelength of light; v is the speed of propagation of acoustic waves in the third and fourth acousto 50978 optical modulators, the piezotransducers of the first and second acousto-optic modulators are located on the opposite faces of the sound cables, the output of the sinusoidal signal generator is connected to the piezoelectric transducer of the first acousto-optic modulator, and the third acousto-optic transducer 10 of the modulator is connected to the input of the spectrum analyzer, while the photodetector is two-dimensional, and the ratio of the length of the acoustic ducts of the first and second acousto-optic modulators to the length of the acoustic ducts of the third and fourth acousto-optical modulators is equal to the number of rows in the photodetector.