RU119123U1 - ACOUSTOPTIC RADIO SIGNAL METER - Google Patents

Abstract

An acousto-optic meter of radio signal parameters, containing a laser, a collimator, an acousto-optic deflector in series on the optical axis, at the optical input of which the laser radiation falls at the Bragg angle, and the measured radio signal is fed to the electrical input of the deflector through its piezoelectric transducer, and in the direction of the diffracted laser radiation, the integrating lens, a line of photodetectors, the outputs of which are connected through a set of video amplifiers and a set of threshold devices to the input of the encoder, characterized in that a Kesters prism is placed between the collimator and the deflector, providing light incidence on the optical input of the acousto-optic deflector simultaneously at both positive and negative angles Bragg, and the acousto-optic deflector itself is made on the basis of LiNbO3 with an oblique cut angle equal to β, and anomalous diffraction, characterized by the presence of two identical passbands ΔfΣ1 and ΔfΣ2 near the differences frequency bending f01 and f02, set by the corresponding value of the angle β and interconnected by f02-f01

Description

The proposed utility model relates to radio measurement technology and can be used as a high-precision meter for the frequency parameters of radio signals in broadband communication systems, direction finding and radio intelligence.

Known acousto-optical (AO) spectrum analyzer with spatial integration [Optical processing of radio signals in real time // O. B. Gusev, S. V. Kulakov, B. P. Razzhivin, D. V. Tigin; under the editorship of Kulakova S.V. - M .: Radio and communication. - 1989. - p. 48], which includes a laser, a condenser and a collimator that are connected in series over the light, forming an optical cascade of the transition from a laser beam to a plane light wave of a given aperture, an acousto-optical deflector (AOD), to the electrical input of which a measured radio signal is supplied , Fourier lens and a recording device in the form of a line of photodetectors.

The reason that prevents the analogue from achieving a technical result is its insufficient operating frequency band and insignificant sensitivity, which is a result of the low diffraction efficiency of the AOD spectrum analyzer in the microwave range.

Signs of an analogue that coincide with the features of the proposed utility model include a laser, a collimator, an acousto-optic deflector, a Fourier lens that implements the Fourier transform of a light signal located in the plane of the acousto-optic deflector and a recording device in the form of a line of photodetectors in series with respect to light.

Also known acousto-optical frequency meter [a.s. USSR No. 126636, MKI 4 G01R 23/16. Acousto-optic frequency meter. Vernigorov N.S., Zadorin A.S., Sharangovich S.N .; publ. 10/23/1986 in bull. No. 39]. The device contains a laser, a collimator, an AOD, a lens and a position-sensitive photodetector sequentially located on the optical axis, and a device for shifting the laser radiation frequency is located between the collimator and AOD at half the light aperture, and phase meters are connected to the outputs of the position-sensitive photodetector, the first inputs of which are loaded to the respective outputs of the photodetectors, and the second inputs are connected to the photodetector located on the optical axis of the frequency meter.

The reason that impedes the achievement of the required technical result is its complexity. In the considered analogue, which has a small operating frequency band, an interdiscrete refinement of the frequency of the measured signal is carried out by determining the location of the diffracted light spot using a series of phase meters, the number of which is equal to the number of elements (photodiodes) in the position-sensitive photodetector. The need to use a large number of phase meters causes the aforementioned complexity of this analogue.

Signs that are common with the claimed utility model are a laser, a collimator, an AOD, a lens acting as an integrating lens, and a line of photodiodes, which are used in the analog as a position-sensitive photodetector, in series with each other.

The closest in technical essence to the claimed device is a prototype device: an acousto-optical meter of frequency parameters of radio signals [Rozdobudko V.V. Acousto-optic meter of frequency parameters of radio signals with nonlinear FM laws // Radio Engineering. - 2000. - No. 3. - p.24-27.].

The prototype device is shown in figure 1.

The prototype device contains a laser 1, a collimator 2, an AOD 3 sequentially located on the optical axis, the optical input of which the laser radiation falls at a Bragg angle, and a measured radio signal is fed to its electrical input through a piezoelectric transducer, and, in the direction of the diffracted laser radiation, an integrating lens 4 and a line of photodetectors 5, the outputs of which are connected to the input of the encoder 8 transforming through a set of video amplifiers 6 and a set of threshold devices 7 vanie position code indicative of the coordinate of the center of the diffracted light spots in the frequency code.

Signs common with the claimed alleged utility model are a series-connected laser 1, collimator 2, AOD 3, the optical input of which the laser radiation falls at a Bragg angle, and a measured radio signal is fed to the electrical input through its piezoelectric transducer, and in the direction of the diffracted laser radiation in series includes an integrating lens 4 and a line of photodetectors 5, the outputs of which are through a set of video amplifiers 6 and a set of threshold devices 7 connected to the input of the encoder 8.

Acousto-optical meters similar in structural composition, operating principle, and functional purpose are described in [1) V. Rozdobudko. Analysis of dynamic errors in acousto-optical measuring instruments for instantaneous frequency of radar signals // Radioelectronics. - 1997. - No. 12. - p. 3-10; 2) Rozdobudko V.V .. Broadband acousto-optic meters of frequency and phase parameters of radio signals // Radio Engineering. - 2001. - No. 1. - p. 79-92.].

The reason that impedes the achievement of the required technical result is the fact that the prototype has a limited band of operating frequencies not exceeding an octave.

The problem the proposed utility model is aimed at is expanding the working frequency band of the acousto-optic radio signal parameters meter and increasing its sensitivity.

The technical result in the claimed utility model is achieved if a Kester prism is placed between the collimator and the deflector, which provides light incidence to the optical input of the acousto-optic deflector at the same time both at the positive and negative Bragg angles, and the acousto-optic deflector itself must be based on LiNbO ₃ with an oblique cut angle equal to β, and anomalous diffraction, characterized by the presence of two identical bandwidths Δf _Σ1 and Δf _Σ2 bend near different frequencies f ₀₁ and f _02, respectively, defined by favoring the magnitude of the angle β, and interconnected among themselves through f ₀₂ -f ₀₁ ≃Δf _Σ1 ≃Δf _Σ2, wherein the length of the piezoelectric transducer acoustooptic light deflector is chosen from the condition of combination of bands Δf _Σ1 and Δf _Σ2 by a predetermined level of non-uniformity of diffraction efficiency.

In order to achieve a technical result, an acousto-optic radio signal parameter meter containing a laser, a collimator, an acousto-optic deflector located in series along the light, the optical input of which the laser radiation falls at a Bragg angle, and a measured radio signal is fed to the electrical input of the deflector through its piezoelectric transducer, and in the direction of the diffracted laser radiation consistently included an integrating lens and a line of photodetectors, the outputs of which through a set view ousiliteley and a set of threshold devices are connected to the input of the encoder, between the collimator and deflector placed prism Kestersa providing incidence of light to the optical input of the acoustooptic deflector as both a positive and a negative angle Bragg, and the acoustooptic deflector is based on LiNbO ₃ with an oblique angle slice equal to β and anomalous diffraction, characterized by the presence of two identical pass bands Δf _Σ1 and Δf _Σ2 near different inflection frequencies f ₀₁ and f ₀₂ defined by the corresponding weight the angle β, and interconnected by means of f ₀₁ -f ₀₂ ≅Δf _Σ1 ≅Δf _Σ2 , and the light length of the piezoelectric transducer of the acousto-optical deflector is selected from the condition of combining the bands Δf _Σ1 and Δf _Σ2 at a given level of diffraction efficiency unevenness.

The proof of the presence of a causal relationship between the claimed features and the achieved technical result is as follows.

As it is known, when using oblique sections in LiNbO _{3, the} acousto-optic interaction for the Stokes and anti-Stokes diffraction components takes place near substantially different frequencies [Balakshiy VI, Parygin VN, Chirkov L.E. Physical principles of acousto-optics. - M .: Radio and communication. - 1985. - 280 p.].

The vector diagram of the AO interaction under consideration and the frequency dependences of the angles of incidence θ _n1 , θ _n2 and diffraction θ _d1 , θ _d2 are shown in Fig.2. In figure 2, a denotes f _01, f ₀₂ - the inflection frequency at which there are a minimum of angles of incidence θ _n1 (f ₀₁ ), θ _n2 (f ₀₂ ); f ₀ is the frequency at which the diffraction angles θ _d1 (f), θ _d2 (f) vanish; Δf _Σ1 and Δf _Σ2 are the working frequency bands of the deflector - the bands of acousto-optic interaction formed at positive θ _n1 (f ₀₁ ) and negative θ _n2 (f ₀₂ ) Bragg angles. Note that the bands Δf _Σ1 and Δf _Σ2 are primarily determined by the divergence of ultrasound, i.e. the length l of the piezoelectric transducer deflector. In figure 2, b is indicated: β is the cut angle LiNbO ₃ or the angle between the z axis and the plane of propagation of ultrasound; N ₀ and N _e are the refractive indices; k _d , k _n1 , k _n2 - wave vectors for diffracted and incident light; K ₁ and K ₂ are the ultrasound wave vectors related to the operating frequency bands Δf _Σ1 and Δf _Σ2 . In this case, the acoustic wave excited by the piezoelectric transducer propagates in the deflector with a velocity ν at an angle (π-β) to the optical axis of the LiNbO ₃ crystal. The diffraction angles θ _d1 , θ _{d2 of the} incident light on the ultrasonic column vanish at a frequency

,

where N ₀ , N _e are the refractive indices for the ordinary and extraordinary waves; (in lithium niobate N ₀ > N _e and N ₀ -N _e << N ₀ ).

The frequencies f ₀₁ and f ₀₂ (the frequencies of the “inflection”), in the vicinity of which extremes are realized - d (θ _n1 , θ _n2 ) / df = 0 the value of the angle of incidence, are defined as

,

.

Moreover, in the vicinity of frequencies f ₀₁ and f _{02, the} normalized amplitude-frequency characteristics of diffraction — the frequency response, can be represented as

where Θ _{n1, n2} = θ _{n1, n2} · 2nν / (λf _01.02 ) normalized angles of incidence; F _1,2 = (ff _01,02 ) / (f _01,02 ) - normalized frequencies; n = 0.5 · (N ₀ + N _e ) is the average value of the refractive index; Q _1,2 = (λ _{, 02} ) / (nν ² ) is the wave parameter of the AO interaction; ; l is the length of the piezoelectric transducer; P _a - sound power in the environment of AO interaction; M ₂ - AO quality factor.

From analysis (1) it follows that at angles of incidence equal to the Bragg angle for each of the frequencies f ₀₁ and f ₀₂ , namely and the deflector has a flat frequency response. The bandwidth of the deflector at frequencies f ₀₁ and f ₀₂ according to the level of unevenness of 3 dB are expressed - and do not depend on the frequency f ₀₁ and f ₀₂ . At angles of incidence equal to and assuming a 3 dB dip at frequencies f ₀₁ and f _02, the pass bands Δf _Σ1 and Δf _Σ2 can be increased by time: .

From the consideration of figure 2. the principle of choosing both the central frequency of the deflector f ₀ (and the acousto-optic meter as a whole) and its total operating frequency band Δf _Σ = Δf _Σ1 + Δf _{Σ2 is clear} .

Since Δf _Σ1 ≃Δf _Σ2 , for a given Δf _{Σ of an} acousto-optic meter, the necessary oblique cut angle in LiNbO ₃ can be found from the condition Δf _Σ1 + Δf _Σ2 = 2 (f ₀₂ -f ₀₁ ), in which the required frequency spacing f is provided in the deflector ₀₂ and f ₀₁ ;

.

In turn, since Δf _Σ1 and Δf _Σ2 are independent of f _01.02 , the length of the piezoelectric transducer of the acousto-optical deflector - l, at which the continuity of the total passband is ensured, can be found from the relation

Thus, the presence of a causal relationship between the claimed features and the achieved technical result is determined by the fact that the Kester's prism is additionally introduced in the proposed radio signal parameters meter, which ensures a fall on the AOD at positive and negative angles of incidence of light, and the AOD itself is based on LiNbO ₃ with an oblique angle of cut and anomalous diffraction, characterized by the presence of two transmission bands.

The invention is illustrated by drawings. Figure 1 shows the structural diagram of the device of the prototype. Figure 2a shows the dependences of the angles of incidence θ _n and diffraction - θ _d light on the frequency of the slow shear wave propagating in the Y0Z plane of the LiNbO ₃ crystal, on the basis of which it is proposed to perform an acousto-optical deflector, which is part of the inventive device. Figure 2, b shows the geometry of the anomalous broadband interaction in the Y0Z plane of the LiNbO ₃ crystal, explaining the fact of the presence of two regions of AO interaction and their relationship with the oblique angle of cut - β.

The structural diagram of the inventive device acousto-optic meter parameters of radio signals is presented in figure 3.

The inventive device contains a laser arranged sequentially in the light - 1 with a wavelength λ, a collimator - 2, made of at least two lenses, a Kesters prism - 3, ensuring the division of the incident laser radiation into two beams and their subsequent fall on the acousto-optical deflector - 4 under different angles, namely: + θ _B1 and - θ _B1 . The electrical input of the acousto-optical deflector 4 through its piezoelectric transducer, the length of which is l, the measured radio signal; in the deflector - 4 it is converted into an ultrasonic analogue, on which the incident laser radiation diffracts and deviates by an angle proportional to the frequency of the incoming signal. Next, the diffracted radiation with the help of an integrating lens 5 is focused on a line of photodetectors - 6 consisting of two parts, each of which is designed to operate in the operating frequency bands Δf _Σ1 and Δf _Σ2 . Light signals are detected by a photodetector, amplified by a set of video amplifiers - 7, reduced to a "logical" form by a set of threshold devices - 8, and fed to an encoder - 9, whose task is to determine the center of a diffracted spot of light that carries information about the frequency of the incoming radio signal.

The principles of operation of the claimed device and the technical result provided by it is as follows.

The light generated by the laser - 1 using a collimator - 2 expands to the required value (in the inventive device, its diameter will determine the frequency resolution of the meter) and is fed to the Kester prism - 3, which, as explained in figure 3, provides a division into two incident laser radiation in intensity in a ratio of 1: 1 and the subsequent drop on the AOD - 4 of one of them at a positive angle, and the second at a negative Bragg angle. Each of the corresponding directions of incidence of light corresponds to (s.Fig.2) its own operating frequency band. On an acoustic analogue of the input radio signal supplied to the piezo-transducer AOD, the laser radiation diffracts, deviating by an angle proportional to the frequency, and in the directions corresponding to “their own” operating frequency bands: Δf _Σ1 or Δf _Σ2 . Using an integrating lens - 5, the diffracted laser radiation is focused on a line of photodetectors - 6, two identical parts of which fall on the bands Δf _Σ1 and Δf _Σ2 . A line of photodetectors - 6, a light signal is detected and amplified by a set of video amplifiers - 7. Then a group of video signals displaying a diffracted light signal is fed to a set of threshold devices - 8, from the outputs of which information about the coordinates of the center of the light spot in the form of the corresponding position code, which is encoded by 9 is converted to the frequency code required by the consumer.

Thus, both in the analogs and prototype, and in the claimed device, the frequency of the input radio signal is measured by converting it into an acoustic analog, modulating it with an auxiliary light signal in the direction (diffraction angle), and then converting it into a light spot, the desired coordinate of the center of which is proportional to the input frequency radio signal; the desired coordinate is digitized in the form specified by the consumer of this information.

We evaluate the degree of increase in the band of operating frequencies and sensitivity provided by the claimed device in comparison with the prototype and analogues, and also consider the factors limiting this increase.

Regardless of the initial (initial) bandwidths of the analogue and prototype in the proposed device under the same remaining conditions, the operating frequency band will be at least twice as large, since in the AOD used in it, two operating frequency bands are useful, which by selecting the appropriate angle the slice β and the length of the transducer l are combined at a given level of diffraction efficiency unevenness. Moreover, if the relative increase in the band is two times, then in absolute terms, its increase cannot exceed an octave.

With an increase in Δf _Σ over an octave in the scheme of Fig. 3, nonlinear products (harmonics) will appear in the plane of the photodetector, the presence of which will impede the proper functioning of the claimed device.

As for the increase in sensitivity in the inventive meter, its increase is due to the dependence of the diffraction efficiency of the AOD on the length of the transducer - l. If we fix the operating frequency bands of the prototype and the claimed device, then in the proposed meter the mentioned strip can be implemented with a significantly larger length of the piezoelectric transducer, and, accordingly, the sensitivity of the latter will be two or more times the sensitivity of the prototype and analogues.

The practical implementation of the inventive acousto-optic meter of radio signal parameters is beyond doubt: almost all the elements and nodes included in it are common to the prototype and analogues.

The inventive device can be made on the basis of the following elements.

The acousto-optical deflector - 4 for the frequency range (0.5-3.0) GHz can be performed on the basis of LiNbO ₃ .

A description of such a range deflector (1.5-2.5) based on anisotropic diffraction is known: [Demidov A.Ya., Zadorin A.S. Study of anomalous acousto-optic interaction in a lithium niobate crystal // News of Universities. Physics. - 1981. - No. 7. - p. 42-47.].

The optical quality requirements of LiNbO ₃ baffles are described in the article [Rozdobudko VV, Bakaryuk T.V. Acoustooptic microwave deflector with surface excitation of ultrasound // Instruments and experimental technique. - 2003. - No. 1. - p. 74-76.].

To the optical elements that make up the meter, there are no special requirements. An example of a description of the Kester prism is contained in the article [G. Lenkova. Analysis and comparison of angular scanning interferometers // Avtometriya. - 1981. - No. 1 - p. 95-100.].

The elements of low-frequency technology included in the claimed device in the form of functional devices, namely, a set of video amplifiers - 7, a set of threshold devices - 8 and an encoder - 9, also do not seem to have specific requirements; all of them can be made on the basis of modern microcircuits and FPGA technologies.

Claims (1)

An acousto-optic meter of radio signal parameters, containing a laser, a collimator, an acousto-optic deflector sequentially located on the optical axis, to which the optical input of the laser radiation falls at a Bragg angle, and a measured radio signal is fed to the electrical input of the deflector through its piezoelectric transducer; lens, a line of photodetectors, the outputs of which are through a set of video amplifiers and a set of threshold devices The devices are connected to the input of the encoder, characterized in that a Kesters prism is placed between the collimator and the deflector, which ensures that the light is incident on the optical input of the acousto-optic deflector at the same time as at a positive or negative Bragg angle, and the acousto-optic deflector is based on LiNbO ₃ with an oblique angle slice equal to β and anomalous diffraction, characterized by the presence of two identical pass bands Δf _Σ1 and Δf _Σ2 near different inflection frequencies f ₀₁ and f ₀₂ defined by the corresponding angle β and interconnected by means of f ₀₂ -f ₀₁ ≃Δf _Σ1 ≃Δf _Σ2 , and the light length of the piezoelectric transducer of the acousto-optic deflector is selected from the condition of combining the bands Δf _Σ1 and Δf _Σ2 at a given level of uneven diffraction efficiency.