RU2033694C1 - Method of transmission of reference signal to points separated in space and device for its realization - Google Patents

Abstract

FIELD: radiolocation. SUBSTANCE: oscillations of carrier frequency are sent over communication lines from each intermediate point to central station. Changes of polarization- dispersion addition of electric lengths of optical communication lines are measured at central station in scale of length of wave of optical carrier frequency. Change of electric length of each of them is determined by formula given in description of invention. Optical lines are manufactured in the form of anisoptropic fiber light guides. Each intermediate point is supplemented with carrier coupler, additional carrier source, additional carrier modulator, polarization analyzer, synchronous detector, clock frequency generator, quarter-wavelength plate. At central station each optical communication line going to proper intermediate point is supplemented with carrier coupler 4, carrier modulator 5, polarization analyzer 6, photodetector 7, two synchronous detectors 9, 10, unit 11 of identification of sign of error signal, reversible counter 12, corrector 13 of phase of reference signal. EFFECT: increased reliability of transmission by enhanced precision of phasing-in of oscillations emitted at intermediate points. 3 dwg

Description

 The invention relates to radar, direction finding using spatially separated antenna systems, as well as to the technique of transmitting accurate time signals. The invention is implemented by transmitting a reference radio signal at intermediate points corresponding to spatially separated hardware complexes.

To achieve high accuracy of direction finding of objects, it is necessary, first of all, to ensure the coherence of the oscillations emitted by the antennas that are part of, for example, a phased antenna array. With large bases of such gratings (10 ⁴ 10 ⁵ λ), the intrinsic instability of the electric lengths (ED) of the paths that transmit the reference signal from the central point to the intermediate ones is of fundamental importance. Simple estimates show that the instability of the angular orientation (Δφ) of the radiation pattern is proportional to the value of the intrinsic phase instability (ΔΨ) of the reference signal transmission path
Δφ≈K ΔΨ (1) where K has the order of the ratio Λ / L (L is the path length). Thus, if the admissible value of Δφ is, for example, 10 ^-6 rad, then for K ∈ [10 ^-4 - 10 ^-5 ] [10 ^-4 10 ^-5 ] ΔΨ ≈ [10 ^-2 - 10 ^-1 rad] For To ensure such a magnitude of the instability of the transmission path, special stabilization or correction systems for ED changes are usually used.

A known method of transmitting a reference signal from a central point to peripheral via cable communication lines and a device for implementing this method. The method consists in measuring the variations in the ED of the cable line by comparing the phase incursions along it in the forward and backward directions at two close frequencies ν ₁ and ν _2. In this case, the reference oscillators ν ₁ and ν ₁ -ν ₂ are located at the central point, and at intermediate generator of emitted frequency ν ₂ Oscillations of the first of them through the circulator enter the cable communication line and to the mixer, where they are mixed with oscillations of the generator ν ₂ received through the same circulator through the cable line. The difference frequency signal ν ₁ -ν ₂ from the mixer is fed to the phase detector of the central point, where it is compared in phase with the oscillations of the second reference oscillator ν ₁ -ν ₂ . Oscillations of the second reference generator are also transmitted via cable communication line to intermediate points. At each intermediate point there is a local generator of the emitted frequency ν ₂ , a circulator, a mixer, a coupler for vibrations ν ₁ -ν ₂ coming along the cable line from the central point, an amplifier for signal ν ₁ -ν ₂ and a phase detector. The signal ν ₁ -ν _2, which is formed as a result of mixing the reference signal ν ₁ with the signal of the local generator ν _2, is fed to one input of the last one. The signal of the second reference generator is transmitted to the second input of the mixer, transmitted via a cable line and passed through the coupler and amplifier. The output voltage of the phase detector, which is proportional to the phase angle of the two oscillations with a frequency of ν ₁ -ν _2, is used to adjust the oscillation phase of the local oscillator ν _2. This method and device have low accuracy due to the high level of reflections in the cable line, and is also characterized by an error due to dispersion phase velocities in the cable line for reference signals at frequencies ν ₁ and ν ₁ -ν ₂
The prototype of the proposed method is a method, the essence of which is as follows. The radio frequency reference signal (frequencies ω) is transmitted from a central point to intermediate ones through an atmospheric optical communication line, modulating with this signal two optical carriers ν ₁ and ν ₂ ; at the intermediate point, these carriers are photodetected, highlighting two signals of the modulation reference frequency (ω), and correct the change in the ED of the air communication channel by the difference in the phase incursions of the two selected reference signals.

A device for implementing the proposed method consists of two optical carriers installed at a central point (frequencies ν ₁ and ν ₂ ), an optical system that coaxially combines the light beams of these sources; an electro-optical modulator, to the radio frequency input of which a reference oscillator (ω) is connected, and coaxially combined outputs of two light carrier sources (ν ₁ and ν ₂ ) are connected to the optical input; The optical output of the modulator is connected to the input of the optical distribution device, which directs the multiplied two-color light beams to the corresponding intermediate points, and at each of the peripheral points a photodetector coupled to the phase meter is installed. The photodetector includes an input optical system directing each of the received light carriers to its photodetector; the output of the first photodetector is connected to one output of the phasemeter, and the output of the second photodetector is connected to the second input of the phasemeter and the input of the phase corrector of the reference signal, the electrical output of the phasemeter is connected to the control input of the phase corrector, the output of the phase corrector is connected to the antenna or mixing element.

However, this method and device have insufficient accuracy of correction of changes in the ED of an overhead communication line, low reliability and noise immunity. The first of these drawbacks is associated with the possibility of phasing errors due to the presence of sections in the central and intermediate points where two light carriers pass through different optical and optoelectronic devices. For example, the presence of two photodetectors (in each channel ν ₁ and ν ₂ ) leads to the appearance of an error due to the non-identity of their phase characteristics. In addition, the measurement of the oscillations of the ED of the communication line is carried out on the wavelength scale of the reference signal, which in some cases may be insufficient. The last two drawbacks are due to the fact that the propagation conditions in the atmospheric optical line are directly affected by hydrometeors and technogenic precipitation, while the optical inputs of the intermediate points are practically not protected from the penetration of both background and directional radiation (interference).

где

и

термические коэффициенты группового показателя преломления (n_г) и двулучепреломления используемых оптических линий связи соответственно.The aim of the invention is to increase the accuracy and reliability of the phasing of the intermediate points on the reference signal. The method consists in generating a reference signal at a central point, transmitting it by modulating the optical carrier through optical communication lines to intermediate points and correcting changes (ΔL (T)) in the electrical length of these lines, measuring and correcting the phase mismatch of the transmitted reference signal with the signal generated at each waypoint. At each intermediate point, a reference signal is generated and transmitted via the same optical communication lines from each intermediate point to the central one; at the central point, the change in the polarization-dispersion additive (Δl (T)) of the electrical lengths of the optical communication lines is measured on the wavelength scale of the optical carrier and determine ΔL (T) by the formula
ΔL (T) Δl (T) (n _g -1)

Where

and

thermal coefficients of the group refractive index (n _g ) and birefringence of the used optical communication lines, respectively.

 To a device for transmitting a reference signal to space-separated points consisting of a reference generator, a carrier source and a carrier modulator installed at a central point, and a carrier receiver of a local generator and a PLL installed at each of the intermediate points, as well as optical communication lines connecting a central point with intermediate, optical communication lines are made in the form of anisotropic fiber optical fibers, a carrier coupler, an additional a carrier source, an additional carrier modulator, a polarization analyzer, a synchronous detector and a clock generator, while the total channel of the carrier coupler is connected to the output of the optical communication line, its input through a quarter-wave plate is connected to the output of the additional carrier source, and its output is connected to the input of an additional a carrier modulator, to the control input of which a local generator output is connected, the output of an additional carrier modulator is connected through a polarization analyzer, whose axis is perpendicular to the polarization of the radiation coming through the optical communication line to the input of the photodetector, the output of which is connected to the input of the synchronous detector, to the control input of which the output of the clock generator is connected, and the output of the synchronous detector is connected to the input of the PLL system, the output of which is connected to the control input local generator.

 At the central point, for each optical link going to the corresponding intermediate point, a carrier coupler, a carrier modulator, a polarization analyzer, a photodetector, two synchronous detectors, an error signal sign identification circuit, a reversible counter, and a reference signal phase corrector are additionally introduced.

In addition, a common clock generator was also introduced for all optical communication lines, while the total channel of the carrier coupler is connected to the input of the corresponding optical communication line, its output is connected to the input of an additional carrier modulator, the optical axes of which are oriented parallel to the anisotropy axes of the optical communication line, controlling the input of the additional carrier modulator is connected to the output of the first harmonic of the clock generator, and the modulator output is through a polarization analyzer, the axis of which is deployed uta at 45 ± 3 ^° relative to the electro-optical axes of the additional carrier modulator, connected to a carrier photodetector, the output of which is connected to the inputs of synchronous detectors of the first and second harmonics of the clock frequency, the control inputs of synchronous detectors are connected to the corresponding outputs of the clock frequency, and the outputs of synchronous detectors are connected to the inputs of the identification circuit of the sign of the error signal, the outputs of which are connected to the inputs of a reversible counter, the analog output of which is connected to the control input the phase rector of the reference signal, the input of which is connected to the output of the reference oscillator, and the output with the control input of the carrier modulator.

 As a result of patent research, it was not established the availability of technical solutions containing the distinctive features of the proposed technical solution. Thus, the proposed technical solution meets the criterion of "significant differences".

 Consider the essence of the proposed method, assuming for simplicity that it is required to transmit a frequency reference signal ω (microwave range) from a central point to one intermediate point. It is supposed to use a polarization-dispersion path (for example, an anisotropic optical fiber (ABC) as a transmission line. For definiteness, we assume that the anisotropy of the transmission path is the difference in group refractive indices for vertically and horizontally polarized light components, i.e.

≪ 1, (1) где B λ /Λ_б нормализованное двулучепреломление;
λ- длина волны света в вакууме;
Λ_б- длина волны поляризационных биений. Известно, что основной причиной, сказывающейся на нестабильность ЭД волоконно-оптического тракта, является изменение температуры окружающей среды. Абсолютное приращение ЭД световода длиной L при изменениях температуры (ΔT) можно представить в виде
ΔL V (n 1) L˙ ΔT, (2) где V ∂(n-1)/∂T термооптический коэффициент (для кварца V ≈ 10^-5 гр^-1). Из выражения (2) легко видеть, что при передаче по волоконному световоду (BC) длиной 1 км СВЧ-огибающей (

≈5 10 ГГц) термодрейф фазы ( ΔL

) имеет порядок π/2 радиан на 1^оС. Запишем выражения, определяющие зависимость электрической длины ABC от температуры для двух ортогональных поляризаций светового поля
L_y(T) n_y (T) ˙ L,
L_x (T) n_x (T) ˙L. (3) Зависимость L(T) можно считать существенно более слабой, чем зависимость n(T) Приращения ЭД при изменениях температуры можно записать в виде
ΔL_x(y)(T) L V_x(y) (n_x(y) 1) ΔT. (4) Тогда для разности температурных приращений L_y(T) и L_x(T) можно получить
Δl(T) ≡ ΔL_y(T) ΔL_x(T) L

T L

ΔT (5) Возьмем отношение приращений ЭД для одной поляризации (4) к разностному приращению ЭД анизотропного ВС для двух поляризаций (5)
R ≡

(6) Для реально существующих ABC

n_y n

<< 1 и V_x ≃ V_y. Будем полагать, что B≈10^-4 и характеризуется линейной зависимостью от температуры, т.е.n _x ≠ n _y ;

≪ 1, (1) where B λ / Λ _{b is the} normalized birefringence;
λ is the wavelength of light in vacuum;
Λ _b - wavelength of polarization beats. It is known that the main reason that affects the instability of the ED of the fiber optic path is the change in ambient temperature. The absolute increment of the ED of a fiber of length L with temperature changes (ΔT) can be represented as
ΔL V (n 1) L˙ ΔT, (2) where V ∂ (n-1) / ∂T is the thermo-optical coefficient (for quartz V ≈ 10 ^-5 g ^-1 ). From expression (2) it is easy to see that when transmitting through a fiber optic fiber (BC) 1 km long, the microwave envelope (

≈5 10 GHz) phase thermal drift (ΔL

) Of the order of π / 2 radians at 1 ° ^C. We write the expression defining the relationship ABC electrical length versus temperature for two orthogonal polarizations of light field
L _y (T) n _y (T) ˙ L,
L _x (T) n _x (T) ˙ L. (3) The dependence L (T) can be considered significantly weaker than the dependence n (T). The increments of the ED with temperature changes can be written as
ΔL _{x (y)} (T) LV _{x (y)} (n _{x (y)} 1) ΔT. (4) Then for the difference in temperature increments L _y (T) and L _x (T), we can obtain
Δl (T) ≡ ΔL _y (T) ΔL _x (T) L

TL

ΔT (5) Let us take the ratio of the DE increments for one polarization (4) to the difference increment of the ED of anisotropic AC for two polarizations (5)
R ≡

(6) For real-life ABCs

n _y n

<< 1 and V _x ≃ V _y . We assume that B≈10 ^-4 and is characterized by a linear temperature dependence, i.e.

1 +

(7) где B_o исходное значение двулучепреломления при температуре T_o;
ΔT приращение температуры
Коэффициент "редукции" R, определяемый выражением (6), не зависит от температуры и является характеристикой данного ABC. Таким образом, выражение (6) носит фундаментальный характер для рассматриваемого способа передачи опорного сигнала. Оно позволяет прогнозировать изменение ЭД световода Δl(T) по измеренному разностному теромодрейфу Δl(T) для двух ортогональных поляризаций. Действительно, переписывая выражение (6) в более удобной форме, получим
ΔL(T) Δl(T) · (n_г-1)

Δl(T)·R (6,a) В этом плане коэффициент R аналогичен коэффициенту A по прототипу, однако существует два существенных различия этих способов. Первое: в предлагаемом техническом решении R обусловлен проявлением поляризационной дисперсией тракта, в прототипе A обусловлен хроматической дисперсией света. Второе: величина Δl(T) здесь изменяется в масштабе длины волны света, а в прототипе аналогичная дисперсионная поправка измеряется в масштабе длины волны опорного сигнала (СВЧ-диапазон)
Согласно проведенным экспериментальным исследованиям, параметры опытного ABC составляют: B 0,8 х 10^-4, ∂B/∂T 0,7 х 10^-7 гр^-1, V 10^-5 гр^-1, n_г ≃ 1-5, L 73 м, R 71,5, при этом изменение температуры, при котором разность электрических длин ABC для двух поляризаций равна λ 0,63 мкм, составляет ΔT_o ^(λ) 0,13^оС. Пересчитаем этот параметр для ABC этого же типа, но длиной 1 км
ΔT $\genfrac{}{}{0ex}{}{\text{(λ)}}{\text{1км}}$

ΔT $\genfrac{}{}{0ex}{}{\text{(}}{\text{o}}$ ^λ)

≃ 9,5·10^-3 гр
Таким образом, при длине линии связи 1 км разность хода двух ортогонально-поляризованных компонент λ возникает при изменении температуры ΔT_o ^(λ)= 9,5 х 10^-3 гр. При этом изменение ЭД линии связи для одной поляризационной компоненты согласно выражению (4) будет иметь порядок ΔL_x(y) 0,048 мм или для фазы СВЧ-опорного сигнала (

10 ГГц) это составит около половины градуса. Приведенные оценки сделаны в связи с тем, что Δl(T) измеряется с дискретом λ хотя известно из практики интерференционных измерений, что этот дискрет может быть существенно уменьшен ( λ/10 и меньше). Кроме того, точность измерения Δl(T) может быть улучшена на порядок за счет увеличения B от 10^-4 до 10^-3 (см. выражение (7). Итак, точность измерения изменений ΔL(T) тракта передачи километровой длины согласно выражению (6, а) определяется выражением d[ ΔL (T)] d [ Δl(T˙] R. Если дискрет измерения d[ Δ l(T)] выбран равным λ= 0,63 мкм, то d[ ΔL(T)]≈ 0,09 мм, если дискрет d[ Δ l(T)] λ /10, то d[Δ L(T)] 0,009 мм.B (T) B

1 +

(7) where B _{o is the} initial birefringence at temperature T _o ;
ΔT temperature increment
The “reduction” coefficient R defined by expression (6) is temperature independent and is a characteristic of this ABC. Thus, expression (6) is fundamental for the considered method of transmitting a reference signal. It allows one to predict the change in the ED of the fiber Δl (T) from the measured difference thermal drift Δl (T) for two orthogonal polarizations. Indeed, rewriting expression (6) in a more convenient form, we obtain
ΔL (T) Δl (T) · (n _g -1)

Δl (T) · R (6, a) In this regard, the coefficient R is similar to the coefficient A of the prototype, however, there are two significant differences between these methods. First: in the proposed technical solution, R is due to the manifestation of the polarization dispersion of the path, in the prototype A due to the chromatic dispersion of light. Second: the value Δl (T) here changes in the scale of the wavelength of light, and in the prototype a similar dispersion correction is measured in the scale of the wavelength of the reference signal (microwave range)
According to experimental studies, the parameters of the experimental ABC are: B 0.8 x 10 ^-4 , ∂B / ∂T 0.7 x 10 ^-7 gr ^-1 , V 10 ^-5 gr ^-1 , n _g ≃ 1-5, L 73 m, R 71.5, and the change in temperature at which the difference in electric lengths of ABC for two polarizations is λ 0.63 μm is ΔT _o ^(λ) 0.13 ^о С. We recalculate this parameter for ABC of the same type but 1 km long
ΔT $\genfrac{}{}{0ex}{}{\text{(λ)}}{\text{1km}}$

ΔT $\genfrac{}{}{0ex}{}{\text{(}}{\text{o}}$ ^λ)

≃ 9.5 · 10 ^-3 gr
Thus, with a communication line length of 1 km, the path difference of two orthogonally polarized components of λ occurs when the temperature ΔT _o ^(λ) = 9.5 x 10 ^-3 gr. In this case, the change in the ED of the communication line for one polarizing component according to expression (4) will be of the order of ΔL _{x (y)} 0.048 mm or for the phase of the microwave reference signal (

10 GHz) this will be about half a degree. The above estimates are made due to the fact that Δl (T) is measured with a discrete λ, although it is known from the practice of interference measurements that this discrete can be significantly reduced (λ / 10 and less). In addition, the measurement accuracy Δl (T) can be improved by an order of magnitude by increasing B from 10 ^-4 to 10 ^-3 (see expression (7). So, the accuracy of measuring changes ΔL (T) of the transmission path of a kilometer length according to the expression ( 6a) is determined by the expression d [ΔL (T)] d [Δl (T˙] R. If the measurement discrete d [Δ l (T)] is chosen to be λ = 0.63 μm, then d [ΔL (T)] ≈ 0.09 mm, if the discrete d [Δ l (T)] λ / 10, then d [Δ L (T)] 0.009 mm.

 In FIG. 1 shows a functional diagram of a device for implementing the proposed method for transmitting a reference signal.

The reference signal transmission device (for example, in a radio interferometer) contains at the central point a carrier wave source 1, a reference oscillator 2, a carrier frequency electro-optical modulator 3, a fiber optic coupler 4, an additional (low-frequency) carrier frequency electro-optical modulator 5, a polarization analyzer 6, photodetector 7, clock generator 8, synchronous detectors 9, 10, error signal sign identification circuit 11, counter 12, phase corrector of reference vibrations 13, fiber optic communication line 14,
At intermediate points, the device comprises a fiber optic coupler 15, an electro-optical carrier modulator 16, a local generator 17; a photodetector 18, a clock generator 19, a synchronous detector 20, a PLL system 21 of a local generator, an additional carrier source 22, a quarter-wave plate 23.

 In this case, the optical communication lines connecting the central point to the intermediate ones are made in the form of anisotropic optical fibers, in each of the intermediate points the total channel of the carrier coupler is connected to the output of the optical communication line, its input through the quarter-wave plate is connected to the output of the additional carrier source, and its output connected to the input of the additional carrier modulator, to the control input of which the output of the local generator is connected, the output of the additional carrier modulator is connected through the fields Rationalization analyzer, whose axis is perpendicular to the polarization of radiation passing through the communication line, to the input of the photodetector, the output of which is connected to the input of the synchronous detector, the control input of which is connected to the output of the clock frequency generator, and the output of the synchronous detector is connected to the input of the PLL, the output of which is connected with control input of a local generator.

At the central point, for each optical communication line that goes to the corresponding intermediate point, the total channel of the carrier coupler is connected to the input of the corresponding optical communication line, its output is connected to the input of the additional carrier modulator, the optical axes of which are oriented parallel to the anisotropy axes of the optical communication line, the control input of the additional the modulator is connected to the output of the first harmonic of the clock generator, and the output of the modulator through the polarization analyzer, whose axis uta 45 ± 3 ^of the electro-optic axes additional modulator carrier is connected to the photodetector carrier, whose output is connected to the inputs of synchronous detectors, the first and second clock frequency harmonics, control inputs of the synchronous detectors are connected to respective outputs of clock generator frequency, and the outputs of the synchronous detectors are connected to the inputs of the identification circuit of the sign of the error signal, the outputs of which are connected to the inputs of a reversible counter, the analog output of which is connected to the control input the phase rector of the reference signal, the input of which is connected to the output of the reference oscillator, and the output with the control input of the carrier modulator.

 The operation of the device to implement the proposed method is more convenient to consider as the relationship of the two subsystems. One of them provides a measurement of the intrinsic thermal drift of the ED of the fiber communication line and corrects the phase of the reference signal. The second subsystem provides the transmission of the reference signal with a pre-adjusted phase from the central point to the intermediate one, comparing the current phases of the reference signal and the local oscillator signal with the generation of the corresponding error signal proportional to their out-of-phase, and the subsequent phase correction of the local oscillator using the PLL. Both systems work with autonomous sources of carrier oscillations of the same frequency, although with some complication of the circuit, one source can be dispensed with. A fundamentally important point is that the radiation of the source of the first subsystem 1 must be linearly polarized, and the radiation of the source of the second subsystem 22 must be circularly polarized. The polarization orientation of the source 1 coincides with one of the main dielectric axes ABC used in the communication line of the central point with the intermediate.

The radiation of the source 22, located at an intermediate point, is converted into circularly polarized by a quarter-wave plate 23. Further, this radiation through one of the two outputs of the directional coupler 15 is introduced into the fiber optic communication line. Since ABC has polarization dispersion, the two orthogonally polarized light components of source 22 during the passage through ABC will acquire a different phase incursion. In this case, the difference in phase incursions of these components depends on temperature and is equal to
Δ φ = (2 π / λ) Δl (T). (8) Arriving at a central point, this radiation is output from ABC through a directional coupler 4 and through one of its outputs is fed to the input of an additional electro-optical modulator 5, which is controlled by a signal of a low-frequency generator 8 clock frequencies As a result of polarization modulation in modulator 5 and the passage of radiation through polarization analyzer 6, whose axis 45 is deployed ^about the axes of the modulator 5 in the intensity of transmitted light components appear at frequencies Ω and 2Ω Their quantities are expressed Jun without phase shift Δ φ as follows:
I _m1 AJ ₁ (Φ ₁ ) sin Δ φ
I _m2 AJ ₂ (Φ ₁ ) cos Δ φ (9) where A is a constant depending on the level of light power,
J ₁ (Φ ₁ ), J ₂ (Φ ₁ ) Bessel functions;
Φ ₁ is the modulation index.

. (10)
В предлагаемом устройстве составляющие I_m1 и I_m2 измеряются с помощью синхронных детекторов 9 и 10. При монотонном изменении фазового сдвига Δ φ во времени имеет место вполне определенная последовательность чередования знаков I_m2 и I_m2. Анализируя эту последовательность, можно определить увеличивается Δ φ или уменьшается. Эту функцию в устройстве выполняет схема 11 идентификации знака сигнала ошибки, выходные сигналы которой управляют реверсивным счетчиком 12. Выходной сигнал последнего поступает на управляющий вход корректора фазы 13 опорного сигнала, т.е. в результате работы первой из названных подсистем посредством корректора фазы 13 осуществляется упреждающая корректировка фазы опорного сигнала. Эта корректировка осуществляется на передающем конце, она равна Δ φ
Вторая подсистема работает следующим образом.In other words, knowing Φ ₁ and measuring I _m1 and I _m2 , we can determine
Δφ arctg

. (10)
In the proposed device, the components I _m1 and I _m2 are measured using synchronous detectors 9 and 10. With a monotonic change in the phase shift Δ φ in time, there is a well-defined sequence of alternating signs I _m2 and I _m2 . By analyzing this sequence, it is possible to determine whether Δφ increases or decreases. This function in the device is performed by the error sign identification circuit 11, the output signals of which control the reversible counter 12. The output signal of the latter is supplied to the control input of the corrector of the phase 13 of the reference signal, i.e. as a result of the operation of the first of the aforementioned subsystems, a phase 13 corrector proactively corrects the phase of the reference signal. This adjustment is carried out at the transmitting end, it is equal to Δ φ
The second subsystem works as follows.

The radiation of source 1 is modulated by polarization (or amplitude) by means of an electro-optical modulator (3) with a reference signal with a pre-adjusted phase. In this case, the reference signal itself has phase modulation at the frequency of “tinting” Ω _o ie

U _o E _o sin (ωt + Φ _o sin Ω _o t) (11) where Φ is _the index of phase modulation.

Through the inlet end of the coupler 4, this modulated carrier enters the communication line 14. The polarization of the radiation source is deployed at ^about 45 ± 3 with respect to the crystallographic axes of the induced modulator 3 and parallel to one of the principal dielectric axes ABC. After passing through the communication line, that is, at the input to the modulator 16 of the intermediate point, the envelope of the light carrier of the source 1 will be coherent with oscillations at the output of the reference generator due to the forward correction of its phase. In the modulator (16), the carrier of the source (1) is re-modulated, but now by the signal of the local generator 17
U ₁ E ₁ sin (ωt + Ψ ₁ (t)), (12) where Ψ ₁ (t) is the random phase drift of the local generator with respect to ωt.

It can be shown that as a result of repeated modulation of the carrier of the source 1 in the light flux after the analyzer 24, a harmonic component arises at a frequency of Ω _o . The amplitude of this component is expressed by the ratio
I _Ωo (t) BJ ₁ (Φ _o ) sin Ψ ₁ (t), (13) where B is a coefficient depending on the depth of carrier modulation and its power;
J ₁ (φ _o ) Bessel function.

By means of a photodetector 18, this signal is extracted from the modulated carrier and fed to the input of the synchronous detector 20, to the control input of which a clock frequency signal Ω _о is supplied. The detected voltage from the output of the synchronous detector is fed to the input of the PLL 21, which controls the phase of the local generator. Thus, when the PLL is closed, the phase of the local oscillator is rigidly tied to the phase of the reference oscillator, the phase of which is previously adjusted taking into account the temperature drift of the ED of the optical communication line.

= 7 ГГц) с помощью блоков 1 3.A specific example of a method for transmitting a reference signal to diversity points is shown in FIG. 1. In the operation of this device, the following sequence of operations is performed:
1. Transmit from the central point the light carrier (λ 0.63 μm), modulated by the reference radio signal (frequency

= 7 GHz) using blocks 1 3.

2. Measure the change in the polarization-dispersion additive (Δl (t)) of the optical transmission line on the carrier (λ 0.63 μm) using the blocks: 22, 23, 15, 4 12, which for the OLS with a length of 1000 m is Δl (ΔT _λ ) 0.63 μs when the temperature changes by 9.5 ˙ 10 ^-3 gr.

 3. Correct the phase of the reference radio signal by the value -sign [Δl (T)] x R λ where sign [Δl (T)] is the sign of the change in the polarization-dispersion additive; R is the reduction coefficient known for this OLS (R 71.5), which is carried out by block 13.

4. Measure the magnitude of the phase mismatch Ψ ₁ (t) of the reference signal coming from the central point to the intermediate in the form of an envelope of the light carrier, with the signal of the local generator, which is determined by the expression
Ψ ₁ (t) arcsin [I _Ωo (t) / BJ ₁ (Φ _o )] where I _Ωo (t) is the amplitude of the phasing error signal at a frequency Ω _о ;
Φ _o - modulation index at the frequency of the phase tint;
B is a coefficient depending on the depth of modulation of the light carrier at the central and intermediate points, respectively, by the reference signal and the signal of the local generator, this operation is carried out by means of blocks 16, 24, 18, 20, 19.

5. Adjust the phases of the local generator by the value Ψ ₁ (t), which is carried out by means of block 21.

 An illustration of the process of generating phase correction signals of the reference signal from the measured increments of the polarization-dispersion additive Δl (t) is shown in FIG. 2 and 3. In FIG. 2 shows one of the possible variants of the identification scheme of the sign of the error signal. This circuit includes: 1.5 Schmidt triggers, 2.6 differentiating circuits, 3.7 limiters, 4.8 key devices.

Consider the waveforms shown in FIG. 3. Suppose that under the influence of temperature fluctuations, the polarization-dispersion additive changes as shown in diagram a. The equidistant lines along the vertical axis correspond to a change in Δl by the wavelength of the carrier oscillation λ. At the same time, at the output of synchronous detectors 9 and 10 (see Fig. 1), the currents will change in accordance with diagrams b and c (see Fig. 3). These currents are supplied to the inputs of comparators 1 and 5 (see Fig. 2), which can be implemented, for example, in the form of Schmidt triggers based on operational amplifiers (op amps). The voltages at the output of comparators 1 and 5 will have the form shown on diagrams d and d. After these signals pass through differentiating circuits 2 and 6 (also based on the op-amp), they will take the form of diagrams e and g, respectively. The limiter 3 passes only positive pulses, and the limiter 7 only negative. The key circuit 4 generates an output signal with the same polarity (positive) of the input signals, it corresponds to diagram 3, and circuit 8 generates a similar signal when the negative pulses coincide at its inputs (diagram and). The signals U ₄ and U ₈ are fed to the "minus" and "plus" inputs of the reverse counter 12 (see Fig. 1), which, firstly, controls the operation of the phase 13 corrector and, secondly, (if necessary) displays the current correction state. At each step of operation of the reversible counter, its contents change in the "plus" or "minus" side, depending on which of its inputs trigger pulses (U ₄ or U ₈ , Fig. 3) come.

The phase corrector can be made in the form of an electrically controlled phase shifter. In this case, the discrete tuning magnitude of the phase shifter in accordance with expression (6, a) is chosen equal to Rλ. Then for the one considered in FIG. In 3 situations, the corrective addition to the phase of the reference signal will have the form shown in diagram K. Comparing diagrams a and k, we can evaluate the accuracy of the correction. It is easy to see that it is determined by the value of the selected discrete, i.e., Rλ Using expressions (5), (6), (6, a), and assuming that L 1 km, λ 0.63 μm, ∂B / ∂T 0.7˙ 10 ^-7 g ^-1 ; V 10 ^-5 gr ^-1 , n 1.5, we find that the temperature change at which Δl (T) changes by 0.63 μm will be 9.5 ˙ 10 ^-3 gr. In this case, the ED of the tract ΔL (T) will change by 0.046 mm. For the reference signal frequency of 7 GHz (Λ 4.3 cm), such a departure of the transmission path ED corresponds to less than half a degree of phase. Since the correction discret in this case is chosen equal to λR, the correction accuracy is no worse than 0.5 ^o phase, or 0.048 mm.

An experimental verification of the feasibility of the proposed method. As a result of studies of multimode ABC, it was confirmed that the temperature coefficient of birefringence in it is of the order of 10 ^-7 deg. This allows to reliably detect a change of the reference signal ED kilometer transmission path value ≈ 0,05 mm (less than 1 ^{on the} phase in the three-centimeter range). If necessary, the accuracy can be improved by an order of magnitude either by reducing the discrete measurement of the interference image, or by increasing the initial birefringence of ABC to 10 ^-3 .

 The proposed method for transmitting a reference signal to spaced-apart intermediate points and a device for its implementation provide a technical effect consisting in increasing the phasing accuracy by measuring the polarization-dispersion difference of the ED path in the light wavelength scale and corresponding correction of the total ED when transmitting the reference signal in several intermediate points and increasing the reliability and noise immunity of the phasing system through the use of closed transmission paths of the type anisotr pnyh single-mode fibers.

Claims (2)

1. A method of transmitting a reference signal to space-separated points, which consists in generating a reference signal at a central point, modulating an optical carrier with it and transmitting a modulated signal along optical lines to intermediate points, correcting changes ΔL (T) of the electrical lengths of these communication lines, measuring and correction of the phase mismatch of the transmitted reference signal with the signal generated in the corresponding intermediate point, characterized in that, in order to increase the reliability of transmission by to increase the accuracy of phasing of the vibrations emitted at the intermediate points, a reference signal is generated at each intermediate point and transmitted on the same optical carrier via optical communication lines towards the central point; at the central point, the changes in the polarization-dispersion additive Δl are measured on the wavelength scale of the optical carrier (T) the electrical lengths of the optical communication lines and determine ΔL (T) by the formula

thermal coefficients of the group refractive index n _g and birefringence of the used optical communication lines, respectively.  2. A device for implementing a method of transmitting a reference signal to space-separated points, comprising a central point connected to intermediate points by optical communication lines, the central point comprising a reference generator, a carrier frequency source and a carrier frequency modulator, and a carrier frequency receiver at the intermediate point, local oscillator and phase locked loop (PLL), characterized in that the optical communication lines are made in the form of anisotropic fiber optical fibers, in each intermediate at the exact point, serially connected sources of the carrier frequency, a quarter-wave plate and a fiber optic coupler, one end connected to the optical communication line, and the other end to the input of the introduced modulator, the output of which through the serial connected polarization analyzer, the carrier frequency receiver, the synchronous detector, are introduced, are introduced, the PLL system and the local oscillator is connected to the input of the modulator, and a clock generator is introduced, the output of which is connected to the second synchronous input detector, and at the central point, an optical coupler, an additional carrier frequency modulator, a polarization analyzer and a photodetector, as well as two synchronous detectors, an error signal sign identification unit, a reversible counter, a reference signal phase corrector and a clock generator are introduced, and the photodetector output connected to the connected inputs of the first and second synchronous detectors, the outputs of which are connected to the inputs of the identification block of the sign of the error signal, the outputs of which are connected to the inputs of a reversible counter, the output of which is connected through the phase corrector of the reference signal to the modulating input of the carrier frequency modulator, the other input of which is connected to the output of the carrier frequency source, and the output of the carrier frequency modulator is connected to one end of the optical coupler, the other end of which is connected to the optical line connection, the output of the clock generator is connected to the input of the reference oscillator, with heterodyne inputs of an additional carrier frequency modulator and the first synchronous detector, stroke "double frequency" clock-frequency generator is connected to the local oscillator input of the second synchronous detector.

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