RU2674074C1 - Radiophoton transmission line for transferring powerful broadband signals and effective excitation of antennas - Google Patents

Abstract

FIELD: radio engineering and communications.

SUBSTANCE: invention relates to radio photonics, including the technique of transmitting high-power broadband radio signals over fiber-optic communication lines to antennas and antenna arrays. An optical splitter, an optical delay line and antennas are introduced into the radiophoton transmission line of powerful broadband signals, the RF modulating signal simultaneously with the current from the bias source is fed to the input of the laser, the optical output of which is connected to the input of the fiber-optic line, the output of which is connected to a symmetric optical splitter, the optical outputs of which are connected to the optical inputs of the first and second photodetectors connected in a differential circuit and operating in the photovoltaic mode, the optical input of the second photodetector is fed through an optical delay line, which provides a delay of the signal by the length of the pulse at the base at the output of the first photodetector, electrical outputs of the photodetectors are the push-pull outputs of the broadband radiophoton transmission path, operating in the AB class, whose load is the antennas.

EFFECT: technical result is increased efficiency, maximum achievable power, broadband (expansion of the instantaneous band of transmitted frequencies), increased identity of channels, improved temperature and time stability, obtained energy independence of antennas, as well as increased efficiency of their excitation.

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Description

The invention relates to techniques for fiber-optic communication, in particular to radio photon transmission paths for communication systems and radars, and more particularly to broadband transmission lines of Radio-in-Fiber (RoF) systems and transmission paths of radio photon receiving-transmitting AFAR (PPM) modules ROFAR) for transmitting high-efficiency high-power broadband signals to broadband antennas and ROFAR antenna arrays and their effective excitation.

For a wide range of applications in modern communication systems, radar, navigation, radio astronomy, etc. it is required to transmit powerful broadband signals directly to the end user (final load) via fiber-optic communication lines (FOCL), for example, to an antenna emitter without subsequent amplification [1-3].

However, to solve the problem of highly efficient transmission of powerful broadband signals over fiber optic lines while maintaining high efficiency during antenna excitation, it is necessary to overcome a number of scientific and technical problems.

In typical low-power analog and digital FOCLs, including for transmitting digital information, video pulses are used, i.e. upon modulation of optical radiation, its intensity varies from a minimum (almost zero value) to a maximum and vice versa.

For example, the analytical representation of a broadband video pulse in general form will be [4, 5]:

- эффективная длительность импульса,

- функция, описывающая форму сигнала.where: A = max {x (t)} is the amplitude of the pulse,

- effective pulse duration,

- a function that describes the waveform.

Such unipolar pulses with a constant component have a maximum of energy in the region of zero frequency and an elongated tail with a sharply decreasing energy (spectral density) at a frequency f >> 0 [4, 5].

However, antennas, even broadband ones, emit only an insignificant part of this spectrum, in the region of the central frequency f _o , and f _o >> 0, therefore the radiation efficiency of antennas excited by video pulses is extremely small [5].

To match the spectra of broadband and ultra-wideband signals supplied to the antenna and the radiation spectrum of the antenna itself, it is necessary to work with bipolar pulses, for example, radio pulses of a Gaussian or other envelope shape [5]:

where: ƒ _o is the central frequency, α, β are the constant attenuation and increase of the envelope.

When the antenna is excited by bipolar broadband (short) pulses with a spectrum of the antenna radiation matched with it, the antenna radiation efficiency increases significantly [5].

However, when constructing the FOCL photon paths for transmitting radio pulses, i.e. pulses with a lower frequency spectrum, as well as any continuous and discrete signals having a carrier frequency (i.e., the ability to work with bipolar signals), it is necessary to select the operating point for modulation (both external and internal) approximately in the middle of the power variation range .

Thus, the optical transmitter, irrespective of the modulation depth, continuously emits about half of its maximum optical power and actually works in class A (according to the classification adopted for electronic amplifiers with the highest achievable efficiency - 30%).

This immediately leads to several negative consequences, including a decrease in efficiency, an increase in shot noise directly proportional to the optical power incident on the photodetector, and a decrease in the dynamic range as a result of an earlier achievement of its saturation threshold. The nonlinear distortion coefficient also increases due to a decrease in the dynamic range and the specifics of the operation of devices in class A, in the output spectrum of which there are even and odd harmonics.

A fundamental solution to these problems is to transfer the operation of optical transmitters to class AB, in which the efficiency is approximately doubled, the constant component of optical radiation is reduced to almost zero, and nonlinear distortion is reduced by suppressing even harmonics. The presence of the initial characteristics of optical modulators with increased nonlinearity for external modulation and the threshold laser current for internal (direct or direct) modulation make it necessary to use the AB class with an insignificant (of the order of several percent) constant component of optical radiation. An example of such a solution is US 20070019896, Class AB microwave-photonic link, published Jan. 25. 2007 year [6].

However, the schemes of this invention have a number of limitations and disadvantages, making it fundamentally impossible to use it as a powerful transmission path.

Known radio photon line for transmitting high-power microwave signals with increased efficiency, operating in class AB [6] (Fig. 1 source), consisting of a laser, an optical amplifier, an optical splitter, two optical modulators with bias sources, a radio frequency divider, an RF phase shifter, two fiber optic lines and two photodetectors included in a balanced circuit operating in the photodiode mode.

The disadvantages of the known scheme are as follows:

The presence of an optical fiber amplifier (EDFA) due to the low overall efficiency of about 10% [7] greatly reduces the overall efficiency of the system.

Optical modulators limit the maximum optical power level to a few hundred mW, which makes such a system fundamentally inapplicable for transmitting powerful (over 1 Watt) signals, and their internal losses significantly reduce the efficiency of using an optical amplifier, reducing the resulting gain [8].

Two separate modulators with separate bias sources and two optical fibers (OM) lead to a significant non-identity of the channels in a whole range of parameters (in terms of transmission coefficient, difference in signal transit times, differential phase, differential temperature and time drift, etc.).

The presence of a radio frequency phase shifter in radio frequency channels fundamentally limits the width of the modulation frequency band, making it practically impossible to work in a wide and especially in an ultra-wide frequency band, and also exacerbates problems with non-identical channels.

The use of balanced photodetectors in the usual (photodiode) mode requires separate bipolar bias sources and leads to an increase in the power dissipated by them, to the energy dependence of the load (antennas), and also to a decrease in the overall system efficiency.

The presence of a double number of transmission line elements and several precision bias sources increases hardware costs, volume, mass and cost, while reducing the total system efficiency.

Known radio photon line for transmitting high-power microwave signals with increased efficiency, operating in class AB [6] (Fig. 2 sources), consisting of a radio frequency divider, radio frequency phase shifter, two lasers with bias sources, two fiber optic lines and two photodetectors included according to the balanced circuit operating in photodiode mode.

The disadvantages of the known scheme are as follows:

The presence of a radio frequency phase shifter in radio frequency channels fundamentally limits the width of the modulation frequency band, making it practically impossible to work in a wide and especially in an ultra-wide frequency band, and also exacerbates problems with non-identical channels.

Two separate lasers with separate bias sources and two OBs lead to a significant non-identity of the channels in a whole range of parameters (in terms of transmission coefficient, difference in signal propagation time, differential phase, differential temperature and time drift, etc.).

The use of balanced photodetectors in the usual (photodiode) mode requires separate bipolar sources of bias and leads to an increase in the power dissipated by them, to the energy dependence of the load, and also to a drop in the overall efficiency of the system.

The presence of a double number of transmission line elements and several precision bias sources increases hardware costs, volume, mass and cost, while reducing the total system efficiency.

The single task this invention is directed to is to simultaneously increase the efficiency of the system and the achievable power of the photon transmitting path — the antenna and antenna drive efficiency, expand the instantaneous frequency band (broadband), increase the identity of channels, improve temperature and time stability, reduce hardware costs and simplification of the scheme. An important and necessary condition was the preservation of work in class AB.

For this purpose, a radio photon line for transmitting powerful broadband signals with increased efficiency is proposed, operating in class AB with a single fiber-optic transmission line and photodetectors included in the differential circuit, performing, simultaneously with photodetection, the function of an inverter of a unipolar (monopolar) pulse signal, and photodetectors work in the photovoltaic mode, alternately with a time spacing of half the length of the bipolar pulse at their output (at the base), provided by cal delay line.

The photodetector outputs are connected to the antenna.

The essence of the invention is to transfer the function of inverting the signal (receiving a push-pull, bipolar signal) from the transmitting part of the line to the receiving one and implementing it simultaneously with photovoltaic conversion from optical to electric bipolar signal in powerful photo-detectors operating in photovoltaic mode alternately due to the optical delay line, included in front of one of the photodetectors included in the differential circuit (Fig. 1A). Powerful quantum-well heterolasers with direct modulation can be used as lasers [9].

Such powerful quantum-well heterolasers (with power up to several tens of watts) can be directly modulated to frequencies of several GHz [10].

As powerful photodetectors, powerful UTC (Uni-Trevelling-Carrier) type photodetectors with an optimized absorption region can be used [11].

The principle of operation of the radio photon transmission path is illustrated in its simplified diagram (Fig. 1A). The initial unipolar (monopolar) pulsed signal of nanosecond duration, intended for transmission through the radiophoton path, is supplied to the electric input of laser 2 (LD) simultaneously with a constant electric bias from source 1 (LD bias), which ensures the operation of a powerful laser from a threshold current, modulating optical power at its output from the minimum near-threshold to maximum values.

A powerful unipolar (monopolar) optical pulse of nanosecond duration appears at the laser output (Fig. 1b). Next, the transmitted pulsed signal of nanosecond duration passes through the fiber-optic communication line 3 (FOCL) and enters a symmetrical optical splitter 4 (OR), where its power is divided equally into two optical branches, from the first branch the optical signal is sent directly to the first powerful photodetector 6 at the output of which there is a first nanosecond electric pulse of positive polarity (at a given polarity of the photodetector on), and from the second branch the signal is fed to the input of the optical delay line 5 (OL ), where it is delayed in time by the length of the first optical pulse at its base (which is equivalent to half the length of the bipolar electric pulse at the output of the photodetectors) and arrives at the second powerful photodetector 7, the output of which produces a second nanosecond electric pulse of negative polarity (for a given switching polarity photodetector).

At the output of these two photodetectors, switched on differentially, i.e. bipolar to obtain a difference signal, and the sum of these two nanosecond pulses gives the load, (which can be used as an antenna), a powerful bipolar pulse of nanosecond duration (Fig. 2).

A single technical result, which can be obtained by carrying out the invention, is simultaneously expressed in the following:

a) in expanding the instantaneous band of transmitted frequencies due to the use of elements in the path that do not limit broadband and the ability to work in an ultra-wide frequency band, the main function being the operation of the radio photon path in class AB mode;

b) in increasing the maximum achievable transmitted power due to the use of elements in the path that do not limit the level of maximum optical and electrical power, the main function being the operation of the radio photon path in class AB mode;

c) in the energy independence of the path exit, i.e. in the absence of the need for electrical power supply of the equipment at the output, due to the operation of powerful photodetectors in the photovoltaic mode and, as a rule, the lack of the need to amplify the received signal of significant power.

d) to increase the identity of the channels, to improve the temperature and time stability due to the transmission of the signal through a single radio frequency and fiber optic channel with optical branching directly in front of the photodetectors;

e) at the same time increasing the efficiency of the system, the radio-photon transmitting path - antenna by increasing the efficiency of both the path itself, due to the lack of the need for additional power sources of powerful photodetectors, and due to the effective excitation of the antenna by bipolar radio pulses with a frequency spectrum matched to the antenna and their time shift positive and negative parts (half waves).

The specified single technical result in the implementation of the invention (Fig. 3) is achieved in that, in comparison with the known radio photon line for transmitting microwave signals with increased efficiency, operating in class AB [6], which is the closest analogue to the claimed one, with common features: two parts, lasers, fiber-optic lines between the two parts, photodetectors, characterized in that the optical splitter 4 (OP), the optical delay line 5 (OLZ) and the antenna 8, 9, and the radio frequency modulating signal at the same time with current from bias source 1 (LD bias) is supplied to the input of laser 2 (LD), the optical output of which is connected to the input of fiber-optic communication line 3 (FOCL), the output of which is connected to optical splitter 4 (OP), the first optical output of which connected to the optical input of the first photodetector 6 (PD1), and the second to the optical input of the second photodetector 7 (PD2) through an optical delay line 5 (OLZ), which provides signal delay by the pulse length at the base at the output of the first photodetector, both photodetectors are connected by differential They also operate in photovoltaic mode and their electrical outputs are push-pull (bipolar) outputs to antennas 8, 9 of the broadband radio photon line operating in class AB.

Thus, a powerful broadband bipolar (bipolar) signal is generated at the output of the radiophoton line, and the optical delay line shifts the negative part of the pulse by the length of its positive part at the base, as shown in FIG. 2.

Such broadband bipolar pulses can increase the excitation efficiency and directivity of the antennas [12].

For example, when the electromagnetic field E is excited in the aperture of the antenna in the form of a bipolar pulse, the directional coefficient D _B becomes equal [12]:

where: D _M - directional coefficient for excitation of the antenna by single pulses.

Thus, the excitation in the aperture of the electromagnetic field antenna in the form of a bipolar pulse (3) increases the directional coefficient D _{B of the} antenna by 9.5 times compared with the directional coefficient D _M for a unipolar monopulse D _M.

Therefore, in aggregate, the overall efficiency gain when applying the proposed push-pull radio photon transmission paths can be up to 18 times.

Information sources:

1. Bahrakh L.D., Zaitsev D.F. Phased antenna arrays based on distributed optical antenna modules // Doklady AN. - 2004. - T. 394, No. 4. - from. 465-468.

2. D.F. Zaitsev. Nanophotonics and its application - Monograph, M .: Ed. "ACTEON", 2012, 445 pp., With ill. ISBN 978-5-91142-045-1.

3. Transceiver optoelectronic module AFAR: Russian Patent RU 2298810 / D.F. Zaitsev. - No. 2005130539; Claim October 4, 2005.

4. Yitzhoki Ya.S., Ovchinnikov N.I. Pulse and digital devices - M.: Publishing. Soviet Radio, 1972, 592 p.

5. Shostko I.S., Almakadma T., Neighbor Yu.E. Analysis of ultra-wideband signals for infocommunication networks // Problems of telecommunications. - 2012. - No. 4 (9), p. 45-62. http://pt.journal.kh.ua

6. Class - AB microwave - photonic link: US 20070019896 A1 / T.E. Darcie, P.F. Drissen, Int. Cl. G02F 1/01; US Cl, 385/1; 01/25/2007.

7. Catalog of IPG Photonics. EARSeries 1 to 50 W Single-Mode High Power Erbium Fiber Amplifiers - www.ipgphotonics.com

8. PowerLog ™ AM-20; AM-40 20/40 GHz Intensity Modulators for Analog Applications. DataScheet / Oclaro. - CA. - 2013, - www.oclaro.com

9. Vinokurov D.A., Zorina C.A., Tarasov I.S. et al. Powerful semiconductor lasers based on asymmetric separate-limiting heterostructures // Physics and Technology of Semiconductors. - 2005. - T. 39, no. 3 - p. 388-393.

10. Zaitsev D.F. Investigation of the frequency potential of powerful quantum-well heterolasers // Antennas. - 2013. - Issue. 8. - p. 50-57.

11. Li J., Xiong B., Luo Y., Sun C, Hao H., Wang J., Han Y., Wang L. and Li H. High-power, wide-bandwidth modified uni-travelingcarrier photodiodes with an optimized depletion region // Applied Physics Express. - 2016. - V. 9, No. 5, - http://dx.doi.org/10.7567/APEX.9.052203

12. The method of excitation of a broadband antenna array and broadband antenna array (options) for its implementation: Russian Patent RU 2295180 / Antsev G.V., Sarychev V.A., Frantsuzov A.D. et al. - No. 2005122185/09; Claim 07/13/2005.

Claims (1)

A radio photon transmission line of powerful broadband signals, containing two parts, a directly modulated powerful laser made in the form of a heterolaser with a bias source, a fiber optic line between two parts, photodetectors, characterized in that an optical splitter, an optical delay line and antennas are introduced, moreover, the radio frequency the modulating signal simultaneously with the current from the bias source is fed to the input of the laser, the optical output of which is connected to the input of the fiber-optic line, the output of which is connected inen with a symmetric optical splitter, the optical outputs of which are connected to the optical inputs of the first and second photodetectors, connected in a differential circuit and operating in the photovoltaic mode, and the signal is fed to the optical input of the second photodetector through an optical delay line, which provides signal delay by the pulse length based on the output of the first photodetector, the electrical outputs of the photodetectors are push-pull outputs of a broadband radio photon transmitting path, ayuschego in class AB, which is a load of the antenna.

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