CN1428609A - Broad-band passive electro-optic transient electromagnetic field measuring system - Google Patents

Abstract

The present invention relates to a broad-band passive electro-optical transient electromagnetic field measuring system, it has the advantages of stong antijamming power, passive probe portion, small volume and board band, and can be used for making pulse electromagnetic field measurement in the complex electromagnetic environment of small space, and includes the successively-connected laser light source, polarization controller, sensor, photoelectric converter and digital oscilloscope, in which the sensor, polarization controller and photoelectric converter are connected by adopting optical cable between them, the sensor probe portion includes integrated optical waveguide modulator, it adopts double-group electrode structure, in which the signal electrode is connected with dipole atenna.

Description

Broadband, passive electro-optic transient electromagnetic field measuring system

The present invention relates to a kind of transient electromagnetic field measuring system, especially relate to a kind of broadband, passive electro-optic transient electromagnetic field measuring system.

In the background technology, in research fields such as electromagnetic compatibility, electromagnetic pulse, require to provide a kind of broadband, probe small size, the electromagnetic field measuring system of passiveization.Test for transient electromagnetic field at present, the normal measurement of adopting following two kinds of methods realization all-wave shape: 1, adopt inductive spacing electric field signals such as bar-shaped monopole, net bat, spherical antenna, be equipped with active emitter follower or differential amplifier, use the coaxial cable for high frequency transmission signals; 2, the Active Optical Fiber transmission system of based semiconductor laser instrument is voltage (electric current) signal with the space electric field conversion of signals of antenna induction, and drives the laser instrument of linear zone work, realizes electric light conversion, again light signal is converted to electric signal in terminal.These two kinds of methods are commonly used to measure the pulse electromagnetic field that frequency band is not too wide, large space is interior, but big because of its volume, as to have aspects such as active circuit restriction is difficult to realize for the field measurement in the especially little space under the complex electromagnetic environment condition.Simultaneously, because of being subjected to the influence of driving circuit, bandwidth also can not be done very highly.

The objective of the invention is to overcome the weak point in the above-mentioned background technology, a kind of broadband, passive electro-optic transient electromagnetic field measuring system are provided, its anti-electromagnetic interference capability is strong, passiveization of probe segment, little, the broadband of volume have solved the complex electromagnetic environment that the traditional measurement means are difficult to realize and the problems of measurement of the spatial field in the little space.

For achieving the above object, the technical solution that the present invention adopts is as follows:

A kind of broadband, passive electro-optic transient electromagnetic field measuring system, its special character is: comprise successively the LASER Light Source, Polarization Controller, sensor, photoelectric transformer and the digital oscilloscope that link to each other, sensor and LASER Light Source and with photoelectric transformer between all adopt transmission cable to be connected.

The sensor can comprise the lithium niobate integrated light guide modulator of lumped parameter type, it adopts two group electrode structures, comprises signal electrode and bias electrode, is respectively applied for sensing test and the adjustment of light beam polarization state, wherein signal electrode is a symmetric mode up and down, is connected with dipole antenna.

Above-mentioned dipole antenna can be two metal bars that are located on the same line, and it is connected with two signal electrodes respectively.

Above-mentioned Polarization Controller can be a wave plate combined formula single-mode fiber Polarization Controller.

Laser instrument output light-wave wavelength can be 1.3 μ m in the above-mentioned LASER Light Source, and its continuous wave peak power output is 0.3mW.

Above-mentioned transmission cable can be the single mode fiber cable of 1.3 mum wavelengths.

Fig. 1 is the block diagram of system of the present invention;

Fig. 2 is a sensor internal modulator electrode structural chart;

Fig. 3 is the sensor equivalent circuit diagram;

Fig. 4 is the system frequency response curve map;

Fig. 5 is system's output amplitude response curve;

Fig. 6 is system's output and laser power size dependence curve figure;

Fig. 7 is system's output and dipole length dependence curve figure.

Referring to Fig. 1 and Fig. 2, comprise successively the LASER Light Source, Polarization Controller, sensor, photoelectric transformer and the digital oscilloscope that link to each other, the employing transmission cable is connected between sensor and Laser Power Devices and the photoelectric transformer.During actual the use, only sensor is placed tested, it is indoor that remainder all is placed on the test shielding.Wherein laser instrument output light-wave wavelength is 1.3 μ m in the LASER Light Source, and the maximum Output optical power of its continuous wave is 3.0mW.Polarization Controller is the single-mode fiber Polarization Controller, is used for adjusting the light beam polarization direction that incides sensor.Transmission cable is the single mode fiber cable of two 1.3 mum wavelengths, and a single mode fiber cable connects LASER Light Source and sensor, and another root single-mode fiber connects sensor and photoelectric transformer.The core component of Sensor section is the lithium niobate fiber waveguide modulator of lumped parameter type, consider that test specification and polarization regulate, modulator adopts two group electrode structures, wherein signal electrode 1 be about symmetrical expression, half-wave voltage is bigger, connects dipole antenna sensing testing field signal.Bias electrode 2 half-wave voltages are less, are used with the single-mode fiber Polarization Controller, are used to regulate the incident beam polarization state, and it is full optics, need not power supply, and volume is very little.Dipole antenna adopts metal aluminium bar or copper rod, and two metal bars are located on the same line, and join with two signal electrodes 1 of integrated light guide modulator respectively.Photoelectric transformer is transformed to electric signal with the pulsed optical signals of modulation, has broadband response and great dynamic range.The oscillograph recording test signal selects for use sample frequency to meet the demands according to the measured signal characteristics, and possesses the digital oscilloscope of store function.

Measuring principle and systematic analysis:

The sensing core devices of system sensor part is the integrated light guide modulator, and it is based on lithium niobate (LiN _bO ₃) the electrooptical effect principle of crystal, be the interference system that an Output optical power has functional relation and changes with institute's making alive.Continuous laser injects single-mode fiber, regulates the single-mode fiber Polarization Controller, forms linearly polarized light Pi, after going into to inject modulator, enters two sections optical waveguides respectively through beam splitting, and each Shu Guangjun passes through under modulator electrode.When external space electric field signal, the voltage that dipole antenna inductive spacing electromagnetic signal produces is added on the modulator electrode, form the opposite electric field of this two-beam of crosscut, make the phase of light wave difference in two light paths that change take place, converge again second bifurcation through the two-beam of phase modulation (PM) and to enter the deferent segment optical waveguide, and interfere generation intensity modulated ripple, its Output optical power P0 changes with the funtcional relationship that induction voltage signal V presses following formula: ${\mathrm{<figure-callout\; id="0"\; label="P"\; filenames="A0113184900093.png"\; state="\{\{state\}\}">P</figure-callout>}}_0=\mathrm{Pi}\&CenterDot;{\mathrm{Cos}}^2\left(\frac{\mathrm{\&Delta;\&phi;}}{2}\right)=\frac{\mathrm{Pi}}{2}\&CenterDot;[1+\mathrm{Cos}(\mathrm{\&phi;}+\frac{\mathrm{\&pi;V}}{V_{\mathrm{\&pi;}}})]$

In the formula, the total phase differential of two light beams when Δ φ is the light outgoing, φ are two intrinsic phase shifts of interfering the arm optical path difference to cause, V _πBe the half-wave voltage of modulator, when φ was pi/2 and V≤V π, following formula became: ${\mathrm{<figure-callout\; id="0"\; label="P"\; filenames="A0113184900093.png"\; state="\{\{state\}\}">P</figure-callout>}}_0=\frac{\mathrm{Pi}}{2}\&CenterDot;(1+\frac{\mathrm{\&pi;V}}{V_{\mathrm{\&pi;}}})$

Therefore, photoelectric transformer output (removal DC component) is approximated to linear relationship with induced voltage V, thereby just can obtain its amplitude, phase information by surveying output light intensity.Referring to Fig. 3, Figure 3 shows that the electrical equivalent circuit of Sensor section, test for transient electromagnetic field, in the frequency range that comprises at whole incoming wave, all satisfying β h＜1, o'clock (β is a wave number, h is half of dipole length), dipole antenna can be considered as electronically small antenna, antenna impedance is approximately capacitive reactance.Therefore, obtain a response characteristic with frequency-independent in order to make system, when using the bar-shaped dipole of electronically small antenna, its load should be capacitive.The integrated light guide modulator has adopted Mach-Zehnder formula lumped parameter intensity modulator as antenna load during design.The electrical equivalent circuit of Sensor section as shown in Figure 3, Z among the figure _LBe modulator input impedance, Za is an antenna impedance, and he is the dipole element effective length, and Lm is the contact inductance (in being concerned about frequency band range, Lm is an a small amount of relatively, can ignore) between metal bar antenna and the modulator electrode.Use equivalent electrical circuit shown in Figure 3, the pass that can derive between photoelectric transformer output Vr (t) and the extra electric field Ei (t) is: $\mathrm{Vr}\left(t\right)=\frac{\mathrm{\&alpha;}\&CenterDot;\mathrm{he}\&CenterDot;\mathrm{Ei}\left(t\right)}{\mathrm{V\&pi;}(1+\mathrm{Cm}/\mathrm{Ca})}$ Wherein α comprises that luminous power size, photoelectric transformer efficient, modulator insert the conversion coefficient of loss and fibre loss etc.

The system works performance:

1, frequency, amplitude response and sensitivity: referring to Fig. 4, select the antenna configurations of 2h=155mm for use, in transverse electromagnetic wave (TEM) cell and GHz transverse electromagnetic wave (GTEM) cell, at 0.1Hz～1MHz and 500KHz～1GHz frequency range system-wide frequency response is measured respectively.During test, on each Frequency point, the regulatory work amplification gain makes the field intensity amplitude at sensor place be 100V/m, and the register system output amplitude is drawn frequency response curve figure as shown in Figure 4.As can be seen-three dB bandwidth is about 0.1Hz～7MHz.Referring to Fig. 5, choose the antenna configurations of 2h=195mm (φ 2), measured the amplitude response of system, draw system's output amplitude response curve as shown in Figure 5.As can be seen, until the field strength range of about 1200V/m, system demonstrates comparatively ideal linearity.When the antenna configurations of choosing 2h=215mm, laser output power is 2.5mW, and during 10 meters Optical Fiber Transmission, system's minimum detectable is to the field intensity signal of 0.5V/m.

2, system's output and luminous power, dipole length dependence: referring to Fig. 6, the experiment of system's output amplitude and luminous power dependence is carried out in gtem cell.During experiment, keep sensor place field intensity constant, regulate the laser output power size, the register system output voltage amplitude.As seen from Figure 6, (＜3mW) increase, the linear increase of system's output amplitude show that increasing input optical power can improve system sensitivity effectively along with luminous power.Referring to Fig. 7, the experiment of system's output amplitude and dipole length dependence is also carried out in gtem cell.The field intensity of sensing station is 100V/m, and signal frequency 200MHz keeps input optical power constant, changes dipole length, the output of testing photoelectronic detector.As can be seen from Figure 7, during less than 175mm, measured value is almost identical with calculated value, the linear ratio of sensor output voltage and dipole length in dipole length.

Compared with prior art, the advantage and the effect that have of the present invention is as follows:

1, the present invention have that antijamming capability is strong, the advantages such as passive, volume are little, broadband, its dynamic model Enclose and be about 60db, frequency response 0.1Hz～700MHz, the about V/m～KV/m of field strength measurement scope, available Pulse electromagnetic field measurement under complex electromagnetic environment or in the little space.

2, the present invention is reasonable in design, and is easy to use, has preferably Social benefit and economic benefit.

Claims (5)

1, a kind of broadband, passive electro-optic transient electromagnetic field measuring system, it is characterized in that: comprise the LASER Light Source that links to each other successively, Polarization Controller, sensor, photoelectric transformer and digital oscilloscope, sensor and lasing light emitter and with photoelectric transformer between all adopt transmission cable to be connected.

2, broadband according to claim 1, passive electro-optic transient electromagnetic field measuring system, it is characterized in that: described sensor comprises the lithium niobate integrated light guide modulator of lumped parameter type, it adopts two group electrode structures, comprise signal electrode (1) and bias electrode (2), wherein signal electrode (1) is a symmetric mode up and down, is connected with dipole antenna.

3, broadband according to claim 2, passive electro-optic transient electromagnetic field measuring system is characterized in that: described dipole antenna is two metal bars that are located on the same line, and it is connected with two signal electrodes respectively.

4, broadband according to claim 3, passive electro-optic transient electromagnetic field measuring system is characterized in that: described Polarization Controller is a wave plate combined formula single-mode fiber Polarization Controller.

5, according to claim 1,2,3 or 4 described broadbands, passive electro-optic transient electromagnetic field measuring system, it is characterized in that: laser instrument output light-wave wavelength is 1.3 μ m in the described LASER Light Source, the maximum Output optical power of continuous wave is 3.0mW, and described transmission cable is the single mode fiber cable of 1.3 mum wavelengths.

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