JPH02184772A - Electric field antenna using optical crystal - Google Patents

Abstract

PURPOSE:To eliminate the influence of an optical cable which is extended round by providing a deflector, optical crystal, and an analyzer. CONSTITUTION:The light from a light source 1 is guided to the optical modulator of the part of an antenna 8 by a multi-mode fiber 12 and its output is guided to a receiver 16 by a fiber 12. In this case, no single-mode fiber is used, so tolerance to bending stress, etc., is obtained. The optical modulator which uses the optical crystal 9 extract a linear polarized wave component having a 45 deg. angle to the optical axis of the crystal 9 from an unmodulated signal and outputs an optically modulated signal which is modulated according to the intensity of an electric field applied to the crystal 9. At this time, the part of the optical modulator is integrated at the antenna part 8, so the specific linear polarized wave component is extracted and then the shape of the elliptic polarized light of the unmodulated signal entering the optical modulator is constant or varied at random. Therefore, the antenna 8 which uses the fiber 12 for the transmission of light signals between the light source 1 and antenna 8 is realized and not influenced by the laying-round state of the optical cable.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention aims at not disturbing the surrounding electromagnetic field distribution by inserting a sensor in order to accurately measure the electric field strength at a certain point in a space. , relates to an electric field antenna in which everything except the electrode for detecting the electric field is made of non-metallic material.

(Prior Art) In recent years, as typified by the problem of automatic cars running out of control, the phenomenon in which digital processing circuits malfunction due to interference waves emitted from light switches has become a problem.

To address this problem, an antenna is needed to measure the level of such impulsive interference.

Micro dipole antennas, conical antennas, and horn antennas are currently used as antennas for measuring impulsive electromagnetic fields.

However, since these antennas use coaxial cables for the connection between the antenna and the signal receiver, the characteristics of the received electromagnetic field are affected by the cable, and the measured level may vary depending on the cable routing situation. Because of this change, it has been difficult to measure with excellent reproducibility. Therefore, antennas that connect the antenna and receiver using optical fibers are being considered. This type of antenna has two mechanisms: one that generates and transmits an optical signal modulated by an electronic circuit inside the antenna, and one that manually generates an optical signal from outside the antenna and uses electro-optic effects such as LiNbO3 inside the antenna. It is classified as one that is modulated and transmitted using an optical crystal.

Of these two types of antennas, the latter has lower sensitivity than the former, but because it does not require a built-in battery, it is effective for long-term observation of strong electromagnetic field pulses that can cause digital equipment to malfunction.

As this type of antenna, the antenna reported by NBS (National Bureau of Standards of the United States) is the most practical. The basic configuration of this antenna is shown in Fig. 1θ.

In Fig. 1θ, 1 is a light source, 2 is a polarizer, 3 is a Babinet-Soleil phase compensator, 4 is a lens, and 5 is an optical fiber holder.
6 is a single mode optical fiber, 7 is a graded index lens (for human power use), 8 is an antenna electrode, 9 is an optical crystal, IO is an analyzer, 11 is a graded index lens (for output), I2 is a multimode fiber, 13 is an optical fiber holder, 14 is a photodetector, 15 is an amplifier, and 16 is a receiver.

As shown in the figure, this antenna uses a helium neon laser as the light source 1 and a 1 lx 1 ma as the optical crystal 9.
Two pieces of +x lOma+ LiTaO3 are used.

The light emitted from the helium neon laser 1 is converted into a linearly polarized component by a polarizer 2, and then converted into a circularly polarized component by a Babinet-Soleil phase compensator 3 (with no electric field applied at the output end of the optical crystal). It is converted into an elliptically polarized wave) and input into the single mode optical fiber 6. The light propagated within the optical fiber is phase modulated by the optical crystal 9. When only a specific plane of polarization is extracted from this phase-modulated optical signal using an analyzer IO, an intensity-modulated optical signal is obtained since the shape of the elliptically polarized wave changes depending on the strength of the applied electric field.

At this time, the relationship between the applied electric field E and the modulation signal Vm is expressed by the following formula (1), where Vi is the amplitude of the optical signal, and α and β are conversion coefficients. From equation (1), if βE is a very small value, the modulation signal strength will be proportional to the applied electric field strength.

The modulated optical signal wave is sent through a multimode fiber to a receiver where it is converted into an electrical signal and detected.

The structure of the antenna is shown in FIG. In Figure 11,
17 is an optical fiber connector, 18 is a receptacle for the optical fiber connector, 19 is a lead for attaching an antenna rod, 20 is a base for fixing the optical circuit, and 21 is a case for the optical circuit. As shown in the figure, an optical crystal 9 and an analyzer 1G are installed at the center of two metal rods (length 15 cm). DC ~ about 2Gl with this antenna
In the frequency range of lz, it is possible to observe electric field strengths resulting in voltages of at least 10 mV across the crystal.

(Problem to be Solved by the Invention) However, as shown in Fig. 1θ, this antenna has an elliptically polarized wave that becomes circularly polarized at the position of the analyzer 10 in the light source portion. Since the transmission is made through the single mode fiber 6 and incident on the optical crystal, if even the slightest stress, such as bending, is applied to the optical fiber, the fiber 6
This method has the disadvantage that the phase of the optical fiber propagating inside changes, making the measurement level unstable, and it cannot be used for measurements in computer rooms or outdoors where optical fibers are frequently routed.

The object of the present invention is to solve these problems and realize an electric field sensor using an optical crystal that can be used in a computer room or outdoors.

(Means for Solving the Problems) A feature of the present invention for achieving the above object is that two polarizers, an optical crystal having an electro-optic effect, a phase compensator, and an analyzer constituting an optical modulator are used. This is an electric field antenna that uses optical crystals that are placed in a narrow gap in a metal rod.

Furthermore, a Matsuhatsu Enda type interferometer can also be used as the optical modulator.

(Function) Light from a light source is guided to an optical modulator in the antenna section by a multimode fiber, and its output is guided to a receiver by a multimode fiber. Since no single mode fiber is used, it is strong against bending stress, etc., and therefore the object of the invention is achieved.

Such a configuration provides the following advantages.

(a) An optical modulator using an optical crystal 9 extracts a linearly polarized wave component having an angle of 45 degrees with respect to the optical axis of the optical crystal 9 from an unmodulated optical signal, and extracts a linearly polarized wave component having an angle of 45 degrees with respect to the optical axis of the optical crystal 9. Outputs a modulated optical modulation signal.

In the basic configuration shown in Figure 1, this optical modulator part is integrated into the antenna section, so the shape of the elliptically polarized wave of the unmodulated optical signal incident on the optical modulator can be changed from that to a specific linearly polarized wave. Since it is sufficient to extract the component, its shape does not need to be a specific shape, and it is sufficient if the shape is constant or randomly fluctuates. Therefore, for example, if an antenna is realized that uses the multimode fiber 12 to transmit optical signals between the light source and the antenna, the shape of the elliptically polarized wave at the end face of the optical fiber on the antenna side will be independent of the stress applied to the optical fiber. , so it will be completely random.

An antenna that is not affected by optical cable routing can be realized.

(b) Since the optical modulator section using the optical crystal 9 is concentrated in a narrow range of the antenna section, fluctuations in the optical axis due to external forces are reduced, and a stable electric field antenna can be realized.

From the above results, the present invention can realize a stable and practical electric field antenna that improves the instability that is a drawback of conventionally reported antennas.

(Example 1) The basic configuration of the present invention is shown in FIG. The features of the present invention are:
Optical circuits such as a polarizer 2, an optical crystal 9 having an electro-optic effect, a Babinet-Soleil phase compensator 3, and an analyzer 1O are gathered in the antenna section. Note that in FIG. 1, the same reference numbers as in FIG. 10 indicate the same members.

A specific embodiment of the present invention is shown in FIG. 22 in Figure 2
is a prism that bends the optical path at right angles. As shown in the figure, the light from the helium neon laser is transmitted through the optical fiber 1.
2. In this embodiment, a graded index optical fiber having a core diameter of 50 μm and a cladding diameter of 125 μm is used as the optical fiber. The light emitted from the optical fiber passes through the optical modulator, enters the optical fiber again, and is sent to the photodetector IO located far from the antenna.
After the signal is converted into an electrical signal, its level is measured by the receiver.

Here, in order to efficiently pass light through the optical modulator,
Cell-hock lenses are attached to both ends of the optical modulator. In order to increase the efficiency of the optical modulator, the strength of the electric field applied to the optical modulator is inversely proportional to the electrode spacing, so the optical signal passing through the optical modulator should be made as thin as possible to improve the optical density used in the modulator. It is necessary to make the crystal thinner. However, compared to single mode fibers, in the case of multimode fibers with a large core diameter, it is difficult to maintain a thin light beam over a long distance.

FIG. 3 shows the structure of the light beam in this embodiment. 2 in Figure 3
3 is a light beam within the optical circuit. In this embodiment, as shown in FIG. 3, the refractive index of the self-hock lens and the position of the optical crystal are adjusted so that the beam passes through the optical crystal 9 at the narrowest position.

From the light converted into a light beam by the Self-Hoc lens, only a linearly polarized component at an angle of 45 degrees with respect to the optical axis of the optical crystal 9 is extracted by a polarizer. The optical signal that has passed through the optical crystal 9 is adjusted to become circularly polarized by the Babinet Soleil phase compensator 3 with no electric field applied, and then only a specific polarized component is extracted by the analyzer lO. .

When an electric field is applied to the optical crystal 9, the phase of only the optical signal polarization component that is the same as the direction in which the electric field is applied changes, so the polarization of the light incident on the analyzer 1O deviates from circular polarization and becomes elliptical polarization. Become. Therefore, the intensity of light passing through the analyzer IO changes, and the optical signal is amplitude-modulated by the electric field intensity.

In this example, 10111X 1 wf is used as the optical crystal.
fixlomm LiNb0. I am using two. The reason why optical crystals of the same size are connected in a two-center row is that the optical axes of these two crystals are connected at right angles to each other to compensate for the temperature dependence of optical crystals. It's for a reason.

Furthermore, as shown in Figure 2, light coming from one direction is reflected by two prisms and returns in the same direction. This allows the antenna to be attached to the end of a single rod, which is convenient for measuring electric field strength in a narrow space.

The sensitivity of this example is shown in FIG. In FIG. 4, the horizontal axis represents the voltage applied to the optical crystal, and the vertical axis represents the output voltage of the photodetector. Also, at this time, the optical power manually applied to the photodetector is 17d [I
m, the modulation frequency is 50 M)iz, the bias voltage of the APD used in the photodetector is 190 V, and the bandwidth of the optical signal receiver is 7.5 kHz. As shown in the figure, this antenna can receive voltages with a minimum strength of 80 dBμV (10 [11 V)].

Further, the frequency characteristics of this example are shown in FIG.

In the figure, the vertical axis is the conversion loss from the applied electric field strength to the output voltage of the photodetector. In the measurement, an electric field of i00 MIlz or less was applied using a TEM cell, and an electric field of 100 MHz or more was applied to the antenna of this example using an antenna installed in an anechoic chamber. Furthermore, in the measurements, antennas with element lengths of 1305 m and 330 mm were measured. As shown in the figure, this example
It can receive electric fields with almost constant sensitivity up to GHz. This is sufficient performance for measuring impulsive electromagnetic pulses that interfere with digital signal processing equipment.

FIG. 6 shows the reproducibility of the measurement data of this example. In the figure,
The vertical axis shows the deviation of the measured values from the trend line. From the figure, it can be seen that in this example, the deviation is ±2.5 dB or less. Currently, the rough standard for measuring the disturbance wave tolerance level of digital equipment is ±3 dB or less, and this embodiment satisfies this condition. This shows that this example has sufficient stability for practical use.

(Example 2) Another example of the present invention is shown in FIG. In Fig. 7, 24 is a resistive film (nichrome in this example) so that the low efficiency increases toward the tip of the antenna rod (5Ω at the center).
/m, 10 to 97 m'' at the tip).As shown in the figure, by applying a resistive film to the surface of the metal rod, resonance of the metal rod can be suppressed (for example, M, ni anda and F, X,
Lies, “A Broad-Band Isotro
pic Real-Time Electric-Fi
eld SensorUsing Re5istive
ly Loaded Dipoles, IEEE
rans, Electromagnetic Co
mpatability, Vol.

EMC-23, No. 3 August 1981. (Reference) Furthermore, a wideband electric field antenna can be realized.

(Example 3) Another example of the present invention is shown in FIG. In FIG. 8, 27 is an electrode for voltage detection. In order to measure overvoltages such as lightning surges that occur between the cores of a communication line, it is necessary to separate the measurement terminal from the ground and perform the measurement in a balanced state with respect to the ground. By making the metal electrodes bilaterally symmetrical as shown in the figure, an electric field sensor that satisfies this condition can be realized with a very simple structure.

(Example 4) Another example of the present invention is shown in FIG. In FIG. 9, 25 is a Matsuhatsu Enda type interferometer, and 26 is an electrode of this interferometer. As shown in the figure, there is not only an optical modulator consisting of a polarizer, an optical crystal with an electro-optic effect, a Babinet-Soleil phase compensator, and an analyzer, but also a Matsuhatsu Enda-type interference device that changes the light intensity depending on the applied voltage. An electric field antenna with a similar effect can be realized by integrating the sensor into the gap between two metal rods that make up a dipole antenna, and connecting the light source and this modulator with a multimode fiber.

(Effects of the Invention) As shown above, the polarizer constituting the optical modulator, the optical crystal having an electro-optic effect, the Babinet-Soleil phase compensator, and the analyzer can be connected to the narrow gap between the two metal rods constituting the dipole antenna. There are the following advantages by integrating the parts.

(a) Since the part of the optical modulator using optical crystal is integrated in a narrow range of the antenna part, the elliptically polarized wave of the unmodulated optical signal incident on the optical modulator does not need to have a specific shape;
The shape may be constant or may vary randomly. Therefore, for example, if you create an antenna that uses a multimode fiber to transmit optical signals between the light source and the antenna, the phase at the end face of the optical fiber on the antenna side will be completely random, regardless of the stress applied to the optical fiber. Therefore, it is possible to realize an antenna that is not affected by the routing of optical cables.

(b) Since the optical modulator section using an optical crystal can be integrated in a narrow area of the antenna section, an electric field antenna that is stable against external forces can be realized.

From the above results, the present invention has the advantage of being able to realize a stable and practical electric field antenna that improves the instability that is a drawback of conventionally reported antennas, and its effects are significant.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing the basic configuration of the present invention, Fig. 2 is a diagram showing a specific configuration according to an embodiment of the invention, Fig. 3 is a diagram showing the shape of a light beam, and Fig. 4 is a diagram similar to that of Fig. 2. Figure 5 is a diagram showing the frequency characteristics of the structure shown in Figure 2. Figure 6 is a diagram showing the reproducibility of measured values in the structure shown in Figure 2. Figure 7 is another example of the present invention. FIG. 8 is yet another embodiment of the present invention, FIG. 9 is yet another embodiment of the present invention, FIG. 10 is a diagram showing the basic configuration of the conventional technique, and FIG. 11 is the conventional technique. It is a specific configuration diagram of the technology. l; Light source, 2: Babinet Soleil phase compensator, 3; Polarizer, 4; Lens, 5; Optical fiber holder 6: Single mode optical fiber, 7: Graded index lens (for manual use), 8; Antenna electrode, 9 ; Optical crystal, lO; Analyzer, II; Graded index lens (for output), 2; Multimode fiber, 3; Optical fiber folder 4: Photodetector, 15; Amplifier, 6; Optical signal receiver, 17 ; Optical fiber connector, 8; Optical fiber connector receptacle, 9. Radar for mounting the antenna rod, 20; Optical circuit fixing board, 21; Optical circuit case, 22. Prism, 23: Light beam, 24: Resistor. Antenna rod with a film deposited on it, 25; Matsuhatsu Enda interferometer, 26; interferometer electrode, 27; electrode for voltage detection.

Claims (3)

[Claims] (1) Two metal rods that make up the antenna are arranged in series with a narrow gap between them, and an optical modulator whose light intensity fluctuates depending on the electric field strength is inserted into the gap and placed at a distance from the antenna. An unmodulated optical signal is transmitted from a light source using an optical fiber, modulated by an optical modulator using a crystal that has an electro-optic effect, and the modulated optical signal component is transmitted to a level measuring device outside the antenna. In an electric field antenna that measures electric field strength by transmitting and detecting it using a fiber, a polarizer that constitutes an optical modulator, an optical crystal with an electro-optic effect, a phase compensator, and an analyzer are combined with the above two An electric field antenna using optical crystals, which is characterized by being arranged in a concentrated manner in a narrow gap in a metal rod. (2) Claim 1 characterized in that a multimode fiber is used as the optical fiber connecting the light source and the optical modulator, and the optical modulator and the level measuring device, and the two metal rods are arranged plane symmetrically. An electric field antenna using the optical crystal described above. (3) The two metal rods that make up the antenna are arranged in series with a narrow gap between them, and an optical modulator whose light intensity fluctuates depending on the electric field strength is inserted into this gap and placed at a distance from the antenna. An unmodulated optical signal is transmitted from a light source using an optical fiber, modulated by an optical modulator using a crystal with an electro-optic effect, and the modulated optical signal component is sent to a level measuring device outside the antenna. In an electric field antenna that measures electric field intensity by transmitting and detecting it using an optical fiber, the optical modulator is realized by a Mach-Zehnder interferometer placed between the two metal bars. Characteristic electric field antenna.