JP3462769B2 - Broadband waveguide optical electric field sensor - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a broadband waveguide type optical electric field sensor suitable for use in electromagnetic field measurement for countermeasures against electromagnetic interference (EMC countermeasures) and as an optical modulator in the information communication industry.

[0002]

2. Description of the Related Art An electronic device may adversely affect other electronic devices such as malfunction due to electromagnetic waves generated from the electronic device. Therefore, the various standards allow the electronic device to withstand the allowable value of electromagnetic waves radiated by the electronic device to the outside and the electromagnetic field radiation from the outside that causes malfunction of the electronic device. Standards for (immunity test) are defined.

When inspecting whether or not an electronic device complies with these standards, the test is performed in an anechoic chamber as shown in FIG. Particularly, in the immunity test, an optical electric field sensor is used to measure an electromagnetic field applied to an electronic device.

The above optical electric field sensor measures the intensity and frequency of electromagnetic waves, and FIG. 4 uses a bulk type Pockels element 16. This optical electric field sensor uses an optical fiber 17 which is a dielectric for connection to the outside, and has no metal portion other than the antenna 20 and the electrode 21 which are the minimum necessary for electric field detection. Therefore, the optical electric field sensor is extremely less likely to disturb the electromagnetic field around the antenna than an ordinary antenna connected to the outside by a metal coaxial line, and when an accurate electromagnetic field measurement is required. used. In addition, in FIG.
Is a polarizer, and 19 is a quarter-lambda plate.

In order to increase the sensitivity of this optical electric field sensor, it is necessary to optimally design the structure of the modulator portion that modulates light with electromagnetic waves. In general, the sensitivity can be increased by narrowing the electrode width of the modulator portion and increasing the electrode length.

FIG. 5 shows that the bulk Pockels element has an electrode length of 30 mm and an electrode interval of 2 mm, and a length of 243 m.
The characteristics of the optical electric field sensor when an m or 126 mm antenna is attached are shown. In order to improve the sensitivity of the optical electric field sensor using this Pockels element, the electrode length of the Pockels element is increased, or Alternatively, it is necessary to narrow the electrode interval. However, by increasing the electrode length, the mutual phase mismatch between the spatial electromagnetic field around the sensor and the light traveling in the Pockels element occurs. As shown in FIG. 4, when the electrode length is 30 mm, the sensitivity is lost at about 2 GHz or higher due to this mismatch. Further, in the structure as shown in FIG. 4, the beam diameter of light cannot be sufficiently narrowed, so that the electrode interval cannot be further narrowed. So, like optical fiber, 10μ
The electrode width can be narrowed to the limit by using a waveguide type optical electric field sensor that utilizes an optical waveguide capable of confining light in a narrow width of about m and guiding the light. However, in the conventional waveguide type electric field sensor,
Since the antenna is a pair of dipole antennas and its length is several centimeters, it was not suitable for detecting high frequency microwaves. Therefore, it has been desired to develop an optical electric field sensor that can be used at higher frequencies.

[0007]

DISCLOSURE OF THE INVENTION The present invention is intended to solve the above-mentioned problems, and it is possible to obtain a high frequency electromagnetic wave without limiting the usable frequency of the optical electric field sensor to the low frequency side. The purpose is to enable measurement with sensitivity, and the purpose is to make the sensitivity of the optical electric field sensor uniform from a low frequency region to a higher frequency region.

[0008]

That is, a broadband waveguide type optical electric field sensor according to the present invention has an optical waveguide provided in the center of a substrate and a length centered on the optical waveguide as described in claim 1. Array of different dipole antennas, and the length and adjacency of each dipole antenna
The intervals between the dipole antennas are arranged logarithmically. The broadband waveguide type optical electric field sensor according to claim 2 is the broadband waveguide type optical electric field sensor according to claim 1, wherein the speed of the electromagnetic wave traveling around the substrate and the speed of the light traveling through the optical waveguide are matched. Therefore, it is characterized in that a substance made of powder or liquid having a specific dielectric constant is filled and arranged around the substrate.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a perspective view showing an embodiment of the sensor of the present invention,
2 is a perspective view showing another embodiment of the present invention, FIG. 3 is a sensitivity characteristic diagram of the sensor of the present invention shown in FIG. 1, FIG. 4 is a perspective view of an optical electric field sensor using a bulk type Pockels element, and FIG. FIG. 6 is a sensitivity characteristic diagram, and FIG. 6 is an explanatory diagram showing a measurement system of an optical electric field sensor and an anechoic chamber.

In FIGS. 1 and 2, reference numeral 1 is a substrate made of a material such as lithium niobate having an electro-optical effect, and an optical waveguide 2 is installed in the center thereof. Reference numeral 3 denotes a dipole antenna arranged in an array with the optical waveguide 2 as a center, and reference numeral 4 denotes an electrode connected to each of the above dipole antennas 3, which is electrically separated from an adjacent antenna. The antenna 3 and the electrode 4 are directly printed on the substrate 1 by a method such as vacuum deposition. Reference numeral 5 denotes a dielectric substance filled around the substrate 1 and made of a powder or liquid having a specific dielectric constant, and 6 denotes a cylindrical container containing the dielectric substance 5.

According to the present invention, the dipole antennas 3 are arranged in an array as described above, so that the antenna has directivity. That is, the antenna gain in the extension direction of the optical waveguide 2 becomes the largest. Furthermore, by matching the direction of the electromagnetic wave to be detected with the traveling direction of light,
Phase matching between light and electromagnetic waves is easily obtained, and an electric field of a higher frequency can be detected as compared with the case where the direction of electromagnetic waves is opposite to the traveling direction of light.

By the way, when the optical electric field sensor is placed in the air, since the speed of the electromagnetic wave traveling around the substrate 1 and the speed of the light traveling in the waveguide do not match, the phases of the electromagnetic wave and the light are higher at higher frequencies. However, as is clear from the thin line in the sensitivity characteristic diagram of the optical electric field sensor shown in FIG. 3, the sensitivity is lost at about 12 GHz. Therefore, in the present invention, the dielectric substance 5 made of powder or liquid having a specific dielectric constant is filled and arranged around the substrate 1. The frequency characteristics of the optical electric field sensor having the structure shown in FIG. 1 was measured, and the optical electric field sensor was placed in the air, and potassium chloride was used as the dielectric substance 5, and the optical electric field sensor was placed therein. The results are shown in FIG. 3 above. As shown by the thick line in this sensitivity characteristic diagram (FIG. 3), the phases of the electromagnetic wave and the light are matched, and as a result, it is possible to detect the electromagnetic wave of high frequency with high sensitivity as compared with the case where the surrounding of the substrate 1 is air. Is possible.

Potassium chloride (KCl) is suitable as the dielectric substance 5 made of powder or liquid having the above-mentioned specific dielectric constant. That is, the dielectric constant of potassium chloride is about 4.
8, which is about 2.1 as the refractive index felt by electromagnetic waves.
Equivalent to 9. On the other hand, the refractive index of light in lithium niobate, which is the material of the substrate 1, is about 2.23, which means that the velocity of the electromagnetic wave around the substrate 1 substantially matches the velocity of the light traveling in the waveguide 2. I understand. At this time, the electromagnetic wave direction and the light traveling direction are made to coincide with each other. As described above, in FIG. 3, the thin line indicates the sensitivity when the optical electric field sensor is placed in air, and the thick line indicates the sensitivity when the optical electric field sensor is placed in potassium chloride. In the case of exposure, the sensitivity is lost at about 12 GHz.
This is a phenomenon that occurs because the phases of the electromagnetic wave and the light are shifted by a half wavelength at this frequency. On the other hand, when the optical electric field sensor is placed in potassium chloride, a sharp decrease in sensitivity at the frequency is not observed. From this fact, a dielectric substance 5 such as potassium chloride is provided around the optical electric field sensor.
It can be seen that the phase matching between the electromagnetic wave and the light is obtained by filling and arranging. Also, it can be seen that the sensitivity is somewhat higher when the dielectric material 5 is filled and arranged.
This is because the dielectric constant of the dielectric material 5 is larger than that of air, so that electromagnetic waves are concentrated.

Further, in another embodiment shown in FIG. 2, uniform sensitivity is obtained over a wide frequency range. That is, when the lengths of the dipole antennas 3 as shown in FIG. 1 are fixed and arranged in an array,
The sensitivity is high at a specific frequency, and therefore it is suitable as an antenna for communication, but is not suitable as an antenna for electromagnetic field measurement that requires uniform sensitivity in a wide frequency range. Therefore, in the present embodiment, as shown in FIG.
The array of dipole antennas 3 was arranged logarithmically. When the dipole antenna 3 is arranged in this way, the antennas have different lengths, and thus each antenna has its own sensitivity to a specific frequency. As a result,
Uniform sensitivity can be obtained in a wide frequency range.

For example, the optical electric field sensor having the above-mentioned configuration is installed in the anechoic chamber 7 shown in FIG. 6, and is generated by the laser light source 9 such as an LD pump laser provided in the measurement room (shield room) 8. The laser light is introduced into the optical waveguide 2 installed in the center of the substrate 1 via the polarization controller 10, and is generated by the signal generator 13 provided in the measurement chamber 8 through the variable amplifier (power amplifier) 14. LPD
By irradiating the optical electric field sensor with the high-frequency signal emitted from A15, modulating the high-frequency signal into an optical signal, introducing the optical signal into the optical signal analyzer 11, and measuring the electromagnetic wave, the high-frequency signal from the low frequency range is increased. It is possible to perform measurement with uniform sensitivity in a wide frequency range. Reference numeral 12 is an arithmetic unit for controlling the operation of the optical signal analyzer 11 and the operation of the signal generator 13.

[0016]

As described above, according to the broadband waveguide type optical electric field sensor of the present invention, when the electromagnetic field is measured by the optical electric field sensor, it is possible to measure with high sensitivity from low frequency to higher frequency. You can Further, it is possible to make the frequency characteristics uniform on the high frequency side, and the like, which is extremely effective.

[Brief description of drawings]

FIG. 1 is a perspective view showing an embodiment of the present invention.

FIG. 2 is a perspective view showing another embodiment of the present invention.

FIG. 3 is a sensitivity characteristic diagram of the sensor of the present invention shown in FIG.

FIG. 4 is a perspective view of an optical electric field sensor using a bulk type Pockels element.

FIG. 5 is a sensitivity characteristic diagram thereof.

FIG. 6 is an explanatory diagram showing an optical electric field sensor and a measurement system of an anechoic chamber.

[Explanation of symbols]

1 substrate 2 Optical waveguide 3 dipole antenna 4 electrodes 5 Dielectric material 6 containers 7 Anechoic chamber 8 measuring room 9 Laser light source 10 Polarization controller 11 Optical signal analyzer 12 arithmetic unit 13 Signal generator 14 Variable amplifier (power amplifier) 15 LPDA 16 Optical electric field sensor 17 optical fiber 18 Polarizer 19 1/4 lambda plate 20 antenna 21 electrodes

─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-9-51307 (JP, A) JP-A-1-204020 (JP, A) JP-A-3-170909 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) G01R 29/08 G02F 1/00-1/125

Claims (2)

(57) [Claims] 1. A central provided with an optical waveguide substrate, said optical waveguide, respectively around the different lengths dipole antenna array, and each dipole en
The length of the tenor and the distance between the adjacent dipole antennas
A broadband waveguide type optical electric field sensor characterized in that intervals are arranged logarithmically. 2. In order to match the speed of electromagnetic waves traveling around the substrate with the speed of light traveling through the optical waveguide, a substance made of powder or liquid having a specific dielectric constant is placed around the substrate. The broadband waveguide type optical electric field sensor according to claim 1.