JPH08313577A - Electric field sensor - Google Patents

Abstract

PURPOSE: To provide an electric field sensor having an excellent temperature characteristic and a high sensitivity by applying a resin-based adhesive having a dielectric constant lower than a specific value between modulating electrodes and a semiconducting resin to the entire surfaces of the modulating electrodes. CONSTITUTION: An incident light waveguide 3, two phase shifting optical waveguides 4 branched from the waveguide 3, and an emitted light waveguide 6 joining the waveguides 4 together are formed on a lithium niobate single- crystal substrate 9. The entire surface of the substrate 9 is coated with an SiO2 film 14 formed as a buffer layer which prevents the absorption of light and a pair of modulated electrodes 5 is formed on the waveguides 4. A silicone resin 12 having a dielectric constant of, for example, 3 and semiconducting resin 13 are applied between the electrodes 5. Then an electric field sensor is constituted by respectively connecting optical fibers 2 and 7 to the waveguides 3 and 6 and connecting an electric field receiving rod antenna 11 to the electrodes 5. Thus the temperature characteristic of the sensor can be improved without deteriorating its sensitivity.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a measuring instrument used for measuring the characteristics of radio waves and electromagnetic noise in the field of EMC, and more particularly to an electric field sensor used for measuring the electric field strength of electromagnetic waves propagating in space.

[0002]

2. Description of the Related Art Information equipment such as computers and communication equipment,
Many electric devices such as FA devices such as robots and controllers such as automobiles and railroads are always affected by electromagnetic noise from the outside and always have a risk of malfunctioning. Therefore, E
In the field of MC, it is important to accurately measure the magnitude of noise that affects the external electromagnetic environment and electric devices, and the noise generated by itself.

Conventionally, there are roughly three methods for measuring electromagnetic noise as described above. (1) a method of receiving using an ordinary antenna and guiding it to a measuring instrument with a coaxial cable; (2) an antenna A method of detecting a signal received by using an optical fiber, converting it to an optical signal, and guiding it to a measuring instrument with an optical fiber,
There is a method in which an optical element is connected between an optical element whose transmitted light intensity changes according to a change in applied electric field intensity and a photodetector connected to a light source and a measuring instrument.

Among these methods, the method using the antenna (1) is the most general, but the electric field distribution may be disturbed due to the presence of an electric cable such as a coaxial cable, or noise may be mixed in the middle of the cable. Therefore, the methods (2) and (3) using an optical fiber have been developed.

In the method (2), the signal detected by the diode is amplified and added to the light emitting diode to be converted into an optical signal which is guided to the photodetector by the optical fiber. Since a battery is required, there is a certain size of metal part and the size is also large.
Further, there is a drawback that the detection sensitivity of the electric field is low and the response speed is slow.

On the other hand, in the method (3), a crystal having an electro-optical effect is used as an optical element for converting the electric field intensity into a change in intensity of transmitted light. As its element structure, the light emitted from the optical fiber is passed through a crystal with a small antenna attached as parallel light with a lens, the polarization state is changed by the electric field in the crystal, and the intensity is changed by an analyzer. There are a bulk type element that is coupled to an optical fiber again, and a waveguide type element that constitutes the above optical element by an optical waveguide provided on a crystal. The waveguide type is usually 10
The detection sensitivity is more than double.

FIG. 1 shows a configuration example of a conventional electric field sensor head using a waveguide type element. In FIG. 1, an incident optical waveguide 3 is formed by diffusing titanium on a lithium niobate (LiNbO ₃ ) single crystal substrate 9 cut out perpendicularly to the c-axis, and the incident optical waveguide 3 is branched from the incident optical waveguide 3. 4 are formed, and the two phase shift optical waveguides 4 merge and combine to form an emission optical waveguide 6. Incident optical waveguide 3
The input optical fiber 2 is coupled to the input end of the output optical fiber 6 and the output optical fiber 7 is connected to the output end of the output optical waveguide 6.
Further, a pair of modulation electrodes 5 are installed on the phase shift optical waveguide 4 and are connected to the rod antenna 11 by lead wires 10.

Further, the input light 1 is incident on the incident optical waveguide 3 from the input optical fiber 2 and then split in energy by the phase shift optical waveguide 4. When an electric field is applied, a voltage is induced in the modulation electrode 5 by the rod antenna 11 to generate electric field components in the phase shift optical waveguide 4 in directions opposite to each other in the depth direction.

As a result, a change in the refractive index is caused by the electro-optical effect, and a phase difference corresponding to the magnitude of the applied electric field is generated between the light waves propagating in the phase shift optical waveguide 4, and they are merged to each other to emerge. When coupled to the light intensity changes due to interference. That is, the intensity of the outgoing light 8 emitted to the outgoing optical fiber 7 changes according to the applied electric field intensity, and the intensity of the applied electric field can be measured by measuring the change in the optical intensity with a photodetector.

[0010]

In the case of a waveguide type electric field sensor using a lithium niobate single crystal substrate, since the crystal substrate has a pyroelectric effect, temperature drift is caused, and accurate electric field measurement is performed in a wide range of environments. I couldn't. Therefore, today, semi-conductive resin (up to several tens of GΩ ・
m) is applied to prevent charging and reduce temperature drift.

However, if a semi-conductive substance is mixed between the electrodes, the capacitance increases, which causes a problem that the sensor sensitivity decreases.

Therefore, an object of the present invention is to solve the above problems and provide a high-sensitivity electric field sensor having good temperature characteristics.

[0013]

SUMMARY OF THE INVENTION The present invention is an electric field sensor head configured to change the intensity of transmitted light according to the applied electric field strength, and an electric field receiving head connected to the electric field sensor head. An antenna, an optical fiber, a light source connected to one end of the optical fiber, and a photodetector for detecting transmitted light, and the electric field sensor head includes an incident optical waveguide formed on a substrate having an electro-optical effect. ,
In an electric field sensor composed of two phase shift optical waveguides branched therefrom, an exiting optical waveguide where they merge, and a modulation electrode formed in the vicinity of the two branched phase shift optical waveguides, at least between the modulation electrodes , Dielectric constant 3
The above-mentioned problem was solved by applying the following resin adhesive (not including 0) and then applying the semiconductive resin on the entire surface of the modulation electrode.

[0014]

If the semi-conductive resin is applied to the entire surface of the modulation electrode, the electrical characteristics of the sensor head, especially the capacitance, increase,
As a result, the sensitivity characteristic of the sensor head is degraded. It is considered that this is because a substance having a high dielectric constant (semiconductive resin) enters between the electrodes. Therefore, based on these facts, the present inventor reduces the sensor sensitivity by applying a semiconductive resin on the entire surface of the modulation electrode after applying a resin-based adhesive having a dielectric constant of 3 or less between at least the electrodes of the modulation electrode. It was possible to fabricate an electric field sensor with good temperature characteristics without doing so.

[0015]

EXAMPLES Examples of the present invention will be described below with reference to FIGS.
Will be described with reference to. 1 is a schematic view of an electric field sensor head using a waveguide type device for explaining the present invention, and FIG. 2 is a sectional view of the electric field sensor head manufactured according to this embodiment.

(Example) As shown in FIGS. 1 and 2, an incident optical waveguide 3, two phase shift optical waveguides 4 branched from the incident optical waveguide 3, and two of them are provided on a lithium niobate single crystal substrate 9. An output optical waveguide 6 is formed in which the phase shift optical waveguide 4 merges. In addition, after coating the entire surface with a silicon dioxide (SiO ₂ ) film 14 as a buffer layer for preventing light absorption, a pair of modulation electrodes 5 is formed on the phase shift optical waveguide 4, and a space between the modulation electrodes 5 is formed. Silicone resin 12 having a dielectric constant of 3 was applied as a resin adhesive. Further, a semiconductive resin 13 (several tens of GΩ · m) is applied on the electrodes, the optical fibers 2 and 7 are connected to the optical waveguides at both ends, and the rod antenna 11 for electric field reception is connected to the modulation electrode 5. Then, an electric field sensor was manufactured.

The minimum electric field detection sensitivity of the electric field sensor produced above in an electric field of a frequency of 500 MHz was measured and found to be 50 dBμV / m. Also, the temperature-10
The change in sensor sensitivity with respect to -60 ° C was within 3%.

(Comparative Example 1) A similar one was prepared except that a silicone resin having a dielectric constant of 3 was changed to a silicone resin having a dielectric constant of 5 between the modulation electrodes of the electric field sensor manufactured in the above-described example, and the above-mentioned example was prepared. The minimum electric field detection sensitivity was measured under the same conditions as. As a result, it was 55 dBμV / m. Further, the change in sensor sensitivity with respect to the temperature of -10 to 60 ° C was the same as that in the above-mentioned embodiment.

(Comparative Example 2) A similar one was manufactured except that a silicone resin having a dielectric constant of 3 was not applied between the modulation electrodes of the electric field sensor manufactured in the above embodiment, and the minimum electric field was applied under the same conditions as in the above embodiment. The detection sensitivity was measured. As a result, 70d
It was B μV / m. Further, the change in sensor sensitivity with respect to the temperature of -10 to 60 ° C was the same as that in the above-mentioned embodiment.

[0020]

As is apparent from the examples and comparative examples described above, according to the present invention, it is possible to provide an electric field sensor having good temperature characteristics without lowering the sensor sensitivity.

[Brief description of drawings]

FIG. 1 is a schematic view of an electric field sensor head using a waveguide type element.

FIG. 2 is a cross-sectional view of an electric field sensor head manufactured according to this example.

[Explanation of symbols]

1 Input Light 2 (Input) Optical Fiber 3 Incident Optical Waveguide 4 Phase Shift Optical Waveguide 5 Modulation Electrode 6 Emitting Optical Waveguide 7 (Emitting) Optical Fiber 8 Emitting Light 9 Lithium Niobate (LiNbO ₃ ) Single Crystal Substrate 10 Lead Wire 11 Rod Antenna 12 Silicone resin with dielectric constant 3 13 Semi-conductive resin 14 Silicon dioxide film

Claims (1)

[Claims] 1. An electric field sensor head configured to change the intensity of transmitted light according to an applied electric field strength, an electric field receiving antenna connected to the electric field sensor head, an optical fiber, and the optical fiber. It is composed of a light source connected to one end and a photodetector for detecting transmitted light,
The electric field sensor head has an incident optical waveguide formed on a substrate having an electro-optical effect, two phase shift optical waveguides branched from the incident optical waveguide, an emission optical waveguide where they join, and the two branched phases. In an electric field sensor including a modulation electrode formed in the vicinity of a shift optical waveguide, a resin adhesive having a dielectric constant of 3 or less (not including 0) is applied at least between the modulation electrodes, and the entire surface of the modulation electrode is semiconductive. An electric field sensor characterized in that a conductive resin is applied.