JP3577616B2 - Electric field sensor - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a measuring instrument used for measuring characteristics of radio waves and electrode noise in the EMC field, and in particular, an electric field sensor for measuring the electric field strength of an electromagnetic wave propagating in a space, and detecting a signal radio wave of a specific frequency such as a broadcast radio wave. The present invention relates to an electric field sensor that also functions as an antenna.
[0002]
[Prior art]
Many electrical devices, such as information devices such as computers, communication devices, FA devices such as robots, and controllers such as automobiles and railways, are always in danger of being affected by malfunctions due to external electromagnetic noise. In the field of EMC, it is important to accurately measure the external electromagnetic environment, the magnitude of noise that influences the noise, and the noise generated by itself.
[0003]
Conventionally, the following three methods are well known for measuring the above-described electromagnetic noise. That is, a first method in which a signal is received using a normal antenna and guided to a measuring device by a coaxial cable, and a second method in which a signal received by using an antenna is detected, converted into an optical signal, and guided to a measuring device by an optical fiber. , And an optical element configured to change the intensity of transmitted light in accordance with the applied electric field strength, to convert the electric field strength change into a light intensity change, and connected to the optical element and a light source and a measuring instrument. This is a third method of connecting optical detectors with an optical fiber.
[0004]
Among these, the first method using an antenna is the most common. However, the electric field distribution may be disturbed by the presence of an electric cable such as a coaxial cable, or noise may be mixed in the middle of the cable. Because of the problem, the second and third methods using an optical fiber have been proposed. Among these methods, the second method is to amplify a signal detected by a diode, convert the signal into an optical signal in addition to a light emitting diode, and guide the signal to an optical detector by an optical fiber. And a battery, a metal part of a certain size is present, and the shape becomes large. In addition, there is a drawback that the electric field detection sensitivity is low and the response speed is slow.
[0005]
On the other hand, the third method uses a crystal having an electro-optical effect as an optical element for converting an electric field intensity into a change in intensity of transmitted light. The element structure is as follows: an antenna is connected, the light emitted from the optical fiber is passed through the crystal as parallel light by a lens, the polarization state is changed by the electric field in the crystal, and after passing through the analyzer, the bulk is coupled to the optical fiber again. There is a waveguide type element that constitutes the optical element by an element and an optical waveguide provided on a crystal. Usually, the waveguide type has a detection sensitivity 10 times or more higher than the bulk type. In addition, a single crystal of lithium niobate having a high electro-optic constant is generally used as a substrate crystal for a waveguide type electric field sensor.
[0006]
FIG. 3 shows a configuration of a conventional electric field sensor. FIG. 4 shows a configuration of a sensor head used for the electric field sensor of FIG. On a lithium niobate single crystal substrate 10 cut out perpendicular to the c-axis, an incident optical waveguide 11, a phase-shifted optical waveguide 12 branched and coupled therefrom, and the two phase-shifted optical waveguides 12 merge and combine. Outgoing optical waveguide 13 is formed. A polarization plane maintaining fiber 8 is coupled to an incident end of the incident optical waveguide 11 for incident light, and a single mode fiber 6 is connected to an exit end of the exiting optical waveguide 13 for exiting light. Further, a pair of modulation electrodes 14 is provided on the phase shift optical waveguide 12 and connected to the antenna 15.
[0007]
The light that has passed through the polarization maintaining fiber 8 from the light source 3 enters the incident optical waveguide 11, where the energy is split into two phase-shifted optical waveguides 12. When an electric field is applied, a voltage is induced on the modulating electrode 14 by the antenna 15, and electric field components in the phase-shifted optical waveguide 12 are generated in opposite directions in the depth direction. As a result, the refractive index changes due to the electro-optic effect, and the phase difference between the light waves propagating through the phase shift optical waveguide 12 changes according to the magnitude of the applied electric field. That is, the intensity of the outgoing light emitted to the single mode optical fiber 8 changes according to the applied electric field, and the applied electric field can be measured by measuring the change in the light intensity with the photodetector 17.
[0008]
[Problems to be solved by the invention]
However, in the above-mentioned conventional electric field sensor, the polarization maintaining fiber used as the incident optical fiber is much more expensive than the single mode fiber. For this reason, especially in the case of an electric field sensor in which the distance between the light source and the sensor head is long, high costs have to be accepted and a measure to overcome the cost has been required.
[0009]
Replacing the input optical fiber from a polarization maintaining fiber with a single mode fiber was naturally expected to be a clue to solving the problem. However, the plane of polarization of the incident light traveling from the light source to the sensor head through the single mode fiber fluctuates. For this reason, the output light level of the sensor head becomes unstable because it depends on the state of the single mode fiber, and the function as an electric field sensor for measuring electric field strength and detecting signal radio waves is significantly reduced.
[0010]
It is an object of the present invention to provide an electric field sensor which solves the above-mentioned problems and which can be reduced in cost and size by using a single mode fiber as an incident optical fiber of a sensor head and which has sufficient original functions. .
[0011]
[Means for Solving the Problems]
According to the present invention, a light source, a sensor head, a light receiver, an incident optical fiber system as an input light transmission path of the sensor head, an output optical fiber as an output light transmission path, and an electric field sensor including an antenna, wherein the light source is The light emitted from the light source is composed of two light sources that are linearly polarized and orthogonal to each other, the two light sources share a single power source, and the incident optical fiber system polarizes the light emitted from the two light sources, respectively. An electric field sensor comprising: an optical coupler that couples via a holding fiber; and a single mode fiber that connects the optical coupler and the sensor head, and the output optical fiber is composed of a single mode fiber. Can be
[0012]
Further, according to the present invention, there is provided an electric field sensor, wherein the sensor head includes a polarizer, and the single mode fiber is configured to couple the optical coupler with the polarizer.
[0013]
Further, according to the present invention, there is provided an electric field sensor, wherein the two light sources are semiconductor-pumped solid-state lasers.
[0014]
Further, according to the present invention, there is provided an electric field sensor, wherein the semiconductor-pumped solid-state laser is a semiconductor-pumped YAG laser.
[0015]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 is a diagram showing a configuration of an electric field sensor according to one embodiment of the present invention. The light source 1 and the light source 2 that share the power supply 20 are semiconductor-pumped YAG lasers that emit linearly polarized light having an emission light wavelength of 1.3 μm and almost equal intensity. The polarization planes of the respective linearly polarized lights are coupled by the optical coupler 9 so as to be perpendicular to each other. Further, these lights propagate in the single mode fiber 5 while maintaining polarization planes perpendicular to each other, and enter the sensor head 4. For this reason, the intensity ratio of the two linearly polarized lights whose polarization planes are perpendicular to each other at the incident end of the sensor head 4 does not change from the point of the optical coupler 9, the output light level is always constant, and the function as the electric field sensor is obtained. Can be fulfilled.
[0016]
In the present embodiment, a sensor head 4 composed of the optical waveguide element shown in FIG. 4 and using a single mode fiber as the incident optical fiber is used. In this case, two linearly polarized lights of a TE wave and a TM wave enter the sensor head 4. Since the extinction ratio of the sensor head including the optical waveguide element is high, the influence of the TM wave can be substantially neglected in the measurement of the electric field strength, and practical measurement can be usually performed. In FIG. 1, the polarization plane of light propagating through the incident optical fiber system is indicated by an arrow.
[0017]
As described above, although the polarization maintaining fiber 7 is used for a very short portion between the light sources 1 and 2 and the optical coupler 9, the optical coupler 9 and the sensor head occupying an overwhelmingly long distance in the electric field sensor as a system. A low-cost single-mode fiber 5 was used in place of the conventional polarization maintaining fiber. Nevertheless, the output light level of the sensor head 4 does not fluctuate and performs its function stably.
[0018]
Further, since the light source 1 and the light source 2 share a single power supply 20, the size and cost of the electric field sensor can be reduced, the peripheral portion of the sensor head 4 can be made simple, and the light source 1 and the light source 2 can be made of semiconductor. The use of the pumped YAG laser enhances reliability.
[0019]
FIG. 2 is a diagram showing a configuration of an electric field sensor according to another embodiment of the present invention. This embodiment is based on the above-described embodiment, and has a configuration in which the sensor head 4 includes the polarizer 16. That is, the planes of polarization of linearly polarized light from the light source 1 and the light source 2 sharing the power supply 20 are perpendicular to each other and coupled by the optical coupler 9, and propagate in the single-mode fiber 5 while maintaining the plane of perpendicular polarization. Only the light (TE wave) of a specific polarization plane is incident on the sensor head 4 by the probe 16. For this reason, it is possible to ignore the characteristics of the sensor head 4 depending on the polarization plane of the incident light, and it is possible to measure the electric field with higher resolution. In FIG. 2, the polarization plane of the light propagating through the incident optical fiber system is indicated by an arrow.
[0020]
Therefore, high-resolution measurement of an electric field becomes possible, and a low-cost single-mode fiber 5 can be provided between the optical coupler 9 and the sensor head 4 in the same manner as in the above-described embodiment. By using a semiconductor-pumped YAG laser as the light source 2, miniaturization and improvement in reliability can be achieved.
[0021]
【The invention's effect】
As described above, according to the present invention, the polarization-maintaining fiber conventionally considered essential is replaced with a single-mode fiber while satisfying the required functions, and the two semiconductor-pumped solid-state laser light sources used for this are replaced with a single semiconductor fiber. Since the power supply is shared, the electric field sensor can be reduced in cost and size, and a highly reliable electric field sensor can be obtained.
[Brief description of the drawings]
FIG. 1 is a diagram showing a configuration of an electric field sensor according to an embodiment of the present invention.
FIG. 2 is a diagram showing a configuration of an electric field sensor according to another embodiment of the present invention.
FIG. 3 is a diagram showing a configuration of a conventional electric field sensor.
FIG. 4 is a diagram showing a configuration of the sensor head of FIG. 3;
[Explanation of symbols]
Reference numerals 1, 2 Light source 4 Sensor head 5, 6 Single mode fiber 7 Polarization maintaining fiber 9 Optical coupler 10 Lithium niobate single crystal substrate 11 Incident optical waveguide 12 Phase shift optical waveguide 13 Outgoing optical waveguide 14 Modulating electrode 15 Antenna 16 Polarization Child 17 Photodetector 20 Power supply

Claims (4)

In an electric field sensor including a light source, a sensor head, a light receiver, an input optical fiber system as an input light transmission path of the sensor head, an output optical fiber as an output light transmission path, and an antenna, the light source is an output light of the light source. Consists of two light sources that are linearly polarized and orthogonal to each other, the two light sources share a single power supply, and the incident optical fiber system outputs the light emitted from the two light sources via polarization maintaining fibers, respectively. An electric field sensor comprising: an optical coupler to be coupled; and a single mode fiber connecting the optical coupler to the sensor head, and the output optical fiber is composed of a single mode fiber. 2. The electric field sensor according to claim 1, wherein the sensor head includes a polarizer, and the single mode fiber is configured to couple the optical coupler and the polarizer. 3. The electric field sensor according to claim 1, wherein the two light sources are semiconductor-pumped solid-state lasers. The electric field sensor according to claim 3, wherein the semiconductor-pumped solid-state laser is a semiconductor-pumped YAG laser.

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