JP2004245731A - Photoelectric field sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a small photoelectric field sensor having isotropy in the electric field detection using a simple constitution. <P>SOLUTION: The photoelectric field sensor is comprises 3 axial photoelectric field sensors 50, each of which is provided in x, y, and z axial direction orthogonal to each other, arranged for detection of the electric fields of x, y, and z axial directions; a light attenuator 54; and an optical detector 55, wherein the 3 axal photoelectric field sensor 50 comprises a light source part comprising light sources 51a, 51b; a 1st polarization wave synthesizer 52a; a 4 port polarized wave demultiplexing light circulator 53; and a Mach-Zehnder interferometer comprising a 2nd polarized wave synthesizer 52b, polarization electrodes and a branching optical wave-guide on an electro-optical crystal substrate. Each modulated light, emitted from each 3 axis photoelectric field sensor modulated by each electric field in the direction of x, y, and z axis, is synthesized by 4 port polarized wave demultiplexing light circulator 53, and inputted to the optical detector 55. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an optical electric field sensor device for measuring an electric field using light, and more particularly to an optical electric field sensor device suitable for measuring the electric field intensity of an electromagnetic wave propagating in an arbitrary direction in space.
[0002]
[Prior art]
An optical electric field sensor using an interference optical waveguide utilizing the electro-optic effect has the following excellent features. That is, since the electric field to be measured is not disturbed because it has almost no metal part, the detection signal is transmitted through an optical fiber so that it is not affected by induction or electric noise on the way, and the electro-optic effect of the crystal is used. , High-speed response is possible and the detection signal can be transmitted as it is with little loss, no power supply is required for the sensor part, and the optical waveguide and antenna electrode are integrated and there is no power supply, so miniaturization is achieved. Is easy. Due to such characteristics, the optical electric field sensor is used for electric field measurement in the EMC field and the like.
[0003]
Before describing an optical electric field sensor capable of measuring an electric field in a three-axis direction as a conventional example, an optical electric field sensor for measuring an electric field in a uniaxial direction used therein will be described with reference to FIG.
[0004]
FIG. 6B is a perspective view showing the structure of a conventional reflection type uniaxial optical electric field sensor. Light incident from the optical fibers 16, 17, or 18 is branched into two branch optical waveguides 13a and 13b via an optical waveguide 15 on a LiNbO ₃ single crystal substrate 14. At this time, an electric field is applied to one of the branch optical waveguides 13a by the metal electrodes 10a and 10b, and the refractive index changes. On the other hand, there is no change in the refractive index due to the electric field in the branch optical waveguide 13b. The light propagating through any of the branch optical waveguides is reflected by the reflecting mirror 11, propagates in the branch optical waveguide in the opposite direction, and is multiplexed again. The light intensity after multiplexing changes. Thereafter, the light is coupled to the optical fiber 16, 17 or 18 and emitted.
[0005]
The metal electrodes 10a and 10b are formed so that the sensitivity in the direction 12 perpendicular to the branch optical waveguides 13a and 13b is increased.
[0006]
Subsequently, a conventional example of an optical electric field sensor device capable of measuring electric fields in three axial directions will be described.
[0007]
When the reflection type one-axis optical electric field sensor shown in FIG. 6 (b) is arranged as shown in FIG. 6 (a), a three-axis optical electric field sensor capable of measuring electric fields in three axial directions is constructed. Can be. That is, the substrates 19a, 19b, and 19c are arranged so as to detect electric fields in the X, Y, and Z directions, respectively. As a result, the light incident from the optical fibers 16, 17, and 18 is modulated by the electric fields in the X, Y, and Z directions, and emitted.
[0008]
FIG. 5 is a block diagram showing a configuration of a conventional three-axis optical electric field sensor device. In FIG. 5, arrows in both directions indicated by solid lines indicate polarization directions, and arrows indicated in one direction indicated by broken lines indicate light traveling directions.
[0009]
The lights emitted from the light sources 61a and 61b are combined by the polarization combiner 62 so that the polarization states are orthogonal to each other, and further divided into three waves by the optical coupler 63. Thereafter, the three waves pass through the polarization-dependent optical circulators 64a, 64b, and 64c, respectively, and enter the three-axis optical electric field sensor 60. The optical signal modulated by the three-axis optical electric field sensor 60 returns to the polarization dependent optical circulators 64a, 64b, 64c again, is guided to the respective photodetectors 65a, 65b, 65c, and is converted into an electric signal.
[0010]
The X, Y, and Z components of the electric field to be measured can be obtained from the electric signals in the X, Y, and Z directions output from the photodetectors 65a, 65b, and 65c. It is obtained by synthesizing an X component, a Y component, and a Z component by calculation in a PC (personal computer) or the like.
[0011]
A three-axis optical electric field sensor device of this type is disclosed in Patent Document 1 below.
[0012]
[Patent Document 1]
Japanese Patent Application Laid-Open No. 2002-257784
[Problems to be solved by the invention]
In general, in electric field measurement in the EMC field and the like, the magnitude (electric field strength) of an electric field due to a propagating electromagnetic wave is a measurement target, and the direction of the electric field vector is often unnecessary. In such a measurement, the conventional method requires one optical coupler, three polarization-dependent optical circulators, and three photodetectors, and furthermore, a detection signal for obtaining the isotropy of the electric field detection. Needs to be calculated on a PC or the like. Therefore, for electric field measurement in the field of EMC and the like, it is important to simplify the optical electric field sensor device in order to reduce the size and cost.
[0014]
Therefore, an object of the present invention is to provide a small-sized optical electric field sensor device having a simple configuration and having isotropy of electric field detection.
[0015]
[Means for Solving the Problems]
In order to solve the above problems, the present invention has the following configurations. That is, the invention according to claim 1 relates to an optical electric field sensor device, a light source unit that generates light of a constant intensity, a demultiplexing unit that demultiplexes the light from the light source unit into three, and a substrate of an electro-optic crystal. A three-axis optical electric field sensor element in which three Mach-Zehnder interferometers each having a modulation electrode and a branch optical waveguide are arranged so as to detect electric fields in orthogonal x, y, and z-axis directions, respectively; Multiplexing means for multiplexing the three signal lights modulated by the three Mach-Zehnder interferometers, and a photodetector for converting the multiplexed signal light into an electric signal and detecting the electric signal. .
[0016]
The invention according to claim 2 relates to the optical electric field sensor device according to claim 1, wherein the demultiplexing means is a four-port polarization splitting optical circulator, and any one of the Mach-Zehnder interferometer and the four-port polarization splitting light. An optical attenuator is inserted between the circulator and a polarization combiner is inserted between the other two of the Mach-Zehnder interferometer and the four-port polarization-separating optical circulator.
[0017]
According to a third aspect of the present invention, there is provided the optical electric field sensor device according to the first or second aspect, wherein the light source unit includes two laser light sources that generate linearly polarized light orthogonal to each other and another polarization combiner. And
[0018]
The invention according to claim 4 relates to the optical electric field sensor device according to any one of claims 1 to 3, wherein the electro-optic crystal is a LiNbO ₃ single crystal, and the branch optical waveguide is formed on a substrate of the LiNbO ₃ single crystal. It is characterized by being formed by diffusing Ti ions.
[0019]
The invention according to claim 5 relates to the optical electric field sensor device according to claim 3, wherein the laser light source is a semiconductor laser light source.
[0020]
The invention of claim 6 relates to the optical electric field sensor device according to claim 3, wherein the laser light source is a semiconductor laser-excited Nd: YAG laser light source.
[0021]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0022]
FIG. 4 is an external perspective view of the three-axis optical electric field sensor according to one embodiment of the present invention. 43 is a three-core polarization maintaining optical fiber, 42 is a non-metallic holding rod, and 41 is a sensor head. The size of this sensor head is φ12 × 35 mm, and accommodates a light modulation unit composed of a reflection type Mach-Zehnder interferometer for measuring electric fields in three axial directions.
[0023]
FIG. 2 is a sectional view of the sensor head section 41 when viewed from above. The uniaxial optical electric field sensor shown in FIG. 3 is arranged on the side surface of the support member 24 of a triangular prism having a cross section of a right isosceles triangle, so that electric fields in the x-axis, y-axis, and z-axis directions can be measured.
[0024]
Each of the uniaxial optical electric field sensors includes a Ti diffusion optical waveguide formed on a LiNbO ₃ crystal substrate 32, and includes a metal electrode 35 for applying a voltage thereto, a reflection mirror 36, and a polarization maintaining optical fiber 31. It is configured. 33 is an incoming / outgoing optical waveguide, and 34a and 34b are branching optical waveguides.
[0025]
Returning to FIG. 2, description of the three-axis optical electric field sensor will be continued. Reference numeral 21 denotes a uniaxial optical electric field sensor that measures an electric field in the x-axis direction, 22 denotes a uniaxial optical electric field sensor that measures an electric field in the y-axis direction, 23 denotes a uniaxial optical electric field sensor that measures an electric field in the z-axis direction, and 25. Is a housing. Although not shown, the direction of the branch optical waveguide of each uniaxial optical electric field sensor and the direction in which the polarization maintaining optical fiber is drawn out are perpendicular to the plane of the drawing. With such a configuration, it is possible to measure electric fields in the three-dimensional orthogonal coordinate axes, x, y, and z axes.
[0026]
Next, an optical electric field sensor device according to the present embodiment will be described with reference to FIG. In FIG. 1, reference numeral 50 denotes a three-axis optical electric field sensor according to the present embodiment, 51a and 51b denote first and second light sources, 52a and 52b denote first and second polarization combiners, and 53 denotes a four-port polarizer. A wave separation optical circulator, 54 is an optical attenuator, 55 is a photodetector comprising a photodiode and an amplifier, and 56 is a polarization maintaining optical fiber. The double-headed arrows indicated by solid lines indicate polarization directions, and the one-directional arrows indicated by broken lines indicate light traveling directions.
[0027]
The wavelength of the light source used at this time is selected to be about 1.2 to 1.6 μm in consideration of the electro-optic effect and the loss in the Ti diffusion waveguide on the LiNbO ₃ substrate. Further, a semiconductor laser pumped Nd: YAG laser having good RIN (relative noise intensity) characteristics and a semiconductor laser with low power consumption are suitable as the light source.
[0028]
When a semiconductor laser-pumped Nd: YAG laser is used as a light source, a laser wavelength of 1.32 μm is easily used, and when a semiconductor laser is used as a light source, a laser wavelength of 1.48 μm that provides a high output is easy to use.
[0029]
Next, the operation of the three-axis optical electric field sensor device will be described.
[0030]
The orthogonally polarized light emitted from the first and second light sources 51a and 51b is input to the port (3) and the port (2) of the polarization combiner 52a via the polarization maintaining optical fiber 56, respectively. The light beams are multiplexed so that the directions are orthogonal to each other, exit from the port (1), and enter the port (1) of the 4-port polarization split optical circulator 53.
[0031]
The light incident on the four-port polarization-separating optical circulator 53 is decomposed into vertical and horizontal polarizations, further rotated by 45 degrees in the polarization direction, and emitted from the port (4) and the port (3). .
[0032]
The light emitted from the port (3) is attenuated by the optical attenuator 54 and then enters the three-axis optical sensor 50.
[0033]
The light emitted from the port (4) is decomposed into vertical and horizontal polarized waves by the polarization combiner 52b, and is incident on the three-axis optical sensor 50.
[0034]
In this manner, the three waves incident on the three-axis optical sensor 50 are subjected to intensity modulation by the electric field to be measured, are again incident on the polarization maintaining optical fiber 56, and the path that has propagated as the outward path is used as the return path. At the port (4) and the port (3) of the four-port polarization-separating optical circulator 53. At that time, the state of polarization returning to the port (4) and the port (3) is maintained at the time of emission.
[0035]
The light that has entered the four-port polarization-separating optical circulator 53 is recombined to form a three-axis composite modulated signal. After exiting from the port (2), the light detector (O / O) passes through the polarization maintaining optical fiber 56. E converter) 55.
[0036]
In such a path of the unmodulated light and the modulated light, the optical attenuator 54 reduces the insertion loss between the light passing through the second polarization combiner 52b and the light not passing through the second polarization combiner 52b. The difference can be compensated. In addition, since the uniaxial optical electric field sensor having the same structure is used for each of the x-axis, the y-axis, and the z-axis, the magnitude (electric field intensity) of the electric field vector to be measured in all three-dimensional directions can be measured. Measurement can be performed without rotating the field sensor head. That is, the isotropy of electric field detection can be easily secured.
[0037]
Further, the optical electric field sensor device of the present embodiment is particularly suitable for measuring the electric field intensity of an electromagnetic wave propagating in an arbitrary direction in space, which is important in EMC measurement and the like.
[0038]
【The invention's effect】
As described above, according to the present invention, in the conventional example, one optical coupler, three polarization-dependent optical circulators, and three photodetectors, a total of seven blocks, are required. One circulator, one optical attenuator, and one photodetector can be used, for a total of three, and the reduction in the number of components has made it possible to reduce the size and cost of the device. Furthermore, the magnitude of the electric field intensity (isotropic data) can be immediately obtained without performing calculation processing on the PC and without rotating the sensor head of the optical electric field sensor device.
[Brief description of the drawings]
FIG. 1 is a block diagram showing an optical electric field sensor device according to an embodiment of the present invention.
FIG. 2 is a cross-sectional view of the sensor head of the optical electric field sensor according to the embodiment of the present invention when viewed from above.
FIG. 3 is a perspective view showing a uniaxial optical electric field sensor for detecting electric fields in x-axis, y-axis, and z-axis, which are components of the optical electric field sensor device according to one embodiment of the present invention.
FIG. 4 is an external perspective view of a three-axis optical electric field sensor according to one embodiment of the present invention.
FIG. 5 is a block diagram of a conventional three-axis optical electric field sensor device.
FIG. 6 is a diagram showing a configuration of a conventional three-axis optical electric field sensor. FIG. 6A is a perspective view showing an arrangement of three one-axis optical electric field sensors, and FIG. 6B is a perspective view showing a one-axis optical electric field sensor which is a component of the three-axis optical electric field sensor.
[Explanation of symbols]
21 Single-axis optical electric field sensor for x-axis direction 22 Single-axis optical electric field sensor for y-axis direction 23 Single-axis optical electric field sensor for z-axis direction 24 Support member 25 Housing 31, 56 Polarization maintaining optical fiber 32 LiNbO ₃ crystal substrate 33 Outgoing optical waveguides 34a, 34b Branch optical waveguide 35 Metal electrode 36 Reflecting mirror 41 Sensor head 42 Non-metallic holding rod 43 Three-core polarization maintaining optical fiber 50 Three-axis optical electric field sensors 51a, 51b Light sources 52a, 52b Polarization combining Detector 53 4-port polarization splitting optical circulator 54 optical attenuator 55 photodetector

Claims (6)

A Mach-Zehnder interferometer including a light source unit that generates light of a constant intensity, a demultiplexing unit that splits the light from the light source unit into three, and a modulation electrode and a branch optical waveguide provided on an electro-optic crystal substrate. Are respectively arranged to detect electric fields in the orthogonal x, y, and z-axis directions, and three signal lights modulated by the three Mach-Zehnder interferometers are used. An optical electric field sensor device comprising: multiplexing means for multiplexing; and a photodetector for converting the multiplexed signal light into an electric signal and detecting the electric signal. The demultiplexing means is a four-port polarization-separating optical circulator, and an optical attenuator is inserted between any one of the Mach-Zehnder interferometers and the four-port polarization-separating optical circulator, and the other of the Mach-Zehnder interferometer The optical electric field sensor device according to claim 1, wherein a polarization combiner is inserted between two and the four-port polarization-separating optical circulators. 3. The optical electric field sensor device according to claim 1, wherein the light source unit includes two laser light sources generating linearly polarized light orthogonal to each other and another polarization combiner. The electro-optical crystal is a LiNbO ₃ single crystal, the branched optical waveguide as claimed in any of claims 1 to 3, characterized in that it is formed by diffusing Ti ions on the substrate of the LiNbO ₃ monocrystal Optical electric field sensor device. The optical electric field sensor device according to claim 3, wherein the laser light source is a semiconductor laser light source. 4. The optical electric field sensor device according to claim 3, wherein the laser light source is a semiconductor laser-excited Nd: YAG laser light source.

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