JP2007078633A - High sensitivity three-axis photoelectric field sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high sensitivity three-axis photoelectric field sensor by possessing a compact sensor head part and obtaining high sensitivity. <P>SOLUTION: Light of a signal light source 12 is converted into an electric signal by entering a uniaxial sensor head out of three-axis sensor heads 11 comprising the three uniaxial sensor heads having a photoelectric converter supplying electric power to a reflection optical modulator connected through an antenna via an optical circulator 13, a first optical switch 14 and a transmission single mode optical fiber 15 and the amplifier, receiving intensity modulation due to an electric field to be measured, returning the same route as outgoing, and entering an O/E converter 16 through the optical circulator 13. Light of a power light source 17 enters the photoelectric converter of the uniaxial sensor head detecting the electric field to be measured via a multi-mode optical fiber 24, a second optical switch 18 and a transmission multi-mode optical fiber 19 to supply electric power to the amplifier. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention mainly relates to an optical electric field sensor that measures an electric field by using an optical modulator based on an interference type optical waveguide, and in particular, a highly sensitive triaxial that is suitable for measuring electric fields in three axial directions of X, Y, and Z. The present invention relates to an optical electric field sensor.

  An optical electric field sensor using an optical modulator based on an interference type optical waveguide utilizing the electro-optic effect has the following excellent features. In other words, since it has almost no metal part, it does not disturb the electric field to be measured, it transmits the detection signal through the optical fiber, so it is not affected by induction or electrical noise, and uses the electro-optic effect of the crystal. The high-speed response is possible, and the detection signal can be transmitted as it is with little loss, and the power supply is not required for the sensor unit. Because of these characteristics, the optical electric field sensor is used for electric field measurement in the EMC field and the like.

  A conventional example of an optical electric field sensor capable of measuring electric fields in the X, Y and Z triaxial directions will be described with reference to FIGS. This is shown in Patent Document 1 and Patent Document 2.

  FIG. 5 is a plan view showing the structure of a uniaxial sensor head that is a constituent element of a triaxial sensor head of a conventional triaxial optical electric field sensor.

Referring to FIG. 5, one-axis direction of the sensor head of an optical electric field sensor for electric field measurements, from the other end on the LiNbO ₃ crystal substrate 57 made of LiNbO ₃ crystal is a reflection mirror 51 provided on one end side Two branched optical waveguides 59a and 59b branched from the incoming / outgoing optical waveguide 58 toward one end side are provided so as to be coupled to the reflecting mirror 51, and the incoming / outgoing optical light on the other end side in the LiNbO ₃ crystal substrate 57 is provided. An optical fiber 52 is coupled to the waveguide 58, and four pairs of opposing metal electrodes 53 serving as antennas for detecting an electric field are installed at predetermined positions sandwiching the branch optical waveguide 59a, thereby reflecting light modulation. The instrument and the antenna are integrated.

  The metal electrode 53 is formed of a combination of triangular metal films, and applies a voltage induced by an electric field in a direction indicated by an arrow (direction of 54.7 degrees with respect to the optical waveguide) to the branched optical waveguide 59a. The pattern is decided.

In this operation, light incident from the optical fiber 52 is branched into two branch optical waveguides 59a and 59b via an input / output optical waveguide 58 on the LiNbO ₃ crystal substrate 57. At this time, one of the branch optical waveguides 59a includes a metal. Although an electric field is applied by the electrode 53 to cause a change in refractive index, the other branch optical waveguide 59b has no change in refractive index due to the electric field, and light propagating through any of the branch optical waveguides 59a and 59b is reflected by the reflection mirror 51. After being reflected, the light propagates in the opposite direction through the branched optical waveguides 59a and 59b and is multiplexed again by the input / output optical waveguide 58. During this multiplexing, interference occurs due to the phase difference caused by the difference in refractive index between the two optical paths, the light intensity after the multiplexing is modulated, and then this modulated light is coupled to the optical fiber 52 and emitted.

  Here, when the optical waveguide only guides a propagation mode that applies intensity modulation of either the TE mode or the TM mode, a single mode optical fiber can be used as it is. When guiding both propagation modes, a polarization separator is required on the incident side, and a polarization-maintaining optical fiber is used as the optical fiber 52.

  FIG. 6 shows a cross-sectional view of a triaxial sensor head of a triaxial electric field measuring optical electric field sensor in which the above three uniaxial sensor heads are mounted on a regular triangular prism support member. As shown in FIG. 6, three reflective optical modulators 64, 65, 66 similar to the above are provided on the side surface of the regular triangular prism support member 63 so that the direction of each optical waveguide is perpendicular to the paper surface of FIG. Deploy.

  As a result, the directions of the metal electrodes of the three reflection type optical modulators are orthogonal to each other, and the voltage induced in each antenna, that is, the metal electrode by the measured electric field components in the three orthogonal axes directions to the reflection type optical modulator. The incident light is modulated.

  FIG. 7 shows the entire configuration of a conventional three-axis optical electric field sensor device. Light emitted from a light source 73 composed of two linearly polarized waves orthogonal to each other includes a single mode optical fiber 78, an optical circulator 74, an optical switch 75, Then, it passes through the transmission single mode optical fiber 76 and enters one reflection type optical modulator of the triaxial sensor head 70, undergoes intensity modulation by the electric field to be measured, and enters the transmission single mode optical fiber 76 again. Thereafter, the modulated light passes through the optical switch 75 and the optical circulator 74, enters the O / E converter 77, and is converted into an electric signal. By selecting an optical modulator by the optical switch 75, it is possible to sequentially measure electric fields in three orthogonal directions.

JP 2002-257484 A JP 2004-212137 A

Since the triaxial optical electric field sensor is usually used for detecting an electric field in a narrow area or an electric field in an area close to the object to be measured, the sensor head portion is required to be downsized. Therefore, as in the above conventional example, a metal electrode pattern placed on a LiNbO ₃ crystal substrate is used as an antenna. In such a case, since the antenna length is limited as described above, the voltage induced in the antenna by the electric field is very small, and the detection sensitivity becomes very small. Therefore, the conventional three-axis optical electric field sensor is limited to the measurement application when the electric field strength is large, and the application area is greatly limited.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a high-sensitivity triaxial optical electric field sensor that has a small sensor head part, has high sensitivity, and can be applied in a wide range.

  In order to achieve the above object, in the high-sensitivity triaxial optical electric field sensor of the present invention, three antennas having sensitivity to electric field components in different directions, and three electric amplifiers connected to the antennas, respectively, A three-axis system comprising three reflective optical modulators that respectively modulate the intensity of incident light with voltages from their respective amplifiers, and three photoelectric converters for supplying power to each of the amplifiers A sensor head, a signal light source for generating unmodulated light, an optical circulator for receiving unmodulated light from the signal light source, and at least three output ports for switching optical paths of light emitted from the optical circulator One optical switch, three signal optical fibers for guiding output light of each port of the first optical switch to the reflective optical modulator, and the reflection An O / E converter that converts the intensity-modulated output light returned from the optical modulator through the optical fiber for the signal, the first optical switch, and the optical circulator into an electrical signal; A power light source for supplying light to the photoelectric converter, three power optical fibers for guiding light from the power light source to the respective photoelectric converters, and emitted from the power light source A second optical switch for switching the light to the three power optical fibers is provided.

  In addition, the first optical switch and the second switch respectively include a non-modulated light from a signal light source and a photoelectric converter that supplies power to one reflective optical modulator and an amplifier connected thereto. It is desirable to have a function of selecting to provide light from the power source.

  The signal light source may be a laser light source that oscillates slightly and oscillates and outputs two linearly polarized waves orthogonal to each other.

  With the above-described configuration, according to the present invention, it is possible to provide a high-sensitivity triaxial optical electric field sensor that has a small sensor head portion, has high sensitivity, and can be applied in a wide range.

  Next, an embodiment of the present invention will be described with reference to FIGS.

  FIG. 2 is an external perspective view of a triaxial sensor head portion in an embodiment of the high sensitivity triaxial optical electric field sensor of the present invention. 22 is a bundle of three optical fibers for signals and three optical fibers for electric power, 21 is a non-metallic holding rod, and 20 is a three-axis sensor head.

  The size of this triaxial sensor head is φ50 × 70 mm, and in order to measure the electric field in the triaxial direction, three antenna rods, three electrical amplifiers, three photoelectric converters, and three reflective optical modulators Is contained.

  A sectional view of the triaxial sensor head 20 as viewed from above is shown in FIG. A uniaxial sensor head 32 that measures an electric field in the x-axis direction, a uniaxial sensor head 33 that measures an electric field in the y-axis direction, and an electric field in the z-axis direction on three side surfaces of a triangular prism support member 31 having an equilateral triangular cross section. A uniaxial sensor head 34 to be measured is disposed. In each uniaxial sensor head, an antenna rod 35, an electrical amplifier 37, a photoelectric converter 38, and a reflective light modulator 36 corresponding to the electric field in each direction are arranged. With such a configuration, electric field measurement in the three-dimensional orthogonal coordinate axes, x, y, and z-axis directions becomes possible.

A schematic diagram of the configuration of the single-axis sensor head used here is shown in FIG. Similar to the conventional sensor head of FIG. 5 described above, the reflective optical modulator 36 includes an input / output optical waveguide 42 made of a Ti diffusion optical waveguide fabricated on a LiNbO ₃ crystal substrate 41, two branched optical waveguides 43, The optical fiber 46 is coupled to the incident end of the input / output optical waveguide 42. The optical electrode 46 includes a metal electrode 44 and a reflection mirror 45 provided with one branch optical waveguide interposed therebetween.

  The antenna rod 35 is installed outside the reflection type optical modulator 36, and the voltage induced therein is amplified by an electric amplifier 37 and applied to the metal electrode 44. The electric amplifier 37 is driven by a voltage induced from a photoelectric converter 38 supplied with power light by a power optical fiber 39.

  4 schematically illustrates the size and arrangement of the antenna rod 35, the amplifier 37, the photoelectric converter 38, and the reflective optical modulator 36 in order to explain the configuration and operation of the sensor head. In practice, however, in order to reduce the influence on the detection of the electric field, it is compactly mounted on the three side surfaces of the support member 31 of the regular triangular prism as shown in FIG.

  In this embodiment, the cross-sectional shape of the support member 31 is an equilateral triangle, and the angle of each antenna rod is 54.7 degrees in the same direction as in FIG. 5, but in the present invention, the antenna rod is a reflection type light modulation. Since it is separated from the vessel, the directions may be orthogonal to each other in combination with the shape of the support member, and the shape of the support member and the angle of the antenna rod are not limited to the above. For example, the cross-sectional shape of the support member can be a right triangle, and the direction of the antenna rod can be a direction of two sides sandwiching the right angle of the right triangle of the optical waveguide direction of the reflective optical modulator.

  In addition, the metal electrode 44 may have a shape in which a voltage is applied to both the two branch optical waveguides 43 in a push-pull manner, and may have a split electrode configuration in order to obtain broadband sensitivity characteristics.

  Next, the highly sensitive three-axis optical electric field sensor of this embodiment will be described with reference to FIG. 11 is a three-axis sensor head of this embodiment, 12 is a signal light source that outputs two linearly polarized waves orthogonal to each other, 13 is an optical circulator, 14 is a first optical switch, and 15 is a transmission single for signal transmission. A mode optical fiber 16 is an O / E converter including a photodiode and an amplifier. On the other hand, 17 is a power light source, 18 is a second optical switch, and 19 is a transmission multimode optical fiber for power transmission.

  Next, the operation of this electric field sensor will be described. Two orthogonally polarized light beams emitted from the signal light source 12 pass through a single-mode optical fiber 23, an optical circulator 13, a first optical switch 14, and a transmission single-mode optical fiber 15, and a three-axis sensor head. 11 is incident on one uniaxial sensor head 11, is subjected to intensity modulation by the electric field to be measured, and enters the transmission single mode optical fiber 15 again. Thereafter, the modulated light passes through the first optical switch 14 and the optical circulator 13, enters the O / E converter 16, and is converted into an electrical signal. On the other hand, the light emitted from the power light source 17 passes through the multi-mode optical fiber 24, enters the triaxial sensor head 11 through the second optical switch 18 and the transmission multi-mode optical fiber 19, and generates an electric field to be measured. The light is incident on the photoelectric converter of the detected single-axis sensor head to generate power, and the power is supplied to the amplifier.

  With respect to the other two axial directions, the first and second optical switches 14 and 18 are operated in the same manner as the first axial direction by switching the optical path.

  With such a configuration, the high-sensitivity three-axis optical electric field sensor according to the present embodiment can measure the electric fields in the three-axis directions by selecting the axes by switching the first optical switch and the second optical switch. It becomes.

  In order to more easily supply power to an electric amplifier for obtaining high sensitivity, a method of feeding power to three amplifiers by one photoelectric converter can be considered. Requires only one optical fiber for power, and the second optical switch is not required. In addition, use of an optical coupler that divides light into three instead of the second optical switch is also conceivable.

  However, in these cases, since the voltage induced in the other antenna when the electric field of one axis is measured is amplified, it may experimentally affect the electric field detection of the axis to be measured. It became clear. Therefore, in the present invention, the photoelectric converter for power supply is separated on each of the three axes, and it is possible to prevent the voltage induced by the antenna from being amplified other than the axis to be measured, thereby preventing the interference. Yes.

  As described above, the conventional three-axis optical electric field sensor has a limited application to the use of measuring a strong electric field as in the case of a tolerance test of an apparatus against electromagnetic noise, that is, an immunity test. The high-sensitivity triaxial optical electric field sensor having a small sensor head portion obtained by the invention and having high sensitivity can obtain a sensitivity improvement of 20 dB or more as compared with the conventional one. It can also be used for measurement, that is, emission measurement applications, and can be applied in a wide range.

  In the highly sensitive three-axis optical electric field sensor of the present invention, the polarization dependency of the optical modulator can be eliminated by using a light source that outputs two linearly polarized waves orthogonal to each other. Thus, the polarization of the optical transmission path can be made independent, the use of general-purpose parts, and the construction of parts almost the same as a single-axis sensor can be realized, thereby realizing a highly practical device.

  The difference between the transmission frequencies of the two light sources described above is a value that is at least twice the upper limit of the measurement frequency so that beat noise generated thereby does not affect the measurement frequency region, for example, when the measurement frequency is 3 GHz. , About 6 GHz or more.

  In addition, a single mode optical fiber can be used as an optical fiber for supplying power for common parts.

The figure which shows the structure of the highly sensitive triaxial optical electric field sensor in one embodiment of this invention. 1 is an external perspective view of a three-axis sensor head according to an embodiment of the present invention. Sectional drawing when the triaxial sensor head in one embodiment of this invention is seen from the upper surface. The figure which shows the structure of the uniaxial sensor head which is a component of the triaxial sensor head in one embodiment of this invention. The top view which shows the structure of the uniaxial sensor head which is a component of the triaxial sensor head of the conventional triaxial optical electric field sensor. Sectional drawing when the triaxial sensor head of the conventional triaxial optical electric field sensor is seen from the upper surface. The figure which shows the structure of the conventional triaxial optical electric field sensor.

Explanation of symbols

11 3-axis sensor head 12 Signal light source 17 Power light source 13, 74 Optical circulator 14 First optical switch 18 Second optical switch 15, 76 Transmission single mode optical fiber 23, 78 Single mode optical fiber 24 Multimode optical fiber 19 Transmission multimode optical fiber 16, 77 O / E converter 20, 70 Triaxial sensor head 21 Non-metal holding rod 22 Bunch of three optical fibers for signals and three optical fibers for power 31, 63 Member 32 Uniaxial sensor head 33 for measuring the electric field in the x-axis direction Uniaxial sensor head 34 for measuring the electric field in the y-axis direction Single-axis sensor head 35 for measuring the electric field in the z-axis direction Antenna rods 36, 64, 65, 66 Reflective light modulator 37 Electrical amplifier 38 Photoelectric converter 46, 52 Optical fiber 39 Power optical fiber 41, 7 LiNbO ₃ crystal substrate 42, 58 input and output optical waveguide 43,59a, 59b branch optical waveguides 44 and 53 metal electrodes 45 and 51 reflecting mirrors

Claims (3)

  Intensity modulation is applied to incident light by three antennas having sensitivity to electric field components in different directions, three electrical amplifiers connected to the antennas, and voltages from the respective amplifiers. A three-axis sensor head comprising three reflective optical modulators and three photoelectric converters for supplying power to each of the amplifiers, a signal light source for generating unmodulated light, and a signal light source An optical circulator to which the unmodulated light is incident, a first optical switch having at least three output ports for switching the optical path of light emitted from the optical circulator, and output light from each port of the first optical switch. Three optical fibers for signals to be led to the reflective optical modulator, the optical fiber for signals from the reflective optical modulator, the first optical switch, the front An O / E converter that converts the intensity-modulated output light returned through the optical circulator into an electric signal, a power light source for supplying light to the photoelectric converter, and the power light source Three power optical fibers for guiding light from the power converter to each of the photoelectric converters, and a second optical switch for switching the light emitted from the power light source to the three power optical fibers A high-sensitivity triaxial optical electric field sensor characterized by comprising:   The first optical switch and the second switch are for the non-modulated light from the signal light source and the power for the photoelectric converter that supplies power to one reflective optical modulator and an amplifier connected thereto, respectively. 2. The high-sensitivity triaxial optical electric field sensor according to claim 1, which has a function of selecting so as to give light from a light source.   3. The high sensitivity according to claim 1, wherein the signal light source is a laser light source that oscillates slightly and oscillates and outputs two linearly polarized waves orthogonal to each other. 3-axis optical electric field sensor.

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