JP2006242840A - Photoelectric field sensor and directivity adjusting method for the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a photoelectric field sensor which prevents the maximum sensitivity orientation of its directivity from shifting due to being dependent on positional relations and length values of a lead wire, an antenna rod and a metallic electrode formed on an electro-optic crystal, or an antenna formed on a print circuit board, and to provide a directivity adjusting method for the photoelectric field sensor. <P>SOLUTION: In the photoelectric field sensor having an optical modulator using an electro-optic effect, an angle between length directions of a modulation electrode and an antenna pattern is given by adding a value of 54.7° to a shift angle Δϕ in the directivity between the direction of the maximum sensitivity and the length direction along which the antenna pattern extends, i.e., the angle=(Δϕ+54.7°). Moreover, in the respective length directions, the length of the lead wire is made shorter than that of the antenna pattern, and the maximum sensitivity is set in a direction of electric field detection (i.e., at the angle between the length direction of the modulator and the length direction of the antenna pattern). <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an optical electric field sensor that measures an electric field using light, and more particularly to a small-sized optical electric field sensor suitable for electric field measurement in a narrow space region and a directivity adjustment method for the optical electric field sensor.

Conventionally, an optical electric field sensor using an interference optical waveguide utilizing an electro-optic effect is
(1) Since there is almost no metal part, the electric field to be measured is not disturbed.
(2) Since the detection signal is transmitted through the optical fiber, no electrical noise is generated due to the influence of electromagnetic induction during the transmission.
(3) By utilizing the electro-optic effect of the crystal, a high-speed response is possible and the detection signal can be transmitted as it is with low loss.
(4) No power is required for the sensor unit.
Since it has the above excellent features, it is used for a wide range of electric field measurements in the EMC field and the like.

FIG. 9 is a perspective view showing the structure of a conventional optical electric field sensor. Light incident from the optical fiber 61 is branched into two optical waveguides 69a and 69b via an optical waveguide 68 on the LiNbO ₃ single crystal substrate 67, and one of the branched optical waveguides 69a has metal electrodes 70a and 70b. An electric field is applied from, causing a change in refractive index. Since the other branched optical waveguide 69b is not subjected to an electric field, the refractive index does not change. The light propagating through any branched optical waveguide is reflected by the reflection mirror 71, propagates in the opposite direction through the branched optical waveguide, is combined again, and is emitted after being coupled to the optical fiber 61. The light propagating through these two optical paths produces a phase difference due to the difference in refractive index, and the light intensity after combining changes. Further, the modulated light passes through an optical fiber or an optical circulator, is guided to a photodetector, and is converted into an electric signal (see Patent Document 1).

  Patent Document 2 discloses an optical electric field sensor represented by EMC measurement (noise measurement) and a method for adjusting the directivity of the optical electric field sensor used for measuring the electric field strength in the field. After splitting the light on an optical crystal substrate having an electro-optic effect, an optical waveguide having a shape that merges again is formed, and a modulation electrode that changes the refractive index of the optical waveguide after branching and an antenna pattern that guides voltage to the modulation electrode are formed. In the optical electric field sensor including the formed optical modulator, there are an optical electric field sensor in which an angle formed by the length direction of the modulation electrode in the dividing direction and the length direction of the antenna pattern is adjusted, and a directivity adjustment method for the optical electric field sensor. This method makes it possible to control the optical electric field sensor, which has been dependent on the directivity of the built-in antenna, to have an arbitrary directivity.

  A technique of an optical electric field sensor having high directivity is disclosed in Patent Document 3. After splitting the light on an optical crystal substrate having an electro-optic effect, an optical waveguide having a shape that merges again is formed, and a modulation electrode that changes the refractive index of the optical waveguide after branching and an antenna pattern that guides voltage to the modulation electrode are formed. In the optical electric field sensor including the formed optical modulator, the length of the side adjacent to the optical waveguide of the antenna pattern is made smaller than the length of the opposite side. This method obtains high directivity by taking a wide antenna pattern area and extending the edge of the antenna pattern.

Japanese Patent Laid-Open No. 2004-219088 JP 2002-55133 A JP 2002-31659 A

  The above-mentioned optical electric field sensor of Patent Document 1 is provided with an antenna rod on the outside or an antenna formed on a printed circuit board to improve sensitivity. In this method, the direction of maximum sensitivity of directivity shifts depending on the relative positional relationship and the length of the metal electrode, lead wire and antenna rod formed on the electro-optic crystal, or the antenna formed on the printed circuit board. There was a problem.

  The above-mentioned optical electric field sensor of Patent Document 2 provides means for controlling the optical electric field sensor, which has been dependent on the directivity of the conventional built-in antenna, to an arbitrary directivity, but is formed on an electro-optic crystal. There is a problem that the maximum sensitivity direction of the directivity has not been solved depending on the relative position and length of the metal electrode, lead wire and antenna rod, or antenna formed on the printed circuit board. .

  The above-described optical electric field sensor of Patent Document 3 obtains high directivity by taking a wide antenna pattern region and extending the edge of the antenna pattern, but the metal electrode, the lead wire and the electrode formed on the electro-optic crystal. There has been a problem that the problem that the maximum sensitivity direction of the directivity shifts depending on the relative position and length of the antenna rod or the antenna formed on the printed circuit board cannot be solved.

  The present invention has been made to solve such problems, and its technical problem is to correlate metal electrodes, lead wires and antenna rods formed on an electro-optic crystal, or antennas formed on a printed circuit board. It is an object of the present invention to provide an optical electric field sensor and a directivity adjustment method for the optical electric field sensor in which the maximum sensitivity direction of directivity does not shift depending on the positional relationship and the length thereof.

  According to a first aspect of the present invention for achieving the above object, after splitting light on an optical crystal substrate having an electro-optic effect, the light is propagated in the opposite direction by the reflecting mirror in the reverse direction and joined again. Optical modulation in which a waveguide is formed, and after branching, a modulation electrode for changing the refractive index of the optical waveguide, an antenna pattern for guiding a voltage to the modulation electrode, and a lead wire connecting the modulation electrode and the antenna pattern are formed In the optical electric field sensor provided with a detector, the angle formed between the length direction of the modulation electrode and the length direction of the antenna pattern is defined as a deviation angle Δφ in directivity between the length direction in which the antenna pattern extends and the maximum sensitivity direction. This is an optical electric field sensor in which an angle obtained by adding 54.7 ° = (Δφ + 54.7 °).

  According to a second aspect of the invention for achieving the above object, after splitting light on an optical crystal substrate having an electro-optic effect, the light is propagated in the opposite direction by the reflecting mirror in the reverse direction and joined again. Optical modulation in which a waveguide is formed, and after branching, a modulation electrode for changing the refractive index of the optical waveguide, an antenna pattern for guiding a voltage to the modulation electrode, and a lead wire connecting the modulation electrode and the antenna pattern are formed In the optical electric field sensor provided with the detector, the length of the lead wire is set shorter than the length of the antenna pattern, and the electric field detection direction with the maximum sensitivity coincides with the length direction in which the antenna pattern extends. It is.

  According to a third aspect of the present invention for achieving the above object, after splitting light onto an optical crystal substrate having an electro-optic effect, the light is propagated in the opposite direction by the reflecting mirror in the reverse direction and joined again. Optical modulation in which a waveguide is formed, and after branching, a modulation electrode for changing the refractive index of the optical waveguide, an antenna pattern for guiding a voltage to the modulation electrode, and a lead wire connecting the modulation electrode and the antenna pattern are formed In the method for adjusting the directivity of an optical electric field sensor provided with a detector, the angle formed between the length direction of the modulation electrode and the length direction of the antenna pattern is the directivity between the length direction in which the antenna pattern extends and the maximum sensitivity direction. This is a directivity adjustment method for an optical electric field sensor that is adjusted to an angle obtained by adding 54.7 ° to the deviation angle Δφ of the optical field sensor = (Δφ + 54.7 °).

  According to a fourth aspect of the invention for achieving the above object, after splitting light on an optical crystal substrate having an electro-optic effect, the light is propagated in the opposite direction by the reflecting mirror in the reverse direction and joined again. Optical modulation in which a waveguide is formed, and after branching, a modulation electrode for changing the refractive index of the optical waveguide, an antenna pattern for guiding a voltage to the modulation electrode, and a lead wire connecting the modulation electrode and the antenna pattern are formed In the method of adjusting the directivity of the optical electric field sensor provided with the detector, the length of the lead wire is set shorter than the length of the antenna pattern, and the electric field detection direction with the maximum sensitivity and the length direction in which the antenna pattern extends It is the directivity adjustment method of the coincident optical electric field sensor.

  After branching light on an optical crystal substrate having an electro-optic effect, a reflecting mirror propagates the branched optical waveguide in the reverse direction to form an optical waveguide that merges again. After branching, the refractive index of the optical waveguide The length of the modulation electrode in an optical electric field sensor comprising an optical modulator having a modulation electrode for varying the voltage, an antenna pattern for guiding a voltage to the modulation electrode, and a lead wire connecting the modulation electrode and the antenna pattern The angle formed by the direction of the antenna pattern and the length direction of the antenna pattern is an angle obtained by adding a directivity deviation angle Δφ of the length direction in which the antenna pattern extends and the maximum sensitivity direction and 54.7 ° = (Δφ + 54.7 °). . In addition, the length of the lead wire is set shorter than the length of the antenna pattern, and the electric field detection direction with the maximum sensitivity is matched with the length direction in which the antenna pattern extends.

  As a result, regardless of the relative positional relationship and length of the antenna of the optical electric field sensor, the directivity is adjusted while correcting the deviation in directivity, and the electric field detection direction with the maximum sensitivity and the length that the antenna pattern extends. By matching the directions, it is possible to provide an optical electric field sensor and a directivity adjustment method for the optical electric field sensor in which the shift of the directivity maximum sensitivity direction is eliminated.

  Hereinafter, an optical electric field sensor according to the best mode for carrying out the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a schematic diagram showing an optical electric field sensor in which the angle of an antenna pattern according to the best mode for carrying out the present invention is adjusted. FIG. 2 is a schematic view showing an optical electric field sensor in which the length of the lead wire according to the best mode for carrying out the present invention is adjusted. FIG. 3 is a graph showing the directivity evaluation result of the sensor output in which the angle of the antenna pattern of the optical electric field sensor according to the best mode for carrying out the present invention is adjusted. FIG. 4 is a diagram showing a directivity evaluation state of the sensor output of the optical electric field sensor. FIG. 5 is a diagram showing the directivity evaluation result of the sensor output of the optical electric field sensor in which the length of the printed circuit board lead wire is adjusted.

An optical electric field sensor according to the best mode for carrying out the present invention comprises a Ti diffusion waveguide fabricated on a LiNbO ₃ substrate, a metal electrode 2 for applying a voltage thereto, a reflection mirror 6 and an optical fiber 7. . The antenna pattern 3a, 3b or antenna rod formed on the printed circuit board and the metal electrode 2 is a waveguide type Mach-Zehnder interferometer in which the metal electrode 2 is connected by lead wires 4a, 4b or wires of the printed circuit board.

  In the best mode for carrying out the present invention, as shown in FIG. 1, the lengths of the lead wires 4a and 4b of the printed circuit board are 4 mm each, the total length of the antenna patterns 3a and 3b is 21 mm, and the metal electrode 2 The length is 6 mm. Next, the directivity of this optical electric field sensor is measured, the directivity deviation angle Δφ = 15 ° due to the positional relationship between the lead wires 4a and 4b of the printed circuit board and the metal electrode 2 is taken into consideration, and the calculated value Considering the correlation between the experimental values, the angle between the length direction of the antenna patterns 3a and 3b and the length direction of the metal electrode 2 is designed to be 68.7 °, so that the maximum of the sensor of 54.7 ° can be obtained. Adjustment is made so that the maximum sensitivities in the sensitivity direction 8 coincide.

  Next, the directivity of the sensor output of this optical electric field sensor is evaluated by the evaluation system shown in FIG. As shown in FIG. 4, an electric field is generated in 10 directions by applying an RF signal to the parallel plates 9a and 9b. After that, the optical electric field sensor is placed between them, and the sensor output in the rotational direction is measured while rotating 360 ° in the rotational direction 11 with the position where the antennas 3a and 3b are parallel to the maximum sensitivity direction 8 of the sensor as the reference 0 °. To do.

  As shown in FIG. 3, in the best mode for carrying out the present invention, the electric field detection direction (angle formed by the length direction of the modulator and the length direction of the antenna pattern) at the position of 0 ° = 54.7 °. It can be seen that the maximum sensitivity matches.

  In the optical electric field sensor according to the best mode for carrying out the present invention, the length direction of the antenna patterns 3a and 3b is inclined by 54.7 ° with respect to the length direction of the metal electrode 2 as shown in FIG. It is manufactured in a shape that extends in the selected direction. The total length of the antenna patterns 3a and 3b is fixed to 21 mm, the length of the metal electrode 2 is fixed to 6 mm, and the length of the lead wires 4a and 4b of the printed circuit board is 2 minutes with respect to the length of the antenna patterns 3a and 3b. 1 or so. Thereafter, after evaluating the directivity of the sensor output, the lengths of the printed circuit board lead wires 4a and 4b are gradually reduced. Finally, the length of the lead wires 4a and 4b of the printed circuit board is set to about 1/10 of the length of the antenna patterns 3a and 3b so that the sensitivity becomes maximum in the maximum sensitivity direction 8 of the sensor. Adjust to.

  Next, the directivity of the sensor output of this optical electric field sensor is evaluated by the evaluation system shown in FIG. FIG. 5 shows that the maximum sensitivity matches the electric field detection direction (angle formed by the length direction of the modulator and the length direction of the antenna pattern) = 54.7 ° at the position of 0 °.

  A comparison between an embodiment of the present invention and a conventional example will be described in detail with reference to the drawings. FIG. 6 is a diagram showing the structure of a conventional optical electric field sensor. FIG. 7 is a graph showing the directivity evaluation result of the sensor output of the conventional optical electric field sensor. FIG. 8 shows the directivity evaluation result of the sensor output measured by connecting only the lead wire to the metal electrode with the conventional optical electric field sensor.

  The optical electric field sensor of the example of the present invention was manufactured in the same manner as the above-described optical electric field sensor according to the best mode of the present invention, and the same evaluation result was obtained.

  The conventional optical electric field sensor includes a Ti diffusion waveguide fabricated on a LiNbO3 substrate, a metal electrode 2 for applying a voltage thereto, a reflection mirror 6 and an optical fiber 7. The antenna pattern 3a, 3b or antenna rod formed on the printed circuit board and the metal electrode 2 is a waveguide type Mach-Zehnder interferometer in which the metal electrode 2 is connected by lead wires 4a, 4b or wires of the printed circuit board.

  In the conventional example, the lengths of the lead wires 4a and 4b of the printed circuit board are 4 mm each, the total length of the antenna patterns 3a and 3b is 21 mm, and the length of the metal electrode 2 is 6 mm. Next, the directivity of the sensor output of this optical electric field sensor was measured.

  In the conventional optical electric field sensor of FIG. 6, the maximum sensitivity direction is the direction of the antenna patterns 3a and 3b unless the sensor is in the maximum sensitivity direction 8 (0 ° and 180 ° positions in the evaluation data of FIG. 7). However, it was deviated from the direction by about 15 °.

  The maximum sensitivity direction of the directivity of the conventional optical electric field sensor is shifted by about 15 ° with respect to the maximum sensitivity direction 8 of the sensor (angle formed by the modulator length direction and the antenna pattern length direction = 54.7 °). In order to investigate the factor, the antenna portion was removed from the conventional optical electric field sensor by the above method, and the directivity of the optical electric field sensor was measured.

  From the measurement results of FIG. 8, it can be seen that the directivities of the sensor outputs of the lead wires 4a and 4b and the metal electrode 2 and the directivity of the sensor outputs of the antenna patterns 3a and 3b are shifted. Further, since the total value of the sensitivity and the sensitivity of the antenna rod attached to the outside becomes the final sensitivity of the optical electric field sensor, it is estimated that the directivity of the conventional optical electric field sensor is shifted by about 15 °.

  As described above, according to the embodiment of the present invention, the directivity is adjusted while correcting the deviation in directivity without depending on the correlated positional relationship and the length of the antenna of the optical electric field sensor, and the electric field detection direction (modulation) The directionality of the optical electric field sensor and the optical electric field sensor in which the deviation of the maximum directionality of directivity has been eliminated by making the maximum sensitivity direction of the directivity coincide with the angle between the length direction of the device and the length direction of the antenna pattern) It was confirmed that an adjustment method could be provided.

The schematic diagram which shows the optical electric field sensor which adjusted the angle of the antenna pattern which concerns on the best form for implementing this invention. The schematic diagram which shows the optical electric field sensor which adjusted the length of the lead wire which concerns on the best form for implementing this invention. The graph which shows the directivity evaluation result of the sensor output of the optical electric field sensor which adjusted the angle of the antenna pattern which concerns on the best form for implementing this invention. The figure which shows the directivity evaluation state of the sensor output of an optical electric field sensor. The graph which shows the directivity evaluation result of the sensor output of the optical electric field sensor which adjusted the length of the printed circuit board lead wire. The schematic diagram which shows the structure of the conventional optical electric field sensor. The graph which shows the directivity evaluation result of the sensor output of the conventional optical electric field sensor. The figure which shows the directivity evaluation result of the sensor output measured by connecting only a lead wire to the metal electrode with the optical electric field sensor of a prior art example. The perspective view which shows the structure of the conventional optical electric field sensor.

Explanation of symbols

1 LiNbO ₃ substrate
2 Metal electrodes 3a and 3b Antenna patterns 4a and 4b Lead wire 5 Printed circuit board 6 Reflection mirror 7 Optical fiber 8 Maximum sensitivity direction 9a and 9b of sensor Parallel plate 10 Electric field direction 11 Optical electric field sensor rotation direction 61 Optical fiber 67 LiNbO ₃ single crystal substrate 69a 69b Optical waveguides 70a, 70b Metal electrode 71 Reflection mirror

Claims (4)

  After branching light on an optical crystal substrate having an electro-optic effect, a reflecting mirror propagates the branched optical waveguide in the reverse direction to form an optical waveguide that merges again. After branching, the optical waveguide is refracted. An optical electric field sensor comprising: a modulation electrode for varying a rate; an antenna pattern for guiding a voltage to the modulation electrode; and an optical modulator having a lead wire connecting the modulation electrode and the antenna pattern. The angle between the length direction of the antenna pattern and the length direction of the antenna pattern is obtained by adding the directivity deviation angle Δφ between the length direction in which the antenna pattern extends and the maximum sensitivity direction to 54.7 ° = (Δφ + 54.7) An optical electric field sensor characterized by   After branching light on an optical crystal substrate having an electro-optic effect, a reflecting mirror propagates the branched optical waveguide in the reverse direction to form an optical waveguide that merges again. After branching, the optical waveguide is refracted. An optical electric field sensor comprising: a modulation electrode for changing a rate; an antenna pattern for guiding a voltage to the modulation electrode; and an optical modulator formed with a lead wire for connecting the modulation electrode and the antenna pattern. An optical electric field sensor characterized in that a length is set to be shorter than a length of the antenna pattern, and an electric field detection direction with maximum sensitivity coincides with a length direction in which the antenna pattern extends.   After branching light on an optical crystal substrate having an electro-optic effect, a reflecting mirror propagates the branched optical waveguide in the reverse direction to form an optical waveguide that merges again. After branching, the optical waveguide is refracted. In a method of adjusting the directivity of an optical electric field sensor comprising a modulation electrode for varying a rate, an antenna pattern for guiding a voltage to the modulation electrode, and an optical modulator formed with a lead wire connecting the modulation electrode and the antenna pattern The angle formed between the length direction of the modulation electrode and the length direction of the antenna pattern is the angle obtained by adding 54.7 ° to the directivity deviation angle Δφ between the length direction in which the antenna pattern extends and the maximum sensitivity direction. = (Δφ + 54.7 °) is adjusted, and the directivity adjustment method of the optical electric field sensor is characterized.   After branching light on an optical crystal substrate having an electro-optic effect, a reflecting mirror propagates the branched optical waveguide in the reverse direction to form an optical waveguide that merges again. After branching, the optical waveguide is refracted. In a method of adjusting the directivity of an optical electric field sensor comprising a modulation electrode for varying a rate, an antenna pattern for guiding a voltage to the modulation electrode, and an optical modulator formed with a lead wire connecting the modulation electrode and the antenna pattern The directivity of the optical electric field sensor is characterized in that the length of the lead wire is set shorter than the length of the antenna pattern, and the electric field detection direction with the maximum sensitivity coincides with the length direction in which the antenna pattern extends. Adjustment method.

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