JP2011112498A - Electromagnetic field measuring apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electromagnetic field measuring apparatus accurately measuring intensity of an electromagnetic field even if a state of polarization of light propagating in an optical fiber varies owing to stress applied to the optical fiber. <P>SOLUTION: The electromagnetic field measuring apparatus is equipped with: a laser light source 11; a polarization controller 13 for converting polarization of laser light into linear polarization; a probe head A having an electro-optical material part 16 whose refractive index varies depending on electric field intensity; a power monitor 18 for measuring a quantity of the laser light transmitted through the polarization controller 13 and sending, to the polarization controller 13, a drive signal for changing a polarization direction of the laser light to make the quantity of the laser light incident to the electro-optical material part 16 constant; an electromagnetic field intensity measuring part 19 for receiving the laser light transmitted through the probe head A and measuring the electric field intensity; and optical fibers 12, F1, F2, F3 and F4 for propagating the laser light from the laser light source 11 to the electromagnetic field intensity measuring part 19. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an electromagnetic field measuring apparatus that measures the strength of an electric field or a magnetic field.

2. Description of the Related Art Conventionally, an electromagnetic field measuring device capable of detecting an electric field or a magnetic field is known as a device for evaluating noise characteristics of an electronic device or evaluating a defense characteristic (immunity) of noise entering the electronic device from the outside.
As such an electromagnetic field measuring device, an electromagnetic field sensor having an electro-optic material or a magneto-optic material whose refractive index changes according to the strength of an electric field or a magnetic field, and transmitting laser light to the electromagnetic field sensor, There is known an apparatus for measuring an electric field or a magnetic field by utilizing the fact that the polarization state of laser light after passing through an electro-optic material or a magneto-optic material is modulated in accordance with the refractive index change of the electro-optic material or the magneto-optic material. (For example, refer to Patent Document 1).
For example, in the electromagnetic field measuring apparatus described in Patent Document 1, laser light incident on an electro-optical material and a magneto-optical material and laser light emitted from the electro-optical material or the magneto-optical material and incident on a light receiver are optical fibers. Has been propagated by.

JP 2008-216036 A

  By the way, when an external force acts on the optical fiber and the optical fiber is bent, stress is generated in the optical fiber and the refractive index of the optical fiber changes, so that the polarization state of the light propagating in the optical fiber changes. It is known to do. For this reason, in the electromagnetic field measurement apparatus described in Patent Document 1, a polarization state in which a change in the polarization state of light due to a change in an electric field or a magnetic field and a change in the polarization state of light according to the stress applied to the optical fiber are combined. Will be detected. As a result, the measurement value indicating the magnitude of the electric field or magnetic field varies depending on the stress applied to the optical fiber, and the accuracy of measuring the electromagnetic field strength may be reduced.

  The present invention has been made in view of the above-described circumstances, and its purpose is to accurately measure the strength of an electromagnetic field even when the polarization state of light propagating in an optical fiber changes due to stress applied to the optical fiber. It is an object to provide an electromagnetic field measuring apparatus capable of performing the above.

In order to solve the above problems, the present invention proposes the following means.
The electromagnetic field measurement apparatus of the present invention includes a light source unit that emits laser light, a polarization controller that converts the polarization of the laser light into linearly polarized light, an electro-optic material or a magnetic material whose refractive index changes according to the strength of the electric field or magnetic field. An electromagnetic field detector having an optical material and detecting the intensity of the electric field or the magnetic field by changing a polarization direction of the laser light transmitted through the polarization controller; and an amount of the laser light transmitted through the polarization controller. A light amount measurement control unit that measures and transmits a drive signal to the polarization controller to change the polarization direction of the laser light so that the light amount of the laser light incident on the electro-optical material or the magneto-optical material is constant; An electromagnetic field intensity measurement unit that receives the laser beam transmitted through the electromagnetic field detection unit and measures the intensity of the electric field or magnetic field; Characterized in that it comprises a and an optical fiber for propagating the laser light from the light source unit up to the electromagnetic field strength measuring portion.

  According to the electromagnetic field measurement apparatus of the present invention, the light amount measurement control unit detects the light amount of the laser light incident on the electro-optical material or the magneto-optical material, and the light amount of the laser light incident on the electro-optical material or the magneto-optical material is maximized. The light quantity measurement control unit controls the polarization controller attached to the optical fiber. As a result, the amount of laser light incident on the electro-optic material or magneto-optic material can be made constant, and the strength of the electromagnetic field can be accurately adjusted even if the polarization state of the light propagating in the optical fiber changes due to the stress applied to the optical fiber. Can be measured.

It is a schematic diagram which shows the structure of the electromagnetic field measuring apparatus of 1st Embodiment of this invention. It is a flowchart for demonstrating operation | movement of the same electromagnetic field measuring apparatus. It is a schematic diagram which shows the structure of the electromagnetic field measuring apparatus of 2nd Embodiment of this invention. It is a flowchart for demonstrating operation | movement of the same electromagnetic field measuring apparatus. It is a schematic diagram which shows the structure of the modification 1 of the same electromagnetic field measuring device. It is a schematic diagram which shows the structure of the electromagnetic field measuring apparatus of 3rd Embodiment of this invention. It is explanatory drawing for demonstrating the effect | action of the same electromagnetic field measuring apparatus. It is a graph for demonstrating the effect | action of the same electromagnetic field measuring apparatus. It is a flowchart for demonstrating operation | movement of the same electromagnetic field measuring apparatus. It is a schematic diagram which shows the structure of the modification 2 of the same electromagnetic field measuring apparatus. (A) is a schematic diagram which shows the structure of the electromagnetic field measuring device of 4th Embodiment of this invention. (B) is a perspective view showing a partial configuration of the electromagnetic field measuring apparatus.

(First embodiment)
Hereinafter, an electromagnetic field measuring apparatus 1 according to a first embodiment of the present invention will be described with reference to FIGS. 1 and 2. FIG. 1 is a schematic diagram showing the configuration of the electromagnetic field measuring apparatus 1. FIG. 2 is a flowchart for explaining the operation of the electromagnetic field measuring apparatus 1.
The electromagnetic field measurement apparatus 1 of the present embodiment can be configured to measure the strength of an electric field or a magnetic field. Below, the structure for measuring the intensity | strength of an electric field with the electromagnetic field measuring apparatus 1 is demonstrated first.

  As shown in FIG. 1, the electromagnetic field measuring apparatus 1 includes a laser light source 11, a polarization controller 13, an optical circulator 14, a probe head (electromagnetic field detector) A, a power monitor (light quantity measurement controller) 18, and And an electromagnetic field intensity measuring unit 19.

An optical fiber 12 is provided between the laser light source 11 and the polarization controller 13. Further, an optical fiber F <b> 1 that propagates laser light is provided between the polarization controller 13 and the optical circulator 14. Further, an optical fiber F2 for propagating laser light is provided between the optical circulator 14 and the probe head A. Further, an optical fiber F3 for propagating laser light is provided between the probe head A and the power monitor 18. Further, an optical fiber F4 for propagating laser light is provided between the optical circulator 14 and the electromagnetic field intensity measurement unit 19.
The optical fiber 12 may be a normal single mode fiber or a polarization maintaining fiber.
The optical fibers F1, F2, F3, and F4 may be ordinary single mode fibers, but are preferably polarization-maintaining fibers.

  In addition, the directions indicated by x, y, and z in FIG.

  The laser light source 11 is a laser light source that emits laser light having a constant intensity.

  The polarization controller 13 is for converting the laser light emitted from the laser light source 11 into linearly polarized light, and has a quarter wavelength plate and a 1/2 for the wavelength of the laser light that transmits the laser light emitted from the laser light source 11. And a wave plate. The quarter-wave plate and the half-wave plate can be individually rotated around the optical axis based on the drive signal from the power monitor 18.

  The optical circulator 14 has a terminal 14A connected to the optical fiber F1, a terminal 14B connected to the optical fiber F2, and a terminal 14C connected to the optical fiber F4. The terminals 14A, 14B, and 14C The light traveling in the forward direction is low loss, and the light traveling in the reverse direction is configured to have high loss. For this reason, the light incident on the terminal 14A is emitted from the terminal 14B, and the light incident on the terminal 14B is emitted from the terminal 14C.

  The probe head A includes a polarizing beam splitter 15 connected to the optical fiber F2, an electro-optic material portion 16 provided in close contact with the polarizing beam splitter 15, and a reflecting mirror formed in close contact with the electro-optic material portion 16. 17. The polarizing beam splitter 15, the electro-optic material portion 16, and the reflecting mirror 17 are epoxy adhesives.

  When the laser beam emitted from the terminal 14B of the optical circulator 14 is incident on the polarization beam splitter 15, the P-polarized component of the laser beam (the polarization component in the x direction shown in FIG. 1) is transmitted to the electro-optic material unit 16 side. The S-polarized component of the laser light (the polarized component in the y direction shown in FIG. 1) is reflected to the power monitor 18 side. The polarizing beam splitter 15 may be a polarizing beam splitter that reflects a component of P-polarized laser light and transmits a component of S-polarized laser light. In this case, the P-polarized component of the laser light enters the power monitor 18.

  The electro-optic material portion 16 is formed by cutting a single crystal of a compound (BSO) containing bismuth, silicon, and oxygen into a few hundred microns square. When the electro-optic material portion 16 transmits laser light, the refractive index changes according to the strength of the electric field surrounding the electro-optic material portion 16.

  The reflecting mirror 17 reflects the laser light that has passed through the electro-optic material portion 16. As a material of the reflecting mirror 17, for example, a dielectric multilayer mirror formed by alternately laminating a dielectric having a relatively low refractive index and a dielectric having a relatively high refractive index can be employed. The laser light reflected by the reflecting mirror 17 is incident on the electro-optic material portion 16 again, passes through the electro-optic material portion 16, and again enters the polarization beam splitter 15.

  The power monitor 18 receives the laser light reflected by the polarization beam splitter 15 and outputs a drive signal for rotating the quarter wavelength plate and the half wavelength plate of the polarization controller 13 based on the amount of the laser light. 13 is transmitted. Further, in the power monitor 18, when the laser light emitted from the laser light source 11 is incident on the electro-optic material portion 16 to the maximum extent, the light amount of the laser light incident on the power monitor 18 is set as a minimum value. The monitor 18 controls the polarization controller 13 so that the light amount of the detected laser beam becomes a minimum value.

  The minimum value set in the power monitor 18 is that of the laser light separated from the polarization beam splitter 15 to the power monitor 18 by irradiating the laser light from the laser light source 11 and operating the polarization controller 13 in the electromagnetic field measuring apparatus 1. This can be set by storing the light amount when the light amount is minimized in the power monitor 18. The power monitor 18 generates a drive signal for driving the polarization controller 13 so as to minimize the amount of laser light detected by the power monitor 18 and transmits the drive signal to the polarization controller 13.

  The electromagnetic field intensity measurement unit 19 is connected to the optical fiber F4 and receives a laser beam emitted from the terminal 14C of the optical circulator 14 and generates an electric signal corresponding to the amount of the laser beam, and a signal line C2. An RF spectrum analyzer 19B that is electrically connected to the light receiving unit 19A and measures the electric field strength based on an electric signal emitted from the light receiving unit 19A.

An operation at the time of use of the electromagnetic field measurement apparatus 1 of the present embodiment having the above-described configuration will be described.
When the electromagnetic field measuring apparatus 1 is driven, first, laser light is emitted from the laser light source 11. This laser light propagates through the optical fiber 12 and enters the polarization controller 13. Then, the laser light is linearly polarized by the polarization controller 13, propagates through the optical fiber F 1, enters the terminal 14 A of the optical circulator 14, and is emitted from the terminal 14 B of the optical circulator 14.

  The laser light emitted from the terminal 14B of the optical circulator 14 propagates through the optical fiber F2 and enters the polarization beam splitter 15. The polarization beam splitter 15 transmits the P-polarized component of the laser light (linearly polarized component polarized in the X-axis direction shown in FIG. 1) and transmits the S-polarized component of the laser light (polarized in the Y-axis direction shown in FIG. 1). (Linearly polarized light component) is reflected to the power monitor 18 side.

The P-polarized component of the laser light is emitted from the polarization beam splitter 15 and passes through the electro-optic material unit 16. At this time, since the refractive index of the electro-optic material portion 16 changes due to the electric field outside the electro-optic material portion 16, the polarization direction of the laser light changes according to the strength of the electric field and enters the reflecting mirror 17. The laser light incident on the reflecting mirror 17 is reflected and transmitted through the electro-optic material portion 16 again, and the polarization direction is further changed at a refractive index corresponding to the electric field as described above, and is incident on the polarizing beam splitter 15. The S-polarized component of the laser light that travels back and forth through the electro-optic material unit 16 and enters the polarization beam splitter 15 is reflected by the polarization plane of the polarization beam splitter 15 to the side opposite to the power monitor 18.
The S-polarized component of the laser light incident on the polarization beam splitter 15 from the terminal 14B of the optical circulator 14 is emitted from the polarization beam splitter 15 and enters the power monitor 18 through the inside of the optical fiber F3.

Below, operation | movement of the power monitor 18 is demonstrated with reference to FIG.1 and FIG.2.
As shown in FIG. 2, in the power monitor 18, first, step S <b> 1 in which the power monitor 18 measures the amount of laser light is performed.
In step S1, the light quantity of the S-polarized component laser beam separated by the polarization beam splitter 15 shown in FIG. 1 is measured. When step S1 ends, the process proceeds to step S2.

  In step S2, when the light quantity of the S-polarized component of the laser light measured in step S1 is equal to the above-mentioned minimum value, step S2 is finished and the adjustment of the polarization direction of the laser light is finished. If the amount of the S-polarized component of the laser light measured in step S1 is larger than the minimum value, step S2 is terminated and the process proceeds to step S3.

  In step S <b> 3, a drive signal for driving the polarization controller 13 is transmitted to the polarization controller 13. When the transmission of the drive signal ends, step S3 ends.

  In the polarization controller 13, the polarization direction of the linearly polarized light emitted from the polarization controller 13 is changed by the drive signal transmitted from the power monitor 18. When a new drive signal is transmitted from the power monitor 18, the polarization controller 13 operates based on the new drive signal.

  The measurement of the light quantity of the S-polarized component of the laser light in the power monitor 18 is continuously performed while the electric field measurement is performed. When the polarization controller 13 is operated by the power monitor 18, the ratio of the P-polarized component and the S-polarized component of the laser light incident on the polarizing beam splitter 15 changes. As a result, the amount of S-polarized component laser light incident on the power monitor 18 changes from the amount of light before the polarization controller 13 is driven.

In the power monitor 18, when the amount of the S-polarized component laser light incident on the power monitor 18 is larger than the amount of light detected immediately before, the direction opposite to the direction in which the polarization direction of the linearly-polarized laser light was changed immediately before. A drive signal for changing the polarization direction to the direction is transmitted to the polarization controller 13.
When the light amount of the S-polarized component laser light incident on the power monitor 18 is smaller than the light amount detected immediately before, the polarization direction is the same as the direction in which the polarization direction of the linearly polarized laser light was changed immediately before. Is transmitted to the polarization controller 13.
The power monitor 18 drives the polarization controller 13 until the amount of S-polarized component laser light detected by the power monitor 18 reaches a minimum value.

  When the optical fiber 12 vibrates or bends, its refractive index varies depending on the stress applied to the optical fiber 12, and the polarization direction of the laser light passing through the optical fiber 12 may vary. By adjusting the polarization direction of the laser light by the 18 and the polarization controller 13, the light quantity of the laser light of the S-polarized component is maintained at the minimum value.

  Therefore, even if the polarization direction of the laser light passing through the optical fiber 12 fluctuates due to the stress applied to the optical fiber 12, the laser light is incident on the electro-optic material part 16 without loss in the polarization beam splitter 15, and the electro-optic material part 16 The amount of laser light incident on is maintained substantially constant.

  The laser light emitted from the electro-optic material unit 16 enters the polarization beam splitter 15. Here, the polarization beam splitter 15 functions as an analyzer, and the laser beam returned by reciprocating once through the electro-optic material unit 16 is a laser beam when the polarization direction is changed in the electro-optic material unit 16. The polarization component having a polarization direction different from the P polarization is reflected by the polarization beam splitter 15. Therefore, the intensity of the laser beam that has passed through the electro-optic material portion 16 and whose polarization direction has changed according to the electric field strength outside the electro-optic material portion 16 is modulated by the polarization beam splitter 15. The laser light transmitted through the polarizing beam splitter 15 is emitted from the polarizing beam splitter 15 and enters the terminal 14B of the optical circulator 14 through the optical fiber F2.

The laser light incident on the terminal 14B of the optical circulator 14 is emitted from the terminal 14C of the optical circulator 14 and enters the light receiving unit 19A of the electromagnetic field intensity measuring unit 19 through the optical fiber F4. The light receiving unit 19A converts the amount of laser light into an electrical signal by photoelectric conversion, and this electrical signal is detected by the RF spectrum analyzer 19B through the signal line C2.
Accordingly, the electric field strength can be measured by the electro-optic material unit 16 using the laser light emitted from the laser light source 11.

  As described above, according to the electromagnetic field measurement apparatus 1 of the present embodiment, the intensity of the laser light incident on the electro-optic material unit 16 is measured by the power monitor 18, and the light amount of the laser light incident on the power monitor 18 is determined. The polarization controller 13 is driven so as to be minimized. As a result, the amount of laser light incident on the electro-optic material portion 16 can be maximized.

  Further, since the polarization direction of the laser light is continuously controlled by the power monitor 18 and the polarization controller 13, the laser that is incident on the electro-optic material portion 16 even if the polarization direction fluctuates due to stress applied to the optical fiber 12. The amount of light can be made constant. As a result, even if the polarization state of the laser light propagating through the optical fiber 12 changes due to the stress applied to the optical fiber 12, the electric field strength can be measured with high accuracy.

  Further, since the laser light separated from the polarization beam splitter 15 enters the power monitor 18 and the polarization controller 13 is driven so that the light amount of the laser light is minimized, the light amount separated on the power monitor 18 side is small. Thus, the laser light can be efficiently incident on the electro-optic material portion 16.

(Second Embodiment)
Next, the electromagnetic field measurement apparatus 2 according to the second embodiment of the present invention will be described with reference to FIGS. 3 and 4. FIG. 3 is a schematic diagram showing the configuration of the electromagnetic field measuring apparatus 2. FIG. 4 is a flowchart for explaining the operation of the electromagnetic field measuring apparatus 2. The present embodiment is different in configuration from the electromagnetic field measurement apparatus 1 of the first embodiment described above in that a probe head A2 provided in place of the probe head A is provided.

  As shown in FIG. 3, the electromagnetic field measurement apparatus 2 includes a polarizer 25 </ b> A connected to the optical fiber F <b> 2 and a beam splitter 25 </ b> B provided in place of the polarization beam splitter 15.

  The polarizer 25A is an optical component that transmits a laser beam having a linearly polarized component polarized in a specific direction. The beam splitter 25B is an optical component that distributes laser light into two in a direction orthogonal to each other at a certain ratio.

  Also in this embodiment, the laser light emitted from the polarization controller 13 is linearly polarized light polarized in the polarization direction determined by the relative positional relationship between the half-wave plate and the quarter-wave plate. The laser light emitted from the polarization controller 13 enters the optical circulator 14 through the optical fiber F1, and further enters the polarizer 25A through the optical fiber F2.

  In the polarizer 25A, the laser beam having a component that matches the polarization direction that can be transmitted through the polarizer 25A is transmitted and emitted to the beam splitter 25B side.

  In the beam splitter 25B, the laser light is separated into the power monitor 18 side and the electro-optic material unit 16 side with a distribution ratio unique to the beam splitter 25B.

  In the present embodiment, the power monitor 18 stores a value obtained by multiplying the light amount of the emitted light from the laser light source 11 by the distribution ratio separated on the power monitor 18 side in the beam splitter 25B as a specified value.

Below, the operation | movement at the time of use of the electromagnetic field measuring apparatus 2 of this embodiment is demonstrated.
In this embodiment, as shown in FIG. 3, the laser light emitted from the laser light source 11 passes through the optical fiber 12, the polarization controller 13, the optical fiber F1, the optical circulator 14, and the optical fiber F2 in this order to the polarizer 25A. Incident. In the polarizer 25A, a laser beam having a unidirectional polarization component that can pass through the polarizer 25A is transmitted and emitted toward the beam splitter 25B.

  In the beam splitter 25B, the laser light is separated according to the above-described distribution ratio and emitted to the electro-optic material portion 16 side, and the others are emitted to the power monitor 18 side. The power monitor 18 receives a laser beam having a light quantity obtained by multiplying the light quantity of the laser light transmitted through the polarizer 25A by the distribution ratio separated to the power monitor 18 side by the beam splitter 25B.

Below, operation | movement of the power monitor 18 is demonstrated with reference to FIG.3 and FIG.4.
As shown in FIG. 4, in the power monitor 18, first, step S1 is performed as in the first embodiment, and the amount of laser light separated to the power monitor 18 side by the beam splitter 25B is measured. Step S1 is complete | finished now and it progresses to step S22.

  In step S22, the value indicating the light amount of the laser light measured in step S1 is compared with the above-described specified value obtained by multiplying the light amount of the emitted light from the laser light source 11 by the distribution ratio of the beam splitter 25B. If the value indicating the light amount of the laser beam measured in step S1 and the specified value are within the predetermined error range, step S22 is terminated. If the value indicating the light amount of the laser beam measured in step S1 and the specified value are out of the predetermined error range, step S22 ends and the drive signal is sent to the polarization controller 13 as in the first embodiment. Is transmitted (step S3). Further, the polarization controller 13 is driven by the power monitor 18 as in the first embodiment.

  In the present embodiment, the power monitor 18 matches the amount of laser light measured in step S1 with the value obtained by multiplying the amount of emitted light from the laser light source 11 by the distribution ratio of the beam splitter 25B (including substantially the same). Thus, the polarization controller 13 is driven. Then, the polarization direction of the laser light emitted from the polarization controller 13 matches the polarization direction that can be transmitted through the polarizer 25A.

  The measurement of the light amount of the laser beam by the power monitor 18 is continuously executed during the electric field measurement by the electromagnetic field measuring apparatus 2. For this reason, similarly to the electromagnetic field measuring apparatus 1 of the first embodiment, even if stress is applied to the optical fiber 12 from the outside and the polarization direction of the laser light changes, the amount of laser light incident on the electro-optic material unit 16 Can be kept constant. As a result, even if the polarization state of the laser light propagating through the optical fiber 12 changes due to the stress applied to the optical fiber 12, the electric field strength can be measured with high accuracy.

(Modification 1)
Below, the modification 1 of the electromagnetic field measuring apparatus 1 is demonstrated with reference to FIG. FIG. 5 is a schematic diagram showing the configuration of the electromagnetic field measurement apparatus according to this modification.
As shown in FIG. 5, this modification is different from the electromagnetic field measurement apparatus of the above-described embodiment in that an electro-optic modulator (EOM) 13 </ b> A is provided instead of the polarization controller 13.

  Although the detailed configuration of the electro-optic modulator 13A is not illustrated, for example, the electro-optic modulator 13A includes an electrode made of an electro-optic crystal and a power supply device that applies a voltage to the electrode. The polarization state is changed.

  Also in this modification, the polarization direction of the laser beam can be changed by the electro-optic modulator 13A based on the drive signal from the power monitor 18, and the electro-optic material is the same as the electromagnetic field measuring apparatus 1 of the first embodiment described above. The amount of laser light incident on the portion 16 can be kept constant.

(Third embodiment)
Subsequently, an electromagnetic field measuring apparatus 3 according to a third embodiment of the present invention will be described with reference to FIGS. FIG. 6 is a schematic diagram showing the configuration of the electromagnetic field measuring apparatus 3. FIG. 7 is an explanatory diagram for explaining the operation of the electromagnetic field measuring apparatus 3. FIG. 8 is a graph for explaining the operation of the electromagnetic field measuring apparatus 3. FIG. 9 is a flowchart for explaining the operation of the electromagnetic field measuring apparatus 3.
The electromagnetic field measurement apparatus 3 of the present embodiment is different in configuration from the electromagnetic field measurement apparatus 1 described in the first embodiment in that a probe head A3 provided in place of the probe head A is provided.

As shown in FIG. 6, the probe head A3 includes a ８ wavelength plate 35B instead of the beam splitter 25B between the polarizer 25A and the electro-optic material unit 16.
The electromagnetic field measuring apparatus 3 includes an optical fiber F33 that is branched from the optical fiber F4. The power monitor 18 is connected to the optical fiber F33, and the laser beam propagated through the optical fiber F33 is a power monitor. 18 is measured.
The 1/8 wavelength plate 35B is an optical component that converts linearly polarized light into elliptically polarized light. When the 1/8 wavelength plate 35B is transmitted twice, it becomes equivalent to a 1/4 wavelength plate and can convert linearly polarized light into circularly polarized light. it can.

  In the present embodiment, the polarizer 25A, the ８ wavelength plate 35B, the electro-optic material unit 16, and the reflecting mirror 17 are closely attached to each other and integrated.

  The optical fiber F33 transmits half of the laser light emitted from the terminal 14C of the optical circulator 14 to the power monitor 18 side by an optical coupler (not shown).

Below, the principle of operation of the electromagnetic field measuring apparatus 3 of this embodiment is demonstrated with reference to FIG.7 and FIG.8.
In FIG. 7, the code | symbol L has shown the advancing direction of the laser beam. The laser light emitted from the polarization controller 13 shown in FIG. 6 and incident on the polarizer 25A is linearly polarized light whose polarization direction has been changed by the polarization controller 13. When this laser light is incident on the polarizer 25A, as shown in FIG. 7, only light having a unidirectional polarization component that can be transmitted through the polarizer 25A is transmitted through the polarizer 25A and emitted toward the 1/8 wavelength plate 35B. Is done.

  The laser light emitted from the polarizer 25A passes through the 1/8 wavelength plate 35B and becomes elliptically polarized light. The elliptically polarized laser light is emitted from the ８ wavelength plate 35B and is incident on the electro-optic material portion 16. Then, as described in the above embodiments, the laser light is refracted according to the intensity of the electric field outside the electro-optical material unit 16 and reflected by the reflecting mirror 17 to reciprocate the electro-optical material unit 16. Thus, the electro-optic material part 16 is transmitted.

  In the present embodiment, the ellipticity of the elliptically polarized laser light changes according to the strength of the electric field because the refractive index of the electro-optic material of the electro-optic material portion 16 changes according to the electric field strength. For example, as schematically shown in FIG. 7, the ellipticity of the elliptically polarized light of the laser beam is the largest at the point P where the electric field strength is the highest, and the ellipticity of the elliptically polarized light of the laser light is the point R where the electric field strength is the lowest. Becomes the smallest.

  The laser beam that has passed through the electro-optic material portion 16 is emitted to the 1/8 wavelength plate 35B side. In the ８ wavelength plate 35B, when the electric field surrounding the electro-optic material unit 16 does not work on the electro-optic material unit 16, elliptically polarized light is converted into circularly polarized light as indicated by a symbol Q in FIG. At this time, as shown in FIG. 7, the laser light whose ellipticity has changed due to the influence of the electric field is not circularly polarized but becomes elliptically polarized light having an ellipticity corresponding to the intensity of the electric field.

  The laser light transmitted through the wavelength plate 35B is incident on the polarizer 25A, and only the laser light of the polarization component that can be transmitted through the polarizer 25A is emitted to the optical fiber F2. For this reason, the intensity of the laser light transmitted through the polarizer 25A and emitted to the optical fiber F2 side is modulated to a light amount corresponding to the ellipticity of elliptically polarized light.

  As shown in FIG. 7, when the laser light incident on the polarizer 25A is linearly polarized light in the same direction as the polarization direction by the polarizer 25A, and there is a modulation electric field, the polarizer 25A is directed to the optical fiber F2 side. The emitted light amount of the emitted laser light changes according to the electric field strength, but the time average of the light amount of the laser light emitted from the polarizer 25A is half of the incident light amount of the laser light incident on the polarizer 25A.

  In the present embodiment, the power monitor 18 is combined with the light amount change of the laser light modulated by the electro-optic material portion 16 by the electric field and the light amount change of the laser light due to the stress applied to the optical fiber 12. At this time, since the power monitor 18 averages and detects the light amount change due to the electric field having a high frequency, among the light amount changes detected by the power monitor 18, the light amount change depending on the modulation electric field is averaged. The change in the amount of light depending on the stress applied to 12 is measured.

  The power monitor 18 controls the polarization direction of the laser light emitted from the polarization controller 13 so that the light quantity measured by the power monitor 18 is half of the light quantity of the laser light emitted from the laser light source 11. The polarization direction of the laser light emitted from 13 is kept constant.

FIG. 8 is a graph showing the ratio (transmittance) of the laser light emitted from the polarizer 25A to the laser light incident on the polarizer 25A. In FIG. 8, the horizontal axis represents the applied voltage due to the modulated electric field detected by the electro-optic material unit 16, and the vertical axis represents the transmittance.
As shown in FIG. 8, in the present embodiment, the transmittance of the laser light in the absence of an electric field is 0.5, and the intensity of the electric field detected by the electro-optic material unit 16 is, for example, as shown in (Expression 1) below. When it fluctuates as shown, the transmittance of the laser light changes according to the relationship shown in the following (formula 2).

  Then, the transmittance of the laser light emitted from the polarizer 25 </ b> A varies according to the variation of the electric field strength as shown in the following (Equation 3) with 0.5 as the center when time is t.

In the present embodiment, in the electro-optic material portion 16, the light is intensity-modulated around the point where the applied voltage is V _π / 2, so that the slope of the laser light transmittance curve is maximized. ing. This is to increase the sensitivity of the electric field in the measurement system using the electromagnetic field measurement apparatus 3.

Below, the operation | movement at the time of use of the electromagnetic field measuring apparatus 3 of this embodiment of the above-mentioned operation principle is demonstrated.
As shown in FIG. 9, first, step S1 is performed as in the first embodiment. At this time, as described above, the power monitor 18 shown in FIG. 6 measures the light amount of the laser light that is affected by the stress applied to the optical fiber 12 and the electric field applied to the electro-optic material portion 16. If the light quantity of a laser beam is measured, step S1 will be complete | finished and it will progress to step S32.

  In step S32, the value indicating the light amount of the laser light measured in step S1 is compared with the light amount of the emitted light from the laser light source 11. If the amount of laser light measured in step S1 is half of the amount of emitted light from the laser light source 11, step S32 ends, and the adjustment of the polarization direction of the laser light ends. If the amount of laser light measured in step S1 is different from half of the amount of emitted light from the laser light source 11, step S32 ends and the process proceeds to step S3.

  In step S3, a drive signal is transmitted to the polarization controller 13 as described in the first embodiment. When the transmission of the drive signal ends, step S3 ends.

When a drive signal is transmitted from the power monitor 18 to the polarization controller 13, the polarization controller 13 is driven in the same manner as described in the first embodiment.
In the present embodiment, the polarization controller 13 is driven by the power monitor 18 so as to be half the light amount of the laser light measured in step S <b> 1 and the light amount of the emitted light from the laser light source 11. Then, the polarization direction of the laser light emitted from the polarization controller 13 matches the polarization direction that can be transmitted through the polarizer 25A. The operation of detecting the light amount of the laser beam by the power monitor 18 is continuously performed during the electric field measurement by the electromagnetic field measuring device 3.

  For this reason, similarly to the electromagnetic field measuring apparatus 1 of the first embodiment, even if stress is applied to the optical fiber 12 from the outside and the polarization direction of the laser light changes, the amount of laser light incident on the electro-optic material unit 16 Can be kept constant. As a result, even if the polarization state of the laser light propagating through the optical fiber 12 changes due to the stress applied to the optical fiber 12, the electric field strength can be measured with high accuracy.

(Modification 2)
Below, the modification 2 of the electromagnetic field measuring apparatus 3 of this embodiment is demonstrated with reference to FIG. FIG. 10 is a schematic diagram showing a configuration of an electromagnetic field measuring apparatus according to this modification.
As shown in FIG. 10, in this modification, instead of the polarization controller 13, the electro-optic modulator (EOM) 13 </ b> A described in Modification 1 of the first embodiment described above is provided. Even if it is such a structure, there can exist an effect similar to this embodiment.

(Fourth embodiment)
Hereinafter, an electromagnetic field measurement apparatus 4 according to a fourth embodiment of the present invention will be described with reference to FIGS. 11 (A) and 11 (B). FIG. 11A is a schematic diagram showing the configuration of the electromagnetic field measuring apparatus 4. FIG. 11B is a perspective view showing a part of the configuration of the electromagnetic field measuring apparatus 4.
As shown in FIGS. 11A and 11B, the electromagnetic field measurement apparatus 4 is configured so that the optical path of the laser light in the electro-optic material unit 16 is along the X-axis direction, the Y-axis direction, and the Z-axis direction. Three configured probe heads A3, B, and C are provided.

  In the present embodiment, an electro-optic material having sensitivity in a direction parallel to the light propagation direction is used for the electro-optic material portion 16. In the probe head A3 that detects the electric field component in the Z-axis direction, the electro-optic material portion 16 is formed as it is on the end face of the ８ wavelength plate 35B. The probe heads B and C for detecting the electric field component in the X-axis direction or the Y-axis direction have prisms 21A and 21B for bending the optical path at a right angle between the ８ wavelength plate 35B and the electro-optic material unit 16. Is provided.

  An optical switch 20 for selecting an optical path between the optical fiber F2 and each probe head is provided between each probe head and the optical fiber F2, and the optical path is selected by the optical switch 20. Then, the probe head on which the laser beam is incident is selected, the laser beam is transmitted to each probe head through the optical fiber F42, and the modulated signal from each probe head is measured through the optical fibers F42, F2, and F4. 19 can be led.

  Also in the present embodiment, similarly to the electromagnetic field measurement apparatus 3 of the third embodiment, the power monitor 18 measures the light amount of the laser light after the laser light is incident on the power monitor 18, and the measured light amount is the laser light source. The polarization controller 13 is operated so as to be half the light amount.

  Even in such a configuration, even if the polarization state of the laser light propagating through the optical fiber 12 changes due to the stress applied to the optical fiber 12 as in the electromagnetic field measuring apparatus described in the above embodiments, the electric field Can be measured with high accuracy.

  In this embodiment, when all of the probe head A3, the probe head B, and the probe head C are used, three electric field components can be measured. Further, different electric field components can be switched and measured by one probe head or a combination of two arbitrary probe heads.

As mentioned above, although embodiment of this invention was explained in full detail with reference to drawings, the concrete structure is not restricted to this embodiment, The design change etc. of the range which does not deviate from the summary of this invention are included.
For example, in each of the above-described embodiments and modifications, the electro-optic material portion 16 having an electro-optic material is used to measure an electric field, but the magneto-optic material portion having a magneto-optic material is used to measure a magnetic field. The electro-optic material portion 16 can be replaced. As a specific material of the magneto-optical material, for example, a bismuth-substituted yttrium iron garnet (Bi-YIG) single crystal can be adopted, and this single crystal is cut into a few hundred microns square to form a magneto-optical material portion. be able to.

  In the electromagnetic field measurement apparatus according to the fourth embodiment of the present invention, two types of prism heads A, B, and C are provided with prisms in order to detect three electric field components. For example, three types of electro-optic materials having sensitivity in the X-axis direction, the Y-axis direction, and the Z-axis direction are prepared, and each material is directly formed on the end face of the 1/8 wavelength plate 35B. A probe head can also be constructed.

  Further, the constituent elements shown in the above-described embodiments and modifications can be combined as appropriate.

  As an application example of the present invention, a probe device for immunity evaluation of an electronic circuit can be cited. In order to know the malfunction mechanism of an electronic device, it is necessary to accurately detect the electric / magnetic field distribution in the vicinity of the electronic circuit inside the device. By using the probe device of the present invention, it is possible to accurately measure an electric field or a magnetic field in the vicinity of an electronic circuit, so that knowledge for knowing the malfunctioning mechanism of the device can be obtained.

1, 2, 3, 4 Electromagnetic field measurement apparatus 11 Laser light source 12 Optical fiber 13 Polarization controller 14 Optical circulator 15 Polarization beam splitter 16 Electro-optic material part 17 Reflector 18 Power monitor 19 Electromagnetic field intensity measurement part

Claims (4)

A light source that emits laser light;
A polarization controller that converts the polarization of the laser light into linearly polarized light;
It has an electro-optic material or a magneto-optic material whose refractive index changes according to the strength of the electric field or magnetic field, and detects the strength of the electric field or the magnetic field by changing the polarization direction of the laser light transmitted through the polarization controller. An electromagnetic field detector;
The amount of the laser light transmitted through the polarization controller is measured, and a drive signal for changing the polarization direction of the laser light so that the amount of the laser light incident on the electro-optic material or the magneto-optic material is constant is polarized. A light intensity measurement control unit for transmitting to the controller;
An electromagnetic field intensity measurement unit that receives the laser light transmitted through the electromagnetic field detection unit and measures the intensity of the electric field or magnetic field;
An optical fiber for propagating the laser beam from the light source unit to the electromagnetic field intensity measurement unit;
An electromagnetic field measuring apparatus comprising: The electromagnetic field detection unit includes a first polarization component polarized in a first direction of the laser light that has passed through the polarization controller, and a second polarization component polarized in a direction orthogonal to the first polarization direction. A polarization beam splitter that separates either one toward the light quantity measurement control unit and separates the other of the first polarization component and the second polarization component toward the electro-optic material or the magneto-optic material;
The light amount measurement control unit transmits a drive signal to the polarization controller so that the light amount of the laser light emitted from the polarization beam splitter and incident on the light amount measurement control unit is minimized. The electromagnetic field measuring apparatus according to claim 1. The electromagnetic field detector is a polarizer that transmits a linearly polarized light component in a specific direction among the polarized light components of the laser light that has passed through the polarization controller;
A beam splitter that separates and emits the laser light transmitted through the polarizer toward the light quantity measurement control unit and the electro-optic material or the magneto-optic material;
The light amount measurement control unit distributes the light amount of the laser light incident on the light amount measurement control unit and the light amount of the laser light emitted from the light source unit to be separated to the light amount measurement control unit side in the beam splitter. The electromagnetic field measurement apparatus according to claim 1, wherein a drive signal is transmitted to the polarization controller so that a value obtained by multiplying the ratio substantially matches. An optical coupler that separates a part of the laser light transmitted through the electromagnetic field detection unit is provided in the optical path between the electromagnetic field detection unit and the electromagnetic field intensity measurement unit,
The light amount measurement control unit receives the laser light transmitted through the electromagnetic field detection unit through the optical coupler, and is emitted from the light amount of the laser light incident on the light amount measurement control unit and emitted from the light source unit. The drive signal is transmitted to the polarization controller so that the value obtained by multiplying the light amount of the laser light by the distribution ratio separated to the light amount measurement control unit side in the optical coupler is substantially the same. The electromagnetic field measurement apparatus according to claim 1.

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