JP4173794B2 - Electric field detection optical device - Google Patents

Description

  The present invention relates to an electric field detection optical apparatus for measuring an electric field by making a laser beam incident on an electro-optical element and using a change in polarization of the laser beam accompanying a change in birefringence of the electro-optical element in accordance with the change in the electric field. About.

  As a conventional electric field detection optical device, for example, there is an electric field detection optical device 110 using an FET (field effect transistor) probe 92 as shown in FIG. The FET probe 92 is used to measure an electrical signal existing in the signal line patterns 99 and 100 arranged on the circuit board 42 on which the circuit under test is configured. For example, in FIG. 9, a contact 93 for contacting the signal line pattern 99 at one point is provided at the tip of the FET probe 92.

  The contact 93 is brought into contact with the signal line pattern 99 at one point, and at the same time, the ground connector 97 drawn from the ground terminal 96 provided in the FET probe 99 is connected to the ground pattern 98. By connecting the ground connection terminal 97 to the ground pattern 98, it is possible to measure the electric potential difference value between the ground pattern 98 and the signal line pattern 99 facing each other.

  A signal line 94 and a ground line 95 are drawn from the FET probe 92 and connected to the FET input signal amplifier 91. The FET input signal amplifier 91 receives the signal from the signal line 94 with a high input impedance, and takes out an electric signal as a voltage with high accuracy. In order to realize this high input impedance, a high input impedance buffer circuit using an FET is provided. The signal amplified by the FET signal amplifier 91 is input to the waveform display device 90. The waveform display device 90 displays a signal waveform on a display device (not shown) according to the input signal.

In another electrical signal measuring device according to the prior art, a conductor as a contact is brought into contact with a signal line to be measured formed on a circuit under measurement at one point. The electric field of the signal line is coupled to the conductor in contact with the signal line, thereby changing the birefringence of the electro-optic material. Here, when laser light is incident on the electro-optic material, polarized light is generated due to a change in the birefringence, and this polarized light is detected by a polarization detector, and the waveform is displayed on a waveform display device.
JP-A-8-262117 (FIG. 4)

  In the above-described conventional electric field detection optical device, as shown in FIG. 9, it is necessary to contact the object to be measured with two points of the contact and the ground terminal, and there is no ground near the measurement point. In this case, it is difficult to measure in a wide band and the current is taken from the signal line, but the measured signal changes due to the disturbance of the measured circuit during measurement, especially in the measured circuit with low driving force. It was difficult to make accurate measurements.

  In addition, in an electric signal measuring apparatus as described in JP-A-8-262117, it is difficult to ensure sufficient sensitivity because the electro-optic material has a small area where the birefringence is changed according to the electric field. .

  The present invention has been made in view of the above, and an object of the present invention is to measure the potential of the electric field induced in the measurement object with low disturbance, high accuracy, wide bandwidth, and relatively compact and economical. An object of the present invention is to provide an electric field detection optical device capable of

In order to solve the problem, the present invention according to claim 1 is an electric field detection optical device for measuring an electric field of a measurement object, wherein the electric field detection optical device is in contact with the measurement object and is coupled to the electric field. A contact, a first electrode connected to the contact and made of a plane having a potential equal to the potential of the electric field, a second electrode made of a plane parallel to the first electrode, and the first electrode An electro-optic element that is in surface contact with each plane of the second electrode and exhibits a birefringence according to the potential of the first electrode, and is sandwiched between the first electrode and the second electrode A laser light source for generating the laser light for irradiating and transmitting the laser light to the electro-optical element, a polarization detecting means for detecting the polarization of the laser light transmitted through the electro-optical element, and the electro-optical element. The polarizing beam splitter and the upstream Wavelength plate, the light transmitted through the electro-optical element is separated into P polarized light and S-polarized light in another polarization beam splitter, along the back surface lead one to the rear surface of the substrate on which the electro-optical elements are arranged by the mirror The other one is advanced along the surface of the substrate on which the electro-optic element is installed, and the light amount of the laser light is adjusted based on data relating to the respective levels of the P-polarized light and the S-polarized light. And laser control means for performing feedback control for the purpose.

  According to a second aspect of the present invention, in the first aspect, the second electrode is connected to the ground.

  According to a third aspect of the present invention, in the first aspect, the second electrode is not connected anywhere.

  Moreover, the present invention according to claim 4 is provided with holding means by an elastic body in any one of claims 1 to 3 for holding the contact state between the contact and the measurement object in a movable state by elasticity. .

According to a fifth aspect of the present invention, in any one of the first to fourth aspects, the polarization maintaining optical fiber for transporting the laser light from the laser light source to the electro-optical element, P-polarized light, and S A separable optical connector is connected to each of the optical fibers for transporting the polarized laser light to the polarization detecting means.

  ADVANTAGE OF THE INVENTION According to this invention, the electric field detection optical apparatus which can measure the electric potential of the electric field induced to the measuring object with a low disturbance, high accuracy, wide band, comparatively compact and economical can be provided.

  FIG. 1 is a diagram showing a first embodiment of an electric field detection optical device according to the present invention. FIG. 1 shows a probe main part 1 which is provided in an electric field detection optical apparatus according to the present invention and which is applied to an electric field measurement probe (not shown) for detecting a potential in combination with the electric field of an object to be measured. . The probe main part 1 includes an electro-optic element 2 whose birefringence changes according to the electric field potential, a first electrode 3 that is in close contact with the electro-optic element 2 in a plane, and the first electrode 3. A second electrode 4 having a plane parallel to each other and in close contact with the electro-optic element 2, a signal line 14 connected to the first electrode 3, and a ground line 15 connected to the second electrode 4 , Fiber collimators 5, 11, 13, polarization beam splitters 6, 8, wave plate 7, upper mirror 9, lower mirror 10, direction mirror 12, incident optical fiber 16, S-wave optical fiber 17, A P-wave optical fiber 18 and a substrate 19 are provided. A laser beam 20 is incident, and a P-wave 21 and an S-wave 22 polarized by the laser beam 20 are output.

  A polarization maintaining fiber is used as the incident optical fiber 16. Even if a disturbance such as twisting of the fiber portion is applied to the polarization maintaining fiber, the laser beam 20 can be guided while maintaining the linearly polarized light. Therefore, even if the probe main part 1 is tilted at an arbitrary angle and measured. The conditions do not change.

  Further, the polarization refers to a light wave that vibrates only in a certain direction with respect to the laser beam 20, that is, P-polarized light (P wave) is a wave in which an electric field vibrates in the incident plane, and S-polarized light (S wave) is It is a wave that vibrates perpendicular to the incident surface.

  In the operation of the probe main part 1, first, the laser light 20 is emitted from the laser diode 39 shown in FIG. 4 through the incident optical fiber 16. This laser beam 20 enters the fiber collimator 5. The fiber collimator 5 is for making the light beam with good parallelism by transmitting the laser light 20. The laser beam 20 that has passed through the fiber collimator 5 enters the polarization beam splitter 6. The polarizing beam splitter 6 prevents the laser light having a disordered polarization which is slightly reflected and returned from the wave plate 7 or the electro-optical element 2 disposed in the next stage from being incident on the incident optical fiber 16 in reverse. Yes. Unnecessary polarized laser light that has entered the polarizing beam splitter 6 is bent in the lateral direction by the polarizing beam splitter 6, is irradiated outside the probe main part 1, and then disappears.

  The laser beam 20 that has passed through the polarization beam splitter 6 passes through the wave plate 7. For example, a quarter wave plate is used as the wave plate 7, and is combined with the polarization beam splitter 6 to form an optical isolator (one-way light element). The laser beam 20 emitted from the polarization beam splitter 6 is converted into circularly polarized light (for example, clockwise rotation) by a quarter wavelength plate, and is incident on the electro-optical element 2 at the next stage. Here, the laser light 20 slightly returns from the electro-optical element 2, and this laser light 20 is circularly polarized light that rotates counterclockwise. The reason why this circularly polarized light is counterclockwise is that the rotational direction of the circularly polarized light is the same and the traveling direction of the light is reversed. When the reflected laser beam 20 passes through the previous wave plate (for example, a quarter wave plate) 7, it returns to linearly polarized light, and the direction of the polarization plane at this time is changed by 90 ° from the forward path. As a result, the light is blocked by the polarization beam splitter 6 and finally the reflected light is prevented from returning to the incident fiber 16.

  The laser light 20 is incident on the electro-optical element 2, where the polarization changes according to the change in the birefringence of the electro-optical element 2. The change in the birefringence of the electro-optic element 2 occurs in response to the change in the potential of the first electrode 3. A signal line 14 is connected to the first electrode 3, and the potential of the first electrode 3 changes according to the change in the potential of the signal line 14. The change in the potential of the first electrode 3 becomes a potential difference relative to the potential of the second electrode 4, and the birefringence of the electro-optic element 2 changes according to this potential difference. A ground line 15 is connected to the second electrode 4, and the potential of the ground line 15 is used as a reference potential for the operation of the probe main part 1. As shown in FIG. 1, the electro-optic element 2 has a substantially rectangular cross section in the longitudinal direction, and the laser beam 20 is incident from the short side of the rectangle and is transmitted along the long side direction. Ejects from the short side. Since the laser light 20 is transmitted through the electro-optic element 2 in the longitudinal direction, a sufficiently long transmitted light path can be secured. For this reason, it is possible to obtain sufficient sensitivity for electric field potential detection.

  As shown in FIG. 2, the change in the potential of the first electrode 3 can be detected by the electro-optical element 2 even with the configuration in which the ground line 15 is omitted. In the case of this configuration, the birefringence of the electro-optic element 2 changes due to the potential difference between the second electrode 4 and the first electrode 3, and the polarization of the laser light 20 also changes accordingly.

  Further, as shown in FIG. 3, even if both the ground line 15 and the second electrode 4 are omitted, a change in the potential of the first electrode 3 can be detected by the electro-optical element 2. In this case, the birefringence of the electro-optic element 2 changes due to the potential difference between the electro-optic element 2 and the first electrode 3. In response to this change, the polarization of the laser light 20 changes.

In addition, the electro-optical element 2 is LT (LiTaO ³ ), LN (LiNbO ³ ), KTP (KTiOPO ₄ ), DAST (4-dimethylamino-N-) having sensitivity to an electric field in a direction orthogonal to the traveling direction of the laser light 20. methyl-4 stilbazolium tosylate), or AANP (2-adamantylamino-5-nitropyridine), (110) cut GaAs, (110) cut CdTe.

  Laser light 20 emitted from the electro-optical element 2 enters the polarization beam splitter 8. In this polarization beam splitter 8, the incident laser beam 20 is divided into a P wave 21 and an S wave 22. In the laser light 20 divided into the P wave 21 and the S wave 22, the P wave 21 enters the upper mirror 9, and the S wave 22 enters the direction mirror 12.

  The S wave 22 incident on the directional mirror 12 is changed in angle to a right angle, passes through the fiber collimator 13, enters the S wave optical fiber 17, and is led out of the probe main part 1. On the other hand, the P wave 21 incident on the upper mirror 9 is changed in angle to a right angle and incident on the lower mirror 10 disposed on the back surface of the substrate 19. The P wave 21 incident on the lower mirror 10 is changed in angle at a right angle, passes through the fiber collimator 11 disposed on the back surface of the substrate 19, enters the P wave optical fiber 18, and enters the probe main part 1. Derived outside.

  FIG. 4 shows a schematic configuration diagram of a signal processing unit 25 for receiving the P wave 21 and the S wave 22 derived from the probe main part 1 shown in FIG. ing. The P wave 21 enters the photodiode 30a through the P wave optical fiber 18. The S wave 22 is incident on the photodiode 30b through the S wave optical fiber 17. The P wave 21 and the S wave 22 are converted into electrical signals by the photodiodes 30a and 30b and output. The output electric signal is input to the differential amplifier 31. The differential amplifier 31 forms a differential input circuit using elements such as an OP amplifier (not shown), and the difference between the input levels of the P wave 21 and the S wave 22 is obtained by the differential amplifier 31 such as the OP amplifier. receive. This differential amplifier 31 cancels unnecessary noise components and the like to obtain necessary electric signals. Further, the electrical signal is filtered by the filter 34, unnecessary frequency components are removed, shaped, and input to the signal processing circuit 35.

  The signal processing circuit 35 performs signal processing for sending the input electrical signal to the waveform display device 36. As this signal processing, voltage amplification, current amplification, addition average output of voltage values, etc. are performed on the original electric signal, and it is set and selected as appropriate according to the configuration of the waveform display device 36, observation conditions of waveform observation, etc. Is done.

  Further, the signal processing circuit 35 is connected to a laser driver control circuit 37. The laser driver control circuit 37 controls a laser diode 39 that outputs the laser light 20 and a laser driver 38 that drives the laser diode 39. Data on the polarization levels of the P wave 21 and S wave 22 is output from the signal processing circuit 37, and the laser driver control circuit 37 controls the laser driver 38 based on the output polarization data. By this control, the light quantity of the laser beam 20 output from the laser diode 39 is adjusted (corrected), and feedback control for performing signal calibration is performed.

  Further, the balance of the differential amplifier 31 is adjusted so as to minimize noise from a differential balance monitor circuit (not shown) that monitors the differential balance by detecting the magnitude of noise from the output of the signal processing circuit 35. Output a control signal. By this control, feedback control for maintaining a good signal S / N is performed.

  FIG. 5 is a diagram showing a configuration of an electric field measurement probe 50 according to the second embodiment of the present invention. This electric field measurement probe 50 is used in an electric field detection optical device and constitutes a hand-held probe, and particularly shows the structure from the generation of the laser beam 20 to the waveform display in FIG. Input laser light 51 enters from the right hand side of the drawing, and this input laser light 51 passes through the polarizing beam splitter 56 and the wavelength plate 57 and enters the electro-optic element 55. The electrorefractive element 55 changes the birefringence according to the electric potential of the electric field contacted by the contact 53, and the polarization of the input laser light 51 changes.

  The input laser beam 51 exits from the electro-optic element 55 and is then separated into a P wave and an S wave (not shown) by the polarization beam splitter 58. The separated laser beam becomes the output laser beam 52, is refracted by the upper mirror 59, and travels toward the back surface (lower surface) of the substrate 54. A lower mirror 60 is disposed on the back surface of the substrate 54, and the output laser light 52 is refracted again by the lower mirror 60. The refracted output laser beam 52 passes through the fiber collimator 61 and is output to the outside of the electric field measurement probe 50. The electric field measurement probe 50 has an outer shape formed by a case 60, and for example, the electric field measurement probe 50 is downsized suitable for being held by hand when measuring an electric field.

  FIG. 6 is a schematic diagram for explaining the contact 53 arranged at the tip of the electric field measurement probe 50 shown in FIG. 5 and the connection between the contact 53 and the electro-optic element 2. The contact 53 is made of a conductive metal or the like, and has a tip formed at an acute angle so as to be able to contact the electric field measurement object at one point. The contact 53 is held by a holder 62. The holder 62 holds the contactor 53 so as to be movable in the left-right direction in the drawing with a predetermined stroke, and this holding is performed with elasticity. Since the contact 53 can move elastically, for example, when the electric field measurement object is a human body or the like, even if some movement or vibration occurs, the contact 53 does not move away from the measurement object, and good contact is maintained. It is. Since the holder 62 elastically holds the contactor 53, the above-described good contact can be achieved by appropriately pressing the contactor 53 against the electric field measurement object.

  The contact 53 is connected by a wire 54 so as to be electrically connected to the signal line 14. The wire 54 is a conductive metal wire, and has flexibility that can flexibly cope with the contact 53 even when it moves in the front-rear direction. The wire 54 is connected to the signal line 14, and the signal line 14 is further connected to the first electrode 3. The contact 53 comes into contact with the object to be measured and is coupled to the electric field, so that the potential becomes equipotential. The electric field potential propagates to the signal line 14 via the wire 54, and the electric potential of the first electrode 3 becomes equal to the electric field potential of the electric field measurement object.

  The potential of the first electrode 3 becomes equal to the potential of the electric field measurement object, and the potential of the second electrode 4 is not affected and does not change with respect to the potential. The birefringence of the electro-optic element 2 changes due to the potential difference between the first electrode 3 and the second electrode 4. Due to this change, the polarization of the laser light 20 transmitted through the electro-optical element 2 changes. The laser beam 20 is preferably transmitted in the vicinity of the first electrode 3 when passing through the electro-optic element 2.

  FIG. 7 is a block diagram showing an outline of the third embodiment according to the electric field detection optical apparatus of the present invention. The electric field detection optical device 60 has basically the same configuration as that of the first and second embodiments of the present invention already described. The electric field detection optical device 60 according to the third embodiment is characterized in that the electric field measurement probe 61 is provided with a ground wire 33.

  This ground line 33 is connected to the second electrode 4 described above, and is connected to the second electrode 4 by connecting to the ground line 15 referred to in FIG. . When measuring the electric field of the electric field measurement object using the electric field measurement probe 61, the contact 53 is brought into contact with the measurement point at one point, and the ground line 33 is connected to the ground portion of the measurement object. In this case, when the electric field measurement object is an electric circuit or the like, the contact 53 is brought into contact with the signal line of the circuit, and the ground line 33 is connected to the ground line of the circuit, thereby connecting the ground line to the reference potential. The electric field potential can be measured.

  Further, the polarization maintaining fiber 65 and the optical fibers 64 and 83 can be separated into the electric field measurement probe 61 side and the probe control unit 67 side by the optical connector 66. Since the probe control unit 67 can be sufficiently separated from the electric field measurement probe 61, the probe control unit 67 itself does not affect the measurement signal. Since separation by the optical connector 66 is possible, a polarization maintaining fiber or an optical fiber having an appropriate length can be used depending on the application and measurement environment.

  In order to perform such measurement, the probe control unit 67 outputs laser light from the laser diode (LD) 70c to the electric field measurement probe 61 via the polarization maintaining fiber 65, and the electric field measurement probe 61 outputs a polarization component. Are input to the photodiodes (PD) 70a and 70b through the optical fibers 83 and 64, respectively. The output of the laser beam and the input of the polarization component are controlled in a unified manner by the control circuit 68, and sufficient sensitivity and sufficient S / N ratio are ensured by feedback control. Finally, a measurement signal output 71 is output via the external output terminal 69 and input to a waveform display device (not shown) or the like, and the electric field measurement is completed.

  FIG. 8 is a configuration diagram for explaining an evaluation experiment for evaluating the performance of the electric field detection optical device of the present invention. In this evaluation experiment, a digital test signal of 10 MHz and 1 V is input to a signal line 79 of a standard 50Ω strip line that is generally used, and a contact of the electric field measurement probe 72 is brought into contact with the signal line 79. The S / N of the measured signal was evaluated. As a result, it was confirmed that the S / N ratio was improved by about 20 dB in the electric field measurement probe of the present invention as compared with the electric field measurement probe according to the prior art.

  The configuration of this evaluation experiment is that an electric field measurement probe 72 and a signal processing device 74 that controls the electric field measurement probe 72 and processes a signal are used, and the waveform display device 75 observes the waveform of the output of the signal processing device 74. evaluated. The evaluation board 77 was provided with a ground surface 82 on one side using a glass epoxy substrate or the like. Further, a signal line 79 is provided in a copper foil pattern on the surface of the evaluation board 77. This signal line 79 is terminated by a termination resistor 81, and a 50Ω resistor is used as the termination resistor 81. A test signal is input from one end of the signal line 79 from the signal source 76. As this test signal, a signal having a digital waveform of 10 MHz and 1 V was used.

The schematic block diagram for demonstrating the probe principal part by 1st Embodiment which concerns on the electric field detection optical apparatus of this invention is shown. The schematic block diagram for demonstrating the modification of the probe principal part by 1st Embodiment which concerns on the electric field detection optical apparatus of this invention is shown. The schematic block diagram for demonstrating the modification of the probe principal part by 1st Embodiment which concerns on the electric field detection optical apparatus of this invention is shown. The schematic block diagram for demonstrating the structure of the electric field detection optical apparatus combined with the electric field measurement probe by 1st Embodiment based on the electric field detection optical apparatus of this invention is shown. The schematic block diagram for demonstrating the structure of the electric field measurement probe by 2nd Embodiment based on the electric field detection optical apparatus of this invention is shown. The schematic block diagram for demonstrating the contactor by the 1st and 2nd embodiment which concerns on the electric field detection optical apparatus of this invention is shown. The schematic block diagram for demonstrating the structure of the electric field detection optical apparatus by 3rd Embodiment based on the electric field detection optical apparatus of this invention is shown. The block diagram for demonstrating the measurement test of the electric field detection optical apparatus of this invention is shown. The schematic block diagram of the electric field detection optical apparatus by a prior art is shown.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Probe main part 2 Electro-optic element 3 1st electrode 4 2nd electrode 5 Fiber collimator 6 Polarizing beam splitter 7 Wave plate 8 Polarizing beam splitter 9 Upper mirror 10 Lower mirror 11 Fiber collimator 12 Direction mirror 13 Fiber collimator 14 Signal line 15 ground line 16 incident optical fiber (polarization-maintaining fiber)
17 S-wave optical fiber (polarization-maintaining fiber)
18 P-wave optical fiber (polarization-maintaining fiber)
DESCRIPTION OF SYMBOLS 19 Substrate 20 Laser light 21 P wave 22 S wave 30a, 30b Photodiode 31 Differential amplifier 32 Differential balance monitor circuit 33 Ground line 34 Filter 35 Signal processing circuit 37 Laser driver control circuit 38 Laser driver 39 Laser diode 53 Contact 62 holder

Claims (5)

An electric field detection optical device for measuring an electric field of a measurement object,
A contact for contacting the measurement object and coupling with the electric field;
A first electrode connected to the contact and comprising a plane having a potential equal to the potential of the electric field;
A second electrode comprising a plane parallel to the first electrode;
An electro-optic element that is in surface contact with the respective planes of the first electrode and the second electrode and exhibits a birefringence according to the potential of the first electrode;
A laser light source that generates the laser light for irradiating and transmitting the laser light to the electro-optic element sandwiched between the first electrode and the second electrode;
Polarization detection means for detecting the polarization of the laser light transmitted through the electro-optic element;
A polarizing beam splitter and a wave plate disposed in front of the electro-optic element;
The light transmitted through the electro-optical element is separated into P-polarized light and S-polarized light by another polarization beam splitter, and one is guided to the back surface of the substrate on which the electro-optical element is disposed by a mirror and travels along the back surface. The other one travels along the surface of the substrate on which the electro-optic element is installed, and feedback for adjusting the amount of the laser light based on the data regarding the respective levels of the P-polarized light and the S-polarized light Laser control means for controlling,
An electric field detection optical device comprising:   2. The electric field detection optical device according to claim 1, wherein the second electrode is connected to a ground.   2. The electric field detection optical device according to claim 1, wherein the second electrode is not connected anywhere.   The electric field detection optical apparatus according to any one of claims 1 to 3, further comprising holding means by an elastic body for holding the contact state between the contact and the measurement object in a movable state by elasticity. Each of the optical fiber for transporting the polarization-maintaining optical fiber for transporting the laser beam from the laser light source to the electro-optical element, the laser beam of P polarized light and S polarized light to the polarization detection means, separation 5. An electric field detecting optical device according to claim 1, wherein a possible optical connector is connected.

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