Optical Voltage Probe

Abstract

To provide an optical voltage probe that enables measurement of a wide range of voltage signals even when only one completed optical voltage probe is used.SOLUTION: A voltage probe head comprises: an optical modulator 1 which includes two modulation electrodes 11, 12, intensity-modulates incident light depending on an applied voltage, and outputs the intensity-modulated incident light; an input / output optical fiber 2 connected to the optical modulator 1; two contact terminal attached portions 5, 6 detachably attached with two contact terminals 3, 4 contactable with points to be measured; signal lines for leading voltage signals generated between the contact terminals 3 and 4 to the modulation electrodes 11, 12; and a package 8. The voltage probe head converts voltage signals into optical intensity modulated signals and output the signals from the input / output optical fiber 2. The voltage probe head is provided with a trimmer capacitor 33 inserted in series with the signal lines and accommodated in the package 8 and adjustment means for adjusting capacitor of the trimmer capacitor from outside the package 8, thereby, amplitude of the voltage signal to be applied can be adjusted by the adjustment means.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an optical voltage probe that applies a voltage signal obtained from a contact terminal to an optical modulator to convert it into an optically modulated signal, and outputs the optically modulated signal through an optical fiber. [Background technology]

[0002] In recent years, various control devices using high-speed CPUs and other devices have been developed, and in order to prevent malfunctions, detection of noise signals generated on the electric circuit boards and other devices, and noise resistance tests of the electric circuit boards, etc. are being carried out. These tests require accurate measurement of input / output signals of electric components installed on the electric circuit boards and electric signals transmitted on the wiring.

[0003] A common method for measuring electrical signals from electrical components or wiring is to use an electrical probe with contact terminals to conduct the electrical signal at the point under test to a measuring instrument such as an oscilloscope, and then measure the transmitted voltage waveform, etc. However, when the ground level of the point under test is different from that of the measuring instrument, or when measuring a voltage signal between two ungrounded points, accurate measurement of the voltage waveform can be difficult due to signal interference from the earth and the influence of the capacitance of the electrical probe. The influence of the above-mentioned ground and capacitance is particularly significant in the high frequency range. Furthermore, many integrated circuits such as ICs and LSIs have input and output impedances that are not 50 Ω, for example, amplifier elements have high input and low output impedance. Therefore, if an electric probe with low input impedance is used to measure the noise input voltage, current will flow into the electric probe, resulting in a probing loading effect that reduces the noise voltage that should be measured.

[0004] To solve this problem, a measuring instrument has been developed that uses an optical voltage probe, which converts the voltage signal into an optical signal and transmits that optical signal to the measuring instrument via an optical fiber. With this method, the capacitance of the probe is very small, so the input impedance is very high, and the point under test and the measuring instrument are completely electrically isolated. The optical voltage probe can measure even high frequency components and can prevent the effects of the ground and the introduction of electrical signal noise along the way.

[0005] Examples of such conventional optical voltage probes are described in Patent Documents 1 and 2. These optical voltage probes use a waveguide-type optical modulator, and an optical intensity modulated signal is obtained by applying a voltage signal from a contact terminal between two modulation electrodes of an interferometric optical modulator formed on a lithium niobate crystal substrate. The optical voltage probe is connected to a device equipped with a light source and an O / E converter via an optical fiber. The optical voltage probe in Patent Document 1 uses a package that has a radio wave shielding effect, enabling accurate measurement of the voltage signal at the measurement point without being affected by ambient electromagnetic noise, while the optical voltage probe in Patent Document 2 makes it possible to reduce the risk of damage due to unexpected voltage input. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 6813763 [Patent Document 2] Japanese Patent Publication No. 2020-8537 Summary of the Invention [Problem to be solved by the invention]

[0007] In the above-mentioned probe, which converts a voltage signal into an optical signal using a waveguide-type optical modulator and measures it, it is possible to design an optimal modulation electrode depending on the magnitude of the voltage signal to be measured. This design allows for the realization of an optical voltage probe that can accommodate a wide range of voltage signals to be measured. However, if the optical modulator used in the optical voltage probe head is fixed, the modulation depth of the optical intensity modulation signal relative to the amplitude of the applied voltage is determined, limiting the range of detectable voltage signal magnitude. The optical voltage probe described in Patent Document 2 incorporates a capacitor in series with the modulation electrode, enabling it to accommodate voltage signals larger than those determined solely by the modulation electrode. However, the measurement voltage range is still limited to a certain range. In other words, conventional optical voltage probes have the problem of being unable to measure a wide range of voltage signals using a single completed optical voltage probe.

[0008] An object of the present invention is to solve the above problems and provide an optical voltage probe that enables measurement of a wide range of voltage signals using only one completed optical voltage probe. [Means for solving the problem]

[0009] In order to solve the above problems, in a first aspect, an optical voltage probe according to the present invention comprises an optical modulator having at least two modulation electrodes, which outputs an intensity-modulated incident light depending on a voltage between the two modulation electrodes, an input optical fiber and an output optical fiber connected to the optical modulator, two contact terminals connected to the modulation electrodes and capable of coming into contact with a point to be measured on an electric circuit or an electric wiring, or two contact terminal attachment parts configured to be detachable by bringing the contact terminals into contact with the point to be measured on the electric circuit or the electric wiring, and a signal line that guides a voltage signal generated between contact terminals to the modulation electrode; and a package that houses the optical modulator and a portion of the input optical fiber and the output optical fiber, the voltage signal being converted by the optical modulator into an optical intensity modulated signal and output from the output optical fiber; the voltage probe head further comprises a capacitor that is inserted in series into one of the signal lines and housed within the package; and adjustment means that adjusts the capacitance of the capacitor from outside the package, so that the amplitude of the voltage signal applied to the modulation electrode can be adjusted by the adjustment means.

[0010] As described above, the optical voltage probe of the present invention includes a capacitor inserted in series in one of the signal lines that conducts the voltage signal between the two contact terminals to the modulation electrode of the optical modulator. The package also includes an adjustment means for adjusting the capacitance of this capacitor from outside the package. Due to the presence of the capacitor inserted in series with the modulation electrode, the amplitude of the voltage signal detected at the contact terminal is reduced by a predetermined ratio that depends on the capacitance of the capacitor and the capacitance of the modulation electrode before being applied to the modulation electrode. Therefore, in the present invention, by making the capacitance adjustable externally, the voltage signal between the contact terminals can be reduced to any desired magnitude before being applied to the modulation electrode. This enables a much wider range of voltage signals to be measured using just one completed optical voltage probe than conventional methods.

[0011] One method for adjusting the capacitance of a capacitor from outside the package is to use a capacitor whose capacitance can be changed by rotating a rotating shaft, such as a commercially available variable capacitor or trimmer capacitor, and to provide a hole in the package so that the rotating shaft can be adjusted from the outside. Another method is to connect capacitors of different capacitances in parallel to one side of the modulation electrode, and then select the output side of the capacitor from the outside and connect it to the signal line.

[0012] In an optical voltage probe, measurements are made by bringing a contact terminal into contact with a measurement point on a circuit board or the like. The contact terminal may be provided integrally with the optical voltage probe, or the optical voltage probe may be provided with a contact terminal attachment section so that the contact terminal can be selected according to the purpose.

[0013] In a second aspect, the present invention is characterized in that, in the optical voltage probe of the first aspect, the minimum value of the capacitance of the capacitor is less than twice the capacitance between the two modulation electrodes, and the amplitude of the voltage signal applied to the modulation electrode when the capacitance of the capacitor is at its minimum value is 2 / 3 or less of the amplitude of the voltage signal applied to the modulation electrode when the capacitance of the capacitor is at its maximum value.

[0014] In the present invention, when the capacitance of the capacitor inserted in series is twice the capacitance between the modulation electrodes, the ratio of the capacitance of the capacitor inserted in series to the capacitance between the modulation electrodes is 2:1. Therefore, the amplitude of the voltage signal applied to the modulation electrode is 2 / 3 of the amplitude at the contact terminal, and the amplitude of the voltage signal detectable at the contact terminal is 1.5 times larger. On the other hand, when the capacitance of the capacitor inserted in series is adjusted to be sufficiently larger than the capacitance between the modulation electrodes, the amplitude of the voltage signal applied to the modulation electrode becomes approximately equal to the amplitude at the contact terminal. Therefore, by adjusting the capacitance of the capacitor in this way, the dynamic range of the detectable voltage signal becomes 1.5 times larger than when there is no capacitor or when the capacitor's capacitance is fixed. A dynamic range of 1.5 times or more larger than conventional methods would greatly expand the applicability of optical voltage probes. Furthermore, when the minimum capacitance of the capacitor is equal to, 1 / 2, or 1 / 3 of the capacitance between the modulation electrodes, the amplitude of the voltage signal applied to the modulation electrode will be 1 / 2, 1 / 3, or 1 / 4 of the amplitude at the contact terminal, respectively. Therefore, the amplitude of the voltage signal detectable at the contact terminal will be even larger, and the dynamic range of the detectable voltage signal will be even larger.

[0015] In a third aspect, the present invention provides the optical voltage probe of the first or second aspect, wherein the capacitor is a variable capacitor incorporated in a housing having a rotating shaft and whose capacitance can be adjusted by rotating the rotating shaft, and the package has a hole for inserting a tool for rotating the rotating shaft from the outside. The invention of this aspect changes the capacitance of a capacitor by inserting a screwdriver or the like through a hole provided in the package and rotating the rotating shaft of a general variable capacitor, trimmer capacitor, or the like.

[0016] In a fourth aspect, the present invention provides an optical voltage probe according to the third aspect, further comprising a means for sealing the hole after the adjustment. Leaving the hole open in the package can cause a deterioration in the shielding effect if the package has an electromagnetic wave shielding effect. Therefore, the deterioration of the shielding effect can be prevented by inserting a shielding material into the hole or by covering the hole with a shielding material. Furthermore, sealing the hole can prevent dust and other particles from entering the package.

[0017] In a fifth aspect, the present invention provides the optical voltage probe of the first or second aspect, characterized in that the capacitor comprises a plurality of capacitors connected in parallel to one side of the modulation electrode, and connection means for selecting at least one of the plurality of capacitors and connecting it in series to the signal line. The invention of this aspect includes, for example, a switch or the like for connecting one terminal of a plurality of capacitors having different capacitances in parallel to one side of the modulation electrode, selecting one of the capacitors and connecting the other terminal to the signal line led from the contact terminal or the contact terminal attachment part, and making the switch operable from outside the package, thereby making it possible to adjust the capacitance of the capacitor inserted in series with the signal line.

[0018] In a sixth aspect, the present invention provides the optical voltage probe of the first or second aspect, further comprising: a plurality of capacitors having different capacitances connected in parallel to one of the modulation electrodes; a plurality of contact terminal mounting parts connected in series to the plurality of capacitors, each of which has a contact terminal that can be brought into contact with a point to be measured on an electric circuit or electric wiring, and a single contact terminal mounting part connected to the other of the modulation electrodes, each of which has a contact terminal that can be brought into contact with a point to be measured on the electric circuit or electric wiring, and which is configured to be attached or detached. The invention of this aspect includes a plurality of contact terminal mounting parts, each of which has a signal line to which capacitors having different capacitances are connected in series, and by selecting a contact terminal mounting part, the capacitance of the capacitor to be inserted in series in the signal line leading from the contact terminal can be selected and adjusted.

[0019] In a seventh aspect, the present invention provides the optical voltage probes of any one of the first to sixth aspects, characterized in that the package has a radio wave shielding effect such that the intensity of the optical intensity modulated signal output when the contact terminal or the contact terminal mounting portion is open and radio waves of a measurement frequency are irradiated is attenuated by 15 dB or more compared to the intensity of the optical intensity modulated signal output in the absence of the package. By covering the optical modulator with a package that has a radio wave shielding effect, it is possible to prevent electromagnetic noise around the measurement location from being received by the modulation electrode of the optical modulator or wiring such as a signal line on the way to the modulation electrode. The inventors have confirmed through experiments that, in an optical voltage probe, a package that has a radio wave shielding effect that attenuates by 15 dB or more the electromagnetic noise signal received in the absence of the package when nothing is connected to the contact terminal can achieve the intended sufficient performance in practice.

[0020] While metal is a typical package material for achieving radio wave shielding, other conductive materials such as carbon are also acceptable, and the package may also be made of a radio wave absorber. The package can be of any shape as long as it can house and cover the optical modulator and the wiring from the contact terminal to the modulation electrode. In optical voltage probes, the contact terminals should be as short as possible to prevent electromagnetic noise from being received from the contact terminals during measurement. Furthermore, if a contact terminal mounting portion is provided, it is desirable for it to be located inside the package surface. If this portion protrudes beyond the package, the overall length of the protruding portion will increase when the contact terminal is connected, and it may act as an antenna for electromagnetic noise.

[0021] In an eighth aspect, the present invention provides the optical voltage probes of any one of the first to seventh aspects, characterized in that the optical modulator is an interferometric optical modulator using an optical waveguide formed on a lithium niobate crystal substrate. The invention of this aspect employs a conventional interferometric optical modulator using an optical waveguide formed on a lithium niobate crystal as the optical modulator. The basic configuration of an interferometric optical modulator is an input optical waveguide extending from the light input side, two phase-shifting waveguides branching from the input optical waveguide, an output optical waveguide where the two phase-shifting waveguides join and connect to the light output side, and a modulation electrode arranged parallel to the phase-shifting waveguide. A voltage signal is applied to the phase-shifting waveguide via the modulation electrode to change the refractive index of the phase-shifting waveguide, and the light passing through the two phase-shifting waveguides joins and interferes, modulating the light intensity. Since a compact, highly efficient, and wide-band optical modulator can be obtained, it is suitable for the optical voltage probe of the present invention.

[0022] In a ninth aspect, the present invention provides the optical voltage probe of the eighth aspect, characterized in that the optical modulator is a reflective optical modulator that internally reflects and returns incident light, and the input optical fiber and output optical fiber are composed of a single input / output optical fiber. The reflective optical modulator of this aspect of the invention uses a configuration in which incident light is reflected in a phase shift waveguide and returned to the incident-side optical waveguide. By using such a reflective optical modulator configuration, light transmits twice as far as a transmissive optical modulator for the same electrode length, making it possible to increase the efficiency and broaden the bandwidth of the optical modulator, and to make it more compact. Furthermore, since only a single optical fiber is connected to the optical modulator, it is easy to handle.

[0023] In a tenth aspect, the present invention provides the optical-voltage probe of the eighth or ninth aspect, characterized in that at least one electrode is provided between the two modulation electrodes and is capacitively coupled to the two modulation electrodes. The invention of this aspect uses a so-called segmented electrode, consisting of multiple electrodes that are longitudinally segmented and capacitively coupled to each other, as the modulation electrode. Generally, increasing the length of the modulation electrode along the optical waveguide increases the modulation efficiency and the detection voltage sensitivity of the optical-voltage probe. However, increasing the length of the modulation electrode increases the capacitance. If the electrode capacitance is large, the equivalent impedance decreases as the frequency of the electrical signal increases, and the voltage applied to the electrode decreases, resulting in a decrease in modulation efficiency. Therefore, for high-frequency signal detection, it is desirable to keep the electrode capacitance as small as possible. A significant means of improving the trade-off between modulation electrode length and capacitance is to use a segmented electrode, in which a single modulation electrode is divided into multiple capacitively coupled electrodes. Using this segmented electrode makes it possible to obtain a high-efficiency, wide-band optical modulator. [Effects of the Invention]

[0024] As described above, the present invention provides an optical voltage probe that allows measurement of a wide range of voltage signals using only one completed optical voltage probe. [Brief explanation of the drawings]

[0025] [Figure 1] 1(a) and 1(b) are schematic diagrams illustrating the configuration of an optical voltage probe according to Example 1, in which FIG. 1(a) is a plan view of a transmission type, FIG. 1(b) is a side view of the transmission type, and FIG. 1(c) is a partially enlarged cross-sectional view of a contact terminal attachment portion. [Figure 2] FIG. 1 is a block diagram of a measurement system using an optical voltage probe according to a first embodiment. [Figure 3] 3A and 3B are diagrams illustrating an example of the configuration of a reflective optical modulator built into the optical voltage probe of Example 1, where FIG. 3A is a plan view and FIG. 3B is an AA cross-sectional view. [Figure 4]4(a) and 4(d) are schematic diagrams illustrating the configuration of an optical voltage probe according to a second embodiment, in which FIG. 4(a) is a plan view of a transmission type, FIG. 4(b) is a partially enlarged plan view showing the configuration of a signal line portion provided with a plurality of capacitors, FIG. 4(c) is a side view of the transmission type, and FIG. 4(d) is a partially enlarged cross-sectional view of a capacitor selection structure. [Figure 5] 5(a) and 5(b) are schematic diagrams illustrating the configuration of an optical voltage probe according to Example 3, in which FIG. 5(a) is a plan view of a transmission type, FIG. 5(b) is a partially enlarged plan view showing the configuration of multiple capacitor electrodes arranged on an optical modulator, and FIG. 5(c) is a side view of the transmission type. DETAILED DESCRIPTION OF THE INVENTION

[0026] The optical voltage probe of the present invention will be described in detail below by way of examples with reference to the drawings. In the description of the drawings, the same elements are given the same reference numerals and redundant description will be omitted. [Example]

[0027] FIG. 1 is a schematic diagram showing the configuration of an optical voltage probe according to Example 1, where FIG. 1(a) is a plan view of a transmission type, FIG. 1(b) is a side view of the transmission type, and FIG. 1(c) is an enlarged partial cross-sectional view of a contact terminal attachment portion.

[0028] 1, the optical voltage probe 10 of this embodiment includes two modulation electrodes 11 and 12, an optical modulator 1 that outputs the intensity-modulated incident light depending on the voltage between the modulation electrodes 11 and 12, and an input optical fiber and an output optical fiber connected to the optical modulator 1. Furthermore, the optical voltage probe 10 includes contact terminal mounting portions 5 and 6 that are configured to be connectable to two contact terminals 3 and 4, respectively, which are configured to be able to come into contact with points to be measured on an electric circuit or electric wiring, and signal lines that guide the voltage signals generated between the contact terminals by bringing the contact terminals 3 and 4 into contact with the points to be measured to the modulation electrodes 11 and 12, respectively.

[0029] In this embodiment, the optical modulator 1 is a reflective optical modulator that internally reflects and returns incident light, and the input optical fiber to the optical modulator 1 and the output optical fiber from the optical modulator 1 are composed of a single input / output optical fiber 2. The tip of the input / output optical fiber 2 is inserted into and fixed in a ferrule 7 in order to adhesively fix the input and output end faces of the optical modulator 1 to each other. The optical modulator 1 is also fixed to a base 9 fixed to a package 8, and the optical modulator 1 and a portion of the input / output optical fiber 2 are housed in the rectangular parallelepiped package 8 made of metal.

[0030] A connection board 30 is fixed adjacent to the optical modulator 1 within the package 8. A connection line portion 31 is provided on the connection board 30 as part of the signal line from the contact terminal 3 to the modulation electrode 11, and a connection line portion 32 is provided as part of the signal line from the contact terminal 4 to the modulation electrode 12. A trimmer capacitor 33 is connected in series to the connection line portion 31 between the modulation electrode 11 and the contact terminal mounting portion 5. The trimmer capacitor 33 is incorporated in a housing having a rotating shaft, and its capacitance can be adjusted by rotating the rotating shaft. A screwdriver is inserted through a hole 34 provided in the top of the package 8 to rotate the minus groove on the top of the trimmer capacitor 33. The connection line portion 32 is an electrode pad connecting the modulation electrode 12 to the contact terminal mounting portion 6. Lead wires connect the modulation electrodes 11 and 12 to the connection line portions 31 and 32, and the connection line portions 31 and 32 to the contact terminal mounting portions 5 and 6, respectively. In addition, in this embodiment, a cover 35 made of metal or conductive material is provided to close the hole 34 in order to prevent deterioration of the shielding effect.

[0031] As shown in FIG. 1(c), the contact terminal mounting portions 5 and 6 each consist of a cylindrical insulator 14 and a cylindrical metal terminal insertion portion 15 housed and fixed inside the insulator. During measurement, the contact terminal 3 is inserted into the terminal insertion portion 15 of the contact terminal mounting portion 5, and the contact terminal 4 is inserted into the terminal insertion portion 15 of the contact terminal mounting portion 6. A lead wire 16 for connection to the connection line portion 31 or 32 is attached to the terminal insertion portion 15, and the insulator 14 is fixed to the package 8. In this embodiment, the contact terminal mounting portions 5 and 6 are located inside the surface of the package 8. The center-to-center distance between the two contact terminal mounting portions 5 and 6 is approximately 5 mm. When the two contact terminals 3 and 4 are attached, the distance P between them is also approximately 5 mm. By spacing the contact terminals 3 and 4 apart by 3 mm or more, a high input impedance is obtained.

[0032] Next, a measurement system using the optical voltage probe 10 of this embodiment will be described. Figure 2 is a block diagram of a measurement system using an optical voltage probe according to Example 1. As shown in Figure 2, incident light 17 is sent to optical voltage probe 10 from optical transmitting / receiving unit 21 through input / output optical fiber 2, and optical intensity modulated signal 18 output from optical modulator 1 is input to transmitting / receiving unit 21 through the same input / output optical fiber 2. The optical transmitting / receiving unit 21 includes a light source 22 such as a semiconductor laser, an O / E converter 23, a transceiver separator 24 for separating the incident light 17 and the optical intensity modulated signal 18, and an amplifier 25. The light emitted from the light source 22 is coupled to the input / output optical fiber 2 through the transceiver separator 24, and the optical intensity modulated signal 18 returning from the input / output optical fiber 2 is input to the O / E converter 23 through the transceiver separator 24. In the O / E converter 23, the optical intensity modulated signal 18 is converted into an electrical signal, amplified by the amplifier 25, and output to an output terminal 26. The electrical signal is input to an input terminal 28 of a measuring instrument 27 such as an oscilloscope. The transceiver separator 24 can be configured using an optical circulator, an optical fiber branch, or a semi-transparent mirror.

[0033] 2 shows a case where a voltage signal applied between two terminals of an electrical component 19 mounted on an electrical circuit board 29 is to be measured as the point under test. Contact terminals 3 and 4 of optical voltage probe 10 are brought into contact with the two terminals of electrical component 19 to be measured.

[0034] As described above, the voltage signal input through the contact terminals 3 and 4 is reduced at a predetermined rate depending on the capacitance of the trimmer capacitor 33 and the capacitance between the modulation electrodes 11 and 12, and is then guided to the modulation electrodes 11 and 12, and this voltage signal is converted into an optical intensity modulated signal 18 by the optical modulator 1. The optical intensity modulated signal 18 is converted into an electrical signal in the optical transmitting / receiving unit 21. By observing the voltage waveform with the measuring instrument 27, the waveform of the voltage signal applied between the two terminals of the electrical component 19 can be determined.

[0035] 3A and 3B are diagrams showing an example of the configuration of a reflective optical modulator 1 built into the optical voltage probe 10 of this embodiment, where FIG. 3A is a plan view and FIG. 3B is a cross-sectional view taken along line AA.

[0036] 3, the optical modulator 1 is composed of a substrate 41 cut by X-cutting from lithium niobate (LiNbO3) crystal, which is a crystal having an electro-optic effect, a branching interference type optical waveguide 42 formed by Ti diffusion on the upper surface side of the substrate 41, a buffer layer 43 formed on the upper surface side of the substrate 41, a modulating electrode section 44 including modulating electrodes 11 and 12 formed on the buffer layer 43, and a light reflecting section 45 installed at one end of the substrate 41. The modulating electrode section 44 is a two-layer film of chromium (Cr) and gold (Au) formed by sputtering or the like.

[0037] The branching interference type optical waveguide 42 is composed of one input / output optical waveguide 42a extending on the input light incident side, and two phase-shifting waveguides 42b and 42c branching off from the input / output optical waveguide 42a. The input / output optical waveguide 42a and the phase-shifting optical waveguides 42b and 42c all have the same width W in the direction perpendicular to their extension direction. The phase-shifting optical waveguides 42b and 42c also have approximately the same length in their extension direction.

[0038] The width W of these optical waveguides is in the range of 5 to 12 μm. The length of the phase-shift optical waveguides 42b and 42c in the extension direction is in the range of 10 to 30 mm. The phase-shift optical waveguides 42b and 42c extend parallel to each other with a predetermined gap between their central portions in the width direction. The gap between the phase-shift optical waveguides 42b and 42c in the central portions is in the range of 15 to 50 μm. There are no particular limitations on the width W of the input / output optical waveguide 42a and the phase-shift optical waveguides 42b and 42c, the lengths of the phase-shift optical waveguides 42b and 42c, and the gap between the phase-shift optical waveguides 42b and 42c, and these dimensions can be set arbitrarily.

[0039] The buffer layer 43 is provided for the purpose of preventing a portion of the light propagating through the optical waveguide 42 from being absorbed by the modulation electrode portion 44. The buffer layer 43 is mainly made of a silicon dioxide (SiO2) film or the like, and has a thickness of about 0.1 to 1.0 μm.

[0040] In the optical modulator 1, the modulating electrode section 44 is composed of a divided electrode consisting of three electrodes 46, 47, and 48 that are divided in the longitudinal direction of the branching interference type optical waveguide 42 and are capacitively coupled to each other. The electrode 46 is a part of the modulating electrode 11, and the electrode 48 is a part of the modulating electrode 12. The electrode 46, which is a part of the modulating electrode 11 on the signal input side, has an electrode section 46a arranged between the phase-shift optical waveguides 42b and 42c. The electrode 47 has electrode sections 47b arranged on both sides of the electrode section 46a with the phase-shift optical waveguides 42b and 42c sandwiched between them, and an electrode section 47a arranged between the phase-shift optical waveguides 42b and 42c. The electrode 48, which is a part of the modulating electrode 12, has electrode sections 48b arranged on both sides of the electrode section 47a with the phase-shift optical waveguides 42b and 42c sandwiched between them. Between the modulation electrodes 11 and 12, the electrodes 46 and 47, and the electrodes 47 and 48 are arranged in series and are capacitively coupled to each other.

[0041] The input / output end face of the input / output optical fiber 2 is coupled to the optical input / output end of the input / output optical waveguide 42a of the substrate 41. The optical reflector 45 reflects light that enters the input / output optical waveguide 42a and propagates through the phase-shift optical waveguides 42b and 42c, and then propagates it back to the input / output optical waveguide 42a from the phase-shift optical waveguides 42b and 42c. When a voltage is applied between the modulation electrodes 11 and 12, electric fields are applied in opposite directions to the two phase-shift optical waveguides 42b and 42c between the electrode portions 46a and 47b and between the electrode portions 47a and 48b. This causes refractive index changes in opposite directions in the phase-shift optical waveguides 42b and 42c, resulting in phase shifts of opposite polarities in the light passing through them. When these light beams merge, they interfere with each other, resulting in a change in intensity. This produces an optical intensity-modulated signal whose optical intensity changes in response to the voltage applied between the modulation electrodes 11 and 12.

[0042] As an example of a specific design value for this embodiment, the capacitance between modulation electrodes 11 and 12 can be set to about 2 pF. In this case, if the capacitance of trimmer capacitor 33 is adjustable between 0.5 and 4 pF, the voltage signal between contact terminals 3 and 4 will be reduced by about 1 / 5 to 2 / 3 through adjustment before being applied between modulation electrodes 11 and 12. Therefore, the dynamic range of voltage signals that can be detected by the optical voltage probe will be more than three times that in the absence of trimmer capacitor 33, making it possible to measure a wide range of voltage signals. [Example]

[0043] Figure 4 is a schematic diagram showing the configuration of an optical-voltage probe according to Example 2, with Figure 4(a) being a plan view of a transmission type, Figure 4(b) being a partially enlarged plan view showing the configuration of a signal line section equipped with multiple capacitors, Figure 4(c) being a side view of the transmission type, and Figure 4(d) being a partially enlarged cross-sectional view of the capacitor selection structure. As shown in Figure 4, in the optical-voltage probe 20 according to Example 2, similar to Example 1, an optical modulator 1 is installed and fixed in a rectangular parallelepiped package 38 made of metal, and the probe is provided with contact terminal mounting sections 5 and 6 configured to connect two contact terminals 3 and 4, respectively, which are configured to be able to contact the point under measurement, and signal lines that guide voltage signals generated between the contact terminals by bringing the contact terminals 3 and 4 into contact with the point under measurement to modulation electrodes 11 and 12, respectively.

[0044] A connection substrate 50 is fixed adjacent to the optical modulator 1 within the package 38. A connection line portion 51 is provided on the connection substrate 50 as part of the signal line from the contact terminal 3 to the modulation electrode 11, and a connection line portion 59 is provided as part of the signal line from the contact terminal 4 to the modulation electrode 12. The connection line portion 59 is an electrode pad that connects the modulation electrode 12 to the contact terminal mounting portion 6. An electrode pad 52 on the modulation electrode 11 side and an electrode pad 53 on the contact terminal mounting portion 5 side are provided facing each other on the connection line portion 51. Four signal line portions consisting of signal line portions 54, 55, 56, and 57 are provided between the electrode pads 52 and 53, and any one of these signal line portions can be selected and connected in series to the signal line from the contact terminal 3 to the modulation electrode 11. An electrode pad connected to electrode pad 52 is provided on the signal line portion 54, with a gap provided between it and electrode pad 53. Chip capacitors having different capacitances are installed on the signal line portions 55, 56, and 57 and connected to the electrode pad 52, and gaps are provided between all of them and the electrode pad 53.

[0045] Furthermore, there is provided an insertion portion 60 with four tubes for inserting shorting rods 58, each of which has a thin metal plate 58a attached to the tip of an insulating rod 58b made of elastic material such as rubber, and which covers from above the gaps between the signal line portions 54, 55, 56, 57 and the electrode pad 53 to short-circuit any of the opposing electrodes. There is also provided a lid 61 for pressing and fixing the shorting rod 58 from above and for covering the insertion portion 60. This allows the shorting rod 58 to selectively short-circuit any of the signal line portions 54, 55, 56, 57 and the electrode pad 53.

[0046] As an example of specific design values for this embodiment, if the capacitance between modulation electrodes 11 and 12 is 2 pF, and the capacitances of the chip capacitors connected to signal line portions 55, 56, and 57 are 4 pF, 1 pF, and 0.5 pF, respectively, the voltage signal between contact terminals 3 and 4 will be 2 / 3, 1 / 3, and 1 / 5, respectively, when it passes through each signal line portion and is applied to the modulation electrode. Therefore, by switching, the dynamic range of the voltage signal that can be detected by the optical voltage probe can be up to five times that of the normal case where the signal passes only through signal line portion 54, making it possible to measure a wide range of voltage signals. [Example]

[0047] FIG. 5 is a schematic diagram illustrating the configuration of an optical-voltage probe according to Example 3. FIG. 5(a) is a plan view of a transmission type, FIG. 5(b) is a partially enlarged plan view showing the configuration of multiple capacitor electrodes arranged on an optical modulator, and FIG. 5(c) is a side view of the transmission type. As shown in FIG. 5, in an optical-voltage probe 70 according to Example 3, similar to Example 1, an optical modulator 81 having modulation electrodes 11 and 12 is installed in a rectangular metal package 88 and fixed by a base 89. This example includes four contact terminal mounting portions 83, 84, 85, and 86 that are connectable to contact terminal 3, which is configured to be in contact with the point under measurement, and contact terminal mounting portion 82 that is connectable to contact terminal 4. A voltage signal generated between the contact terminals when contact terminals 3 and 4 are brought into contact with the point under measurement is guided to modulation electrodes 11 and 12 via a signal line that passes through one of contact terminal mounting portions 83, 84, 85, and 86 and contact terminal mounting portion 82. The basic structure of the contact terminal attachment portions 82 to 86 is the same as that of the contact terminal attachment portions 5 and 6 .

[0048] The modulation electrodes of the optical modulator 81 of this embodiment have modulation electrodes similar to the modulation electrodes 11 and 12 of the optical modulator 1 of Example 1, and electrode pads 71 and 72 are added to the modulation electrodes 11 and 12, respectively, as lead-out sections for these electrodes. The electrode pad 72 is an electrode pad for connecting the modulation electrode 12 to an electrode terminal lead-out section 82. As shown in Figure 5(b), the electrode pad 71 is provided with an electrode pad 73 connected to the electrode pad 71, and capacitor electrodes 74, 75, and 76 consisting of electrode pads facing the electrode pad 71 with different intervals d between them, and the electrode pad 73 and the capacitor electrodes 74, 75, and 76 are connected to electrode terminal lead-out sections 83, 84, 85, and 86, respectively. That is, the electrode pad 71 and the capacitor electrodes 74, 75, and 76 form capacitors of different capacitances, and by selecting the electrode terminal take-out parts 83, 84, 85, and 86 to which the connection terminal 3 is connected, the voltage signal generated between the connection terminals 3 and 4 is guided to the modulation electrodes 11 and 12 via the capacitors of different capacitances inserted in series.

[0049] As an example of specific design values for this embodiment, if the capacitance between modulation electrodes 11 and 12 is 2 pF, and the widths of capacitor electrodes 74, 75, and 76 are 1 to 2 mm and the distances d between them and electrode 71 are approximately 2.5 μm, 5.0 μm, and 10 μm, respectively, then the capacitances of the capacitors formed between them and electrode 71 will be approximately 1 to 3 pF, 0.5 to 1.5 pF, and 0.3 to 0.8 pF, respectively. As a result, when the voltage signal between contact terminals 3 and 4 passes through contact terminal mounting portions 84, 85, and 86 and is applied to the modulation electrodes, it will be approximately 1 / 2, 1 / 3, and 1 / 5, respectively. Therefore, the dynamic range of the voltage signal detectable by the optical voltage probe is significantly expanded compared to the normal case where the signal passes only through contact terminal 83.

[0050] As described above, the optical voltage probe of the present invention is capable of measuring a voltage signal in a much wider range than conventionally possible.

[0051] Needless to say, the present invention is not limited to the above-described embodiments, and various modifications are possible depending on the purpose. For example, the capacitor inserted in series with the signal line and housed within the package, and the adjustment means for adjusting the capacitance of the capacitor from outside the package, may be other than those shown in the above-described embodiments. Furthermore, the optical modulator used may be a transmissive optical modulator, not just a reflective one. When a segmented electrode is used as the modulation electrode, the number of segments can be set as desired depending on the frequency, amplitude, etc. of the target measurement voltage. The modulation electrode does not have to be a segmented electrode. The shape, structure, connection, and fixing methods of the contact terminals and contact terminal mounting portions can also be selected according to the purpose. Furthermore, the material of the package can also be selected according to the purpose. The shape and structure of the package can also be selected as desired. [Explanation of symbols]

[0052] 1 Optical modulator 2 Input / Output Optical Fiber 3,4 contact terminal 5,6,82,83,84,85,86 Contact terminal mounting part 7 Ferrules 8,38,88 packages 9,89 Base 10, 20, 70 Optical Voltage Probe 11,12 Modulation electrode 13 Fixing parts 14 Insulators 15 Terminal insertion part 16 lead wire 17 Incident light 18 Optical Intensity Modulation Signal 19 Electrical Components 21 Optical transmitting and receiving unit 22 Light source 23 O / E converter 24 Transmitter / receiver separator 25 amps 26 Output terminal 27 Measuring instruments 28 input terminals 29 Electrical Circuit Board 30,50 Connection board 31, 32, 51, 59 Connecting line section 33 Trimmer capacitor 34 holes 35,61 Lid 41 PCB 42 Branching and interference optical waveguide 42a Input / output optical waveguide 42b, 42c Phase-shifting optical waveguide 43 Buffer layer 44 Modulation electrode section 45 Light reflecting part 46,47,48 electrode 46a,47a,47b,48b Electrode part 52, 53, 71, 72, 73 Electrode pads 54, 55, 56, 57 Signal line section 58 Shorting rod 58a metal plate 58b Insulator rod 60 Insertion part 74, 75, 76 Capacitor electrodes

Claims

1. an optical modulator including at least two modulation electrodes, which modulates the intensity of incident light depending on a voltage between the two modulation electrodes and outputs the modulated light; an input optical fiber and an output optical fiber connected to the optical modulator; two contact terminals connected to the modulation electrodes and capable of contacting points to be measured on an electric circuit or electric wiring; a signal line that leads a voltage signal generated between the contact terminals by bringing the contact terminals into contact with the point to be measured to the modulation electrode; a package that houses the optical modulator and a portion of the input optical fiber and the output optical fiber, an optical voltage probe that converts the voltage signal into an optical intensity modulated signal by the optical modulator and outputs the signal from the output optical fiber, a modulation electrode side electrode pad connected to one of the two modulation electrodes; a plurality of capacitors having different capacitances and one electrode of which is connected in parallel to the electrode pad; and connection means for selecting one of the plurality of capacitors and connecting it in series to the signal line, the package has a lid; the connecting means includes a contact terminal-side electrode pad connected to one of the two contact terminals, a shorting rod having a conductive material at its tip, and an insertion portion formed on the lid of the package into which the shorting rod can be inserted and fixed; the other electrodes of the plurality of capacitors are disposed opposite the electrode pads on the contact terminal side with a certain gap therebetween, an optical voltage probe which connects the selected capacitor to the electrode pad on the contact terminal side by inserting the shorting rod from the insertion portion and pressing it down from above so as to cover the gap between the electrode arranged opposite the electrode pad on the contact terminal side of a selected capacitor from among the plurality of capacitors and the electrode pad on the contact terminal side from above.

2. an optical modulator including at least two modulation electrodes, which modulates the intensity of incident light depending on a voltage between the two modulation electrodes and outputs the modulated light; an input optical fiber and an output optical fiber connected to the optical modulator; two contact terminals that can be brought into contact with points to be measured on an electric circuit or electric wiring; two contact terminal attachment portions connected to the modulation electrodes and configured to allow the contact terminals to be attached and detached; a signal line that leads a voltage signal generated between the contact terminals by bringing the contact terminals into contact with the point to be measured to the modulation electrode; a package that houses the optical modulator and a portion of the input optical fiber and the output optical fiber, an optical voltage probe that converts the voltage signal into an optical intensity modulated signal by the optical modulator and outputs the signal from the output optical fiber, a modulation electrode side electrode pad connected to one of the two modulation electrodes; a plurality of capacitors having different capacitances and one electrode of which is connected in parallel to the electrode pad; and connection means for selecting one of the plurality of capacitors and connecting it in series to the signal line, the package has a lid; the connecting means includes an electrode pad on one of the two contact terminal mounting portions that is connected to the contact terminal mounting portion, a shorting rod having a conductive material at its tip, and an insertion portion formed on the lid of the package into which the shorting rod can be inserted and fixed; the other electrodes of the plurality of capacitors are disposed opposite the electrode pads on the contact terminal attachment portion side with a certain gap provided therebetween, an optical voltage probe which connects the selected capacitor to the electrode pad on the contact terminal mounting portion by inserting the shorting rod from the insertion portion and pressing down and fixing it from above so as to cover from above the gap between the electrode arranged opposite the electrode pad on the contact terminal mounting portion of any selected capacitor from the plurality of capacitors.

3. an optical modulator including at least two modulation electrodes, which modulates the intensity of incident light depending on a voltage between the two modulation electrodes and outputs the modulated light; an input optical fiber and an output optical fiber connected to the optical modulator; two contact terminals that can be brought into contact with points to be measured on an electric circuit or electric wiring; a plurality of contact terminal attachment portions connected to the modulation electrodes and configured to allow the contact terminals to be attached and detached; a signal line that leads a voltage signal generated between the contact terminals by bringing the contact terminals into contact with the point to be measured to the modulation electrode; a package that houses the optical modulator and a portion of the input optical fiber and the output optical fiber, an optical voltage probe that converts the voltage signal into an optical intensity modulated signal by the optical modulator and outputs the signal from the output optical fiber, an electrode pad connected to one of the two modulation electrodes; a plurality of capacitors having different capacitances connected in parallel to the electrode pads and connected in series to the contact terminal attachment portions, one of the plurality of contact terminal attachment portions is connected to the other of the two modulation electrodes; the rest of the plurality of contact terminal attachment portions are connected in series to any one of the plurality of capacitors; an optical voltage probe characterized in that a contact terminal attached to a contact terminal attachment portion connected to the other of the two modulation electrodes and a contact terminal attached to any one of the remaining contact terminal attachment portions connected to any one of the plurality of capacitors are brought into contact with the point to be measured.

4. 4. The optical voltage probe according to claim 3, wherein a plurality of capacitors having different capacitances connected in parallel to the electrode pads and connected in series to the contact terminal attachment portions have capacitor electrodes arranged opposite the electrode pads with different intervals between them, and each of the plurality of capacitors has a capacitance corresponding to the size of the intervals.

5. 5. The optical voltage probe according to claim 1, wherein the minimum capacitance of the plurality of capacitors is less than twice the capacitance between the two modulation electrodes.

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