JP6883234B2 - Voltage probe head - Google Patents

Description

The present invention relates to a voltage probe head in which a voltage signal obtained from a contact terminal is applied to an optical modulator to convert it into an optical modulation signal, and the optical modulation signal is output by an optical fiber.

In recent years, various control devices using high-speed CPUs and the like have been developed, and in order to prevent malfunctions, noise signals generated on the electric circuit boards and the like and noise immunity tests on the electric circuit boards and the like have been performed. It is done. In these tests, it is required to accurately measure the input / output signals of the electric components installed on the electric circuit board and the electric signals transmitted on the wiring.
A general method for measuring electrical signals of electrical components and wiring is to guide the electrical signal at the point to be measured to a measuring instrument such as an oscilloscope with an electrical probe having a contact terminal and measure the transmitted voltage waveform or the like. is there. However, when the ground level of the point to be measured is different from that of the measuring instrument, or when measuring the voltage signal between two points that are not grounded, the signal from the ground may be mixed or the capacity of the electric probe may affect it. Therefore, it becomes difficult to measure the accurate voltage waveform. Especially in the high frequency region, the influence of the above ground and capacitance is large.

As a means for solving this problem, a measuring instrument of a method of converting a voltage signal into an optical signal and guiding the optical signal to the measuring instrument by an optical fiber has been developed. In this method, the measurement point and the measuring instrument are completely electrically separated without being affected by the capacitance of the electric probe, so that it is possible to prevent the influence of the ground and the mixing of electric signal noise in the middle.

Examples of such conventional measuring instruments are described in Patent Documents 1 and 2.
Patent Document 1 describes a voltage probe using a bulk type optical modulator. That is, a voltage signal of a contact terminal is applied to a crystal having an electro-optical effect, incident light sent from an optical fiber is reflected in the crystal to change the polarization state, and the change is light intensity modulated through an analyzer. It is configured to be light and guided to an O / E converter by an optical fiber.
Patent Document 2 describes a voltage probe using a waveguide type optical modulator. A light intensity modulation signal is obtained by applying a voltage signal of a contact terminal to a modulation electrode of a branched interference type light modulator formed on a lithium niobate crystal substrate. A device including a light source and an O / E converter and a voltage probe head are connected by an optical fiber.

Japanese Unexamined Patent Publication No. 63-196863 Japanese Unexamined Patent Publication No. 8-35998

In the probe for measuring a voltage signal by converting it into an optical signal by the above-mentioned waveguide type optical modulator, it is possible to design an optimum modulation electrode depending on the magnitude of the voltage signal to be measured. This design allows for a wide range of voltage signals. However, when the light modulator used for the voltage probe head is fixed, the degree of modulation of the light intensity modulated signal with respect to the amplitude of the applied voltage is determined, and the range of the magnitude of the detectable voltage signal is limited.
Further, in the waveguide type optical modulator, the modulation electrode has a fine structure and the electrode spacing is very narrow, about several to several tens of μm. Therefore, in the measurement, the modulation electrode is larger than the contact terminal as expected. When a voltage signal is applied, the modulation electrode is destroyed. As a result, there was a risk that the voltage probe head would break.

As described above, the voltage probe head that measures the voltage signal by converting it into an optical signal with a conventional optical modulator has a limited measurement voltage range, and there is a risk of destruction due to an unexpected voltage input from the contact terminal. There was a problem that there was.

An object of the present invention is to solve the above problems, to set a large range of detectable voltage signals for a fixed light modulator, and to reduce the risk of destruction due to an unexpected voltage input. The purpose is to provide a voltage probe head.

In order to solve the above problems, from the first viewpoint, the voltage probe head according to the present invention includes an optical modulator that intensity-modulates and outputs incident light depending on the voltage applied to the modulation electrode, and the optical modulator. It is provided with a connected input optical fiber and an output optical fiber, a contact terminal configured to be able to contact the measurement point, and a signal line for guiding a voltage signal between the contact terminal and the reference point to the modulation electrode. A voltage probe head that converts the voltage signal into a light intensity modulated signal by the optical modulator and outputs it from the output optical fiber, and is either the signal line or a line connecting the reference point and the modulation electrode. It has a capacitor inserted in series, and the amplitude of the voltage signal is reduced by a predetermined ratio depending on the capacitance of the capacitor and the capacitance of the modulation electrode and applied to the modulation electrode. It is a feature.

In the voltage probe head of the present invention, the voltage signal between the contact terminal and the reference point is inserted in series into either a signal line that guides the voltage signal to the modulation electrode of the optical modulator or a line that connects the reference point and the modulation electrode. Has a capacitor. Due to the presence of this capacitor, the amplitude of the voltage signal detected at the contact terminal is reduced by a predetermined ratio depending on the capacitance of the capacitor and the capacitance of the modulation electrode and applied to the modulation electrode. If the capacitance of the capacitor inserted in the signal line or the line connecting the reference point and the modulation electrode is C1, the capacitance of the modulation electrode is C2, and the amplitude of the voltage signal detected at the contact terminal is Vo, it is applied to the modulation electrode. The amplitude Vm of the voltage signal to be generated is theoretically Vm = Vo · C1 / (C1 + C2). That is, the voltage applied to the modulation electrode is reduced to C1 / (C1 + C2) times. The magnification can be arbitrarily selected by selecting the value of C1, for example, 1/2 times, 1/10 times, 1/100 times, and the like. Actually, it is necessary to consider the influence of stray capacitance added by the structure around the signal line and the modulation electrode.
In the present invention, the potential detected by the same contact terminal as that used for the measurement point may be used as the potential of the reference point. In this case, the voltage signal between the two contact terminals is guided to the modulation electrode by the signal line.

As described above, in the present invention, the amplitude of the voltage signal applied to the modulation electrode is changed by selecting the capacitance C1 of the capacitor to be inserted in the signal line or the line connecting the reference point and the modulation electrode. The range of the magnitude of the detectable voltage signal can be selected by selecting the capacitance C1 of the capacitor.
Further, in the first measurement, the capacitance C1 of the capacitor inserted in the signal line or the line connecting the reference point and the modulation electrode is set to a sufficiently small value to sufficiently reduce the voltage sensitivity, and the measured point is measured. By changing the capacitance C1 of the capacitor to a value suitable for the measurement after grasping the approximate voltage amplitude, it is possible to prevent an excessive voltage signal from being applied to the modulation electrode.

From the second aspect, in the voltage probe head of the first aspect, the light modulator is a branched interference type optical modulator using an optical waveguide formed on a lithium niobate crystal substrate. It is characterized by that. The invention of this aspect uses a conventionally used branch interference type optical modulator using an optical waveguide formed on a lithium niobate crystal. The basic configuration of a branched interference type optical modulator is an input optical waveguide extending from the incident side of light, two phase-shift optical waveguides extending bifurcated from the input optical waveguide, and the two phase-shift optical waveguides. It is composed of an output optical waveguide that merges and connects to the light emission side, and modulation electrodes arranged in parallel with the phase shift waveguide. A voltage signal is applied to the phase-shifted optical waveguide via a modulation electrode to change the refractive index of the phase-shifted optical waveguide, and the light passing through the two phase-shifted optical waveguides merges and interferes to modulate the light intensity. To. Since a small size, high efficiency, and wide band optical modulator can be obtained, it is suitable for the voltage probe head of the present invention.

From the third aspect, in the voltage probe head of the second aspect, the light modulator is a reflection type optical modulator that internally reflects incident light and turns it back, and is the same as the input optical fiber. The output optical fiber is characterized in that it is composed of one input / output optical fiber.
The light-reflecting light modulator of the present invention of the present invention uses a configuration in which incident light is reflected in a phase-shift waveguide and returned to the optical waveguide on the incident side. By using such a reflective light modulator configuration, light is transmitted twice as long as the same electrode length as compared to a transmissive light modulator, so that the efficiency of the light modulator can be improved. Wider bandwidth and smaller size are possible.

From the fourth aspect, in the voltage probe head of the second or third aspect, the modulation electrode is a divided electrode composed of a plurality of electrodes divided in the longitudinal direction of the optical waveguide and capacitively coupled to each other. It is characterized by being. In general, increasing the length of the modulation electrode along the optical waveguide increases the modulation efficiency and the detection voltage sensitivity of the voltage probe head. However, if the length of the modulation electrode is increased, the electric capacity increases. When the electrode capacitance is large, the equivalent impedance decreases as the frequency of the electric signal increases, and the voltage applied to the electrodes decreases, so that the modulation efficiency decreases. Therefore, it is desirable that the capacitance of the electrode is as small as possible for high-frequency signal detection. A promising means for improving the trade-off relationship between the length of the modulation electrode and the electric capacity is a split electrode obtained by dividing one modulation electrode into a plurality of capacitively coupled electrodes. By using this divided electrode, a high-efficiency, wide-band optical modulator can be obtained.

From a fifth aspect, in the voltage probe heads of the second to fourth aspects, the light modulator is installed in a housing, the signal line is fixed to the housing, and one end is the modulation electrode. It has a connection line portion connected to, and the capacitor is inserted in series with any of the connection line portions.
In the invention of this viewpoint, by installing the intensityally unstable optical modulator to which the optical fiber is connected in the housing, the voltage probe head can be easily handled, and further, the connection line portion to which the capacitor is installed can be provided. By fixing to the housing, the capacitor can be easily installed or replaced.
Here, as the material of the housing, a metal such as aluminum, copper, or stainless steel, a resin such as plastic, or acrylic can be used. The shape of the housing may be such that the optical modulator can be housed inside. Further, the connecting line can be fixed and stored inside the housing, or can be fixed outside the housing.
When measuring the voltage signal between two contact terminals, there are two connection lines, one of which is connected in series with a capacitor, one end of which is connected to the signal input side of the modulation electrode, and the other end of which is modulated. It is connected to the ground side of the electrode. The other ends of them are connected to their respective contact terminals.

From the sixth aspect, the present invention is characterized in that, in the voltage probe head of the fifth aspect, the connecting line portion is composed of a coplanar line. In the invention of the present viewpoint, by configuring the connecting line portion with the coplanar line, it is possible to measure the voltage signal in the microwave region. In this case, a chip capacitor is desirable as the capacitor to be inserted.

From a seventh aspect, the present invention has a coaxial connector fixed to the housing in the voltage probe head of the sixth aspect, one end of the central conductor of the coaxial connector is conducted to the contact terminal, and the like. The end is characterized in that it is conducted to the connecting line portion. In the invention of this aspect, it is desirable that the housing to which the coaxial connector is fixed is made of a metal material. In this case, the voltage signal from the measurement point is guided to the central conductor of the coaxial connector via the contact terminal, and the potential of the reference point becomes the outer peripheral conductor. The contact terminal may be directly fixed to the central conductor of the coaxial connector fixed to the housing. Alternatively, the coaxial connector fixed to the housing may be connected to another coaxial connector, and the contact terminal may be fixed to the connected coaxial connector. In this case, the connection terminal can be easily removed from the voltage probe head, and the contact terminal can be easily replaced according to the measurement purpose.

As described above, according to the present invention, a voltage probe head capable of setting a large range of a voltage signal that can be detected for a fixed light modulator and reducing the risk of destruction due to an unexpected voltage input can be provided. can get.

The plan view which shows typically the structure of the voltage probe head which concerns on Example 1. FIG. The block block diagram of the measurement system using the voltage probe head of Example 1. FIG. It is a figure which shows typically an example of the structure of the reflection type light modulator built in the voltage probe head of Example 1, FIG. 3A is a plan view, and FIG. 3B is a sectional view. The plan view which shows typically the structure of the voltage probe head which concerns on Example 2. FIG. The plan view which shows typically the structure of the voltage probe head which concerns on Example 3. FIG.

Hereinafter, the voltage probe head of the present invention will be described in detail with reference to the drawings. In the description of the drawings, the same elements are designated by the same reference numerals, and the duplicated description will be omitted.

FIG. 1 is a plan view schematically showing the configuration of the voltage probe head according to the first embodiment, and FIG. 2 is a block configuration diagram of a measurement system using the voltage probe head according to the first embodiment.

In FIG. 1, the voltage probe head 10 of the first embodiment has an optical modulator 1 that intensity-modulates and outputs incident light depending on the voltage applied to the modulation electrode, and an input / output connected to the optical modulator 1. It includes an optical fiber 2, a contact terminal 3 configured to be in contact with a measurement point, and a signal line that guides a voltage signal between the contact terminal 3 and a reference point to a modulation electrode.
In the first embodiment, the light modulator 1 is a reflective light modulator that internally reflects incident light and turns it back, and is an input optical fiber to the light modulator 1 and an output optical fiber from the light modulator 1. Is composed of one input / output optical fiber 2. The modulation electrode of the light modulator 1 includes an electrode pad 11 for a signal electrode and an electrode pad 12 for a ground electrode for connection with an external electrode.
Further, in the first embodiment, a contact terminal 4 similar to the contact terminal 3 used for the measurement point is provided, and the potential detected by the contact terminal 4 is used as the potential of the reference point. That is, the voltage signal between the two contact terminals 3 and 4 is guided to the modulation electrode by the signal line.

The light modulator 1 is installed in the housing 5, and the connection board 6 is fixed in the housing 5 adjacent to the light modulator 1. On the connection board 6, a connection line portion 7 is provided as a part of the signal line from the contact terminal 3 to the electrode pad 11, and a connection line portion 8 is provided as a part of the line from the contact terminal 4 serving as a reference point to the electrode pad 12. Is installed.
The connection line 7 is inserted and connected in series between the signal side electrode 7a connected to the contact terminal 3, the modulator side electrode 7b connected to the electrode pad 11, the signal side electrode 7a, and the modulator side electrode 7b. It is equipped with a chip capacitor 9. The connection line portion 8 connects the contact terminal 4 and the electrode pad 12.
Here, as the material of the housing 5 and the connecting substrate 6, metals such as aluminum, copper and stainless steel, plastics, resins such as acrylic, and glass materials can be used. The housing 5 has various forms such as a U-shaped cross section surrounding only the side surface, a box shape with an open upper surface, a closed type in which only the optical fiber 2 and the contact terminals 3 and 4 are projected. Is possible.

As described above, in the first embodiment, the voltage signal from the contact terminal 3 is guided to the signal electrode via the connection line portion 7 having the chip capacitors 9 arranged in series, and the potential of the reference point is the contact terminal. It is guided from 4 to the ground electrode via the connecting line portion 8.

Here, assuming that the capacitance of the chip capacitor 9 is C1 and the capacitance between the electrode pads 11 and 12 of the modulation electrode of the optical modulator 1 is C2, the amplitude of the voltage signal applied to the modulation electrode is C1 / (C1 + C2) times. Will be reduced to. For example, when a split electrode is used as the modulation electrode, the value of C2 can be about 1 to 5 pF. Therefore, if the capacitance of the chip capacitor 9 is set to C1 = 0.5 pF, the amplitude of the voltage signal applied to the modulation electrode Is reduced to 1/3 to 1/11 with respect to the voltage amplitude between the contact terminals 3 and 4.
In FIG. 1, a chip capacitor 9 is connected between the connection line portion 8 connected from the contact terminal 4 serving as a reference point and the electrode pad 12 for the ground electrode, and the chip capacitor 9 of the connection line portion 7 is removed. Even if the signal side electrode 7a and the modulator side electrode 7b are directly connected, the same effect of the present invention as described above can be obtained.

Next, a measurement system using the voltage probe head 10 of the first embodiment will be described.
As shown in FIG. 2, incident light 14 is sent from the optical transmission / reception unit 21 to the voltage probe head 10 through the input / output optical fiber 2, and the light intensity modulation signal 15 output from the light modulator 1 is the same input / output light. It is input to the transmission / reception unit 21 from the fiber 2.
The optical transmission / reception unit 21 includes a light source 22 such as a semiconductor laser, an O / E converter 23, a transmission / reception separator 24 for separating incident light 14 and a light intensity modulation signal 15, and an amplifier 25. The light emitted from the light source 22 is coupled to the input / output optical fiber 2 through the transmission / reception separator 24, and the light intensity modulation signal 15 from the input / output optical fiber 2 is input to the O / E converter 23 through the transmission / reception separator 24. In the O / E converter 23, the light intensity modulation signal 15 is converted into an electric signal, amplified by the amplifier 25, and output to the output terminal 26. The electric signal is input to the input terminal 28 of a measuring instrument 27 such as an oscilloscope. The transmission / reception separator 24 can be configured by using any of an optical circulator, an optical fiber branch, and a semi-transmissive mirror.

FIG. 2 shows a case where a voltage signal applied to an electric component 16 incorporated on an electric circuit board 13 is measured as a measurement point. The contact terminal 3 of the voltage probe head 10 is brought into contact with the signal line side of the electric component 16, and the contact terminal 4 is brought into contact with the ground potential side. The tips of the contact terminals 3 and 4 can have various forms according to the frequency of the electric signal to be measured. A structure similar to the contact portion of a normal electric probe can be used.

As described above, the voltage signals detected at the contact terminals 3 and 4 are converted into the light intensity modulation signal 15 by the light modulator 1, and the light intensity modulation signal 15 is converted into an electric signal in the light transmission / reception unit 21. .. By observing the voltage waveform with the measuring instrument 27, the voltage signal waveform applied to the electric component 16 can be grasped.

FIG. 3 is a diagram schematically showing an example of the configuration of the reflection type optical modulator 1 built in the voltage probe head 10 of the first embodiment, FIG. 3A is a plan view, and FIG. 3B is a plan view. ) Is a cross-sectional view.

_{In FIG. 3, the light modulator 1 is formed by cutting out a lithium niobate (LiNbO 3} ) crystal, which is a crystal having an electro-optical effect, by X-cutting, and Ti diffusion on the upper surface side of the substrate 41. The branched optical waveguide 42, the buffer layer 43 formed on the upper surface side of the substrate 41, the modulation electrode 44 formed on the buffer layer 43, and one end of the substrate 41 were installed. It is composed of a light reflecting unit 45. The modulation electrode 44 is a two-layer film of chromium (Cr) and gold (Au) formed by sputtering or the like.

The branch interference type optical waveguide 42 is formed of one input / output optical waveguide 42a extending to the incident side of the input light and two phase shift waveguides 42b, 42c extending bifurcated from the input / output optical waveguide 42a. Has been done. In the input / output optical waveguide 42a and the phase shift optical waveguides 42b and 42c, the widths W in the direction perpendicular to the stretching direction are all equal. Further, the lengths of the phase-shifted optical waveguides 42b and 42c in the extending direction are substantially the same.

The width W of these optical waveguides is in the range of 5 to 12 μm. The length of the phase-shifted optical waveguides 42b and 42c in the stretching direction is in the range of 10 to 30 mm. The central portions of the phase-shifted optical waveguides 42b and 42c are separated from each other at predetermined intervals in the width direction and extend in parallel with each other. The distance between the phase-shifted optical waveguides 42b and 42c in the central portion is in the range of 15-50 μm. The input / output optical waveguide 42a, the width W of the phase-shift optical waveguides 42b and 42c, the lengths of the phase-shift optical waveguides 42b and 42c, and the spacing between the phase-shift optical waveguides 42b and 42c are not particularly limited, and their dimensions are arbitrary. Can be set to.

The buffer layer 43 is provided for the purpose of preventing a part of the light propagating through the optical waveguide 42 from being absorbed by the modulation electrode 44. The buffer layer 43 is mainly _{made of a silicon dioxide (SiO 2} ) film or the like, and its thickness is about 0.1 to 1.0 μm.

In the light modulator 1, the modulation electrode 44 is composed of three electrodes 46, 47, and 48 that are divided in the longitudinal direction of the branch interference type optical waveguide 42 and are capacitively coupled to each other. The electrode 46 having the electrode pad 11 on the signal input side has an electrode portion 46a arranged between the phase shift optical waveguide 42b and 42c. The electrode 47 has an electrode portion 47b arranged on both sides of the electrode portion 46a with the phase shift optical waveguides 42b and 42c interposed therebetween, and an electrode portion 47a arranged between the phase shift optical waveguides 42b and 42c. The electrode 48 having the electrode pad 12 on the ground side has electrode portions 48b arranged on both sides of the electrode portion 47a with the phase shift optical waveguides 42b and 42c interposed therebetween. Between the electrode pads 11 and 12, the electrodes 46 and 47 and the electrodes 47 and 48 are capacitively coupled to each other and arranged in series.

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 light reflecting unit 45 reflects the light incident from the input / output optical waveguide 42a and propagating through the phase-shifted optical waveguides 42b and 42c, and returns the light from the phase-shifted optical waveguides 42b and 42c to the input / output optical waveguide 42a and propagates the light. By applying a voltage to the modulation electrode 44, electric fields are applied in opposite directions to the two phase-shifted optical waveguides 42b and 42c between the electrode portions 46a and 47b and between the electrode portions 47a and 48b. As a result, the refractive indexes of the phase-shifted optical waveguides 42b and 42c change in opposite directions, and the light passing through them undergoes phase-shifting of opposite polarities, and when the light merges, they interfere with each other and have an intensity of intensity. Change will occur. As a result, a light intensity modulated signal having a light intensity change corresponding to the voltage applied to the modulation electrode 44 can be obtained.

FIG. 4 is a plan view schematically showing the configuration of the voltage probe head according to the second embodiment.
As shown in FIG. 4, in the voltage probe head 20 of the second embodiment, the same optical modulator 1 as in the first embodiment is installed in the housing 35, and the connection board 36 is housed adjacent to the optical modulator 1. It is fixed in the body 35. The housing 35 is made of a metal material, and a coaxial connector 37 is fixed to the outside of the housing 35. The contact terminal 3 is connected and fixed to the central conductor 37a of the coaxial connector 37, and the contact terminal 4 is connected and fixed to the outer peripheral conductor of the coaxial connector 37.

On the connection substrate 36, between the signal side electrode 17a connected to the central conductor 37a of the coaxial connector 37, the modulator side electrode 17b connected to the electrode pad 11, the signal side electrode 17a, and the modulator side electrode 17b. A connection signal line 17 with a chip capacitor 19 inserted and connected in series is arranged. Further, on both sides of the connection signal line 17, ground electrodes 38 connected to the outer peripheral conductor of the coaxial connector 37 are arranged. The connection signal line 17 and the ground electrode 38 form a connection line portion including a coplanar line.

Also in the voltage probe head 20 of the second embodiment, the amplitude of the voltage signal between the contact terminals 3 and 4 is reduced by a predetermined ratio determined by the capacitances of the chip capacitor 9 and the modulation electrode, and is applied to the modulation electrode. In the second embodiment, by configuring the connecting line portion with the coplanar line, it is possible to measure the voltage signal in the microwave region.

FIG. 5 is a plan view schematically showing the configuration of the voltage probe head according to the third embodiment.
As shown in FIG. 5, in the voltage probe head 30 of the third embodiment, the optical modulator 1 is installed in the housing 35 and the connection board 36 is adjacent to the optical modulator 1 as in the second embodiment. It is fixed in the housing 35. The housing 35 is made of a metal material, and a coaxial connector 32 is fixed to the outside of the housing 35. The coaxial connector 32 is configured to be connectable to the coaxial connector 33, and the contact terminal 3 is fixed to the central conductor 33a of the coaxial connector 33, and the contact terminal 4 is connected and fixed to the outer peripheral conductor of the coaxial connector 33. In the third embodiment, by removing the coaxial connector 33 from the coaxial connector 32, the contact terminals 3 and 4 can be easily removed from the voltage probe head. If a coaxial connector 33 that can be connected to the coaxial connector 32 and is provided with various contact terminals according to the measurement purpose is prepared, the contact terminals can be easily replaced according to the shape of the measurement point. ..

In the third embodiment as well, as in the second embodiment, the connection signal line 17 having the chip capacitors 19 inserted and connected in series on the connection board 36 and the ground electrodes arranged on both sides thereof. 38 forms a connecting line portion composed of a coplanar line.

Also in the voltage probe head 30 of the third embodiment, the amplitude of the voltage signal between the contact terminals 3 and 4 is reduced by a predetermined ratio determined by the capacitances of the chip capacitor 9 and the modulation electrode, and is applied to the modulation electrode.

As described above, in the present invention, the amplitude of the voltage signal applied to the modulation electrode can be changed by selecting the capacitance of the capacitor to be inserted into the signal line, and it can be detected by selecting the capacitance of the capacitor. The range of voltage signal magnitude can be selected.
Furthermore, in the first measurement, the capacitance of the capacitor to be inserted into the signal line is set to a sufficiently small value to make the voltage sensitivity sufficiently small, and after grasping the approximate voltage amplitude of the measurement point, the capacitance of the capacitor is obtained. By changing the value to a value suitable for the measurement, it is possible to prevent an excessive voltage signal from being applied to the modulation electrode.

Needless to say, the present invention is not limited to the above-described embodiment, and various modifications can be made depending on the intended purpose. For example, the method of the light modulator used may be not only a reflection type but also a normal transmission type light modulator. When a divided electrode is used as the modulation electrode, the number of divided electrodes can be arbitrarily set according to the frequency, amplitude, and the like of the target measurement voltage. The modulation electrode does not have to be a split electrode. The housing for accommodating the light modulator can be made of various materials and has various structures. The installation location of the capacitor inserted in the signal line is not limited to the connection line portion, and may be connected to, for example, the electrode pad of the modulation electrode. Further, the form of the capacitor to be inserted into the line is not limited to the method of inserting individual parts such as a chip capacitor, and for example, an electrode gap or the like is provided in the connection line portion to form a portion having a function as a capacitor. You may. The shape, structure, connection and fixing method of the contact terminal can also be selected according to the purpose.

1 Optical modulator 2 Input / output optical fiber 3,4 Contact terminal 5,35 Housing 6,36 Connection board 7.8 Connection line part 7a, 17a Signal side electrode 7b, 17b Modulator side electrode 9,19 Chip capacitor 10,19 20, 30 Voltage probe head 11, 12 Electrode pad 13 Electric circuit board 14 Incident light 15 Light intensity modulation signal 16 Electrical component 17 Connection signal line 21 Optical transmission / reception unit 23 O / E converter 24 Transmission / reception separator 25 Amplifier 26 Output terminal 27 Measuring instrument 28 Input terminals 32, 33, 37 Coaxial connectors 33a, 37a Center conductor 38 Ground electrode 41 Board 42 Branch interference type optical waveguide 42a Input / output optical waveguide 42b, 42c Phase shift optical waveguide 43 Buffer layer 44 Modulation electrode 45 Light reflector 45 46, 47, 48 Electrodes 46a, 47a, 47b, 48b Electrodes

Claims (7)

An optical modulator that intensity-modulates incident light depending on the voltage applied to the modulation electrode and outputs it.
An input optical fiber and an output optical fiber connected to the light modulator,
A contact terminal configured to be able to contact the point to be measured on the electric circuit or electrical wiring,
A signal line that guides a voltage signal generated between the contact terminal and the reference point to the modulation electrode by bringing the contact terminal into contact with the measurement point.
A voltage probe head that converts the voltage signal into an optical intensity modulation signal by the light modulator and outputs the voltage signal from the output optical fiber.
It has a capacitor inserted in series with either the signal line or the line connecting the reference point and the modulation electrode.
A voltage probe head characterized in that the amplitude of the voltage signal is reduced by a predetermined ratio depending on the capacitance of the capacitor and the capacitance of the modulation electrode and applied to the modulation electrode.
The voltage probe head according to claim 1, wherein the light modulator is a branch interference type optical modulator using an optical waveguide formed on a lithium niobate crystal substrate. The light modulator is a reflection type optical modulator that internally reflects incident light and turns it back, and is characterized in that the input optical fiber and the output optical fiber are composed of one input / output optical fiber. The voltage probe head according to claim 2. The voltage probe head according to claim 2 or 3, wherein the modulation electrode is a divided electrode composed of a plurality of electrodes divided in the longitudinal direction of the optical waveguide and capacitively coupled to each other. The light modulator is installed in a housing, the signal line has a connection line portion fixed to the housing and one end connected to the modulation electrode, and the capacitor is connected in series with any of the connection line portions. The voltage probe head according to any one of claims 2 to 4, wherein the voltage probe head is inserted. The voltage probe head according to claim 5, wherein the connecting line portion is composed of a coplanar line. 6. The sixth aspect of claim 6, wherein the coaxial connector is fixed to the housing, one end of the central conductor of the coaxial connector is conducted to the contact terminal, and the other end is conducted to the connection line portion. Voltage probe head.

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