JP2000131345A - Electro-optical sampling oscilloscope - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electro-optical sampling oscilloscope wherein the configuration of an optical system is simplified for smaller device. SOLUTION: A light-emitting circuit 20 which generates a reference laser light La0, a directional coupler 23 which, while splitting the reference laser light La0 into a signal light La1 and a reference light La2, mixes a signal light La1' and a reference light La2' to generate a signal light La3, an electro-optical crystal 28 of optical nature which changes its refractive index according to the electric field due to a measured signal coupled through a metal pin 27, a reflection mirror 29 which reflects the signal light La1 as the signal light La1', a reflection plate 30 which reflects the reference light La2 as the reference light La2', and a light-receiving circuit 31 which receives the signal light La3, are provided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electro-optic sampling oscilloscope used for measuring various signals.

[0002]

2. Description of the Related Art In recent years, an electro-optic sampling oscilloscope which can measure a circuit under test without disturbing the circuit under test is used for signal measurement of a circuit under test which handles a signal having a very high bit rate of, for example, 2.4 Gbps. Have been.
Here, the electro-optic sampling oscilloscope uses an electro-optic probe that detects a signal to be measured using an electro-optic effect.

Further, the above-mentioned electro-optic sampling oscilloscope has the following advantages. (1) Since a ground wire is not required when measuring a signal, the measurement is easy. (2) The metal pin at the tip of the electro-optic probe is connected to the circuit system. Since each is insulated, high input impedance can be realized, and as a result, the state of the point to be measured is hardly disturbed. (3) Since it uses optical pulses, it is possible to perform broadband measurement up to the order of GHz. In particular, it is used for measurement of communication information systems whose speed is increasing.

FIG. 6 is a schematic side view showing the structure of an electro-optic probe used in a conventional electro-optic sampling oscilloscope. In this figure, reference numeral 4 denotes an electro-optic probe, and when an electric field generated by a signal under measurement is applied to the electro-optic crystal and a laser beam is incident on the electro-optic crystal, the polarization of the laser beam is changed. The signal to be measured is detected using the principle that the state changes.

[0005] In the electro-optical probe 4, reference numeral 5 denotes a metal pin having a tapered tip portion, which is in contact with a signal line (not shown). The metal pin 5 has a function of facilitating an electric field generated by the signal to be measured transmitted through the signal line to act on an electro-optic crystal 7 described later. Reference numeral 6 denotes a disk-shaped insulator, and an end of the metal pin 5 is attached to the center of the back surface. That is, the metal pin 5
It is held by the insulator 6. The electro-optic crystal 7 has B
SO (Bi ₁₂ SiO ₂₀ ) is formed in a cylindrical shape,
It has an optical property that its refractive index changes by the Pockels effect, which is a primary electro-optical change, according to the electric field coupled through the metal pin 5.

Reference numeral 8 denotes a reflecting mirror, which is a dielectric multilayer mirror that is deposited on the back surface of the electro-optic crystal 7. This reflecting mirror 8 reflects the laser beam La transmitted through the electro-optic crystal 7. The electro-optic crystal 7 is joined to the surface of the insulator 6 via the reflecting mirror 8.

Reference numeral 9 denotes a substantially cylindrical case, which has a cylindrical portion 9b and a tip portion 9a formed in a tapered shape at one end of the cylindrical portion 9b and having a through hole formed along an axis. Are integrally formed. The metal pin 5, the insulator 6, the electro-optic crystal 7, and the reflecting mirror 8 are accommodated in the tip 9a.

Reference numeral 10 denotes a polarization maintaining optical fiber that connects between the connector 11 and a laser generator (not shown).
The laser generator generates linearly polarized laser light La. In addition, the connector 11 is configured such that the laser light La emitted from the emission end 11 a is formed by the electro-optic crystal 7 and the reflecting mirror 8.
At a position where the light is incident perpendicularly to the light. 12
Is a collimating lens disposed on the left side of the connector 11 and converts the laser light La into parallel light.

Reference numeral 13 denotes a polarization beam splitter disposed on the left side of the collimating lens 12, which makes the polarization component of the laser beam La parallel to the plane of the paper go straight, and the laser beam La perpendicular to the plane of the paper. Is polarized by 90 degrees with respect to the direction in which the laser beam La travels, and travels straight.
Reference numeral 14 denotes a Faraday element disposed on the left side of the polarization beam splitter 13, and rotates the polarization of the laser beam La transmitted through the polarization beam splitter 13 by 45 degrees with respect to the paper surface.

Reference numeral 15 denotes a half-wave plate disposed to the left of the Faraday element 14 so that the crystal axis direction is inclined by 22.5 degrees. Be parallel. Reference numeral 16 denotes a polarization beam splitter disposed to the left of the half-wave plate 15, and has the same configuration as the polarization beam splitter 13. 17 is
A wavelength plate disposed on the left side of the polarization beam splitter 16;
a / S (Signal / No.) of the output signal of the electro-optical probe 4 finally obtained by adjusting the intensity balance of
adjust ise).

Reference numeral 18 denotes a first photodiode disposed above the polarization beam splitter 16, and the first photodiode 18 converts the laser light La split by the polarization beam splitter 16 into a first light.
And outputs the same to a differential amplifier (not shown). Reference numeral 19 denotes a second photodiode disposed above the polarization beam splitter 13, which converts the laser beam La branched by the polarization beam splitter 13 into a second electric signal S2, and converts the laser signal La into a second electric signal S2. Output to the dynamic amplifier.

In the above configuration, the metal pin 5 shown in FIG.
When the leading end of the device is brought into contact with a signal line (not shown), an electric field corresponding to the level of the signal under measurement transmitted through the signal line is coupled to the electro-optic crystal 7. Thereby, the refractive index of the electro-optic crystal 7 changes according to the intensity of the electric field. In this state, when the laser light La is emitted from a laser light generator (not shown), the laser light La is emitted from the emission end 11a of the connector 11, and then the collimator lens 12, the polarization beam splitter 13, the Faraday element 14 , Half-wave plate 15, polarizing beam splitter 16, and wave plate 17
Through the surface of the electro-optic crystal 7.

As a result, the polarization state of the laser light La propagating inside the electro-optic crystal 7 changes. Then, the laser beam La having undergone the polarization change is reflected by the reflecting mirror 8, emitted from the surface of the electro-optic crystal 7, and branched by the polarizing beam splitter 16. One of the split laser beams La is converted into a first electric signal S1 by a first photodiode 18, and the first electric signal S1 is converted to a first electric signal S1.
Is input to the differential amplifier.

The other laser beam La split by the polarization beam splitter 16 is split by the polarization beam splitter 13 in the direction of the second photodiode 19, and then the second electric signal is split by the second photodiode 19. Converted to S2. And the second electric signal S2 is
Input to the differential amplifier. Thus, in the differential amplifier, after the first electric signal S1 and the second electric signal S2 are differentially amplified, the differentially amplified signal is used as an output signal of the electro-optical probe 4 as an electro-optical sampling oscilloscope. Input terminal. As a result, the display section of the electro-optic sampling oscilloscope displays the waveform of the signal under measurement transmitted on the signal line and the like.

[0015]

By the way, in the above-mentioned conventional electro-optic sampling oscilloscope,
The configuration of the direct detection system is adopted in which the polarization state of the laser beam La having undergone the polarization change is directly detected by the first photodiode 18 and the second photodiode 19. However, in the above-described electro-optic sampling oscilloscope, the collimating lens 12, the polarizing beam splitter 1 and the
3. Since the Faraday element 14, the half-wave plate 15, the polarizing beam splitter 16 and the wave plate 17 are used, the optical system becomes complicated and the apparatus becomes large. The present invention has been made under such a background, and an object of the present invention is to provide an electro-optic sampling oscilloscope that can simplify the configuration of an optical system, and can further reduce the size of the device.

[0016]

According to a first aspect of the present invention, there is provided a light emitting unit for generating a reference laser beam, wherein the reference laser beam is incident on a surface of the light emitting unit and the intensity of an electric field generated by the signal to be measured. The electro-optic crystal whose refractive index changes, a reflecting mirror formed on the back surface of the electro-optic crystal and reflecting the reference laser light transmitted through the electro-optic crystal, and reflected light reflected by the reflecting mirror. Based on the output light of the multiplexed light, the multiplexed light generating means for generating the multiplexed light having the same frequency, the multiplexing means for multiplexing the reflected light and the multiplexed light, and And a detecting means for detecting. The invention according to claim 2 is a light emitting unit that generates a reference laser beam, the electro-optic crystal whose refractive index changes according to the intensity of an electric field generated by the signal under measurement, and the electro-optic crystal. A reflecting mirror formed on the back surface, a branching means for splitting the reference laser light into a signal light and a reference light, and making the signal light incident on the surface of the electro-optic crystal; and a reciprocating optical path length and half of the signal light. A reflection plate that is disposed to face the branching unit with a reciprocating optical path length having a wavelength difference and that reflects the reference light as multiplexed light, reflected light reflected by the reflecting mirror, and the multiplexed light And a detecting means for detecting the signal under measurement based on the output light of the multiplexing means. According to a third aspect of the present invention, there is provided a light emitting unit for generating a reference laser beam, and the reference laser beam is incident on a surface of the light emitting unit, and the refractive index changes according to the intensity of an electric field generated by the signal under measurement. The electro-optic crystal, a reflecting mirror formed on the back surface of the electro-optic crystal and reflecting the reference laser light transmitted through the electro-optic crystal, and a multiplexed light having the same frequency as the reflected light reflected by the reflecting mirror. The generated multiplexed light generating means, multiplexes the reflected light and the multiplexed light, and outputs a first output light and a second output light having a phase opposite to that of the first output light. Multiplexing means, first conversion means for converting the first output light into a first signal, second conversion means for converting the second output light into a second signal, Amplifying means for differentially amplifying the second signal and the second signal; Based on the output signal, the characterized by comprising a detecting means for detecting the signal to be measured. The invention according to claim 4 is a light emitting unit that generates a reference laser beam, the electro-optic crystal whose refractive index changes according to the intensity of an electric field generated by the signal under measurement, and an electro-optic crystal. A reflecting mirror formed on the back surface, a branching means for splitting the reference laser light into a signal light and a reference light, and making the signal light incident on the surface of the electro-optic crystal; and a reciprocating optical path length and half of the signal light. A reflection plate disposed opposite to the branching unit with a reciprocating optical path length having a wavelength difference and reflecting the reference light as multiplexed light, and multiplexing the reflected light and the multiplexed light, First
Multiplexing means for outputting the output light of the above, and a second output light having a phase opposite to that of the first output light, a first conversion means for converting the first output light into a first signal, The second output light to a second
A second converting means for converting the first signal and the second signal into differential signals; a differential amplifying means for differentially amplifying the first signal and the second signal; Detecting means for detecting a signal. According to a fifth aspect of the present invention, in the electro-optic sampling oscilloscope according to the first or third aspect, the multiplexed light generating means and the multiplexing means are constituted by optical waveguide elements. I do. Claim 6
The invention described in (1) is characterized in that, in the electro-optic sampling oscilloscope according to (2) or (4), the branching means and the multiplexing means are constituted by optical waveguide elements.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS <First Embodiment> An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing a configuration of a main part of an electro-optic sampling oscilloscope according to a first embodiment of the present invention. The electro-optic sampling oscilloscope shown in FIG. 1 detects a signal under measurement by homodyne detection.

In FIG. 1, reference numeral 20 denotes a light emitting circuit provided on the main body of an electro-optic sampling oscilloscope (not shown), which emits a reference laser beam La0 to one end surface of an optical fiber 21. Reference numeral 22 denotes an electro-optic probe. As described above, when a laser beam is incident on the electro-optic crystal in a state where an electric field generated by the signal under measurement is applied to the electro-optic crystal, the laser beam The signal to be measured is detected using the principle that the polarization state changes. In this electro-optic probe 22, reference numeral 23 is, for example, a 3 × 2 directional coupler, which has an optical branching and optical multiplexing function. In the example shown in FIG. 1, the directional coupler 23 is used as a 2 × 2 directional coupler.

The directional coupler 23 includes an optical fiber 21
The reference laser beam La0 incident through the optical fiber is branched into a signal beam La1 and a reference beam La2, and the signal beam La1 is split into an optical fiber 24.
And the reference light La2 is emitted to one end face of the optical fiber 25. On the other hand, the directional coupler 23 is connected to a signal light La 1 ′ to be described later,
The optical fiber 26 is multiplexed (interfered) with a later-described reference light La2 ′ incident through the optical fiber 26 as a later-described signal light La3.
Out to one end face of

Reference numeral 27 denotes a metal pin, reference numeral 28 denotes an electro-optic crystal, and reference numeral 29 denotes a reflecting mirror. These metal pins 2
7, the electro-optic crystal 28 and the reflecting mirror 29 have the same configuration as the metal pin 5, the electro-optic crystal 7 and the reflecting mirror 8 shown in FIG. That is, the electro-optic crystal 28 has an optical property that its refractive index changes due to the Pockels effect, which is a primary electro-optic change, according to the electric field of the signal under measurement coupled through the metal pin 27. ing.
The reflection mirror 29 is deposited on the back surface of the electro-optic crystal 28, and reflects the signal light La1 transmitted through the electro-optic crystal 28 as signal light La1 '.

Reference numeral 30 denotes a reflector disposed near the other end surface of the optical fiber 25, and reflects the reference light La2 emitted from the other end surface of the optical fiber 25 as the reference light La2 '. Here, one of the input / output ends of the directional coupler 23 is
The difference between the reciprocating optical path length up to 9 and the reciprocating optical path length from the other input / output end of the directional coupler 23 to the reflection plate 30 is a half wavelength. When the difference is a half wavelength, high sensitivity is obtained. Is obtained. The difference between the two reciprocating optical path lengths does not necessarily have to be a half wavelength.

A light receiving circuit 31 receives the signal light La3 incident through the optical fiber 26.
It has a light / electric conversion function of converting a3 into an electric signal. This electric signal is a signal corresponding to the signal under measurement. It is desirable to use polarization-maintaining optical fibers as the optical fibers 21, 24, 25, and 26 described above.

In the above configuration, the metal pin 2 shown in FIG.
When the tip of 7 is brought into contact with a signal line (not shown), an electric field corresponding to the level of the signal under measurement transmitted through the signal line is coupled to electro-optic crystal 28. Thereby, the refractive index of the electro-optic crystal 28 changes according to the intensity of the electric field. In this state, when the reference laser light La0 is emitted from the light emitting circuit 20, the reference laser light La0 enters the directional coupler 23 via the optical fiber 21. Then, the reference laser light La0 is split by the directional coupler 23 into a signal light La1 and a reference light La2. The frequency of the signal light La1 and the frequency of the reference light La2 are the same.

Here, when the signal light La1 is circularly polarized,
The x component x1 and the y component y1 of the signal light La1 are expressed by the following equations (1) and (2), where ω is the angular frequency of the reference laser beam La0, t is the time, and A is a constant. x1 = A · sin (ωt) (1) y1 = A · cos (ωt) (2)

The signal light La1 emitted from one of the input / output ends of the directional coupler 23 enters the surface of the electro-optic crystal 28 via the optical fiber 24, and then is reflected by the reflection mirror 29.
To propagate inside the electro-optic crystal 28. As a result, the polarization state of the signal light La1 propagating inside the electro-optic crystal 28 changes. During propagation, the crystal axis of the electro-optic crystal 28 is adjusted so that the phase of the x component x1 of the signal light La1 does not change and the phase of the y component y1 changes. Then, the signal light La1 having undergone the polarization change is reflected by the reflecting mirror 29, and then enters the one input / output end of the directional coupler 23 via the optical fiber 24 as the signal light La1 '. Here, the x component x1 'in the signal light La1'
Is represented by the following equation (3), where m is a coefficient determined by the number of reflections and the reflection state, and A is a constant. On the other hand, the y component y1 'is expressed by the following (4) when the amount of phase change is Δφ. ) Expression. x1 ′ = A · sin (ωt + mπ) (3) y1 ′ = A · cos (ωt + mπ + Δφ) (4)

On the other hand, the reference light La2 emitted from the other input / output end of the directional coupler 23 propagates through the optical fiber 25 and is reflected by the reflector 30 as the reference light La2 '. Then, the reference light La2 'is input to the other input / output end of the directional coupler 23 via the optical fiber 25.
Here, the x component x2 ′ in the reference light La2 ′ is expressed by the following equation (5), where n is an integer and A is a constant, while the y component y2 ′ is expressed by the following equation (6). expressed. x2 ′ = A · sin (ωt + nπ) (5) y2 ′ = A · cos (ωt + nπ) (6)

As a result, in the directional coupler 23, the signal light La1 'and the reference light La2' are multiplexed (mixed), and the signal light La3 is generated. This signal light La3 is a signal light indicating a change in the polarization plane of the signal light La1 propagating through the electro-optic crystal 28, in other words, a signal light corresponding to the change in the signal under measurement. Here, the y component y3 of the signal light La3 is expressed by the following equation (7). y3 = y1 '+ y2' (7) Then, when the above expressions (4) and (5) are substituted into the right side of the above expression (7), The following equation (8) is derived. y3 = A · cos (ωt + mπ + Δφ) + A · cos (ωt + nπ) = A · 2 · cos (ωt + (m + n) π / 2 + Δφ / 2) ... (8)

In the above equation (8), A · 2 · c
os (ωt + (m + n) π / 2 + Δφ / 2) represents a baseband signal (carrier) component of the reference laser beam La0, and cos (Δφ / 2 + (mn) · π /
2) represents the envelope of the signal component to be measured.
Further, as can be seen from the above-mentioned cos (Δφ / 2 + (mn) · π / 2), the condition for maximizing the sensitivity to the small fluctuation Δφ is the position of the signal light La1 ′ and the reference light La2 ′. Since the phase difference is a half wavelength (π + 2 · k · π (k is an integer)), it is expressed by the following equation (9). (Mn) · π / 2 = π / 2 + k · π (9)

The signal light La3 is transmitted to the optical fiber 2
6, after being incident on the light receiving circuit 31 through the light receiving circuit 31
Is converted into an electric signal. As a result, the display section of the electro-optic sampling oscilloscope displays the waveform of the signal under measurement transmitted on the signal line and the like.

As described above, according to the electro-optic sampling oscilloscope according to the above-described first embodiment, the polarization beam splitter 13 necessary for the direct detection method is used.
Since the polarization beam splitter 16 and the like (see FIG. 6) are unnecessary, the configuration of the optical system can be simplified as compared with the conventional electro-optic sampling oscilloscope, and the device can be downsized.

<Second Embodiment> Next, the configuration of an electro-optic sampling oscilloscope according to a second embodiment of the present invention will be described with reference to FIG. In FIG. 2, FIG.
The same reference numerals are given to the portions corresponding to the respective portions, and the description thereof is omitted. 2, an electro-optic probe 40 is newly provided in place of the electro-optic probe 22 shown in FIG. 1, and a half mirror 41 and a dummy optical circuit 42 are provided instead of the optical fibers 24 and 25 shown in FIG. Is newly provided.

The half mirror 41 shown in FIG. 2 is disposed on the left side of the electro-optic crystal 28 in FIG.
Of the reference laser beam La0 emitted from the other end face of the
% As a signal light La1 in a direction perpendicular to the reference laser light La0, and the remaining 5% of the reference laser light La0.
0% is transmitted as the reference light La2 in the direction in which the reference laser light La0 travels straight.

Reference numeral 42 denotes a dummy optical circuit disposed below the half mirror 41 in the figure, and adjusts the refractive index of the propagation path of the reference light La2. That is, the dummy optical circuit 42
A reciprocating optical path length from the half mirror 41 to the reflecting mirror 29;
The difference between the half mirror 41 and the reciprocating optical path length from the half mirror 41 to the reflection plate 30 disposed near the entrance / exit end face of the dummy optical circuit 42 is set to a half wavelength. This dummy optical circuit 42
Is made of, for example, glass.

In the above configuration, the metal pin 2 shown in FIG.
When the tip of 7 is brought into contact with a signal line (not shown), an electric field corresponding to the level of the signal under measurement transmitted through the signal line is coupled to electro-optic crystal 28. Thereby, the refractive index of the electro-optic crystal 28 changes according to the intensity of the electric field. In this state, the reference laser light L emitted from the light emitting circuit 20
a0 is guided to the half mirror 41 via the optical fiber 21. As a result, a part of the reference laser light La0 is incident on the surface of the electro-optic crystal 28 as the signal light La1 by the half mirror 41, and then propagates inside the electro-optic crystal 28 toward the reflection mirror 29.

As a result, the polarization state of the signal light La1 propagating inside the electro-optic crystal 28 changes. Then, the signal light La1 which has undergone the polarization change is reflected by the reflecting mirror 29 into the signal light L1.
After being reflected as a1 ', it is emitted from the surface of the electro-optic crystal 28. Further, a part of the signal light La1 ′ passes through the half mirror 41 and is incident on the other end surface of the optical fiber 26.

On the other hand, the remainder of the reference laser beam La0 is transmitted through the half mirror 41 as the reference beam La2, propagates through the dummy optical circuit 42, and is reflected by the reflector 30 as the reference beam La2 '. After the reference light La2 ′ propagates through the dummy optical circuit, a part of the reference light La2 ′ is incident on the other end surface of the optical fiber 26 by the half mirror 41.

Thus, in the optical fiber 26,
The signal light La1 'and the reference light La2' are multiplexed (mixed) to generate a signal light La3. Here, the signal light La3 is a signal light indicating a change in the polarization plane of the signal light La1 propagating through the electro-optic crystal 28, in other words, a signal light corresponding to a change in the signal under measurement.

The signal light La3 is transmitted to the optical fiber 2
6, after being incident on the light receiving circuit 31 through the light receiving circuit 31
Is converted into an electric signal. As a result, the display section of the electro-optic sampling oscilloscope displays the waveform of the signal under measurement transmitted on the signal line and the like.

As described above, according to the electro-optic sampling oscilloscope according to the above-described second embodiment, the same effect as the electro-optic sampling oscilloscope according to the first embodiment can be obtained.

<Third Embodiment> Next, the configuration of an electro-optic sampling oscilloscope according to a third embodiment of the present invention will be described with reference to FIG. In FIG. 3, FIG.
The same reference numerals are given to the portions corresponding to the respective portions, and the description thereof is omitted. In FIG. 3, a directional coupler 50 and an optical fiber 51 are newly provided. In FIG. 3, the directional coupler 23 is used as a 1 × 2 type.

The directional coupler 50 shown in FIG. 3 is provided on the main body (not shown) of the electro-optic sampling oscilloscope, and transmits the reference laser beam La0 incident through the optical fiber 21 to one end of the optical fiber 51. And the signal light La3 incident through the optical fiber 51 is emitted to one end surface of the optical fiber 26. The optical fiber 51 is
The input / output end of the directional coupler 50 and the input / output end of the directional coupler 23 are connected. That is, in the electro-optic sampling oscilloscope according to the third embodiment, a main body (not shown) and the electro-optic probe 22 are connected by one optical fiber 51. This optical fiber 51
It is desirable to use a polarization-maintaining optical fiber.

In the above configuration, the metal pin 2 shown in FIG.
When the tip of 7 is brought into contact with a signal line (not shown), an electric field corresponding to the level of the signal under measurement transmitted through the signal line is combined with the electro-optic crystal 28, and the refractive index of the electro-optic crystal 28 Changes according to the strength of the electric field. In this state, when the reference laser light La0 is emitted from the light emitting circuit 20, the reference laser light La0 enters the directional coupler 23 via the optical fiber 21, the directional coupler 50, and the optical fiber 51. Then, the reference laser beam La0 is split into a signal beam La1 and a reference beam La2 by the directional coupler 23 in the same manner as the operation described above.

The signal light La 1 emitted from one of the input / output ends of the directional coupler 23 is incident on the surface of the electro-optic crystal 28 via the optical fiber 24. As a result, the polarization state of the signal light La1 propagating inside the electro-optic crystal 28 changes. The signal light La1 having undergone this change is reflected by the reflecting mirror 29, then emitted from the surface of the electro-optic crystal 28, and then, via the optical fiber 24, to one of the input / output ends of the directional coupler 23. Incident.

On the other hand, the reference light La2 emitted from the other input / output end of the directional coupler 23 propagates through the optical fiber 25 and is reflected by the reflector 30 as the reference light La2 '. Then, the reference light La2 'is input to the other input / output end of the directional coupler 23 via the optical fiber 25.

As a result, in the directional coupler 23, the signal light La1 'and the reference light La2' are multiplexed (mixed) to generate the signal light La3. And this signal light La3
Is guided to the directional coupler 50 via the optical fiber 51, guided to one end surface of the optical fiber 26 by the directional coupler 50, and further received by the light receiving circuit 31. As a result, the display section of the electro-optic sampling oscilloscope displays the waveform of the signal under measurement transmitted on the signal line and the like.

As described above, according to the electro-optic sampling oscilloscope according to the third embodiment described above, only one optical fiber 51 is required to connect between the main body and the electro-optic probe 22. Can be reduced in size.

<Fourth Embodiment> Next, the configuration of an electro-optic sampling oscilloscope according to a fourth embodiment of the present invention will be described with reference to FIG. In FIG. 4, FIG.
The same reference numerals are given to the portions corresponding to the respective portions, and the description thereof is omitted. 4, an optical fiber 54 and a first photodiode 5 are used instead of the light receiving circuit 31 shown in FIG.
5. Second photodiode 56 and differential amplifier 57
Is provided.

The directional coupler 23 shown in FIG. 4 is used as a 3 × 2 type, and is used, for example, for coherent optical fiber communication from the output end to which one end of the optical fiber 54 is connected. The signal light La3 ′ having the opposite phase to the signal light La3 is emitted like the balanced light receiving circuit. The first photodiode 55 receives the signal light La3 incident via the optical fiber 26, and converts the signal light La3 into a first electric signal S1. Second photodiode 56
Receives the signal light La3 'incident through the optical fiber 54, and converts it into a second electric signal S2. The differential amplifier 57 includes a first electric signal S1 and a second electric signal S2.
Are differentially amplified. It is desirable to use a polarization-maintaining optical fiber as the optical fiber 54.

In the above configuration, the metal pin 2 shown in FIG.
When the tip of 7 is brought into contact with a signal line (not shown), an electric field corresponding to the level of the signal under measurement transmitted through the signal line is combined with the electro-optic crystal 28, and the refractive index of the electro-optic crystal 28 Changes according to the strength of the electric field. In this state, when the reference laser light La0 is emitted from the light emitting circuit 20, the reference laser light La0 is split into the signal light La1 and the reference light La2 via the optical fiber 21 and the directional coupler 23. . Here, it is assumed that the reference laser beam La0 includes a noise component due to fluctuation or the like.

The signal light La1 is applied to the electro-optic crystal 28.
Is reflected by the reflecting mirror 29 as signal light La1 ', and is incident on the input / output end of the directional coupler 23 via the optical fiber 24. At the same time, after the reference light La2 propagates through the optical fiber 25, the reference light
The light is reflected as a2 'and is incident on the input / output end of the directional coupler 23 via the optical fiber 25.

As a result, in the directional coupler 23, the signal light La1 'and the reference light La2' are multiplexed (mixed), for example, as in a balanced light receiving circuit used for coherent optical fiber communication. , And a signal light La3 ′ having an opposite phase to the signal light La3 is generated. The signal light La3 is transmitted through the optical fiber 26 to the first
Is converted to a first electric signal S1. On the other hand, the signal light La3 'is guided to the second photodiode 56 via the optical fiber 54, and is converted into a second electric signal S2.

In the differential amplifier 57, the first
The electric signal S1 and the second electric signal S2 are differentially amplified. At this time, the first electric signal S1 and the second electric signal S2
Are out of phase, the noise component included in the reference laser beam La0 is cancelled. As a result, the display section of the electro-optic sampling oscilloscope displays the waveform of the signal under measurement transmitted on the signal line and the like.

As described above, according to the electro-optic sampling oscilloscope according to the above-described fourth embodiment, since the noise component included in the reference laser beam La0 is canceled by the differential amplifier 57, the output of the differential amplifier 57 The S / N of the signal can be improved, and the detection sensitivity of the signal under measurement can be improved.

<Fifth Embodiment> FIG. 5 is a diagram showing a configuration of a main part of an electro-optic sampling oscilloscope according to a fifth embodiment of the present invention. In this figure, parts corresponding to the respective parts in FIG. 1 are denoted by the same reference numerals, and description thereof is omitted. 5, an optical waveguide device 100 is provided instead of the directional coupler 23 shown in FIG. The optical waveguide element 100 shown in FIG. 5 has a function of branching and coupling an optical signal, similarly to the directional coupler 23 (see FIG. 1). In this optical waveguide device 100, 100a
Is an optical waveguide connected to the other end of the optical fiber 21, and guides the reference laser light La0 to the optical branching / coupling unit 100b.
The optical branching / coupling unit 100b branches the reference laser beam La0 into the signal light La1 and the reference light La2, and combines (combines) the signal light La1 ′ with the reference light La2 ′, and combines the signal light La1 with the signal light La2.
Output as a3.

An optical waveguide 100c guides the signal light La1 branched by the optical branching / coupling section 100b to the electro-optic crystal 28, while transmitting the signal light La1 'to the optical branching / coupling section 100b.
Lead to. 100d is the light branching / coupling unit 100b and the reflector 3
0, which is an optical waveguide formed between the optical
The reference light La2 branched by 00b is guided to the reflection plate 30, while the reference light La2 ′ reflected by the reflection plate 30 is guided to the light branching / coupling unit 100b. This optical waveguide 100d corresponds to the optical fiber 25 shown in FIG. Here, the difference between the reciprocating optical path length of the optical waveguide 100c and the reciprocating optical path length of the optical waveguide 100d is a half wavelength, and high sensitivity is obtained when the difference is a half wavelength. The difference between the two reciprocating optical path lengths does not necessarily have to be a half wavelength.

In the above configuration, the metal pin 2 shown in FIG.
When the tip of 7 is brought into contact with a signal line (not shown), an electric field corresponding to the level of the signal under measurement transmitted through the signal line is coupled to electro-optic crystal 28. Thereby, the refractive index of the electro-optic crystal 28 changes according to the intensity of the electric field. In this state, when the reference laser light La0 is emitted from the light emitting circuit 20, the reference laser light La0 enters the optical branching / coupling unit 100b via the optical fiber 21 and the optical waveguide 100a. Then, the reference laser beam La0 is split into the signal light La1 and the reference light La2 by the optical splitter / coupler 100b. Here, the frequency of the signal light La1 and the frequency of the reference light La2 are the same.

The signal light La1 is transmitted to the optical waveguide 10
0c through the surface of the electro-optic crystal 28 via
The light propagates inside the electro-optic crystal 28 toward the reflection mirror 29. As a result, the polarization state of the signal light La1 propagating inside the electro-optic crystal 28 changes. Then, the signal light La1 having undergone the polarization change is reflected by the reflecting mirror 29, and then is emitted from the surface of the electro-optic crystal 28, and then the optical waveguide 10
The light is incident on the optical branching / coupling unit 100b through the line 0c.

On the other hand, the reference light La2 propagates through the optical waveguide 100d and is reflected by the reflector 30 as the reference light La2 '. Then, the reference light La2 ′ is
The signal is input to the optical branching / coupling unit 100b via the line d. As a result, in the optical branching / coupling unit 100b, the signal light La1 ′
And the reference light La2 ′ are multiplexed (mixed) to generate the signal light La3. Here, the signal light La3 is the electro-optic crystal 2
8 is a signal light indicating a change in the plane of polarization of the propagating signal light La1.

The signal light La3 is transmitted to the optical fiber 2
6, after being incident on the light receiving circuit 31 through the light receiving circuit 31
Is converted into an electric signal. As a result, the display section of the electro-optic sampling oscilloscope displays the waveform of the signal under measurement transmitted on the signal line and the like.

Although the embodiment of the present invention has been described in detail with reference to the drawings, the specific configuration is not limited to this embodiment, and there are design changes and the like without departing from the gist of the present invention. Even this is included in the present invention. For example, in the electro-optic sampling oscilloscope according to the first, third and fourth embodiments described above, the optical fiber 24
And a configuration of optical fiber coupling using an optical fiber 25 is adopted.
Alternatively, a configuration may be adopted in which the reflector 30 and the reflector 30 are spatially coupled.

Further, in the electro-optic sampling oscilloscope according to the first to fifth embodiments described above, an example was described in which BSO was used as the electro-optic crystal 28. However, the present invention is not limited to this. LN (LiNbO ₃ ), CdTe or BTO (Bi
₁₂ TiO ₂₀ ) may be used. Further, in the electro-optic sampling oscilloscope according to the above-described first embodiment, the configuration in which the phase difference between the signal light La1 ′ and the reference light La2 ′ is set to a half wavelength has been described. In order to improve the accuracy of the phase difference, A phase difference adjusting means for finely adjusting the phase difference by bending the optical fiber 24 or the optical fiber 25 may be provided. As the phase difference means, an optical fiber 2
There are a temperature control type EO crystal in which the phase difference is controlled by changing the ambient temperature of 4 or 25, and a voltage control type EO crystal. Further, in the electro-optic sampling oscilloscope according to the above-described second embodiment, the example using the dummy optical circuit 42 made of glass shown in FIG. 2 has been described, but without providing the dummy optical circuit 42, the half mirror 41 A configuration in which the space between the dummy optical circuit 42 and the dummy optical circuit 42 is used may be adopted.

In the electro-optic sampling oscilloscope according to the third embodiment described above, a circulator may be used instead of the directional coupler 50. Similarly, in the electro-optic sampling oscilloscope according to the above-described second embodiment, a directional coupler may be used instead of the half mirror 41.

In the electro-optic sampling oscilloscopes according to the first to fifth embodiments, when the electric field due to the signal to be measured sufficiently acts on the electro-optic crystal 28, the metal pin 27 may not be provided. Good.

In the electro-optic sampling oscilloscope according to the first to fourth embodiments described above, an example in which the optical fiber 25 and the reflecting plate 30 are provided to generate the reference light La2 'having the same frequency as the signal light La1'. As described above, instead of the optical fiber 25 and the reflection plate 30, a laser light generating device that causes the laser light having the same frequency as the signal light La1 'to enter the directional coupler 23 may be provided.

In addition, in the electro-optic sampling oscilloscope according to the above-described first to fifth embodiments, when the phase of the light source of the light emitting circuit 20 is not stable, the light receiving circuit 3
In step 1, square detection may be performed.

[0066]

As described above, according to the present invention,
Since a polarization beam splitter or the like used in a conventional electro-optic sampling oscilloscope is not required, the configuration of the optical system can be simplified, and the device can be downsized. Furthermore, according to the third and fourth aspects of the present invention, since the noise component included in the reference laser beam is canceled by the differential amplifier, the S / N of the output signal of the differential amplifier can be improved. As a result, the effect of improving the detection sensitivity of the signal under measurement can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a main part of an electro-optic sampling oscilloscope according to a first embodiment of the present invention.

FIG. 2 is a diagram illustrating a configuration of a main part of an electro-optic sampling oscilloscope according to a second embodiment.

FIG. 3 is a diagram showing a configuration of a main part of an electro-optic sampling oscilloscope according to a third embodiment.

FIG. 4 is a diagram showing a configuration of a main part of an electro-optic sampling oscilloscope according to a fourth embodiment.

FIG. 5 is a diagram showing a configuration of a main part of an electro-optic sampling oscilloscope according to a fifth embodiment.

FIG. 6 is a diagram showing a configuration of an electro-optic probe in a conventional electro-optic sampling oscilloscope.

[Explanation of symbols]

 REFERENCE SIGNS LIST 20 light emitting circuit 21 optical fiber 22 electro-optic probe 23 directional coupler 28 electro-optic crystal 29 reflecting mirror 30 reflector 31 light receiving circuit 40 electro-optic probe 41 half mirror 42 dummy optical circuit 50 directional coupler 55 first photodiode 56 second photodiode 57 differential amplifier 100 optical waveguide device

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Yuki Yanagisawa 4-19-7 Kamata, Ota-ku, Tokyo Inside Ando Electric Co., Ltd. (72) Inventor Jun Kikuchi 4-19-7 Kamata, Ota-ku, Tokyo Ando Inside Electric Co., Ltd. (72) Inventor Junichi Banjo 4-19-7 Kamata, Ota-ku, Tokyo Ando Electric Co., Ltd. Inside (72) Yoshio Endo 4-19-7 Kamata, Ota-ku, Tokyo Ando Within Electric Co., Ltd. (72) Inventor Mitsuru Shinagawa Tokyo, Shinjuku-ku, Tokyo 3-19-2 Nippon Telegraph and Telephone Corporation (72) Inventor Tatsuo Nagatsuma 3-2-1, Nishi-Shinjuku, Shinjuku-ku, Tokyo Japan Inside Telegraph and Telephone Corporation (72) Inventor Junzo Yamada 3-19-2 Nishi-Shinjuku, Shinjuku-ku, Tokyo Japan Telegraph and Telephone Corporation

Claims (6)

[Claims] A light emitting means for generating a reference laser beam, the electro-optic crystal having a surface on which the reference laser beam is incident, and a refractive index of which changes according to an intensity of an electric field generated by the signal to be measured; A reflecting mirror formed on the back surface of the electro-optic crystal and reflecting the reference laser light transmitted through the electro-optic crystal; and generating multiplexed light to generate multiplexed light having the same frequency as the reflected light reflected by the reflecting mirror. Means, multiplexing means for multiplexing the reflected light and the multiplexed light, and detection means for detecting the signal under measurement based on the output light of the multiplexing means. Electro-optic sampling oscilloscope. 2. A light emitting means for generating a reference laser beam; the electro-optic crystal whose refractive index changes according to the intensity of an electric field generated by the signal under measurement; and a reflection formed on the back surface of the electro-optic crystal. A mirror, branching means for splitting the reference laser light into a signal light and a reference light, and making the signal light incident on the surface of the electro-optic crystal; and a reciprocator having a difference between a reciprocating optical path length of the signal light and a half wavelength. A reflector that is disposed opposite to the branching unit with an optical path length and reflects the reference light as multiplexed light; and a multiplex that multiplexes the reflected light reflected by the reflecting mirror and the multiplexed light. An electro-optic sampling oscilloscope comprising: means for detecting the signal under measurement based on output light from the multiplexing means. 3. A light emitting means for generating a reference laser beam, the electro-optic crystal having a surface on which the reference laser beam is incident and whose refractive index changes according to the intensity of an electric field generated by the signal under measurement; A reflecting mirror formed on the back surface of the electro-optic crystal and reflecting the reference laser light transmitted through the electro-optic crystal; and generating multiplexed light to generate multiplexed light having the same frequency as the reflected light reflected by the reflecting mirror. Means for multiplexing the reflected light and the multiplexed light to output a first output light and a second output light having an opposite phase to the first output light; First conversion means for converting the first output light into a first signal; second conversion means for converting the second output light into a second signal; and the first signal and the second signal. Differential amplifying means for differentially amplifying the signal of Based on the electro-optical sampling oscilloscope, characterized by comprising detecting means for detecting the signal to be measured. 4. A light emitting means for generating a reference laser beam; the electro-optic crystal whose refractive index changes according to the intensity of an electric field generated by the signal under measurement; and a reflection formed on a back surface of the electro-optic crystal. A mirror, branching means for splitting the reference laser light into a signal light and a reference light, and making the signal light incident on the surface of the electro-optic crystal; and a reciprocator having a difference between a reciprocating optical path length of the signal light and a half wavelength. A reflecting plate disposed opposite to the branching unit with an optical path length, and reflecting the reference light as multiplexed light; and a multiplexing of the reflected light and the multiplexed light, and a first output light. Combining means for outputting the first output light and second output light having the opposite phase; first converting means for converting the first output light into a first signal; Second conversion means for converting output light into a second signal; and the first signal and the second signal. A differential amplifying means for the signals differential amplifier based on said output signal of the differential amplifying means, the electro-optical sampling oscilloscope, characterized by comprising detecting means for detecting the signal to be measured. 5. The electro-optic sampling oscilloscope according to claim 1, wherein the multiplexed light generating means and the multiplexing means are constituted by optical waveguide elements. 6. The electro-optic sampling oscilloscope according to claim 2, wherein said branching means and said multiplexing means are constituted by optical waveguide elements.