JPH07128408A - Eo probe - Google Patents

Abstract

PURPOSE:To enhance S/N ratio of a non-contact electric test probe using an EO (electric optical effect) element and a laser light. CONSTITUTION:An EO element 101, a deflection beam splitter 103 that separates a laser light modulated by an electric field of an object 102 to be measured to an inphase one and an antiphase one and photodetectors 104, 105 are integrated into a unit and the unit is rotated so that separation ratio of quantities of the in-phase and antiphase of the laser is controlled to be equalized. One of the detectors 104, 105 is moved to be adjusted so that the phases of the separated lasers 108c, 108d are adjusted. The difference between the separated lasers of which optical quantities and phases are adjusted is obtained so that a noise caused by the laser light 108a is removed and S/N ratio is enhanced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an EO probe which is a non-contact type voltage measuring device for testing an electric circuit in a non-contact manner, and more particularly to an optically actuated input optical system for eliminating a noise component caused by a laser light source of the EO probe. Regarding the road.

[0002]

2. Description of the Related Art Conventionally, a non-contact type voltage measuring device using a laser beam of this type does not apply a capacitive load to an electric circuit which is an object to be measured, as disclosed in Japanese Patent Application Laid-Open No. 3-6465. It is used for the purpose of enabling accurate waveform observation even in the high frequency region.

Next, this conventional non-contact type voltage measuring device will be described with reference to the drawings.

FIG. 3 is a block diagram showing an example of a conventional non-contact type voltage measuring device using a laser beam.

The frequency of the laser light emitted from the laser light source 301 is stabilized at a specific frequency. The optical path of this light is changed by the mirror 302, and the beam splitter 30
3, passes through the convex lens 304 and the microcell 305, and is focused on the electrode of the IC 306 formed on the wafer. Light reflected from this electrode is again transmitted to the microcell 305,
After passing through the convex lens 304 to become parallel light, it is reflected by the beam splitter 303 and is incident on the photodetector 310. Here, the microcell 305 is one in which a gas having a Stark effect is filled.

The photodetector 310 converts a light signal into an electric signal by using a photodiode, a mercury cadmite tellurite detector or the like. The output signal of the photodetector 310 is synchronously detected with the reference signal of the oscillator 308 by the lock-in amplifier 311, and only the component in synchronization with the reference signal is detected. As a result, the drift of the light intensity of the laser light source 301 can be removed and a signal with a good S / N ratio can be detected. Further, the detection signal is a first derivative of the light absorption intensity because the frequency-modulated laser light is synchronously detected. Convex lens 30 of microcell 305
A transparent thin film electrode that is conductive and allows light to pass through is attached to the surface of No. 4, and a voltage based on the ground potential of the IC 306 is applied to this electrode by a DC amplifier 307.
Since the voltage of the DC amplifier 307 is in balance with the oscillation frequency of the laser light source 301, the light absorption frequency of the gas in the microcell 305 is located at a position where the change of the voltage of the electrode of the IC 306 and the change of the signal output by the lock-in amplifier 311 are proportional. Is set to come. Here, when the voltage of the electrode on the IC 306 changes, the microcell 3 is caused by the Stark effect.
The light absorption frequency of the gas in 05 changes, the detected light intensity changes, and the output of the lock-in amplifier 311 changes.

Another example is one in which only the drift of the light intensity of the laser light source is compensated.

[0008]

In the above-mentioned conventional non-contact type voltage measuring device using laser light, the voltage applied to the electric circuit (here, IC) as the DUT is used as the reference signal of the lock-in amplifier. Synchronize. That is, there is a problem that it can be applied only to the waveform observation of the signal whose frequency is known in advance in the electric circuit.

Further, in another example, since only the drift of the light intensity of the laser light source is compensated, the change of the polarization plane is changed as the change of the voltage of the object to be measured by using the EO (electro-optical effect) element. In case of catching, it is impossible to compensate the change of the light quantity reflected by the beam splitter due to the rotation of the polarization plane of the laser beam due to the drift of the polarization plane of the laser light source and the natural birefringence of the EO element, and the detection voltage of the DUT is insufficient due to insufficient light input to the photodetector. There is a problem of decrease.

[0010]

The EO probe of the present invention is a non-measuring device for measuring an object to be measured using a laser beam and an EO element that is applied by an electric signal of the object to be measured and modulates the polarization state of the laser beam. In a contact electric signal test EO probe, a polarization beam splitter that separates the measured laser light reflected by the object to be measured and passed through the EO element into in-phase and anti-phase components, and both separated components of the measured laser light are electric signals. It is equipped with a structure that integrates a photodetector that converts the light into two components.By rotating the integrated structure, the incident angle of the polarization plane of the laser light to be measured with respect to the polarization beam splitter is adjusted, and the light amounts of both separated components are made the same. The function to adjust the amount and the function to adjust the phase difference between the laser light components by adjusting the optical path difference of the measured laser light separated into in-phase and anti-phase by moving the photodetector. Is characterized in that it comprises a function of removing noise components by taking the difference between the two components of the separated measured amount of laser light is adjusted phase difference.

[0011]

Embodiments of the present invention will now be described with reference to the drawings.

FIG. 1 is a block diagram showing an optical system path to which an embodiment of the EO probe according to the present invention is applied, and FIG. 2 shows a change in light intensity of the laser light source shown in FIG. 1 and a laser light modulated by a signal under measurement. FIG. 7 is a diagram showing both in-phase and anti-phase components after separation of the state of light intensity change.

In FIG. 1, the EO element 101 is applied with an electric field by sandwiching the EO element 101 with an electric signal at a measurement point 110 on the object to be measured 102 and a transparent thin film electrode 111 which is conductive and transmits light. , The polarization state of the laser light 108a that is incident on the EO element 101 and reflected by the dielectric multilayer reflective film 112 on the opposite end face is modulated.

As the EO element, for example, uniaxial crystal lithium niobate is used in a vertical operation. When an electric field is applied to this EO element, the refractive index changes due to the Pockels effect, and the polarization state of the laser light passing through this EO element changes. That is, the polarization plane rotates in proportion to the applied electric field.

The mirror 109 is for guiding the laser beam 108a to the EO element 101. The convex lens 113 is a parallel laser beam 108a for measuring a minute measurement point.
Is for condensing the laser light and returning the laser light reflected and returned to parallel light.

The EO probe of this embodiment comprises a polarization beam splitter 103 and photodetectors 104 and 10.
Fix 5 so that each positional relationship is unchanged,
The light receiving unit 106 has a function of rotating the laser beam 108b as an axis. As a result, the DUT 10
The polarization plane of the laser beam 108b and the polarization beam splitter 10 in the state where no electric signal is applied to the second measurement point 110.
3 can be controlled, and the laser beam 108 can be controlled.
laser light 108 by the polarization beam splitter 103 of FIG.
The light quantity separation ratio to c and 108d is determined by the light receiving unit 106.
Can be controlled by rotating the laser beam 10
The light amounts of 8c and 108d can be adjusted to the same amount. That is, the bias in the initial state is adjusted so that the detection sensitivity is higher and the output of the photodetector is proportional to the electric signal at the measurement point 110 of the DUT 102.

The polarization beam splitter 103 uses a laser beam 1
08b is for separating in-phase and anti-phase (P polarized light, S polarized light). The photodetectors 104 and 105 are optical converters that convert the separated laser beams 108c and 108d into electric signals, and the differential amplifier 107 detects the signal component by taking the difference between the in-phase and anti-phase electric signals. It is a thing.

The laser beam 108b transmitted through the EO element 101, reflected, and modulated by the electric signal at the measuring point 110 on the object 102 to be measured is rotated by the light receiving unit 106 so that its polarization plane and the polarization beam splitter 103 are separated. The relationship is adjusted, and the polarized beam splitter 103 separates the laser lights 108c and 108d of the same phase and opposite phases into the laser lights 108c and 108d, which are respectively incident on the photodetectors 104 and 105, and are converted into electric signals.

The polarization beam splitter 103 is capable of steplessly adjusting the separation ratio of the amount of output light separated from the incident light, depending on the positional relationship with the polarization plane of the incident light. In-phase component 201, anti-phase component 202
As shown in, the drift of the light intensity of the incident light appears in the same phase in both in-phase and anti-phase, and the signal component modulated by the electric signal at the measurement point 110 appears in anti-phase.

The optical path difference is adjusted by moving one of the photodetectors 105 in parallel with the optical axis of the laser beam 108d, and the polarization beam splitter 103 converts the laser beam 108b into the in-phase and anti-phase by adjusting the optical path difference. Both the optical phase difference between the laser beams 108c and 108d generated during the separation and the phase difference between the electric signals generated during the photoelectric conversion by the photodetectors 104 and 105 are adjusted.

The lasers separated as described above and adjusted so that the separation ratios of the laser light in the state where no electric signal is applied to the measurement point 110 of the DUT 102 are the same and the phase difference is adjusted. The lights 108c and 108d are converted into electric signals by the photodetectors 104 and 105, and are input to the operational amplifier 107 as positive and negative inputs, respectively, and when an electric signal is applied to the measurement point 110, the output of the operational amplifier 107 is output. Is a signal with a good S / N ratio in which the light intensity drift of the laser light source is removed and the rotation of the polarization plane of the laser light due to the drift of the polarization plane and the natural birefringence of the EO element is compensated.

In the above description, lithium niobate is used as the EO element, but lithium tantalate may be used as the EO element. In this case, the difference in the elements only affects the sensitivity and the operation is the same, and
There is no significant difference in sensitivity between lithium niobate and lithium tantalate.

[0023]

As described above, since the EO probe of the present invention does not use the applied signal to the object to be measured as the reference signal, it is not necessary to synchronize with the signal to be measured and any signal can be measured. This is advantageous in that it does not require an additional circuit for synchronization.

The EO probe of the present invention eliminates the light intensity drift of the laser light source and compensates for the polarization plane drift of the laser light source and the rotation of the laser light polarization plane due to natural birefringence of the EO element. There is an effect that the detection sensitivity of the signal and the S / N ratio of the detected signal can be improved.

In the EO probe of the present invention, the positional relationship between the plane of polarization of the laser light and the polarization beam splitter that separates the laser light into both in-phase and anti-phase components can be controlled to control the laser light. The separation ratio of both in-phase and anti-phase components can be easily controlled and adjusted, and the phase difference between in-phase and anti-phase components can be easily controlled and adjusted by moving the photo detector. There is no need to adjust the gain and phase of the operational amplifier when extracting the electrical signal to be measured from both the in-phase and anti-phase components converted to, and there is an effect that an electrical additional circuit for that is not required.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an optical system path to which an embodiment of an EO probe according to the present invention is applied.

FIG. 2 is a diagram showing changes in the light intensity of the laser light source in FIG. 1 and changes in the light amount of the laser light modulated by the signal under measurement for both in-phase and anti-phase components after separation.

FIG. 3 is a block diagram showing an example of a conventional non-contact type voltage measuring device using laser light.

[Explanation of symbols]

 101 EO Element 102 Object to be Measured 103 Polarizing Beam Splitter 104 Photodetector 105 Photodetector 106 Photoreceptor Unit 107 Operational Amplifier 108a-d Laser Light 109 Mirror 110 Measurement Point 111 Transparent Thin Film Electrode 112 Dielectric Multilayer Reflective Film 113 Convex Lens 201 In-Phase Component 202 Inverse Phase Component 301 Laser Light Source 302 Mirror 303 Beam Splitter 304 Convex Lens 305 Micro Cell 306 IC 307 DC Amplifier 308 Oscillator 309 Moving Stage 310 Photodetector 311 Lock-in Amplifier

Claims (3)

[Claims] 1. A non-contact electrical signal test for measuring an object to be measured using a laser beam and an EO (electro-optical effect) element which is applied by an electrical signal of the object to be measured and modulates a polarization state of the laser beam. In the EO probe for use, a polarization beam splitter that separates the measured laser light reflected by the object to be measured and passed through the EO element into in-phase and anti-phase components, and both components of the separated measured laser light into electrical signals. The photodetector for conversion has an integrated structure, and the integrated structure is rotated to adjust the incident angle of the polarization plane of the laser beam to be measured with respect to the polarization beam splitter. The function to adjust the amount of light to the same amount, and the optical path difference of the measured laser light separated into the in-phase and anti-phase is adjusted by moving the photodetector to adjust the phase difference between both components of the laser light. A function of adjusting, EO probe characterized in that it comprises a function of removing noise components by taking the difference between the two components of the separated in-phase and negative-phase measured amount of laser light is adjusted phase difference. 2. The EO probe according to claim 1, wherein the photodetector is a photodetector, a photodiode, or a photoelectric tube. 3. The EO element is lithium niobate or lithium tantalate.
Alternatively, the EO probe described in 2.