JP5645011B2 - Modulated light analyzer and electric field or magnetic field measuring probe device using the modulated light analyzer - Google Patents

Description

  The present invention relates to a technique for analyzing a signal in which orthogonal polarization components are modulated by carrier waves and sidebands, respectively. In particular, when a phase difference occurs between the polarization components in the transmission path, the modulated light analyzing apparatus that correctly measures the amplitude and phase of the carrier wave and the sideband wave by analyzing the phase difference and removing the influence of the transmission path. It is about. Furthermore, the present invention is an apparatus for measuring an electric field or a magnetic field using the electro-optic effect or magneto-optic effect by applying the modulated light analyzing apparatus, and corrects an error generated from a transmission line to obtain a more accurate measurement value. The present invention relates to an electric field or magnetic field detection probe apparatus.

  It is well known that in a system for transmitting light including a carrier wave obtained by modulating polarization and sidebands orthogonal to the carrier wave, the refractive index fluctuates in the orthogonal direction in the transmission path. For example, when a signal is propagated to the slow axis and the fast axis of a polarization-preserving optical fiber (hereinafter abbreviated as PMF), the refractive index of the slow axis and the fast axis fluctuates due to bending and swinging of the PMF, and propagates through each. The phase of light varies relatively. More specifically, for example, in an apparatus that measures an electric field or a magnetic field using the electro-optic effect, the installation position constantly changes between the probe unit of the measuring instrument and the modulated light analysis apparatus having a signal analysis function. This problem is noticeable when connected by PMF, and it has been reported that the measured value fluctuates several percent. Also, in the propagation of light in the atmosphere, it is known that the refractive index fluctuates as the density of each point changes with the flow of air.

  The present invention relates to an electric field or magnetic field detection probe apparatus. As one of measuring apparatuses used for measuring an electric field, a surface potential, or a magnetic field in a region to be measured with almost no disturbance, EO ( Measuring devices using the electro-optic) effect and the MO (magnet-optic) effect are already well known.

  For example, Patent Document 1 (US Pat. No. 3,605,013) discloses a current measurement system using an optical fiber exhibiting a Faraday effect. Patent Document 2 (US Pat. No. 4,002975) discloses voltage measurement using an optical crystal whose polarization direction changes according to the intensity of an electric field or magnetic field.

  Patent Document 3 (Japanese Patent Laid-Open No. 2005-292068) discloses a technique for electrically detecting a phase fluctuation between polarized waves caused by a transmission path such as a PMF and adjusting it by mechanical means. By making light incident on an optical crystal such as an electro-optic crystal, a magneto-optic crystal, or a piezoelectric (photoelastic) crystal to which a physical quantity such as an alternating electric field or an alternating magnetic field is applied, and detecting the light emitted from the optical crystal A measurement system for obtaining a signal corresponding to an AC electric field, an AC magnetic field, a sound pressure, and the like is disclosed. This is intended to suppress the decrease in sensitivity due to the displacement of the optical crystal, and the light source output linearly polarized light from the light source is transmitted to the optical crystal, and the light source output linearly polarized light is measured by the measured physical quantity through the optical crystal. Polarization modulation and transmission to the polarization adjuster by the circulator, polarization-modulated light is converted to arbitrary polarization by the polarization adjuster, the arbitrary polarization is separated into orthogonal linear polarization by the polarization separation means, and the separated linearly polarized light is light The detector converts it into an electrical signal, the electrical signal is output as a differential signal by a differential amplifier, the differential signal is output as an amplitude signal and a phase signal of a physical quantity to be measured by a lock-in amplifier, and the photocurrent of the photodetector And the amplitude signal from the lock-in amplifier are input to the control signal processing unit, and the polarization signal is controlled by the control signal processing unit so that the photocurrents are equal and the amplitude signal is maximized. It is intended to regulate any polarization Te.

US Pat. No. 3,605,013 U.S. Pat. No. 4,200,275 JP 2005-292068 A

  When a signal modulated as a polarization component is transmitted, the refractive index ellipsoid of the transmission path may change. In this case, it is known that a phase difference occurs between polarization components of orthogonal polarization planes. There is a problem that an error occurs in the transmitted data due to the fluctuation of the phase difference. This problem is particularly known as a problem that a phase difference occurs between the light propagating along the fast axis and the slow axis of the polarization maintaining optical fiber.

  Therefore, in the modulated light analyzing apparatus of the present invention, there is no restriction on the system for modulating and transmitting the polarized light by performing optical computation on the side receiving the polarized light and electrically computing the output of the photoelectric conversion means. Without variation, the fluctuation of the measured value due to the fluctuation of the phase difference in the transmission line is extracted.

  Moreover, the electric field or magnetic field detection probe apparatus of the present invention uses the above-described modulated light analysis apparatus to constitute an electric field or magnetic field sensor using the electro-optic effect or the magneto-optic effect. This is an optical magnetic field measurement optical probe in which the measured value does not fluctuate with respect to the swinging of the probe part because the probe part that can be grasped with one hand in both size and weight is connected to the optical detection system with an optical fiber. Is realized.

The modulated light analyzer of the present invention is
The elliptically polarized light including the carrier wave and the sideband having the plane of polarization orthogonal to the carrier wave is set as the incident light to be analyzed.
First light branching means for branching the incident light into first and second polarized light;
The first polarized light is incident light, crosses in any direction of ± π / 4 radians with respect to the polarization planes of the carrier wave and the sideband wave, and is separated into two mutually orthogonal polarization components. Polarization splitting means of
First and second photoelectric conversion means for measuring the respective intensities of the two polarization components orthogonal to each other;
A quarter-wave plate that applies to the second polarization and provides a phase difference between the polarization components;
The second polarized light exiting the ¼ wavelength plate is made incident light, crossed in any direction of ± π / 4 radians with respect to the carrier wave and the sideband polarization plane, and converted into two polarization components orthogonal to each other. A second polarization splitting means for separating;
Third and fourth photoelectric conversion means for measuring the intensity of each of the two polarization components separated by the second polarization branching means and orthogonal to each other;
A signal for inputting all the outputs of the first, second, third and fourth photoelectric conversion means and calculating the intensity of each carrier wave or sideband of the incident light, or a part or all of the phase thereof. A processing circuit;
A first signal generator for generating a first reference signal for designating a frequency for analyzing the incident light to be analyzed;
The signal processing circuit includes the intensity at the specified frequency of the first difference signal, which is the difference between the outputs of the first and second photoelectric conversion means, and the outputs of the third and fourth photoelectric conversion means. The phase difference between the carrier wave of the incident light to be analyzed and the sideband wave is calculated from a first ratio of the second difference signal, which is a difference between them, to the intensity at the specified frequency.

In addition to the above features, the signal processing device in the modulated light analysis device of the present invention includes:
Generating a sum signal of the first difference signal and a second difference signal having a phase shift corresponding to π / 2 or −π / 2 radians of the frequency component of the first reference signal; A first integrated value obtained by integrating a product of the signal and the first reference signal over an integer period of the reference signal, the sum signal, and the first reference signal by π / 2 or −π / 2. A second integrated value obtained by integrating the product with the signal shifted in radians over the above period, and
From the sum of the square value of the first integrated value and the square value of the second integrated value, the product of the intensity of the carrier wave to be analyzed and the intensity of the sideband is obtained.
The signal processing circuit is included in the first reference signal and the sideband of the incident light to be analyzed based on the first ratio and the ratio between the first integrated value and the second integrated value. The phase difference between the reference signal and a signal having the same frequency is calculated.

Further, the present invention is an electric field or magnetic field detection probe device using the above modulated light analysis device,
A light source that outputs linearly polarized light;
An electric or magneto-optic crystal whose refractive index changes with an electric or magnetic field;
The modulated light analyzer according to claim 1;
An optical path including a polarization-preserving optical fiber for guiding the linearly polarized light to the electric or magneto-optical crystal and guiding an output transmitted or reflected by the electric or magneto-optical crystal to the modulated light analyzer;
Comprising
It has a function of measuring at least one of the frequency and intensity of the electric field or magnetic field applied to the electro- or magneto-optical crystal, and the relative phase of the reference signal and the carrier wave.

Further, the electric field or magnetic field detection probe device of the present invention has the above configuration,
Means for modulating linearly polarized light from the light source;
A second signal generator for generating a second reference signal;
Comprising
The linearly polarized light is light incident on the electro- or magneto-optic crystal modulated by a second signal reference;
The electro-optic or magneto-optic crystal performs frequency mixing of the modulation component by the second reference signal included in the incident light and the electric field or magnetic field to be measured, and the output light has an intermediate frequency corresponding to the first frequency. The modulated light analyzing apparatus uses an optical heterodyne method for performing analysis processing on the first frequency component.

In addition to the above configuration,
The optical path is
A second light branching means;
With a bidirectional light path,
The second light branching means sends the linearly polarized light incident from the light source to the electric or magneto-optical crystal via the bidirectional optical path, and returns light from the electric or magneto-optical crystal to the bidirectional In this case, the bidirectional optical path includes a polarization-maintaining optical fiber.

According to the present invention, it is possible to passively compensate for signal fluctuation caused by refractive index fluctuation for each polarization plane of the optical path and to stabilize the received signal. Further, in the electric field or magnetic field measurement probe device using the above-described modulated light analysis device, the measurement deterioration due to the fluctuation of the PMF generated when the measurement terminal and the modulated light analysis device transmit light using the PMF is guaranteed. can do. Furthermore, in the electric field or magnetic field measurement probe apparatus using the heterodyne method, the ellipsometer can limit the function of performing signal detection and processing to a certain frequency, which further contributes to measurement stabilization.

It is a block diagram which shows the structural example of the ellipsometer 20 of this invention. Incident light has polarization planes orthogonal to each other, one of which is a carrier wave and the other is a polarization modulated by a sideband (see FIG. 4C), and is incident on the first optical branching means 5 and substantially equal. The light is branched into first and second polarized light. The first polarized light is supplied by the first polarization branching means 7 with two polarizations orthogonal to each other having an orientation of ± π / 4 radians with respect to the sideband of the incident light or the plane of polarization of the carrier. 3. Separated into fourth and fourth polarized light. The third polarization is photoelectrically converted by the first photoelectric conversion means 9, and the fourth polarization is photoelectrically converted by the second photoelectric conversion means 10 and input to the signal processing circuit 14. The second polarized light, which is the other output of the first light branching means 5, has a direction of ± π / 4 radians by the second polarization branching means 8 through the λ / 4 plate 6 and has a direction of ± π / 4 radians. The light is branched into two orthogonal polarizations, that is, fifth and sixth polarizations. The fifth polarized light is photoelectrically converted by the third photoelectric conversion means 11 and the sixth polarized light is photoelectrically converted by the fourth photoelectric conversion means 12 and input to the signal processing circuit 14. In the figure, reference numeral 13 denotes first signal generating means for supplying the signal processing circuit 14 with a first reference signal having a frequency to be analyzed. 1 is a block diagram showing a configuration of a first embodiment of an electric or magneto-optical probe apparatus of the present invention. The polarized light emitted from the light source 1 that outputs the polarized light is incident on the optical path 3 including the polarization-preserving optical fiber (PMF) via the second optical branching unit 2 and is guided to the irradiation of the electric or magneto-optical crystal 4. Alternatively, the output transmitted or reflected by the magneto-optical crystal 4 is guided to the ellipsometer 20. The ellipsometer 20 analyzes and measures the frequency and intensity of the electric field or magnetic field applied to the electric or magneto-optical crystal from the incident light, and the relative phase of the reference signal and the carrier wave. It is preferable that a means for adjusting the direction of polarization of the incident light, for example, a λ / 2 plate, is provided between the second light branching means 2 and the ellipsometer. FIG. 5 is a block diagram showing a second embodiment of the electrical or magneto-optical probe apparatus of the present invention. In contrast to the first embodiment, a modulation device 16 for modulating polarized light and a second signal generating means 15 for supplying the signal are added. It is a figure which shows the state of polarized light in the ellipsometer of this invention. (A) is a diagram showing the polarization of the light source 1, which is linearly polarized light in the vertical direction (hereinafter referred to as the Y axis) on the drawing. (B) shows the polarized light immediately after leaving the electric or magneto-optical crystal 4. It shows that sidebands are generated in the polarization component in the horizontal direction (hereinafter referred to as the X axis) modulated in the electro- or magneto-optical crystal 4 by an electric field or a magnetic field. The carrier wave is a Y-axis component. (C) shows the polarized light when the light emitted from the electro-optic or magneto-optic crystal 4 causes a phase difference φ between the X-axis and Y-axis components through the transmission path. (D) is a diagram showing the third polarized light separated by the first polarization splitting means 7, and (E) is a diagram showing the fourth polarized light 25 similarly separated by the first polarization splitting means 7, It is a figure which shows the polarized light of the (D) u-u 'and (E) vv' component which cross | intersects an axis | shaft with the angle of (pi) / 4. It is a figure which shows the state of polarization in the ellipsometer of this invention, (F) is an electric field vector figure which shows the polarization plane of the 2nd polarization | polarized-light 23 after passing the (lambda) / 4 board 6, (G). The electric field vector diagram when the coordinate axis of the fifth polarization of the second polarization branching unit 8 output is tilted by π / 4 radians, (H) is the fourth polarization of the second polarization branching unit 8 output. In the embodiment of FIG. 3, the first reference signal 33 from the first signal generating means 13, the second reference signal 30 from the second signal generating means 15, and the object to be measured that is the signal under measurement are emitted. FIG. 4 is a schematic diagram showing a relationship between frequencies of an electric field or a magnetic field 31. The polarized light modulated by the second reference signal 30 is further modulated by an electric field or magnetic field 31 incident on the electro-optic or magneto-optical crystal 4 and emitted from the object to be measured. As a result, the electric field or magnetic field 31 generated by the device under test is frequency converted to produce an intermediate frequency signal 32. The ellipsometer 20 analyzes a frequency component equal to the first reference signal 33 in the intermediate frequency signal 32. This is equivalent to analyzing the electric field or magnetic field 31 generated by the object to be measured. The frequency to be measured, which is the sum of the frequency of the first reference signal 33 and the frequency of the second reference signal 30, is the frequency position of the electric field or magnetic field that is actually analyzed. The measured frequency may be a difference between the frequency of the first reference signal 33 and the frequency of the second reference signal 30. It is a figure which shows the Example of the optical part of the ellipsometer 20 shown in FIG. The incident light 28 is branched into the first polarized light 22 and the second polarized light 23 by the first light branching means 5, and the first polarized light 22 is incident on the first polarization branching means 7, and the polarization planes are orthogonal to each other. The light is separated into the third polarized light 24 and the fourth polarized light 25 and is incident on the first photoelectric conversion means 9 and the second photoelectric conversion means 10. The second polarized light 23 is bent by the reflecting mirror 21 and a phase difference is added between the polarization plane components by the λ / 4 plate 6. Then, the second polarized light 23 enters the second polarization branching unit 8 and is orthogonal to each other. 26 and the sixth polarized light 27, and enters the third photoelectric conversion means 11 and the fourth photoelectric detection means 12. The outputs of the four photoelectric conversion means are input to a signal processing circuit for analysis.

  Embodiments of the present invention will be described below in detail with reference to the drawings. In the following description, devices having the same function or similar functions are denoted by the same reference numerals unless there is a special reason.

  FIG. 1 shows a block diagram of an ellipsometer 20 that is an embodiment of the present invention. The incident light is polarized light that is modulated by a carrier wave and the other by a sideband in the planes of polarization orthogonal to each other. The incident light is incident on the first optical branching means 5 and is substantially equal to the first and second polarized light. Branches into 22 and 23. The first polarized light 22 is obtained by the first polarization branching means 7 so as to have two polarizations orthogonal to each other with an orientation of ± π / 4 radians with respect to the sideband of the incident light or the polarization plane of the carrier wave, that is, Separated into third and fourth polarizations 24 and 25. The third polarization 24 is photoelectrically converted by the first photoelectric conversion means 9, and the fourth polarization 25 is photoelectrically converted by the second photoelectric conversion means 10 and input to the signal processing circuit 14. The second polarized light 23 which is the other output of the first light branching means 5 is branched into the fifth and sixth polarized lights 26 and 27 by the second polarization branching means 8 through the λ / 4 plate 6, The signals are photoelectrically converted by the third photoelectric conversion means 11 and the fourth photoelectric conversion means 12 and input to the signal processing circuit 14. The first signal generation means 13 supplies the signal processing circuit 14 with a first reference signal having a frequency to be analyzed.

The signal processing circuit 14 determines the intensity of the first difference signal at the specified frequency from the difference between the outputs of the first photoelectric conversion unit 9 and the second photoelectric conversion unit 10, the third photoelectric conversion unit 11, and the first photoelectric conversion unit 11. 4. Determine the intensity of the second difference signal, which is the difference between the outputs of the four photoelectric conversion means 12, at the designated frequency, and further determine the intensity of the intensity of the first difference signal and the intensity of the second difference signal. From the ratio of 1, the phase difference between the carrier wave of the incident light to be analyzed and the sideband is calculated.
Furthermore, a sum signal of the first difference signal and a second difference signal subjected to phase shift corresponding to π / 2 or −π / 2 radians of the frequency component of the first reference signal is generated, and A first integrated value obtained by integrating the product of the sum signal and the first reference signal over an integer period of the reference signal, the sum signal, and the first reference signal by π / 2 or −π A second integrated value obtained by integrating the product of the signal with a / 2 radian phase shift over the above period,
From the sum of the square value of the first integrated value and the square value of the second integrated value, the product of the intensity of the carrier wave to be analyzed and the intensity of the sideband is obtained.
The signal processing circuit 14 is included in the first reference signal and the sideband of the incident light to be analyzed, based on the first ratio and the ratio between the first integrated value and the second integrated value. The phase difference between the reference signal and the signal having the same frequency is calculated. The processing of the signal processing circuit 14 can be performed by an analog arithmetic circuit, or can be performed by digital signal processing by digitizing the photoelectric conversion means input.

  FIG. 4 shows the signal processing process of the present invention. 4A shows the polarized light emitted from the light source 1, and FIG. 4B shows, for example, the polarization planes of the sideband and the carrier generated as a result of modulation by an electric field or magnetic field applied to the electro-optic or magneto-optic crystal 4. Indicates. When this is described in a matrix, FIG.

  This light is input to the ellipsometer 20 with a relative phase difference due to distortion of the transmission path or the like. The state of the polarization plane at this time is shown in FIG. Here, when described as a phase difference of φ in the carrier wave, the following equation 2 is obtained.

ここで、ｉは虚数単位である。

Here, i is an imaginary unit.

FIG. 4D shows the third polarized light output from the first polarization splitting means 7.
The electric field of the polarization component in the uu ′ direction is shown in the following equation.

FIG. 4E shows the fourth polarized light output from the second polarization splitting means 8.
The electric field of the polarization component in the vv ′ direction is expressed by the following equation (4).

  FIG. 5F is an electric field vector diagram showing the polarization plane of the second polarized light after passing through the λ / 4 plate 6 and can be expressed as follows.

FIG. 5G shows the fifth polarized light output from the second polarization splitting means 8.
The electric field of the polarization component in the uu ′ direction is as follows.

FIG. 5H shows the sixth polarized light output from the second polarization splitting means 8.
The electric field of the polarization component in the vv ′ direction is as follows.

  After applying Euler's formula to the exponential function from Equations 3, 4, 6, and 6 representing the electric fields of polarized light 3, 4, 5, and 6, the complex intensity is multiplied by the conjugate complex number, that is, from the first. Calculation of the outputs of the fourth photoelectric conversion means 9 to 12 is as follows.

The output of the first photoelectric conversion means;

The output of the second photoelectric conversion means;

The output of the third photoelectric conversion means;

The output of the fourth photoelectric conversion means;

  The first difference signal is obtained by subtracting the output of the second photoelectric conversion means from the output of the first photoelectric conversion means. Therefore, subtracting Equation 9 from Equation 8 yields:

  The second difference signal is obtained by subtracting the output of the fourth photoelectric conversion means from the output of the third photoelectric conversion means. Accordingly, subtracting Equation 10 to Equation 11 yields the following:

  The phase difference φ between the carrier wave and the sideband can be obtained as follows from the ratio of Equations 12 and 13.

  Further, the following expression is obtained by adding the result of Expression 12 to Expression 13 by performing π / 2 or −π / 2 radian phase shift.

  When this result is multiplied by sin (θ ± δ) or cos (θ ± δ) as a reference signal and integrated over an integer (n) times the reference signal period (2π), the result is as follows. However, the integration time is sufficiently shorter than the change time of φ so that φ can be regarded as constant over the integration time. For δ, the phase of the signal having the same frequency as that of the first reference signal 33 included in the sideband of the incident light to be analyzed, that is, the phase of the signal (sin (θ)) at the time of measurement, and the first This reflects the difference in the phase of the reference signal 33, that is, the phase of the signal (sin (θ + δ)) during the calculation process.

となるので、積abを求めることができる。

Therefore, the product ab can be obtained.

  Eventually, by applying the phase difference φ obtained from Equation 7 and the product ab to Equation 13 or Equation 14, sin (θ), that is, the phase θ proportional to the intensity of the electromagnetic field to be measured can be obtained. it can. Moreover, it converts into the measured electromagnetic field intensity | strength from the comparison with the electromagnetic field intensity used as a reference | standard. In this way, phase fluctuations caused by bending of the polarization-maintaining optical fiber can be corrected by calculating the electric signal without adjusting the optical system, and stable without being affected by the fluctuations described above. Measurement can be realized.

  Here, the quarter-wave plate 6 can be used even if there is a manufacturing error of about 1/16 wavelength. In addition, the signal processing circuit 14 can be configured by an analog arithmetic unit, but a digital arithmetic unit that converts an input signal into a digital signal and performs digital processing is desirable in terms of stable operation.

  FIG. 2 is a block diagram showing an embodiment of a probe device for measuring an electric field or a magnetic field using the polarization analyzer 20 for polarized light according to the present invention. The electric field or magnetic field is obtained by applying a phenomenon in which the refractive index changes due to the electric or magnetic Kerr effect in the electric or magneto-optical crystal 4 installed in the electric field or magnetic field generated by the object to be measured 19 and from the amount of change in the refractive index. It measures the magnitude of an electric or magnetic field.

  Polarized light emitted from the light source 1 that outputs polarized light enters the optical path 3 including the polarization-preserving optical fiber via the second optical branching means 2 and is guided to the irradiation of the electric or magneto-optical crystal 4. The output transmitted or reflected by the electric or magneto-optical crystal 4 is guided to the ellipsometer 20. The ellipsometer 20 analyzes and measures the intensity of the same frequency component as the reference signal of the electric field or magnetic field applied to the electro- or magneto-optic crystal 4 from the incident light, and the relative phase of the reference signal and the carrier wave. It is preferable that a means for adjusting the direction of polarization of the incident light, for example, a λ / 2 plate is provided between the second light branching means 2 and the ellipsometer 20.

  FIG. 3 is a block diagram showing an embodiment of the electric or magnetic probe apparatus 20 using the optical heterodyne method. The polarized light emitted from the light source 1 is modulated by the modulation device 16 with the second reference signal from the second signal generating means 15 and is incident on the electric or magneto-optical crystal 4 via the second light branching means 2 and the optical path 3. To do. The incident polarized light is modulated by the influence of the electric field or magnetic field generated by the object to be measured 19, travels back along the optical path 3, and enters the polarization analyzer 20 by the second light branching unit 2 to analyze the polarization. receive. The ellipsometer 20 has the same frequency component intensity as the first reference signal from the first signal generating means 13 in the signal component of the electric field or magnetic field that has influenced the electric or magneto-optic crystal 4 from the analysis result of the polarization, A phase difference between the second reference signal and the frequency component of the electric field or magnetic field is measured. A second signal generator 15 for generating a second reference signal is added in this embodiment for the heterodyne detection method.

  FIG. 6 shows the first reference signal 33 from the first signal generating means 13, the second reference signal 30 from the second signal generating means 15, and the electric field generated by the object to be measured that becomes the signal to be measured. The relationship of the frequency of the magnetic field 31 is shown. The polarized light modulated by the second reference signal 30 is incident on the electric or magneto-optical crystal 4 and is modulated by the electric field or magnetic field 31 generated by the object to be measured. As a result, the electric field or magnetic field 31 generated by the device under test is frequency converted to produce an intermediate frequency signal 32. The ellipsometer 20 analyzes a frequency component equal to the first reference signal 33 in the intermediate frequency signal 32. This is equivalent to analyzing the electric field or magnetic field 31 generated by the object to be measured. The frequency to be measured, which is the sum of the frequency of the first reference signal 33 and the frequency of the second reference signal 30, is the frequency position of the electric field or magnetic field that is actually analyzed.

  In the present embodiment, it is desirable to set the frequency of the first reference signal to a relatively low frequency, for example, about 1 MHz, and to set the frequency of the second reference signal close to the operating frequency of the device under test. As a result, the ellipsometer of the present invention only needs to respond to the frequency of the first reference signal, so that the processing speed may be slow, and the frequency of the first reference signal is fixed to a specific frequency by fixing the frequency. Since it is sufficient to respond, a narrow band and high performance filter can be introduced.

FIG. 7 shows an embodiment of the optical portion of the ellipsometer 20 shown in FIG. The incident light 28 is branched into the first polarized light 22 and the second polarized light 23 by the first light branching means 5, and the first polarized light 22 enters the first polarized light branching means 7, and the polarization planes are orthogonal to each other. The light is branched into the third polarized light 24 and the fourth polarized light 25 and is incident on the first photoelectric conversion means 9 and the second photoelectric conversion means 10. The second polarized light is bent by the reflecting mirror 21 and a phase difference is added between the polarization plane components by the λ / 4 plate 6, and then enters the second polarization branching unit 8 and the polarization planes are orthogonal to each other. The polarized light 26 and the sixth polarized light 27 are branched into the third photoelectric conversion means 11 and the fourth photoelectric detection means 12. The outputs of the first to fourth photoelectric conversion means are input to the signal processing circuit 14 for analysis. The first light branching means 5 may be a simple semi-transparent mirror, but in this embodiment, a cube beam splitter is used. As the first and second polarization branching means, a polarization separation plate , a lotion prism, a Woratomson prism, a Savart plate, a Glan laser prism, a polarization separation plate, a polarization beam splitter, or the like can be used. In this embodiment, a Savart plate is used. As the first to fourth photoelectric conversion means, for example, a photoelectric tube, a photomultiplier tube, a photodiode, a phototransistor, an avalanche photodiode, or the like can be used.

  Since the ellipsometer of the present invention has a function of analyzing and canceling the change in the birefringence of the medium in the light transmission path, it is also possible to measure the change in the birefringence of the medium. Therefore, it can be applied to an analysis method in a laser radar.

1 light source 2 the second light branching means 3 optical path or bidirectional optical path 4 electrical or magneto-optical crystal 5 first optical branching unit 6 lambda / 4 plate 7 first polarization splitting means 8 second polarization splitting means 9 1st photoelectric conversion means 10 2nd photoelectric conversion means 11 3rd photoelectric conversion means 12 4th photoelectric conversion means 13 1st signal generation means 14 Signal processing circuit 15 2nd signal generation means 16 Modulator 19 Measurement object 20 Ellipsometer 21 Reflector 22 First polarization 23 Second polarization 24 Third polarization 25 Fourth polarization 26 Fifth polarization 27 Sixth polarization 28 Incident light 30 Second reference signal 31 Electric field Or magnetic field 32 intermediate frequency signal 33 first reference signal

Claims (5)

The elliptically polarized light including the carrier wave and the sideband having the plane of polarization orthogonal to the carrier wave is set as the incident light to be analyzed.
First light branching means for branching the incident light into first and second polarized light;
The first polarized light is incident light, crosses in any direction of ± π / 4 radians with respect to the polarization planes of the carrier wave and the sideband wave, and is separated into two mutually orthogonal polarization components. Polarization splitting means of
First and second photoelectric conversion means for measuring the respective intensities of the two polarization components orthogonal to each other;
A quarter-wave plate that applies to the second polarization and provides a phase difference between the polarization components;
The second polarized light exiting the ¼ wavelength plate is made incident light, crossed in any direction of ± π / 4 radians with respect to the carrier wave and the sideband polarization plane, and converted into two polarization components orthogonal to each other. A second polarization splitting means for separating;
Third and fourth photoelectric conversion means for measuring the intensity of each of the two polarization components separated by the second polarization branching means and orthogonal to each other;
A signal for inputting all the outputs of the first, second, third and fourth photoelectric conversion means and calculating the intensity of each carrier wave or sideband of the incident light, or a part or all of the phase thereof. A processing circuit;
A first signal generator for generating a first reference signal for designating a frequency for analyzing the incident light to be analyzed;
The signal processing circuit includes the intensity at the specified frequency of the first difference signal, which is the difference between the outputs of the first and second photoelectric conversion means, and the outputs of the third and fourth photoelectric conversion means. The phase difference between the carrier wave of the incident light to be analyzed and the sideband is calculated from the first ratio of the second difference signal, which is the difference between them, to the intensity at the designated frequency. Modulated light analyzer. Generating a sum signal of the first difference signal and a second difference signal having a phase shift corresponding to π / 2 or −π / 2 radians of the frequency component of the first reference signal; A first integrated value obtained by integrating a product of the signal and the first reference signal over an integer period of the reference signal, the sum signal, and the first reference signal by π / 2 or −π / 2. A second integrated value obtained by integrating the product with the signal shifted in radians over the above period, and
From the sum of the square value of the first integrated value and the square value of the second integrated value, the product of the intensity of the carrier wave to be analyzed and the intensity of the sideband is obtained.
The signal processing circuit is included in the first reference signal and the sideband of the incident light to be analyzed based on the first ratio and the ratio between the first integrated value and the second integrated value. The modulated light analyzing apparatus according to claim 1, wherein a phase difference between the reference signal and a signal having the same frequency is calculated. A light source that outputs linearly polarized light;
An electric or magneto-optic crystal whose refractive index changes with an electric or magnetic field;
The modulated light analyzer according to claim 1;
An optical path including a polarization-preserving optical fiber for guiding the linearly polarized light to the electric or magneto-optical crystal and guiding an output transmitted or reflected by the electric or magneto-optical crystal to the modulated light analyzer;
Comprising
An electric field or magnetic field detection probe apparatus having a function of measuring at least one of a frequency and intensity of an electric field or a magnetic field applied to the electric or magneto-optical crystal, and a relative phase of a reference signal and a carrier wave. In addition to the configuration of claim 3,
Means for modulating linearly polarized light from the light source;
A first signal generator for generating a second reference signal;
Comprising
The linearly polarized light is incident on the electro- or magneto-optic crystal modulated by a second signal reference;
The electro-optic or magneto-optic crystal performs frequency mixing of the modulation component of the second reference signal included in the incident light and the electric field or magnetic field to be measured, and outputs an intermediate frequency corresponding to the first frequency. 4. The electric field or magnetic field detection probe apparatus according to claim 3, wherein the modulated light analyzing apparatus uses an optical heterodyne method for generating a component and performing an analysis process on the first frequency component. The optical path is
A second light branching means;
With a bidirectional light path,
The second light branching means sends the linearly polarized light incident from the light source to the electric or magneto-optical crystal through the bidirectional optical path, and returns light from the electric or magneto-optical crystal to the bidirectional light. Exiting to the ellipsometer through the optical path,
5. The electric field or magnetic field detection probe device according to claim 3, wherein the bidirectional optical path includes a polarization maintaining optical fiber.

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