JPH07181205A - Optical measuring apparatus - Google Patents

Abstract

PURPOSE:To provide an excellent optical measuring apparatus which enables the measuring of a magnetic field or a current with a high accuracy utilizing an magnetooptical effect. CONSTITUTION:2-wavelength light is emitted from a two-wave light source 21. Control light with a frequency omega passes through a control light path 11. Measuring light with the frequency omega+DELTA omega is admitted to a measuring light path 12 and after turned to a circularly polarized light with a lambda/4 plate 24a, it is transmitted through a magnetooptical medium 1 to undergo a Faraday rotation according to the intensity of a magnetic field. The measuring light subjected to the Faraday rotation is turned to a linearly polarized light again with the lambda/4 plate 24b again, overlapped with the control light passing through the control light path 11 with a beam combiner 9 and passes through a polarizer 3 to be incident into a photo detector 5 as hetrodyne interfering light. A detection signal is inputted into a phase change detection circuit 22 to detect a variation of a phase thereby enabling the measuring of changes in the length of the measuring light path according to a mag netic field or a current.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical application measuring device for measuring a physical variable such as a magnetic field or an electric current by utilizing a magneto-optical effect.

[0002]

2. Description of the Related Art In general, an optical application measuring device utilizes a magnetic induction birefringence effect (a birefringence phenomenon that appears when light passes through a magnetic substance), which is one of the magneto-optical effects, to generate magnetic fields, currents, etc. Is a device for measuring the physical variable of. Two typical examples of such an optical application measuring device will be shown below.

First, FIG. 5 shows an optical application measuring apparatus utilizing the Faraday effect, which includes a magneto-optical medium 1, a light source 2, a polarizer 3, a polarizing beam splitter 4, and two photodetectors 5.
a, 5b, and a polarization plane rotation angle detection circuit 6. Here, the Faraday effect means that when a linearly polarized light wave is transmitted through a magneto-optical medium arranged in a magnetic field,
This is a phenomenon in which the plane of polarization rotates by an angle proportional to the strength of the magnetic field due to the difference in refractive index for left and right circularly polarized light.

That is, when measuring a physical variable such as a magnetic field or an electric current using this device, first, the light emitted from the light source 2 is converted into linearly polarized light by the polarizer 3,
The magneto-optical medium 1 arranged in the magnetic field is transmitted to rotate the Faraday. Next, the linearly polarized light emitted from the magneto-optical medium 1 is separated into two orthogonal polarization components (x component and y component) by the polarization beam splitter 4, and this x component
The linearly polarized components of the component and the y component are made incident on the two photodetectors 5a and 5b, respectively, and converted into electric signals. Finally, in the polarization plane rotation angle detection circuit 6, the rotation angle of the polarization plane is detected from the measured light intensity ratio of these two components from the electrical signals of the x component and the y component, and the magnetic field or current is detected from this rotation angle. Ask for.

Next, FIG. 6 shows an optical application measuring apparatus using the interferometry, which shows a magneto-optical medium 1 exhibiting the Faraday effect.
, Coherent light source 7, beam splitter 8, beam combiner 9, photodetector 5, and phase difference detection circuit 10
It consists of This device utilizes the fact that the refractive index of light changes due to a magnetic field.

That is, when measuring a physical variable such as a magnetic field or a current using this apparatus, first, the light emitted from the coherent light source 7 is split by the beam splitter 8 so that it does not pass through the magnetic field. The optical path 11 and the measuring optical path 12 passing through the magneto-optical medium 1 arranged in the magnetic field are passed respectively. In this case, the optical path length difference between the reference optical path 11 and the measurement optical path 12 changes in proportion to the strength of the magnetic field.
Then, the two light waves that have thus passed through the reference optical path 11 and the measurement optical path 12 are caused to interfere with each other by the beam combiner 9 and are converted into electric signals. Finally, the phase difference detection circuit 10 obtains the measurement light intensity from the electric signal of the interference light to detect the phase difference, and obtains the magnetic field or the current.

[0007]

By the way, the conventional optical application measuring device as described above has the following problems. That is, firstly, any of the methods is a method of measuring the light intensity and obtaining the change of the magnetic field or the current based on the change, but the change of the magnetic field or the current is linearly dependent on the change of the measured light intensity. Since it does not exist, the calculation of the magnetic field or current based on the light intensity is complicated. Secondly, from the non-linear relationship with the measured light intensity of the magnetic field or current as described above, it is difficult to grasp the relationship with the change of the magnetic field or current, especially in the light intensity within a certain range, so that the measurement accuracy decreases. To do. Third
In addition, since the physical variable directly measured is the light intensity, the influence of the light intensity variation due to the light source and other causes appears as a direct error, and the measurement accuracy is reduced.

The present invention has been proposed in order to solve the above-mentioned drawbacks of the prior art, and its object is to make it possible to measure a magnetic field or current with high accuracy by utilizing the magneto-optical effect. It is to provide an excellent optical application measuring device.

[0009]

In order to achieve the above object, the present invention provides an optical application measuring device for measuring a target physical variable (magnetic field or current) by utilizing a magneto-optical effect. In particular, the present invention proposes an apparatus for measuring a change in optical path length according to a target physical variable (magnetic field or current) by using heterodyne interferometry.

First, the apparatus according to claim 1 has a two-wavelength light source, a reference light path, a measurement light path, a light detecting means, and a phase change detecting means. Of these, the two-wavelength light source is different
It is a means of emitting light of one wavelength. The reference optical path is configured so that the light of the first wavelength emitted from the two-wavelength light source passes without causing a change in the optical path length due to the target physical variable (magnetic field or current). The measurement optical path includes a magneto-optical medium, and is configured such that the light of the second wavelength emitted from the dual-wavelength light source passes through the magneto-optical medium. The light detection means is means for photoelectrically converting interference light of two light waves, that is, the reference light that has passed through the reference light path and the measurement light that has passed through the magneto-optical medium of the measurement light path to obtain a beat signal. The phase change detection means detects the phase change of the beat signal obtained by the light detection means, and thereby the target physical variable (magnetic field or current)
It is a means for measuring the change in optical path length due to.

According to a second aspect of the present invention, there is provided the apparatus according to the first aspect.
In addition to the configuration of the device of (1), the measurement optical path includes an optical path that reciprocates in the magneto-optical medium.

On the other hand, the apparatus according to claim 3 has a two-wavelength light source, two optical paths, a light detecting means, and a phase change detecting means. Of these, the two-wavelength light source is a means for emitting light of two different wavelengths. The two optical paths include a magneto-optical medium, and light of two wavelengths emitted from a two-wavelength light source is bidirectionally transmitted through the magneto-optical medium. The light detection means is means for photoelectrically converting interference light of two light waves that have passed through two optical paths to obtain a beat signal.
The phase change detecting means is means for measuring the change in the optical path length due to the target physical variable (magnetic field or current) by detecting the phase change of the beat signal obtained by the light detecting means.

[0013]

According to the present invention having the above structure, the following effects can be obtained.

First, in the apparatus according to claim 1, 2
When the light of two wavelengths is emitted from the wavelength light source, the light of the first wavelength passes through the reference optical path in which the optical path length does not change due to the magnetic field or the current to become the reference light, and the light of the second wavelength is measured. The measurement light is transmitted through the magneto-optical medium in the optical path. In this case, the optical path length of the measurement optical path changes depending on the magnetic field or the current. Subsequently, the light detection means photoelectrically converts the interference light of the two light waves, such as the reference light and the measurement light, to obtain a beat signal, and then the phase change detection means detects the phase change of the beat signal. The change in the optical path length of the measurement optical path due to the magnetic field or the current can be measured.

As described above, in the apparatus according to the first aspect, the change in the optical path length of the measurement optical path according to the magnetic field or the current is measured as the phase change of the beat signal by the heterodyne interferometry. In this case, the change in the magnetic field or the current is proportional (linearly dependent) to the phase change in the beat signal, so that it is not necessary to perform a special calculation process as compared with the conventional device that measures the light intensity, and the change in the magnetic field or the current is reduced. The accuracy of change measurement is improved. And again, the measurement accuracy of this device is 2
Since it depends only on the wavelength stability of the wavelength light source and is hardly affected by the fluctuation of the light intensity due to the dual wavelength light source and other causes, the measurement accuracy is improved also from this point.

Further, in the apparatus according to claim 2,
In addition to the operation of the device according to the first aspect, the following operation is further obtained. That is, since the measurement light reciprocates in the magneto-optical medium, it is possible to cancel the phase change due to the influence of the optical rotation other than the magnetic field or the current, so that the measurement accuracy is further improved.

On the other hand, in the apparatus according to claim 3, 2
When light of two wavelengths is emitted from the wavelength light source, the light of these two wavelengths is bidirectionally transmitted through the magneto-optical medium. Then, after the photodetection means photoelectrically converts the interference light of the two light waves thus bidirectionally transmitted through the magneto-optical medium to obtain a beat signal, the phase change detection means detects the phase change of the beat signal. By detecting, the change in the optical path length of the measurement optical path due to the magnetic field or the current can be measured.

Therefore, also in the device of claim 3, the change of the optical path length of the measurement optical path according to the magnetic field or the current is measured as the phase change of the beat signal by the heterodyne interferometry, as in the device of claim 1. Therefore, as described above, as compared with the conventional method based on the light intensity, it is not necessary to perform a special calculation process, and the measurement accuracy of the change in the magnetic field or the current is improved. Moreover, in this device, the phase change due to the influence other than the magnetic field or the current can be canceled by detecting the phase change of the interference light of the two light waves that have been transmitted bidirectionally in the magneto-optical medium. The accuracy is further improved.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A plurality of embodiments according to the present invention will be described below with reference to FIG.
This will be described with reference to FIGS. The same parts as those of the conventional example shown in FIGS. 5 and 6 are designated by the same reference numerals, and the description thereof will be omitted.

(1) First Embodiment FIG. 1 is a principle view showing an embodiment of the optical application measuring device according to the first aspect. This device, as shown in FIG.
A wavelength light source 21, a reference light path 11, a measurement light path 12 including the magneto-optical medium 1 arranged in a magnetic field, a photodetector 5, and a phase change detection circuit 22, each of which is a two-wavelength light source of the present invention, Reference light path, measurement light path, light detection means,
And a transfer change detecting means.

FIG. 2 is a configuration diagram showing a specific configuration of the optical application measuring device of FIG. In this device, the two-wavelength light source 21 is composed of a single-wavelength coherent light source 7 and an optical frequency shifter 23. Further, on the emission side of the optical frequency shifter 23, the light of two wavelengths is separated and the reference optical path 1
1 and a polarization beam splitter 4 forming a measurement optical path 12 are arranged. Further, λ / 4 plates 24a and 24b are respectively arranged on the incident side and the emitting side of the magneto-optical medium 1 of the measurement optical path 12, and the reference optical path 11 is provided in front of the optical path of the λ / 4 plate 24b on the emitting side. And a beam combiner 9 for interfering the light passing through the measurement optical path 12. Further, the polarizer 3 and the photodetector 5 are sequentially arranged between the beam combiner 9 and the photodetector 5, and the beat signal obtained by the photodetector 5 is input to the phase change detection circuit 22. Is configured.

When measuring a magnetic field or current using this apparatus, first, the two-wavelength light source 21 emits light of two wavelengths of frequencies ω and ω + Δω. More specifically, the coherent light source 7 emits light of a single wavelength, and the optical frequency shifter 23 separates the light into two wavelengths of frequencies ω and ω + Δω which are orthogonal to each other. Then, the lights of the two wavelengths are separated by the polarization beam splitter 4 and are incident on the reference optical path 11 and the measurement optical path 12 as reference light and measurement light, respectively.

After that, the reference light of the frequency ω passes through the reference light path 11 without being affected by the magnetic field or the current. Also,
The measuring light of frequency ω + Δω enters the measuring optical path 12 and passes through the magneto-optical medium 1. Here, the magneto-optical medium 1 is
Since the optical path length for circularly polarized light changes depending on the magnetic field or the electric current, the measuring light incident on the measuring optical path 12 first has λ / 4.
The linearly polarized light is converted to circularly polarized light by the plate 24a, and this circularly polarized light passes through the magneto-optical medium 1 and undergoes Faraday rotation according to the strength of the magnetic field.

The Faraday-rotated measurement light is converted from circularly polarized light into linearly polarized light again by the λ / 4 plate 24b, and the beam combiner 9 makes the reference optical path 1
The reference light that has passed through 1 is superposed, passes through the polarizer 3, and enters the photodetector 5 as heterodyne interference light. In this case, the detection light is beat light having a difference frequency Δω of two wavelengths and is detected as a sinusoidal beat signal. The phase of the sine wave of the beat signal changes according to the strength of the magnetic field or the magnitude of the current when the optical path length in the magneto-optical medium 1 changes due to the magnetic field or the current. Therefore, by inputting this detection signal to the phase change detection circuit 22 and detecting the amount of phase change by this phase change detection circuit 22,
It is possible to measure the change in the optical path length of the measurement optical path depending on the magnetic field or the current.

As described above, in this embodiment, the change in the optical path length of the measurement optical path according to the magnetic field or the current is measured as the phase change of the beat signal by the heterodyne interferometry. In this case, since the change in the magnetic field or the current is proportional (linearly dependent) to the phase change of the beat signal, it can be easily obtained as a variable proportional to the phase change. As a result, it is not necessary to perform a special calculation process as compared with the conventional device that directly measures the light intensity where the change of the magnetic field or the current is not linearly dependent. In this connection, there is no fixed range where it is difficult to understand the relationship with changes in magnetic field or current,
The effect of improving the measurement accuracy of changes in the magnetic field or the current is also obtained. Moreover, the measurement accuracy of this device depends only on the wavelength stability of the two-wavelength light source 21.
Since it is hardly affected by the fluctuation of the light intensity due to the other factors, the measurement accuracy is improved from this point as well. Therefore, in this embodiment, it is possible to provide an excellent optical application measuring device capable of measuring the magnetic field or the current with high accuracy.

(2) Second Embodiment FIG. 3 is a block diagram showing an embodiment of the optical application measuring device according to the present invention. In this device, the two-wavelength light source 21
Is composed of a single wavelength coherent light source 7 and an optical frequency shifter 23, as in the first embodiment.
A polarization beam splitter 4 that separates two wavelengths of light and forms a reference light path 11 and a measurement light path 12 is disposed on the emission side of the optical frequency shifter 23. Then, the λ / 4 plate 24a, the magneto-optical medium 1, and the reflecting mirror 25a are sequentially arranged in the measurement optical path 12, and the measurement light from the polarization beam splitter 4 is supplied to the λ / 4 plate 24a and the magneto-optical medium 1.
The outward path that reaches the reflecting mirror 25a via the
A round-trip optical path is formed, which is reflected by a and is returned to the polarization beam splitter 4 via the magneto-optical medium 1 and the λ / 4 plate 24a. Similarly, also on the side of the reference optical path 11, the λ / 4 plate 24b and the reflecting mirror 25b are sequentially arranged to form a reciprocal optical path. Except for this part, the structure is similar to that of the first embodiment.

In the apparatus of the present embodiment thus constructed, the measurement light from the polarization beam splitter 4 is first
The linearly polarized light is converted to circularly polarized light by the λ / 4 plate 24a, and this circularly polarized light passes through the magneto-optical medium 1 and undergoes Faraday rotation according to the strength of the magnetic field. The measurement light thus Faraday-rotated is reflected by the reflecting mirror 25a, then again passes through the magneto-optical medium 1, and is Faraday-rotated according to the strength of the magnetic field. After this, the measurement light is emitted from the λ / 4 plate 24.
The circularly polarized light is converted again to linearly polarized light by a and returned to the polarization beam splitter 4. On the other hand, the reference light from the polarization beam splitter 4 is first converted from linearly polarized light to circularly polarized light by the λ / 4 plate 24b, reflected by the reflecting mirror 25b, and then again changed from circularly polarized light to linearly polarized light by the λ / 4 plate 24b. It is converted, returned to the polarization beam splitter 4, and superposed on the measurement light. The subsequent processing is the same as in the first embodiment described above.

As described above, in this embodiment, the measurement light travels back and forth in the magneto-optical medium 1, so that the phase change due to the influence of the optical rotation other than the magnetic field or the current can be canceled. Therefore, compared to the first embodiment, the error can be further reduced and the measurement accuracy of the change in the magnetic field or the current can be further improved.

(3) Third Embodiment FIG. 4 is a block diagram showing an embodiment of the optical application measuring device according to the present invention. In this device, the two-wavelength light source 21
Is composed of a single-wavelength coherent light source 7 and an optical frequency shifter 23, as in the first and second embodiments. A beam splitter 8 and a polarization beam splitter 4 are sequentially arranged on the emission side of the optical frequency shifter 23. The polarization beam splitter 4 separates the two wavelengths of light and makes them incident on the two λ / 4 plates 24a and 24b, respectively, to form a left-handed optical path and a right-handed optical path. That is, this polarization beam splitter 4 and two λ / 4 plates 24
One loop-shaped optical path is formed by a and 24b and the magneto-optical medium 1, and two optical paths that bidirectionally pass through the magneto-optical medium 1 are formed. Except for this part, the structure is similar to that of the first and second embodiments.

In the apparatus of this embodiment having such a configuration, the lights of two wavelengths from the polarization beam splitter 4 are incident on the λ / 4 plate 24a and the λ / 4 plate 24b, respectively, and inside the magneto-optical medium 1. After being transmitted in both directions, it returns to the polarization beam splitter 4 again via the λ / 4 plate 24b and the λ / 4 plate 24a on the opposite side, and they are superimposed. The subsequent processing is the same as in the first and second embodiments described above.

As described above, in the present embodiment, the phase change of the interference light of the two light waves transmitted bidirectionally in the magneto-optical medium 1 is detected, so that the phase change due to the influence other than the magnetic field or the current is canceled. You can Therefore, the first
The error can be further reduced and the measurement accuracy of the change in the magnetic field or the current can be further improved as compared with the embodiment.

(4) Other Embodiments The present invention is not limited to the above-mentioned embodiments, and for example, a specific arrangement of a light source, optical paths, light detecting means, phase change detecting means, etc. Is freely selectable.

[0033]

As described above, according to the present invention,
By using the heterodyne interferometry, it is possible to provide an excellent optical application measurement device that can measure a magnetic field or current with high accuracy.

That is, according to the invention of claim 1, light of two wavelengths respectively passing through the reference optical path which is not influenced by the magnetic field or the current and the measuring optical path including the magneto-optical medium are caused to interfere with each other, and the phase change thereof is caused. By detecting, the measurement accuracy can be improved.

Further, according to the invention of claim 2, by interfering the reference light with the measuring light that reciprocates in the magneto-optical medium, in addition to the effect of the invention of claim 1, optical rotation other than the magnetic field or the current is generated. Since the influence can be removed, the error can be reduced and the measurement accuracy can be further improved.

Further, according to the invention of claim 3, in addition to the effect of the invention of claim 1, the magnetic field is detected by detecting the phase change of the interference light of the two light waves transmitted bidirectionally in the magneto-optical medium. Alternatively, effects other than the current can be removed, so that errors can be reduced and measurement accuracy can be further improved.

[Brief description of drawings]

FIG. 1 is a principle diagram showing a first embodiment of an optical measurement device according to the present invention.

FIG. 2 is a configuration diagram showing a specific configuration of the optical application measuring device of FIG.

FIG. 3 is a configuration diagram showing a second embodiment of the optical application measuring device according to the present invention.

FIG. 4 is a configuration diagram showing a third embodiment of the optical application measuring device according to the present invention.

FIG. 5 is a configuration diagram showing an example of a conventional optical application measurement device using the Faraday effect.

FIG. 6 is a configuration diagram showing an example of a conventional optical application measurement device using an interferometry method.

[Explanation of symbols]

 1 ... Magneto-optical medium 2 ... Light source 3 ... Polarizer 4 ... Polarization beam splitter 5, 5a, 5b ... Photodetector 6 ... Polarization plane rotation angle detection circuit 7 ... Coherent light source 8 ... Beam splitter 9 ... Beam combiner 10 ... Phase difference Detecting circuit 11 ... Reference optical path 12 ... Measuring optical path 21 ... Two-wavelength light source 22 ... Phase change detecting circuit 23 ... Optical frequency shifter 24a, 24b ... λ / 4 plate 25a, 25b ... Reflecting mirror

Claims (3)

[Claims] 1. An optical application measuring apparatus for measuring a target physical variable using a magneto-optical effect, comprising: a two-wavelength light source that emits light of two different wavelengths; and a second wavelength light source that emits light from the two-wavelength light source. A second wavelength emitted from the two-wavelength light source, which includes a reference optical path configured to allow light having a wavelength of 1 to pass without causing a change in optical path length due to the target physical variable, and a magneto-optical medium. Interference light of two light waves, that is, the measurement light path configured so that the light of the above-mentioned transmits through the magneto-optical medium, the reference light that has passed through the reference optical path, and the measurement light that has passed through the magneto-optical medium of the measurement optical path are photoelectrically converted. And a phase change detection means for measuring a change in the optical path length due to the target physical variable by detecting a phase change in the beat signal obtained by the light detection means. Was Optical application measuring apparatus, wherein the door. 2. The optical application measuring apparatus according to claim 1, wherein the measurement optical path includes an optical path that reciprocates in the magneto-optical medium. 3. An optical application measuring device for measuring a target physical variable using a magneto-optical effect, comprising a two-wavelength light source for emitting light of two different wavelengths, and a magneto-optical medium, wherein the two wavelengths are included. 2 emitted from the light source
Two optical paths configured so that lights of one wavelength are bidirectionally transmitted through the magneto-optical medium, and optical detection for obtaining a beat signal by photoelectrically converting interference light of two light waves that have passed through the two optical paths. Means and a phase change detecting means for measuring a change in the optical path length due to the target physical variable by detecting a phase change in the beat signal obtained by the light detecting means. measuring device.