JPH04332817A - Light applied measurement method - Google Patents

Abstract

PURPOSE:To measure an amount to be measured without being influenced by light transmission loss. CONSTITUTION:A light modulation part 12 comprising a light emitting part 11, a polarizer 23, a birefringence element 22 and a light detector 24, a light receiving part 13 and a measuring part 14 are provided. The light emitting part 11 is equipped with a light emission source 15 for generating light of wavelength lambda1 and a light emission source 16 for generating light of wavelength lambda2. The light receiving part 13 separately receives a light output of wavelength lambda1 and a light output of wavelength lambda2 generated by the light modulation part 12. The measuring part 14 calculates a ratio of light outputs of both wavelengths and calculates an amount to be measured from relation between the ratio in light outputs and the amount to be measured. A range of the amount where the light output to be a numerator of the ratio shows a large change while the light output to be a denominator of the ratio shows a slight change in the vicinity of the maximum value is specified to be a measurement range.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical measurement method for measuring a predetermined measured quantity such as pressure, electric field, magnetic field, etc. using a birefringent element.

0002

2. Description of the Related Art A measuring device for measuring pressure is shown in FIG. 8 as an example of a conventional optical measuring device using a birefringent element. In the figure, reference numeral 1 denotes a light emitting source, and this light emitting source 1 is connected to a fiber collimator 3 through an optical fiber 2. A light emitting section is composed of a light emitting source 1, an optical fiber 2, and a collimator 3. 4 is a linear polarizer provided to transmit only the 45 degree polarized component of the parallel light beam output from the collimator 2, and a glass block 5 as a birefringent element is placed in front of this polarizer 4. There is. In front of the glass block 5, an analyzer 6 made of a linear polarizing plate whose polarization direction is different from the polarizer 4 by 90 degrees is arranged, and the polarizer 4, the glass block 5, and the analyzer 6 constitute a light modulation section. has been done. A light receiving lens 7 is placed in front of the analyzer 6.
are arranged, and the light receiving lens 7 is connected to a light receiver 9 through an optical fiber 8. The light receiving lens 7, the optical fiber 8, and the light receiver 9 constitute a light receiving section, and the output of this light receiving section is given to the measuring section 10.

[0003] In the above measuring device, a pressure P to be measured is applied to the glass block 5. Light that enters the optical fiber 2 from the light emitting source 1 is output from the collimator 3 as a parallel beam bundle. The polarizer 4 transmits only the 45 degree polarized component of this parallel light beam. 45 obtained from polarizer 4
The degree-polarized light enters the glass block 5, but the external pressure P causes optical anisotropy inside the glass block, causing a difference in the speed of light in the vertical and horizontal directions. The output light is a combination of a vertical component (direction of compressive stress in the glass block) and a horizontal component that have a phase difference, and becomes elliptically polarized light inscribed in a quadrilateral like a Lissajous figure. Since the analyzer 6 allows only the long axis (or short axis) direction component of this elliptically polarized light to pass through, the light that has passed through the analyzer 6 becomes light whose intensity is modulated by the pressure P to be measured. This light intensity modulated light is transmitted to the light receiving lens 7.
and an optical fiber 8 to a light receiver 9, and is converted into an electrical signal by the light receiver 9. The measurement unit 10 calculates the pressure to be measured P from the electrical signal given from the light receiver 9 and outputs the measured value of the pressure.

0004

[Problem to be Solved by the Invention] In conventional optical applied measurement devices, changes in optical transmission loss in the measurement system, such as bending loss in optical fibers and coupling loss in connectors, appear as changes in output, resulting in measurement errors. The problem was that it became large.

As shown in FIG. 9, a polarizing beam splitter capable of extracting a p-polarized light component and an s-polarized light component from the incident light is used as the analyzer 6, and two optical fibers A are connected to the analyzer 6. ,B outputs I,I which are inverted from each other
A method is known in which the optical transmission loss is compensated for by extracting the output power and averaging these outputs.

However, this method is not practical because it assumes that the losses of the two optical fibers A and B are equal.

SUMMARY OF THE INVENTION An object of the present invention is to provide an optical measurement method that can eliminate the influence of changes in optical transmission loss in a measurement system and improve measurement accuracy.

[0008]

[Means for Solving the Problems] In the optical measurement method of the present invention, a birefringent element that internally produces optical anisotropy depending on the quantity to be measured is disposed between a linear polarizer and an analyzer. A light modulation unit is provided, and the light modulation unit is supplied with light with a wavelength λ1 and light with a wavelength λ2, and the light intensity of both wavelengths is modulated by the amount to be measured, so that the wavelength λ1 obtained from the light modulation unit is The optical output I1 of wavelength λ2 and the optical output I2 of wavelength λ2 are respectively received separately.

[0009] The optical output I1 having the wavelength λ1 and the optical output I2 having the wavelength λ2 may be received in a time-sharing manner by one optical receiver, or in real time by using two optical receivers, one for the wavelength λ1 and the other for the wavelength λ2. You can go there.

After receiving the optical outputs I1 and I2, while the optical output I2 shows a slight change near the maximum value with respect to the quantity to be measured, the optical output I1 changes from the minimum value side to the maximum value with respect to the quantity to be measured. The measurement range is defined as the range of the measured quantity in which a characteristic showing a large change from the maximum value side to the minimum value side or from the maximum value side to the minimum value side is defined as the measurement range, and the ratio of the optical outputs I1 and I2 in the measurement range is I1 /
The measurable quantity is determined from the relationship between I2 and the measurable quantity.

The above measurement range can be adjusted to a desired range by placing a wavelength plate between the linear polarizer and the birefringent element and shifting the phase of the light of wavelengths λ1 and λ2 incident on the birefringent element. It is possible to do so.

If there is a range of measured quantities in which the optical outputs I1 and I2 have a phase difference of approximately 180 degrees, the sum of the optical outputs I1 and I2 (I1 + I2) becomes approximately constant within that range. Therefore, in this case, the ratio I1/(I1
+I2) or I2/(I1 +I2), and the quantity to be measured may be determined from the relationship between the calculated ratio and the quantity to be measured.

[0013] As the birefringence element that produces internal optical anisotropy depending on the amount to be measured, an appropriate birefringence element is used depending on the amount to be measured. For example, when measuring pressure, a transparent block made of glass, acrylic resin, or the like can be used. Further, when measuring an electric field, a block of electro-optic crystal such as BSO (bismuth silicon oxide) having a Pockels effect is used.

When a magnetic field is the quantity to be measured, a block of magneto-optical material such as YIG (yttrium, iron, garnet), which has the property of rotating the plane of polarization of transmitted light according to the applied magnetic field element) is used as a modulation means. In this case, the magneto-optical element to which the magnetic field to be measured is applied is placed between the linear polarizer and the analyzer, and the plane of polarization is set between the magneto-optical element and the linear polarizer according to the wavelength of the incident light. Using a light modulation section further disposed with a rotator rotated by a predetermined angle, the light modulation section is supplied with light of wavelength λ1 and light of wavelength λ2, and the light intensity of both wavelengths is modulated by the magnetic field to be measured,
An optical output I1 having a wavelength λ1 and an optical output I2 having a wavelength λ2 obtained from the optical modulator are respectively received. From the characteristics of the optical outputs I1 and I2 with respect to the magnetic field to be measured, it is found that while the optical output I2 shows a slight change in the vicinity of the maximum value with respect to the magnetic field to be measured, the optical output I1 increases from the minimum value side to the maximum value with respect to the magnetic field to be measured. Select the characteristic of the part that shows a large change from the value side or from the maximum value side to the minimum value side, set the range of the magnetic field to be measured that gives the selected characteristic as the measurement range, and measure the optical outputs I1 and I2 in the measurement range. The magnetic field to be measured is determined from the relationship between the ratio I1 /I2 and the magnetic field to be measured.

In the method of the invention, wavelengths λ1 and λ
2 only need to be different, and even if λ1 < λ2, λ1
>λ2 is also fine.

[0016] As a matter of course, in this specification, the term "quantity to be measured" means a quantity that is directly measured by applying light, and does not necessarily mean a quantity that is the final objective of measurement. For example, in the case of optical PT that measures voltage, the voltage is ultimately measured by measuring the electric field around a conductor to which voltage is applied using the Pockels effect, but the measurement method of the present invention The measured quantity is the "electric field". Also light C
In the case of T, the current is ultimately measured by detecting the magnetic field around the conductor through which the current flows using a magneto-optical element (Faraday element). The quantity is the "magnetic field".

[0017]

[Operation] As described above, the light with the wavelength λ1 and the light with the wavelength λ2 are supplied to the light modulator, and the wavelength λ obtained from the light modulator is
If the optical output of wavelength λ2 and the optical output of wavelength λ2 are received separately, and the ratio of the output of both wavelengths or the ratio of the optical output of either wavelength to the sum of the optical output of both wavelengths is calculated, Since optical transmission loss is canceled by the numerator and denominator of the ratio, it is possible to perform measurements without being affected by changes in optical transmission loss such as bending loss of optical fibers and coupling loss of connectors. . In this case, in order to improve measurement accuracy, it is desirable that the optical output I2 (reference output) at wavelength λ2, which is the denominator of the ratio, does not change much in the measurement range. Additionally, in general, the lower the input power of a photoreceiver, the greater the proportion of background noise in the signal to be detected, and the worse the S/N ratio becomes. It is desirable that I2 be as large as possible. Therefore, the reference output I2
It is desirable to maintain a value as large as possible within the measurement range and to have as little variation as possible. On the other hand, in order to improve measurement resolution and measurement accuracy, it is desirable that the optical output I1, which is the numerator of the ratio, exhibits as large a change as possible with respect to the quantity to be measured.

Since the optical output shows a substantially sinusoidal change with respect to the quantity to be measured, the area where the optical output is large and its change is small is the area around the maximum optical output. Further, the region where the light output changes greatly is a region where the light output changes from the minimum value side to the maximum value side, or a region where the light output changes from the local maximum value side to the local minimum value side. Therefore, as in the present invention, while the optical output I2 shows a slight change near the maximum value with respect to the measured quantity, the optical output I1 changes from the minimum value side to the local maximum side with respect to the measured quantity, or the optical output I1 changes from the local minimum value side to the local maximum side, or The measurement accuracy can be improved by selecting a characteristic of a portion that shows a large change from the side to the minimum value side and setting the range of the measured quantity that gives the selected characteristic as the measurement range.

Depending on the difference between the wavelengths λ1 and λ2, the optical outputs I1 and I2 may be approximately 1 in a specific range of the measured quantity.
It may have a phase difference of 80 degrees. If the maximum values of the optical outputs I1 and I2 are approximately equal, then in this specific range the sum of the optical outputs (I1 + I2) will be approximately equal to 1/2 of the amplitude of each optical output, and the sum of the optical outputs (I1
+I2) with respect to the measured quantity becomes close to zero. Therefore, in this case, the optical outputs I1 and I2 are approximately 18
The ratio of the optical output I1 to the sum of the optical outputs (I1 + I2) in a range with a phase difference of 0 degrees: I1 / (I1 + I2 )
, or the sum of the optical output I2 and the optical output (I1 + I2)
By calculating the ratio I2/(I1 +I2) and determining the amount to be measured from the relationship between the calculated ratio and the amount to be measured, measurement can be performed with high accuracy.

As described above, in the measurement method of the present invention, a specific range is selected as the measurement range based on the characteristics of the optical outputs I1 and I2, so the modulation section is composed of a linear polarizer, a birefringent element, and an analyzer. In this case, the range of measurable quantities that can be measured is limited. In order to be able to measure a measurand in a desired range, the range of the measurand that exhibits characteristics suitable for use in measurement may be shifted. For this purpose, a wavelength plate may be disposed between the linear polarizer and the birefringent element of the light modulation section to shift the phase of the light having wavelengths λ1 and λ2 by a predetermined amount. When the wave plate is arranged in this way, the range exhibiting characteristics suitable for measurement moves in accordance with the amount of phase shift by the wave plate, so the measurement range can be adjusted to a desired range.

[0021]

[Example] Figures 1 and 2 show an example in which the present invention is applied when measuring pressure, and Figure 1 shows the overall configuration of an optical measurement device that implements the method of the present invention. , Figure 2
shows a top view of the vicinity of the light modulation section in FIG. In these figures, 11 is a light emitting section, and 12 is a light modulating section (sensor section) that modulates the light given from the light emitting section 11 by the measured pressure P.
, 13 is a light receiving section that receives the optical output obtained from the light modulating section 12, and 14 is a measuring section that calculates the pressure to be measured from the optical output received by the light receiving section 13.

The light emitting unit 11 includes a first light source 15 that generates light with a wavelength λ1 and a second light source 16 that generates light with a wavelength λ2, and these light sources 15 and 16 each emit light. It is connected via fibers 17 and 18 to the input side of coupler 19. The output side of the coupler 19 is connected to a collimator 21 through an optical fiber 20. 1st
and second light emitting sources 15 and 16 and optical fibers 17 and 1
8, a coupler 19, an optical fiber 20, and a collimator 21 constitute a light emitting section 11.

The light modulator 12 includes a glass block 22 as a birefringent element, a linear polarizer 23 and an analyzer 24 which are arranged opposite to each other in the light transmission direction with the glass block 22 in between.
It consists of The direction of linear polarization of the polarizer 23 is 45 with respect to the perpendicular direction (direction of compressive stress of the birefringent element).
The analyzer 24 is composed of a polarizing plate tilted at an angle of 45 degrees, and the direction of linearly polarized light thereof is tilted at 45 degrees in a direction opposite to that of the polarizer with respect to the vertical direction. That is, the polarizer 23 and the analyzer 24 are provided so that their polarization directions are orthogonal to each other.

The light receiving section 13 includes a light receiving lens 25 that receives the light output from the analyzer 24 of the light modulating section, and a light receiving lens 25 that is connected to the light receiving lens 25 via an optical fiber 26 to receive the light output from the light modulating section. Optical output with wavelength λ1 (wavelength λ
A demultiplexer 27 separates light into wavelength λ2 (light of wavelength λ2 modulated by pressure P) and light output of wavelength λ2 (light of wavelength λ2 modulated by pressure P); It consists of first and second light receivers 30 and 31 connected via fibers 28 and 29, respectively. Here the first
The photoreceiver 30 receives the optical output of the wavelength λ1 and provides the measuring section 14 with an electrical signal corresponding to the received optical output. Further, the second 31 receives the optical output of wavelength λ2 and provides the measuring section 14 with an electrical signal corresponding to the received optical output.

The measuring section 14 calculates the ratio of the optical output of the wavelength λ1 and the optical output of the wavelength λ2, and calculates the pressure to be measured from the relationship between the ratio of the optical outputs and the pressure to be measured.

In the optical application measurement device shown in FIG. 1, the wavelength λ1 output from the first light source 15 and the second light source 16
and λ2 are mixed by a coupler 19 and supplied to an optical fiber 20, which passes through a collimator 21 and is applied to a polarizer 23 as a parallel beam.

The light applied to the polarizer 23 becomes linearly polarized light tilted at 45 degrees and enters the glass block 22. Inside the glass block 22, optical anisotropy occurs due to the applied pressure P to be measured, so the glass block 22
The output light from the analyzer 24 becomes elliptically polarized light, and the output from the analyzer 24 becomes a light intensity modulated light output.

Here, assuming that the pressure applied to the glass block is P, the constant is K, and the maximum value of the optical output is Io, the optical modulation output I1 at the wavelength λ1 is given by the following equation.

I1 = Io[1-cos {K(P/λ1)}]

...(1) Similarly, the optical modulation output I2 of wavelength λ2 is given by the following equation.

I2 = Io[1-cos {K(P/λ2)}]

...(2) Here, when λ2 = 1.5 λ1, the characteristics of the optically modulated outputs I1 and I2 with respect to the measured pressure P are as follows from the curves ■ and ■ in Fig. 3, respectively, when Io = 1.
become that way. That is, for light of wavelength λ1, pressure P=P
The optical modulation output reaches its first peak at the point o, but for light of wavelength λ2, the optical modulation output reaches its first peak at the point (λ1/λ2)×Po.

Here, assuming that the transmission loss of the measurement system is 1/γ, adding this factor to equations (1) and (2), we get (
Equations 1) and (2) are the following equations (1)' and (2), respectively.
)´It becomes like the expression.

I1 = (Io/γ) [1-cos {K( P/λ
1)}]
...(1)' I2 = (Io/γ) [1-cos{
K(P/λ2)}]
...(2)' Here, the ratio R=I1/I
2, R=I1 /I2 = [1-cos
{K( P/λ1)}]/[1-cos{K( P/λ
2)}]

...(3) In equations (1) or (2), γ changes due to changes in the bending loss of the optical fiber and changes in the coupling loss of the connector, so when the measured pressure P is calculated using these equations, In this case, it is unavoidable that the measurement error will increase to some extent.

On the other hand, as is clear from equation (3), the optical output ratio R is not affected by transmission loss. Therefore,
If the optical output of wavelength λ1 and the optical output of wavelength λ2 are respectively received, the ratio of both optical outputs is calculated, and the measured pressure P is calculated from equation (3), it is possible to avoid the influence of transmission loss. Pressure measurements can be made without

As mentioned above, the ratio of optical outputs I1 /I2
In order to obtain the measured quantity with high precision from the relationship between It is desirable to show a significant change.

Therefore, when Io = 1 and I1, I2, and I1/I2 are plotted against pressure P, the curves ■, ■, and ■ in FIG. 3 are obtained, respectively. As is clear from FIG. 3, in the range of P' to P'', the optical output I1 changes significantly linearly from the minimum value side to the maximum value side with respect to the measured pressure P. On the other hand, the optical output I2 ( Although the reference output (reference output) changes near the maximum value, the range of change in the optical output I2 in this range is sufficiently narrow compared to the range of change in the optical output I1.Therefore, when calculating the pressure to be measured, this P' By selecting the characteristics in the range of ~2P'' and taking the ratio of I1 and I2 with this range P'~2P'' as the measurement range, the ratio R of the optical output and the pressure P can be calculated without being affected by transmission loss. can be matched and accurate measurement values can be obtained.

In general, while the optical output I2 at the wavelength λ2 shows a slight change near the maximum value with respect to the measured quantity, the wavelength λ2
1, where the optical output I1 shows a significant change from the minimum value side to the local maximum side or from the local maximum side to the local minimum side with respect to the measured quantity, and select the characteristic of the part that gives the selected characteristics. By setting the range of the quantity as the measurement range, the correspondence between the ratio of the optical outputs of both wavelengths and the quantity to be measured can be set to a substantially linear relationship, and accurate measurement can be performed.

In the above embodiment, when measuring using the ratio of the optical outputs I1 and I2 in the region P' to 2P'', adjustments are made so that P' to 2P'' is the desired measurement range. It is preferable to do so. To do this, a wavelength plate may be inserted between the polarizer 23 and the birefringent element 22, and the wave plate may shift the phase of the light incident on the birefringent element by an appropriate amount. For example, in order to set P' as the zero point of the measured pressure,
As shown by the broken line in , a wavelength plate 32 may be disposed between the polarizer 23 and the birefringent element 22 to shift the phase of the light having the wavelength λ1 by a wavelength of P'/2Po. When the P'/2Po wavelength plate 32 for the wavelength λ1 is inserted in this way, an optical bias is applied and the zero point of the pressure to be measured moves to P'. In this case, the wavelength plate 32 has a wavelength λ2
For light of (=α・λ1), (P′/2Po)
It acts as a (1/α) wavelength plate.

In the above embodiment, the direction of the linearly polarized light of the polarizer 23 and the direction of the linearly polarized light of the analyzer 24 are made to be perpendicular to each other.
Both may be arranged so that the directions of linearly polarized light are the same. When the polarizer 23 and analyzer 24 are arranged in this way, the optical outputs I1 and I2 of both wavelengths λ1 and λ2 are as follows.
When I1 /I2 of both optical outputs are plotted against the measured pressure P, the curves ■, ■, and ■ in FIG. 4 are obtained, respectively.

In this case as well, the optical output I1 at wavelength λ1
I1 changes significantly with respect to the pressure (measured quantity) P, and the optical output I2 of the wavelength λ2 changes slightly near the maximum value, for example, in the region Pp' to Pp'' in FIG.
, I2 and take the ratio R of both, the ratio R
Accurate measurement values can be obtained by making the correspondence between the pressure and the pressure to be measured almost linear.

In addition, in FIGS. 3 and 4, if the measurement range is set to a narrower range before and after the pressure at which the optical output I2 shows the maximum value, the range of change in the optical output I2 becomes even narrower.
Furthermore, measurement accuracy can be improved.

In the above embodiment, a demultiplexer 27 is provided in the light receiving section to receive the optical outputs of wavelengths λ1 and λ2 individually in real time, but in the present invention, the optical outputs of both wavelengths are Since it is only necessary to distinguish between wavelengths λ and receive the light, one receiver can time-divisionally detect wavelengths λ without using a demultiplexer.
1 and λ2 may be detected alternately.

Depending on the difference between the wavelengths λ1 and λ2, the optical outputs I1 and I2 may be approximately 1 in a specific range of the measured quantity.
It may have a phase difference of 80 degrees. For example, Figure 5(C)
In the range of 8Po to 10Po, the optical output I1 at the wavelength λ1 and the optical output I2 at the wavelength λ2 have a phase difference of approximately 180 degrees, and I1 can be seen as the inversion of I2. In this case, if the maximum values of the optical outputs I1 and I2 are equal, then in this specific range the sum of the optical outputs (I1 + I2) is 1/1/2 of the amplitude of each optical output.
2, and the change in the sum of optical outputs (I1 + I2) with respect to the measured quantity becomes close to zero.

Therefore, in this case, the optical outputs I1 and I
2 selects a characteristic in a range in which the phase difference is approximately 180 degrees, and selects a characteristic in a range where 2 is a phase difference of approximately 180 degrees to obtain a range of 8Po to 10Po that provides the selected characteristic.
The first or second half of the measurement range is defined as the measurement range, and the relationship between the ratio I1 / (I1 + I2 ) of the optical output I1 and the sum of the optical outputs (I1 + I2 ) in the measurement range and the measured quantity, or in the measurement range The sum of the optical output I2 and the optical output (I1 +
By determining the amount to be measured from the relationship between the ratio I2/(I1 + I2) and the amount to be measured, it is possible to eliminate the influence of loss and perform measurement with high accuracy.

In the above embodiment, pressure was measured, but when measuring an electric field using the Pockels effect, etc.
When a birefringent element that produces optical anisotropy when a measured quantity is applied is used as a modulation means, the present invention can be implemented with a configuration similar to the above.

When detecting a magnetic field, a magneto-optical element (Faraday element) that rotates the polarization plane of transmitted light by an angle corresponding to the strength of the magnetic field is used as a modulation means, and this magneto-optical element is used as a linear polarizer. It is known that a modulator can be configured by placing the modulator between the linear polarizer 23 and the magneto-optical element 22', as shown in FIG. By adding the optical rotator 33 to the optical rotator 33, it becomes possible to perform highly accurate measurements.

In the configuration shown in FIG. 6, the linearly polarized light that has passed through the polarizer 23 is incident on the optical rotator 33. When linearly polarized light passes through optical rotator 23, its plane of polarization is rotated by an angle determined by the wavelength. Therefore, the wavelength λ1 that passed through the optical rotator 23
The linearly polarized light of wavelength λ2 and the linearly polarized light of wavelength λ2 enter the magneto-optical element 22' in states rotated by different angles. Therefore, a predetermined phase difference occurs between the characteristics of the optical output I1 having the wavelength λ1 obtained from the analyzer 24 with respect to the magnetic field and the characteristics of the optical output I2 having the wavelength λ2 with respect to the magnetic field. In this case, the characteristics of the optical outputs I1 and I2 obtained from the analyzer 24 with respect to the magnetic field H are as shown in FIG. 7, for example.
The range from H' to H'' in the same figure is taken as the measurement range, and the ratio I1 /I2 of the optical output is calculated in the measurement range, and this ratio I1 /I2 is calculated.
By determining the magnetic field from the relationship between I2 and the magnetic field, the magnetic field can be measured with high accuracy.

[0047]

Effects of the Invention As described above, according to the present invention, the wavelength λ
1 and the light with wavelength λ2 are supplied to the optical modulator, and the optical output with wavelength λ1 and the optical output with wavelength λ2 obtained from the optical modulator are received separately, and the ratio of the optical outputs of both wavelengths is calculated. Or, by taking the ratio of the optical output of either wavelength to the sum of the optical outputs of both wavelengths, factors related to optical transmission loss are removed, so the bending loss of the optical fiber,
Measurement can be performed without being affected by changes in optical transmission loss such as connector coupling loss.

In particular, in the invention described in claim 1 or 4, while the optical output I2, which is the denominator of the ratio, shows a slight change near the maximum value, the optical output I1, which is the numerator of the ratio, shows a large change. The range of the measured quantity in which the characteristics can be obtained is taken as the measurement range, and the optical output ratio I1 /I2 is taken in this measurement range, which has the advantage of improving the S/N ratio and increasing the measurement accuracy. be.

Further, according to the invention described in claim 2, by arranging a wavelength plate between the linear polarizer and the birefringent element of the light modulation section, the range of the measured quantity in which the above characteristics can be obtained can be widened. Since it is shifted, there is an advantage that the measurement range can be adjusted to a desired range by appropriately selecting a wavelength plate.

Furthermore, according to the invention described in claim 3, the characteristics of the portion where the optical outputs I1 and I2 have a phase difference of approximately 180 degrees are selected, and the ratio I1 is adjusted within the range of the measured quantity giving the selected characteristics. /(I1 +I2) or I2/
Since (I1 + I2) is taken, there is an advantage that the change in the denominator of the ratio can be reduced and measurement can be performed with high accuracy.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram schematically showing the configuration of an apparatus used in an optical measurement method according to an embodiment of the present invention.

FIG. 2 is a top view showing the configuration of main parts in FIG. 1;

FIG. 3 is a diagram showing the optical output I1 of the wavelength λ1 received by the light receiving section, the optical output I2 of the wavelength λ2, and the optical output ratio I1 /I2 with respect to the measured quantity in the embodiment of the present invention. be.

FIG. 4: Optical output I1 at wavelength λ1 and optical output I2 at wavelength λ2 received by the light receiving section in another embodiment of the present invention.
FIG. 2 is a diagram showing the ratio of optical output I1 /I2 to the measured quantity.

FIG. 5(A) is a diagram showing the sum of the optical output I1 at the wavelength λ1 and the optical output I2 at the wavelength λ2 received by the light receiving section with respect to the measured quantity in another embodiment of the present invention. be. (B) is the ratio I1/(I1+I2
) is a diagram showing the measured quantity. (C) is a diagram showing the optical outputs I1 and I2 with respect to the measured quantities, respectively.

FIG. 6 is a configuration diagram schematically showing the configuration of an apparatus used in another embodiment of the present invention.

7 is a diagram showing an example of the characteristics of the optical output of the embodiment of FIG. 6 with respect to the measured quantity; FIG.

FIG. 8 is a configuration diagram schematically showing the configuration of an apparatus used in a conventional optical measurement method.

FIG. 9 is an explanatory diagram illustrating a method for reducing the influence of optical transmission loss that has been proposed in a conventional optical measurement method.

[Explanation of symbols]

11... Light emitting section, 12... Light modulating section, 13... Light receiving section, 14...
Measuring unit, 15...first light emitting source, 16...second light emitting source, 1
7, 18, 20, 26, 28, 29...optical fiber, 19
...Coupler, 21...Collimator, 22...Birefringence element, 23
... linear polarizer, 24 ... analyzer, 27 ... demultiplexer, 30 ... first light receiver, 31 ... second light receiver.

Claims (4)

[Claims] Claim 1: A light modulation unit including a birefringence element that generates optical anisotropy internally depending on the quantity to be measured is arranged between a linear polarizer and an analyzer, and a light with a wavelength λ1 and a light with a wavelength λ2. The light of both wavelengths is modulated in intensity by the quantity to be measured, and the optical output I1 with the wavelength λ1 and the optical output I2 with the wavelength λ2 obtained from the optical modulation section are respectively received and applied to the quantity to be measured. On the other hand, while the optical output I2 shows a slight change near the maximum value, the optical output I1 shows a large change from the minimum value side to the local maximum side or from the local maximum side to the local minimum side with respect to the measured quantity. An optical applied measurement method characterized in that the range of the measured quantity for which characteristics can be obtained is defined as a measurement range, and the measured quantity is determined from the relationship between the optical output ratio I1 /I2 in the measurement range and the measured quantity. 2. A wavelength plate is disposed between the linear polarizer and the birefringent element, and the wavelength plate shifts the phase of light incident on the birefringent element to adjust the measurement range to a desired range. The optical application measurement method according to claim 1, characterized in that: 3. A light modulation unit including a birefringent element that generates optical anisotropy internally depending on the quantity to be measured is arranged between a linear polarizer and an analyzer. The light of both wavelengths is modulated in intensity by the amount to be measured, and the optical output I1 with the wavelength λ1 and the optical output I2 with the wavelength λ2 obtained from the optical modulation section are respectively received, and the optical output I
1 and I2 have a phase difference of approximately 180 degrees, the ratio of the optical output I1 to the sum of the optical outputs (I1 + I2) is I1 / (I1 + I2
) or the sum of the optical output I2 and the optical output (I1 + I2
), and calculates the measured quantity from the relationship between the calculated ratio and the measured quantity. 4. A magneto-optical element to which a magnetic field to be measured is applied is arranged between a linear polarizer and an analyzer, and a polarization plane is arranged between the magneto-optical element and the linear polarizer according to the wavelength of the incident light. A light modulation section is further provided with an optical rotator that rotates the light by a predetermined angle, and the light modulation section is supplied with light of wavelength λ1 and light of wavelength λ2, and the light intensity of the light of both wavelengths is modulated by the magnetic field to be measured. , receives the optical output I1 with the wavelength λ1 and the optical output I2 with the wavelength λ2 obtained from the optical modulator, and while the optical output I2 shows a slight change near the maximum value with respect to the magnetic field to be measured, the optical output I1 The measurement range is defined as the range of the magnetic field to be measured in which a characteristic that shows a significant change from the minimum value side to the local maximum side or from the local maximum side to the local minimum side with respect to the measured magnetic field is defined as the measurement range. An optical application measurement method characterized by determining a magnetic field to be measured from a relationship between a ratio I1 /I2 of optical outputs I1 and I2 and a magnetic field to be measured.