JPH02132389A - Light applied magnetic field sensor - Google Patents

Abstract

PURPOSE:To improve accuracy and sensitivity by setting the center wavelength of light used for magnetic field measurement nearby zero-point wavelength and its half-value width to >=10nm, and nearly eliminating the quantity of light on a shorter wavelength side than the absorption end wavelength of a magnetooptic element at upper-limit temperature of use. CONSTITUTION:The wavelength distribution of light which passes through the magnetooptic element 5 is set so that temperature variation in Verdet's constant V'e is nearly zero. Here, the center wavelength is set nearby the zero-point wavelength of the Verdet's constant Ve and the quantity of light on the shorter- wavelength side than the absorption end wavelength is set almost to zero. Namely, light having center wavelength and half-value width corresponding to the composition ratio X of the magnetooptic element 5 is used and the quantity of light on the shorter wavelength side than the absorption end wavelength is set almost to zero, thereby almost eliminating the temperature variation in effective Verdet's constant V'e. Consequently, the light-applied magnetic field sensor which has high accuracy and high sensitivity and does not depend upon temperature and humidity is obtained.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention is an optical application magnetic field that detects a magnetic field (or a current that generates a magnetic field) using a magneto-optical element having Faraday rotation ability (magneto-optical rotation). The present invention relates to sensors, and particularly to optical magnetic field sensors that have low temperature dependence, high precision, and high sensitivity.

[Prior Art] Figure 3 is a configuration diagram showing a conventional optical magnetic field sensor.
In the figure, (1) is a light source consisting of an LD (laser diode) or LED (light emitting diode), etc., (2) is an optical fiber that transmits the light emitted from the light source (1), (
3) is a collimator lens disposed at the tip of the optical fiber (2), and (4) is a polarizer that polarizes the light that has passed through the collimator lens (3).

(5) is a magneto-optical element having Faraday rotation ability, and is arranged so that light via the polarizer (4) is incident thereon. The magneto-optical element (5) has a composition ratio of Cd. It is made of a semiconductor single crystal material that satisfies 4MBTe (O<x<0.7), for example,
Journal of Crystal Growth
Al of Crystal Growth) (Vol. 52, 1981), pages 614 to 618.

(6) is an analyzer into which the light that has passed through the magneto-optical element (5) is incident, and is arranged so that its polarization direction is at a relative angle of 45° with respect to the polarizer (4). . 7)
is a condenser lens that converges the light that has passed through the analyzer (6), (8) is an optical fiber that transmits light with the condenser lens (6) as the input end, and (k) is a condenser lens that includes a light receiving element and is transmitted through the optical fiber (8). This is an optical receiver that detects the light that is generated.

Next, the operation of the conventional optical magnetic field sensor shown in FIG. 3 will be explained.

The light emitted from the light source ( ) is guided to the collimator lens (3) via the optical fiber (2), becomes a thousand lines of light, and is then linearly polarized by the polarizer (4) and sent to the magneto-optical element (
5).

At this time, when a magnetic field H is applied in the direction in which the light passes, the plane of polarization of the linearly polarized light is rotated by a small angle θ due to the Faraday effect. Of the light emitted from the end of the magneto-optical element (5), a component with a polarization angle of 45° passes through the analyzer (6) and is transmitted via the condenser lens (7) and the optical fiber (8). The light is received by the optical receiver (9) and measured as a light amount signal.

This change in the amount of light corresponds to a change in the (usually alternating current) magnetic field (1), so the optical magnetic field sensor can detect the magnetic field H or the current that generates the magnetic field H.

The rotation angle θ of the plane of polarization due to the Faraday effect while passing through the magneto-optical element (5) is as follows: θ-L-Ve-H ...■ However, ■e : Expressed by Verdet constant. Here, since the relative angle of the polarization directions between the polarizer (4) and the analyzer (6) is 45 degrees, the amount of light passing through the analyzer (6) is the amount of light from the polarizer (4). If the light intensity is Io and the transmittance at the magneto-optical element (5) is 1, then I - I o (1 + sin2θ)/2Io [1 + si
n(2L・Vel{)]/2 − ■Roar. ■As is clear from the formula, the amount of light passing through the analyzer (6) is:
A DC bias component Io/2, which corresponds to the light intensity halved by the relative angle of 45° of the analyzer (6), and an AC component Io-sin(2L-V), which corresponds to the change in the intensity of the magnetic field H.
e−H)/2. Therefore, the amount of light (2) changes linearly with changes in the alternating current component, and the magnetic field H can be measured based on the change in the amount of light (2), that is, the change in the light signal.

Also, since the rotation angle θ is very small, the sensor sensitivity R given by the ratio of the AC component and the DC bias component is as follows: It depends on the Verdet constant Ve regardless of the transmission loss of the optical fiber (8). Since the Verdet constant Ve varies depending on the temperature, the sensor sensitivity R has a temperature characteristic that depends on the Verdet constant Ve, and the measured value differs depending on the temperature even for the same magnetic field I.

To prevent this, conventional optical magnetic field sensors, for example,
Applied Physics (Appl. Phys. Lett.) J(
Volume 46, No. 11, June 1, 1985) No. 1016
L D or L as described on page and page 1017
A light source (1) is a combination of an ED and an interference filter. That is, a narrow band L whose center wavelength is the zero point wavelength where the Verdet constant Ve does not change with temperature and whose half-value width is about 1 degree.
D, or a broadband LED with a half-width of about 50 nm
A light source (
1) to reduce temperature dependence.

However, an optical magnetic field sensor using an LD has been proposed, for example, in the IEEE Journal of Q
uantu+nE Electronic) J Vol.
．． QE-18, No. l. As stated in O.
Lick S where the fluctuation of the LD light amount, that is, the DC bias component is large.
It is known that the N ratio (accuracy) deteriorates. On the other hand, L
It is obvious that when an interference filter is combined with an ED to narrow the band, the amount of light decreases and the sensor sensitivity R deteriorates.

It is also known that the transmittance of the magneto-optical element (5) depends on the wavelength, and that it hardly transmits light with wavelengths shorter than the absorption edge wavelength.Furthermore, the absorption edge wavelength shifts to the longer wavelength side as the temperature rises. known to shift. Therefore, in order to eliminate the influence of the absorption edge wavelength at the upper limit temperature of use, it may be possible to block light below the absorption edge wavelength. ), it is known that transmittance varies depending on temperature and humidity.

Figure 4 shows the change in transmittance of a filter using an optical thin film with respect to humidity. The solid line indicates the dry state, the broken line indicates the state with water attached, and the curves connecting the points marked with x and ○ indicate the state with water attached, respectively. This is a transmission characteristic that occurs when the adhesion of the particles is incomplete.

Furthermore, the wavelength distribution of the light source (1) depends on the temperature, especially for LE
In the case of D, it is known that the center wavelength shifts to the longer wavelength side when the temperature increases.

FIG. 5 shows the temperature characteristics of an LED having a center wavelength near 650 n +n, for example, and the rate of change of the center wavelength in this case is about 0.15 n/'C.

[Problems to be Solved by the Invention] As described above, the conventional optical magnetic field sensor uses a light source (1) having a narrow band wavelength distribution, so sufficient accuracy and sensor sensitivity cannot be obtained, and Even if you try to remove light below the absorption edge wavelength by combining a broadband light source with an optical filter, the characteristics of the optical filter change depending on temperature and humidity, and the center wavelength of the light source (1) changes depending on the temperature. There was a problem that sufficient accuracy could not be obtained.

The present invention was made to solve the above-mentioned problems, and an object of the present invention is to obtain a highly accurate and highly sensitive optical magnetic field sensor.

[Means for Solving the Problems] The optical magnetic field sensor according to the present invention has a half-value width of 10 with the center wavelength of the light used for magnetic field measurement being in the vicinity of the zero point wavelength.
nm or more, and the amount of light on the shorter wavelength side than the absorption edge wavelength of the magneto-optical element at the upper limit temperature of use is made almost zero, so that the temperature fluctuation of the effective Verdet constant is made almost zero, and the absorption edge wavelength at the upper limit temperature of use is made almost zero. Another magneto-optical element is provided to block light with shorter wavelengths, and the light source and another magneto-optical element are housed in a thermostatic oven.

[Function] In this invention, focusing on the fact that the wavelength characteristics of the Verdet constant change complementary to each other around the zero point wavelength due to temperature changes, the effective Verdet constant is determined using broadband light with the center wavelength near the zero point wavelength. Temperature fluctuations in the constant are offset, light with wavelengths shorter than the absorption edge wavelength is reliably blocked by another magneto-optical element, and temperature changes in the light source and another magneto-optical element are prevented and stabilized.

[Example] An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing one embodiment of the present invention, and (1
) to (9) are the same as described above.

(10) is another magneto-optical element provided in the light source (1), Cdl-'yMnyTe, where Y:manganese composition ratio (Y<X), The composition ratio Y is smaller than the ratio X.

Generally, the absorption edge wavelength of a magneto-optical element becomes shorter as the composition ratio of manganese increases.
The absorption edge wavelength of 10) is determined by the absorption edge wavelength of the magneto-optical element (5) for magnetic field detection.
) is longer than the absorption edge wavelength of Therefore, in this case, the other magneto-optical element (10) is designed to block light having a wavelength shorter than the absorption edge wavelength of the magneto-optical element (5) at the upper limit temperature of use.

(11) is a constant temperature bath that houses the light source (1) and another magneto-optical element (10) and maintains it at a constant temperature.

Next, the operation of one embodiment of the present invention shown in FIG. 1 will be explained. Note that the basic operation for detecting the magnetic field H is as described above, and will not be explained here.

In FIG. 1, the wavelength distribution of light passing through the magneto-optical element (5) shows that the temperature fluctuation of the effective Verdet constant Ve is almost zero (
Practically speaking, it is set to 1% or less. Here, the center wavelength is set near the zero point wavelength of the Verdet constant Ve, and the half-width is set to a wide band of 10 nm or more,
Moreover, it is set so that the amount of light on the shorter wavelength side than the absorption edge wavelength is approximately zero.

Usually, an LED is used as the light source (1) that emits light with such a broadband wavelength distribution. In addition, with another magneto-optical element (10), light with a shorter wavelength than the absorption edge wavelength is
It has also been definitely removed.

In addition, the effective Verdet constant ve is obtained by weighted averaging the Verdet constant Ve (λ) for each wavelength with respect to the wavelength distribution of light, and from ye=SVe(λ)Io(λ)dλ/Io'・=■ This is the value given. However, ■0(λ) is the light intensity for each wavelength, and Io' is the average light intensity, and Io'=iIo(λ
)dλ (see Japanese Patent Application No. 63-178720).

Substituting the effective Verthet constant e obtained from the equation (2) into the above equation (2), the amount of light passing through the analyzer (6) is: I - I o'[L+sin(2L -H -e)]/
2#Io'(1+2L-H-Ve)/2 ・"■.

Actually, the transmittance T of the magneto-optical element (5) is not 1, so if the light amount on the light source (1) side is Io (λ) and the transmittance T (λ) for each wavelength is considered, the magneto-optical element The amount of transmitted light Io7(
λ) is obtained from Io7(λ)-■o(λ)T(λ) ・■. Therefore, the effective Verdet constant ve is exactly:
■Formula where ■oT is substituted for Io(λ) in the formula, e=5Ve(
λ) I OT(λ) dλ/ S I OT(λ) dλ
...Represented by ■.

The rate of temperature fluctuation of the effective Verdet constant e becomes closer to the temperature fluctuation rate of the wavelength characteristic of the Verdet constant Ve as the half-width of the passing light becomes narrower, so the center wavelength of the light should be set near the zero point wavelength. For example, the temperature fluctuation of the effective Verdet constant Ve is approximately O.

In addition, as the temperature rises, the temperature characteristics of the Verdet constant Ve tend to increase on the short wavelength side and decrease on the long wavelength side, centering on the zero wavelength side, and the temperature fluctuation width is larger on the short wavelength side than on the long wavelength side. is known to be larger. Therefore, in order to make the temperature fluctuation of the effective Verdet constant Ve almost 0,
As the half-value width increases, it is necessary to shift the center wavelength to a longer wavelength side than the zero point wavelength.

In addition, if the half-width is too wide, the amount of light will decrease due to the influence of the absorption edge wavelength of the upper limit temperature, and the rate of temperature fluctuation will be almost 0.
It will no longer become. Normally, the half width is 10 n In ~ 5
Although it is set to about 0 nm, if the composition ratio K is set to a value close to 0.7, the absorption edge wavelength becomes shorter, so the half width can be shifted to 50 nm or more.

That is, by using light with a center wavelength and half-width corresponding to the composition ratio κ of the magneto-optical element (5) and setting the light amount on the shorter wavelength side than the absorption edge wavelength to almost zero, temperature fluctuations in the effective Verdet constant e can be reduced. can be reduced to almost 0.

For example, the composition ratio X of the magneto-optical element (5) is 0.38 to 0.
．． 56, the center wavelength is visible light (630 nm to 69 nm).
0 nm) and a half width of 20 nm to 30 nm as the light source 1), and the composition ratio κ is 0.04 to 0.0 nm. 13.
5, the center wavelength is infrared (800nm to 850nm)
+n) and a half-value width of 10 nm to 20 nm as a light source (
1).

Furthermore, as is clear from equations (1) and (2), the temperature characteristic of the effective Verdet constant e is determined by the amount of light Io (λ) or the amount of transmitted light Io7
As long as the wavelength distribution of (λ) does not change, the Verdet constant Ve
Similarly, it changes linearly, but in reality, as the temperature rises, the absorption edge wavelength affects the wavelength within the half-width, so it changes by about 2% within the operating temperature range.

However, since another magneto-optical element (10) blocks light with wavelengths shorter than the absorption edge wavelength, the temperature characteristics of the effective Verdet constant ve are improved by 0.1% within the operating temperature range.
The degree of variation varies. At this time, another magneto-optical element (1
The reduction in the overall light amount due to the addition of 0) is about 5% because only a small portion of the light amount in the wavelength distribution is blocked, and has almost no effect on the sensor sensitivity.

Furthermore, since the light source (1) and another magneto-optical element (10) are housed in a thermostatic chamber (11) and kept at a constant temperature,
Adverse effects such as center wavelength shift and transmission characteristic shift due to temperature changes do not occur. Furthermore, since the other magneto-optical element (10) is a semiconductor single crystal like the magneto-optical element (5), it is stable and not affected by humidity.

As described above, sensor sensitivity is improved by using broadband light to obtain a sufficient amount of light for magnetic field detection, and accuracy is also improved because there is less temperature variation in the effective Verdet constant Ve, which corresponds to sensor sensitivity. do.

In the above embodiment, a light source (
1) and another magneto-optical element (10) are housed here, but they may be housed individually in separate thermostats.

Although another magneto-optical element (10) was provided on the light source (1) side, it was provided on the optical receiver (9) side as shown in FIG.
) and the optical receiver (9) together with the thermostat (11).

[Effects of the Invention] As described above, according to the present invention, the center wavelength of the light used for magnetic field measurement is near the zero point wavelength, and the half-width is 10 n.
m or more, and the amount of light on the shorter wavelength side than the absorption edge wavelength of the magneto-optical element at the upper limit temperature of use is set to almost zero to offset temperature fluctuations in the effective Verdet constant, and another magneto-optical element is provided to lower the upper limit of use. Light with wavelengths shorter than the absorption edge wavelength at temperature is blocked, and the light source that emits light and another magneto-optical element are housed in a thermostatic chamber to prevent temperature changes, so temperature and humidity can be reduced. This has the effect of providing a highly accurate and highly sensitive optical magnetic field sensor that does not depend on .

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing one embodiment of the present invention, Fig. 2 is a characteristic diagram showing another embodiment of the invention, Fig. 3 is a block diagram showing a conventional optical magnetic field sensor, and Fig. 4 is a block diagram showing a conventional optical magnetic field sensor. A characteristic diagram showing the change in transmittance of a filter using an optical thin film with respect to humidity, and FIG. 5 is a characteristic diagram showing a change in the center wavelength of an LED with respect to temperature. (1)...Light source (5)...Magneto-optical element (
10)...Another magneto-optical element (11)...Thermostatic chamber H...Magnetic field In the drawings, the same reference numerals indicate the same or equivalent parts.

Claims (1)

[Claims] As a material for a magneto-optical element that converts the intensity of a magnetic field into an optical signal by the Faraday effect, there are ▲numerical formulas, chemical formulas, tables, etc.▼ However, X: composition ratio of manganese (0<X<0 .7) in an optical magnetic field sensor that detects a magnetic field applied in the direction of light passing based on a signal change of light passing through the magneto-optical element, wherein the Verdet constant, which is a proportional coefficient of the signal change, is used. The wavelength of the light that does not change in temperature is taken as the zero point wavelength, and the Verdet constant Ve (λ) for each wavelength is weighted averaged with respect to the wavelength distribution of the light, and @V@_e=[∫V_e(λ)I_O_T(λ )dλ]
/[∫I_O_T(λ)dλ] However, I_O_T(λ)
: When the value obtained from the amount of transmitted light for each wavelength is the effective Verdet constant @V@_e, the wavelength distribution of the light is such that the center wavelength is near the zero point wavelength and the half-width is 10 nm or more, and The amount of light on the shorter wavelength side than the absorption edge wavelength of the magneto-optical element at the upper limit temperature is set to be almost zero, and the temperature fluctuation of the effective Verdet constant @V@_e is made almost zero, and the upper limit temperature for use is In order to block light having a wavelength shorter than the absorption edge wavelength of the magneto-optical element, another magneto-optical element having the composition ratio of Y:manganese (Y<X) is provided, and the above-mentioned An optical magnetic field sensor characterized in that a light source that emits light and the other magneto-optical element are housed in a thermostatic oven.