JP2013134086A - Magnetic field measuring device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To measure a multi-directional component regarding magnetic fields at the same position and to suppress output level reduction caused by resonance.SOLUTION: An alkali metal atom is sealed in a gas cell 13 as a medium for rotating a polarized plane of light in accordance with the intensity of a magnetic field when the magnetic field is given under irradiation with polarized light. An irradiation section 11 irradiates the alkali metal atom with irradiation light having a linearly polarized component, respectively, from a plurality of different axes. A measuring instrument 14 measures a rotation amount of the polarized plane of each of irradiation light transmitted through the gas cell 13, respectively. An adder 15 adds the measured rotation amounts and outputs an addition signal corresponding to the added value. A VCO 17 generates a periodic signal of a frequency corresponding to the addition signal. A phase shifter 19 imparts a phase difference which is predetermined in accordance with each axis to the periodic signal generated by the VCO 17 and outputs the signal as a phase difference periodic signal. A modulator 12 uses the phase difference periodic signal to modulate the intensity of each of corresponding irradiation light.

Description

  The present invention relates to a magnetic field measurement apparatus using light.

  A magnetic field measurement device using light measures a minute magnetic field generated from a living body such as a magnetic field from the heart (magnetomagnetic field) or a magnetic field from the brain (magnetomagnetic field). Expected. For the measurement of the magnetic field, a medium that causes the magnetic moment to be polarized is used. As this medium, a solid element such as diamond provided with a lattice defect caused by nitrogen, or a gas cell in which a gas such as an alkali metal atom is sealed is used. By irradiating this element with pump light, the energy of atoms in the element is excited according to the magnetic field, and the polarization plane of the probe light transmitted through this element is rotated by the magneto-optic effect. The magnetic field measuring apparatus measures the rotation angle of this polarization plane as magnetic field information.

  In these magnetic field measurement apparatuses, attempts have been made to measure the magnetic field for each component in a plurality of directions. In Patent Document 1, components in a plurality of directions of a magnetic field are detected by using solid-state magnetic sensors such as Hall elements and magnetoresistive elements and arranging them in different detection directions. In recent years, a plurality of optically pumped magnetic sensors have been proposed as methods that do not use SQUID (Superconducting Quantum Interference Device), and attempts have been made to increase sensitivity (Non-Patent Documents 1 to 3).

JP 2008-96261 A

I. K. Kominis, T. W. Kornack, J. C. Allred, and M. V. Romalis, "A subfemtotesla multichannel atmic magnetometer", Nature, 422, 596-599 (2003) G. Bison, N. Castagna, A. Hofer, P. Knowles, J.-L. Schenker, M. Kasprzak, H. Saudan, and A. Weis2, "A room temperature 19-channel magnetic field mapping device for cardiac signals ", APPLIED PHYSICS LETTERS 95, 173701 (2009) D. Budker et al., "Nonlinear magneto-optical rotation with frequency-modulated light", Phys. Rev. A, 65, 055403 (2002)

  The magnetic sensor disclosed in Patent Document 1 can detect multidirectional components regardless of the sensing method or the type of element. However, this magnetic sensor has a complicated structure. Further, since this magnetic sensor detects different directional components by sensors placed at different positions, strictly speaking, it does not detect multidirectional components for the magnetic field at the same position. Furthermore, if this is arrayed and the magnetic distribution is measured, the spatial resolution may be reduced. This problem is the same in the magnetic sensor using the SQUID.

Moreover, since the direction of the magnetic field vector component which can measure all the magnetic sensors mentioned in the nonpatent literatures 1-3 is fixed, it is impossible to measure a some component.
Further, Non-Patent Document 3 introduces a method for improving the measurable range by frequency modulation. In this method, in addition to the + 1st order resonance frequency corresponding to the measurement magnetic field, the 0th order, the −1st order, etc. Since a plurality of frequencies are mixed and cause resonance, the output level is lowered. In addition, this method has a problem that it is difficult to specify the magnetic field strength when the frequencies approach each other.

  An object of the present invention is to measure multi-directional components for magnetic fields at the same position and to suppress a decrease in output level due to resonance.

In order to solve the above-described problem, the magnetic field measurement apparatus according to the present invention rotates the polarization plane of the light according to the strength of the magnetic field when a magnetic field is applied when the polarized light is irradiated. A medium, an irradiation unit for irradiating the medium with irradiation light having a linearly polarized light component from a plurality of different axes, and a measuring instrument for measuring the amount of rotation of the polarization plane of each irradiation light transmitted through the medium An adder that adds each rotation amount measured by the measuring instrument and outputs an addition signal corresponding to the addition value, an oscillator that generates a periodic signal having a frequency corresponding to the addition signal, and the oscillator The phase shifter that gives a predetermined phase difference according to each axis to the periodic signal and outputs it as a phase difference periodic signal, and the irradiation light of each axis irradiated by the irradiating unit respectively correspond to each other. Said phase difference with phase difference Characterized by comprising a modulator for modulating with the period signal.
According to this configuration, it is possible to measure the multi-directional component for the magnetic field at the same position, and to suppress a decrease in output level due to resonance.

Preferably, in the above-described aspect, a filter that removes a high frequency component of the addition signal is provided, and the oscillator generates a periodic signal having a frequency corresponding to the addition signal from which the high frequency component has been removed by the filter. Good.
According to this configuration, it is possible to suppress short-period oscillation caused by the influence of disturbance or the like.

In the above aspect, the modulator may modulate the light intensity of the irradiation light of each axis using the phase difference periodic signal having a corresponding phase difference. According to this configuration, the magnetic field can be measured by adjusting the intensity of the irradiation light.
In the above-described aspect, the modulator may modulate the wavelength of the irradiation light of each axis using the phase difference periodic signal having a corresponding phase difference. According to this configuration, the magnetic field can be measured by adjusting the wavelength of the irradiation light.

In the above-described aspect, the adder may acquire each rotation amount measured by the measuring instrument over a predetermined period, and calculate and add time averages in the period.
According to this configuration, it is possible to suppress an error due to temporal variation of the rotation amount measured by the measuring instrument.

In the above aspect, the irradiation unit includes a laser beam output unit that outputs laser light having a linear polarization plane, and a branch path that branches the output light of the laser beam output unit according to the number of axes. It may be.
According to this configuration, the number of laser light sources can be reduced to one.

In the above-described aspect, the irradiation unit is provided for each laser beam output unit that outputs a laser beam having a linear polarization plane, and emits the input laser beam in a direction corresponding to each axis. And a switching unit that sequentially and cyclically switches the output light of the laser beam output unit to each of the emission units.
According to this configuration, the laser light can be emitted in each direction without reducing the light intensity of the laser light output from the laser light output unit.

It is a figure showing the whole magnetic field measuring device composition concerning an embodiment of the present invention. It is a figure for demonstrating a gas cell. It is a figure for demonstrating a w-axis. It is a figure which shows an example of an adder. It is a figure for demonstrating a phase difference period signal. It is a figure for demonstrating the principle which measures a magnetic field with the measuring device of a one beam system. It is a figure which shows arrangement | positioning of the vibration direction of light and alignment which observed -w direction from + w direction in the modification. It is a figure which shows the arrangement | positioning of the vibration direction and alignment of light when an applied magnetic field is parallel to a w-axis in a modification. It is a figure which shows the whole structure of the magnetic field measuring apparatus in a modification. It is a figure which shows the irradiation part in a modification.

1. Embodiment 1-1. Configuration FIG. 1 is a diagram showing an overall configuration of a magnetic field measurement apparatus 1 according to an embodiment of the present invention. The magnetic field measurement device 1 is a so-called one-beam type measurement device that combines irradiation with pump light by irradiation with probe light. The irradiation unit 11 includes a light source 111 and a branch path 112. The light source 111 is a laser beam output device (laser beam output unit) that outputs a laser beam having a frequency corresponding to the transition of an ultrafine structure level of atoms sealed in a gas cell 13 described later. Specifically, the wavelength of this laser beam is a wavelength corresponding to between the ground state ultrafine structure quantum number F and the excited state ultrafine structure quantum number F-1 of the gas atom enclosed in the gas cell 13. .

  The branch path 112 branches the laser light generated by the light source 111 in three different directions. The branch path 112 guides the laser light generated by the light source 111 to one of the above-described three directions by using, for example, an optical fiber, a waveguide, or an AOM (Acousto Optic Modulator). The branch path 112 includes a polarizing plate and the like. This polarizing plate extracts a beam (irradiation light) having a linearly polarized light component in a predetermined direction from the laser light guided in one of the three directions. This beam whose polarization component has been adjusted is irradiated to the gas cell 13. That is, the irradiation part 11 irradiates the irradiation light which has a linearly polarized component with respect to the gas atom (after-mentioned) enclosed with the gas cell 13 along each direction from said three directions, respectively.

  The modulator 12 modulates the light intensity (radiation intensity) of the beam irradiated in three directions by the branch path 112 using a phase difference periodic signal that is a periodic signal having a corresponding phase difference. This periodic signal is, for example, a sine wave. As a result, the light intensity of the beam irradiated in the three directions fluctuates with the period indicated in the periodic signal.

  The gas cell 13 is a glass cell (element) in which gas atoms are enclosed. Here, the gas atom is an alkali metal atom such as potassium (K), rubidium (Rb), cesium (Cs), or the like. These gas atoms have a property as a medium that rotates the plane of polarization of transmitted light according to the strength of the magnetic field. The gas cell 13 transmits the above-described beam irradiated from the modulator 12. The above-mentioned beam transmitted through the gas cell 13 is guided to the measuring instrument 14 by an optical fiber or the like. The material of the gas cell 13 is not limited to glass, and may be resin or the like as long as the material transmits the beam. Further, the inner wall of the gas cell 13 may be subjected to non-relaxation coating with hydrocarbon or the like.

  FIG. 2 is a diagram for explaining the gas cell 13. In FIG. 2, the space in which the gas cell 13 is arranged is represented by an xyz right-handed coordinate space. In this space, the direction along the x-axis is referred to as the x-axis direction. Of the x-axis directions, the direction in which the x component increases is referred to as + x direction, and the direction in which the x component decreases is referred to as -x direction. Similarly, for the y and z components, the y-axis direction, + y direction, -y direction, z-axis direction, + z direction, and -z direction are defined.

  As shown in FIG. 2, the shape of the gas cell 13 is substantially a cube, and each side thereof extends along the x-axis direction, the y-axis direction, and the z-axis direction. The modulator 12 irradiates the gas cell 13 with beams Bx, By, and Bz, respectively, along three directions of + x direction, + y direction, and + z direction. Therefore, the beams Bx, By, and Bz are irradiated with a period designated so as to be substantially orthogonal to the surface of the gas cell 13, respectively.

  Here, a vector is assumed in which unit vectors extending in three directions of + x direction, + y direction, and + z direction are combined. The direction along the combined vector is called the + w direction, and the axis extending in the + w direction is called the w axis.

  FIG. 3 is a diagram for explaining the w-axis. In FIG. 3, the xyz coordinate space is displayed by a so-called cabinet projection method. When a vector in the xyz coordinate space is represented by a component (x, y, z), the unit vector in the x-axis direction is (1, 0, 0), and the unit vector in the y-axis direction is (0, 1, 0). Thus, the unit vector in the z-axis direction is (0, 0, 1). A vector (1, 1, 1) obtained by combining these three unit vectors extends in the w-axis direction. A magnetic field having a strength determined in advance in the w-axis direction is applied to the gas cell 13. This magnetic field is called a bias magnetic field.

  As shown in FIG. 2, the beam Bx has a linearly polarized component along the direction of the arrow Dx. The arrow Dx direction is a direction along a vector obtained by combining unit vectors in the + y direction and the + z direction. That is, the arrow Dx direction is a direction orthogonal to the x-axis direction. The beam By has a linearly polarized component along the arrow Dy direction. The arrow Dy direction is a direction along a vector obtained by combining unit vectors in the + z direction and the + x direction. That is, the arrow Dy direction is a direction orthogonal to the y-axis direction. The beam Bz has a linearly polarized component along the direction of the arrow Dz. The arrow Dz direction is a direction along a vector obtained by combining unit vectors in the + x direction and the + y direction. That is, the arrow Dz direction is a direction orthogonal to the z-axis direction.

  The magnetic field measuring apparatus 1 includes measuring instruments 14 respectively corresponding to the three directions of + x direction, + y direction, and + z direction described above. The three measuring instruments 14 receive the above-described beams irradiated in the corresponding directions and transmitted through the gas cell 13. Each measuring instrument 14 measures the amount of rotation that the linearly polarized light component included in the beam has rotated through the gas cell 13, that is, the rotation angle of the polarization plane.

  The adder 15 adds the rotation amounts measured by the measuring instruments 14 and outputs an addition signal corresponding to the added value. FIG. 4 is a diagram illustrating an example of the adder 15. For example, an adder circuit shown in FIG. 4 is used as the adder 15. This adder circuit adds signals Sx, Sy, Sz indicating the amount of rotation of the polarization plane for each beam in the x, y, z directions, and outputs the result as “Sx + Sy + Sz”.

  The amplifier 16 is an amplifier that amplifies the addition signal output from the adder 15, and includes a circuit for optimizing the gain and phase of the feedback system configured by the magnetic field measurement apparatus 1. A voltage controlled oscillator (VCO) 17 is a voltage controlled oscillator, and generates a periodic signal indicating an oscillation frequency determined based on the output level of the amplifier 16.

  The periodic signal generated by the VCO 17 is input to the phase shifter 19. The phase shifter 19 gives a predetermined phase difference to the periodic signal generated by the VCO 17 according to the x-axis direction, the y-axis direction, and the z-axis direction. For example, the phase difference according to the x-axis direction is 0, the phase difference according to the y-axis direction is (2π / 3), and the phase difference according to the z-axis direction is (4π / 3). The phase shifter 19 outputs the periodic signal with the phase difference as a phase difference periodic signal.

As described above, the modulator 12 modulates the irradiation light of each axis irradiated by the irradiation unit 11 using the phase difference periodic signal having the corresponding phase difference. Each of these phase difference periodic signals is output by the phase shifter 19.
FIG. 5 is a diagram for explaining the phase difference periodic signal. As shown in FIG. 5, the light intensities of the beams Bx, By, and Bz change with time along the corresponding sine waves (phase difference periodic signals) output by the phase shifter 19. Since the beams Bx, By, and Bz are controlled so that their phase differences are equal to each other, each light intensity becomes a three-phase alternating current. The frequency indicated by the phase difference periodic signal is hereinafter referred to as a modulation frequency.

1-2. Operation Next, an operation of measuring a magnetic field by the magnetic field measurement apparatus 1 will be described.
FIG. 6 is a diagram for explaining the principle of measuring a magnetic field by a one-beam type measuring apparatus. In the following, among the coordinate symbols shown in the figure, a symbol in which a black circle is drawn in a circle with a white inside represents an arrow heading from the back side to the near side. In a one-beam type measuring device, when linearly polarized light is irradiated to gas atoms enclosed in a gas cell, the probability distribution of the magnetic moment that occurs when the gas atoms are optically pumped and the energy changes is a spherically symmetric origin distribution. Change from. For example, at the energy transition of the hyperfine structure level F → F ′ = F−1, the probability distribution of the magnetic moment of the gas atom has a shape corresponding to the region R ₁ extending along the direction of vibration of the linearly polarized light. Become. This probability distribution is called alignment.

That is, as shown in FIG. 6 (a), for example, a linearly polarized light oscillation direction of the electric field is along the parallel arrows D ₀ direction + y direction, is irradiated toward the + x-direction, the gas which the linearly polarized light passes through Alignment distributed in the region R ₁ along the y-axis direction occurs in the atoms. When a magnetic field is applied here, the alignment rotates with the direction of the magnetic field as the axis of rotation. This rotational speed is proportional to the strength of the applied magnetic field. This exercise is called precession exercise. The spin polarization of gas atoms forms a steady state by the relaxation action determined by the system simultaneously with precession. When the direction of the steady state of this spin polarization is different from the direction of the linearly polarized light of the transmitted light, the polarization plane of the linearly polarized light is rotated by the linear dichroism.

FIG. 6B shows the rotation angle φ of the polarization plane when the vibration direction of the linearly polarized electric field is viewed in the −x direction. Since the rotation angle φ has a correlation with the strength of the magnetic field in the + x direction, the strength of the magnetic field in the x-axis direction inside the gas cell 13 can be obtained by measuring the rotation angle φ. In the one-beam method, the direction D _M of the magnetic field to be measured is the direction in which light is irradiated (the + x direction in FIG. 6).

  As shown in FIG. 1, the magnetic field measurement apparatus 1 constitutes a feedback system. By operating this feedback system, light is irradiated to gas atoms in synchronization with the precession frequency proportional to the strength of the applied magnetic field. Thereby, alignment is amplified and it becomes a kind of resonance state. When the magnetic field fluctuates, the system follows the frequency corresponding to the fluctuation. That is, the magnetic field measurement apparatus 1 has a feedback circuit, thereby forming a phase locked loop.

  For example, consider a case where the bias magnetic field described above is applied in the w-axis direction and a magnetic field other than the bias magnetic field (hereinafter referred to as a transverse magnetic field) is not applied. When the modulator 12 is operating at a modulation frequency corresponding to the precession frequency, the alignment direction and the vibration direction at the time when the linearly polarized light is irradiated coincide with each other. The rotation angle measured by the device 14 becomes zero, and a stable state is obtained. However, when the precession frequency is slower than the modulation frequency, the alignment direction and the vibration direction do not match, so the measurement results of all the measuring instruments 14 become positive, and the oscillation frequency of the signal generated by the VCO 17 increases. To do. As a result, the magnetic field measurement apparatus 1 is adjusted in a direction in which the precession motion frequency and the modulation frequency match.

  On the other hand, when a magnetic field to be measured is applied, a magnetic field vector in which the applied magnetic field is combined with a bias magnetic field is directed in a tilted direction without being parallel to the w axis. Since the alignment of gas atoms rotates around the tilted magnetic field vector, the rotation angles measured by the measuring instruments 14 show different values. Based on the modulation frequency at this time and the measurement results of the measuring instruments 14, the magnetic field measurement apparatus 1 calculates the magnetic field to be measured.

  Specifically, it is as follows. Here, consider the alignment when the beam is blocked from the state in which the magnetization is saturated with any one beam and then precessed. Further, it is assumed that the transverse magnetic field is very small with respect to the magnetic field component in the w-axis direction. FIG. 7 is a diagram illustrating the vibration direction and alignment arrangement of light observed in the −w direction from the + w direction in this modification.

  If the applied magnetic field B, which is a transverse magnetic field, is zero, the gas atoms enclosed in the gas cell 13 are in a state where there is no precession action. In this state, when irradiated with irradiation light having a linearly polarized component along the arrow Dz direction and propagating toward this gas atom in the z-axis direction, alignment caused by optical pumping by the irradiation light is directed to the arrow Dz direction. .

  On the other hand, when there is an applied magnetic field B that is a transverse magnetic field (not zero), the alignment precesses about this, and the direction of the resulting alignment is assumed to be the direction of arrow Dz2.

  Let δM be the vector of the difference between the arrow Dz direction and the arrow Dz2 direction. Since this δM is assumed to be minute compared to the direction of the arrow Dz and the direction of the arrow Dz2, it is assumed that it is in a plane normal to the w axis. A displacement δM in the same direction occurs with respect to the alignment with respect to the x-axis and the y-axis. The value measured by the measuring instrument 14 by the irradiation light having the linearly polarized component along the arrow Dz direction is a vector obtained by projecting a vector indicated by the arrow Dz2 direction onto a plane having the z-axis as a normal line, and the arrow Dz direction. It is proportional to an angle θ (not shown) formed with the vector. Using approximation, the angle θ is proportional to the length of the line segment that projects δM toward the plane with the w axis as the normal. This line segment is in a plane perpendicular to the z-axis and having the w-axis as a normal line. When the length of δM is normalized, the length of the projection component is cos α as shown by the following equation (1).

  When the outputs for the beams in the direction of the arrow Dx and the direction of the arrow Dy are similarly calculated by changing the direction of the line segment, the following expressions (2) and (3) are obtained.

  Adding the right side of each equation gives zero for any α. That is, if the processing of the adder 15 is simple addition, the output becomes zero, so that the feedback system of FIG. 1 is stabilized at a constant frequency. The magnitude of the applied magnetic field B corresponds to the modulation frequency, and its direction can be calculated from the output of each measuring instrument 14.

  Consider a case where the applied magnetic field B is parallel to the w-axis (that is, the applied magnetic field B is not a transverse magnetic field) and there is no influence of magnetization due to optical pumping. FIG. 8 is a diagram showing the vibration direction of light and the alignment arrangement when the applied magnetic field B is parallel to the w-axis in this modification. As shown in FIG. 8, when irradiation light having a linearly polarized component along the arrow Dz direction is irradiated, alignment caused by optical pumping by the irradiation light is directed to the arrow Dz direction. Further, the alignment rotates with the applied magnetic field B as an axis. A vector of a difference between the rotated alignment and the alignment before the rotation is represented by δMz. When the length of δMz is normalized, the length of the projection component is cos α as shown by the above-described equation (1).

  Since this relationship has the same value for all axes, if the processing of the adder 15 is simple addition, the output is 3 cos α. From this result, the frequency change of the VCO 17 is generated, and the modulation frequency and the precession frequency are adjusted to coincide with each other by the action of the feedback system.

  As described above, the magnetic field measurement apparatus 1 measures the strength of the magnetic field applied to one position regardless of its direction. In addition, the magnetic field measurement apparatus 1 does not measure a magnetic field in one direction with light in one direction, but measures a magnetic field using light in a plurality of directions, so that a frequency other than the + 1st order resonance frequency corresponding to the measurement magnetic field. It is difficult to mix. Therefore, the use of the magnetic field measurement apparatus 1 suppresses a decrease in output level.

2. Modification The above is the description of the embodiment, but the contents of this embodiment can be modified as follows. Further, the following modifications may be combined.
(1) In the above-described embodiment, the modulator 12 irradiates the gas cell 13 with the laser light output from the light source 111 as a beam along the x, y, and z directions. Or four or more directions. In this case, the phase shifter 19 may output the phase difference periodic signal so that the phase intervals of the beams irradiated in the respective directions are equal.

(2) In the above-described embodiment, the addition signal of the adder 15 is input to the amplifier 16 as it is. However, a part of the addition signal of the adder 15 is added between the adder 15 and the amplifier 16 or the VCO 17. A filter 18 to be removed may be provided. FIG. 9 is a diagram showing an overall configuration of the magnetic field measurement apparatus 1a in this modification. The magnetic field measurement device 1a is different from the magnetic field measurement device 1 described above in that a filter 18 is provided between the adder 15 and the amplifier 16. The filter 18 removes a component (high frequency component) equal to or higher than a predetermined threshold value from the addition signal output from the adder 15 and supplies a component (low frequency component) less than the threshold value to the amplifier 16. It is a low-pass filter. The feedback configuration of modulator 12 → gas cell 13 → measurement instrument 14 → adder 15 → amplifier 16 → VCO 17 → modulator 12 may cause unintended oscillation due to the configuration, but by providing the filter 18, Such oscillation can be eliminated.

(3) In the above-described embodiment, the modulator 12 modulates the light intensity of the beam in the three directions using the corresponding sine wave (phase difference periodic signal) output from the phase shifter 19. The shape of the phase difference periodic signal is not limited to a sine wave. For example, the modulator 12 may modulate the light intensity of the beams in the three directions into corresponding rectangular waves and triangular waves, respectively. In this case, the phase shifter 19 may output these rectangular waves, triangular waves, and the like.

(4) In the above-described embodiment, the magnetic field measurement apparatus 1 includes the gas cell 13 that is a glass cell (element) in which gas atoms are sealed. However, the polarization plane of the transmitted light is changed to the strength of the magnetic field. A medium other than gas atoms may be used as the medium to be rotated accordingly. For example, the magnetic field measurement apparatus 1 may use a solid element such as diamond provided with a lattice defect by nitrogen as the medium.

(5) In the above-described embodiment, the propagation directions of the three beams are orthogonal to each other, and the vibration direction of the electric field is not orthogonal. However, this is not limited as long as any three magnetization directions can be detected. For example, the branch path 112 may be arranged so that the vibration directions of the linearly polarized light components included in the three branched beams are orthogonal.

(6) In the above-described embodiment, the modulator 12 modulates the light intensity of each beam by using the corresponding phase difference periodic signal, but modulates the wavelength of each beam by using this phase difference periodic signal. May be. When the wavelength of the beam is changed, the amount of light having a wavelength that contributes to excitation of gas atoms among the light contained in the beam increases or decreases. Further, the beam transmittance in the gas cell 13 may vary depending on the wavelength. Therefore, when the beam wavelength is changed, the amount of light transmitted through the gas cell increases or decreases. That is, the modulator 12 modulates the light intensity of the beam by modulating the wavelength.

(7) In the embodiment described above, the adder 15 acquires and adds the rotation amount measured by each measuring instrument 14 and outputs an addition signal corresponding to the added value. The addition is not limited to this. For example, the adder 15 may acquire the rotation amount measured by each measuring instrument 14 over a determined period, and calculate and add time averages during that period. Note that the adder 15 may be included in the filter 18 shown in the modified example 2. For example, a predetermined high-frequency component may be removed from the time average before this addition. Thereby, even if the rotation amount measured by each measuring instrument 14 fluctuates in a short period of time, the influence thereof is difficult to appear in the magnetic field measurement, and errors due to the time fluctuation are suppressed.

(8) In the embodiment described above, the irradiation unit 11 includes the light source 111 and the branch path 112, but may include the switching unit 112 b and the emission unit 113 instead of the branch path 112. FIG. 10 is a diagram showing the irradiation unit 11b in this modification. The emitting unit 113 is provided for each axis in the x-axis direction, the y-axis direction, and the z-axis direction, and emits laser light input by an optical fiber or the like in a direction corresponding to each axis. The switching unit 112b is a device that time-division-multiplexes signals, and causes the output light of the light source 111 to be sequentially switched and incident on the emission unit 113. Thereby, the irradiation part 11 does not need to have a branch path. The irradiation unit 11 irradiates the laser light in a plurality of directions without reducing the light intensity of the laser light output from the light source 111.

  As described above, a single light source is not switched in a time division manner by the switching unit 112b, but a plurality of VCSELs (Vertical Cavity Surface Emitting Lasers) are assigned to each beam. , And may be independently modulated.

DESCRIPTION OF SYMBOLS 1,1a ... Magnetic field measuring device 11, 11b ... Irradiation part, 111 ... Light source, 112 ... Branching path, 112b ... Switching part, 113 ... Emitting part, 12 ... Modulator, 13 ... Gas cell, 14 ... Measuring instrument, 15 ... Adder 16 ... Amplifier 17 ... VCO 18 ... Filter 19 ... Phase shifter

Claims (7)

When a magnetic field is applied when polarized light is irradiated, a medium that rotates the polarization plane of the light according to the strength of the magnetic field;
An irradiating unit configured to irradiate the medium with irradiation light having a linearly polarized light component from different axes;
A measuring instrument for measuring the amount of rotation of the polarization plane of each irradiation light transmitted through the medium;
An adder that adds each rotation amount measured by the measuring instrument and outputs an addition signal corresponding to the added value;
An oscillator that generates a periodic signal having a frequency according to the addition signal;
A phase shifter that gives a predetermined phase difference according to each axis to the periodic signal generated by the oscillator and outputs it as a phase difference periodic signal;
A magnetic field measuring apparatus comprising: a modulator that modulates irradiation light of each axis irradiated by the irradiation unit using the phase difference periodic signal having a corresponding phase difference. A filter for removing high frequency components of the sum signal,
The magnetic field measurement apparatus according to claim 1, wherein the oscillator generates a periodic signal having a frequency corresponding to an addition signal from which a high frequency component has been removed by the filter. The magnetic field measuring apparatus according to claim 1, wherein the modulator modulates the light intensity of the irradiation light of each axis using the phase difference periodic signal having a corresponding phase difference. The magnetic field measuring apparatus according to claim 1, wherein the modulator modulates the wavelength of the irradiation light of each axis using the phase difference periodic signal having a corresponding phase difference. The said adder acquires each rotation amount measured by the said measuring device over the determined period, respectively calculates the time average in the said period, and adds, respectively. The magnetic field measurement apparatus according to item 1.   The said irradiation part has any one of the laser beam output part which outputs the laser beam with a linear polarization plane, and the branch path which branches the output light of a laser beam output part according to the number of axes | shafts. The magnetic field measurement apparatus according to item 1. The irradiation unit is a laser beam output unit that outputs a laser beam having a linear polarization plane, and a plurality of emission units that are provided for each axis and emit the input laser beam in a direction according to each axis, 6. The magnetic field measurement apparatus according to claim 1, further comprising: a switching unit that sequentially switches the output light of the laser light output unit to the respective emission units in a cyclic manner.

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