CN102931987A - Quantum interference device, atomic oscillator, and magnetic sensor - Google Patents

Abstract

Quantum interference devices, atomic oscillators, and magnetic sensors. The EIT phenomenon is efficiently generated in an atomic group having a Doppler-spread optical resonance wavelength distribution. Consists of: LD (2) that emits each resonance light; a center wavelength generating unit (1) that generates the center wavelength of the LD; an oscillator (9) that oscillates at 1 frequency equivalent to the energy difference (ΔE12) between two different ground states /2 frequency; oscillator (10), oscillating to produce a frequency much smaller than Doppler spread; EOM (Electron Optical Modulation Element) (3, 4), using electrical signals to implement frequency modulation on the resonant light (11) emitted from the LD The gas chamber (5) changes the light absorption according to the wavelength of the light (12) modulated by the EOM (4), and seals gaseous alkali metal (cesium) atoms; the light detector (light detection unit) (6) detects The light (13) transmitted from the gas chamber; the frequency control unit (7), detects the EIT state of the gas chamber according to the output of the light detector, and controls the output voltage.

Description

Quantum Interference Devices, Atomic Oscillators, and Magnetic Sensors

This application is a divisional application of an invention patent application with an application date of February 5, 2010, an application number of 201010113602.x, and an invention title of "Quantum Interference Device, Atomic Oscillator, and Magnetic Sensor".

technical field

The present invention relates to quantum interference devices, atomic oscillators, and magnetic sensors, and more particularly, to techniques for efficiently generating the EIT phenomenon.

Background technique

Electromagnetically induced transparency method (sometimes called EIT method, CPT method) atomic oscillator is an oscillator that utilizes the phenomenon that when two kinds of resonant light with different wavelengths are irradiated to an alkali metal atom at the same time, the two kinds of Absorption of resonance light ceases (EIT phenomenon). Fig. 24(a) shows the energy state of one alkali metal atom. As is well known, when the alkali metal atoms are individually irradiated with first resonant light having a wavelength corresponding to the energy difference between the first ground state level 23 and the excited level 21, or having wavelengths corresponding to the energy difference between the second ground state level 24 and the excited level When the second resonant light of the wavelength of the energy difference between the energy levels 21, will cause light absorption. However, when the first resonant light and the second resonant light are simultaneously irradiated to the alkali metal atom, and the frequency difference between the simultaneously irradiated first resonant light and the second resonant light is the same as that of the first ground state energy level 23 and the second ground state energy When the energy difference (ΔE12) between levels 24 is exactly the same, the system in Figure 24(a) is in the overlap state of the two ground state energy levels, that is, the state of quantum interference, and the excitation to the transition to the excited level 21 stops, resulting in a transparent (EIT) phenomenon. By using this phenomenon to detect a sudden change in the light absorption operation when the wavelength difference between the first resonant light and the second resonant light deviates from ΔE12, and controlling it as a signal, a high-precision oscillator can be manufactured. In addition, since ΔE12 changes sensitively according to the strength or fluctuation of the external magnetic field, it is possible to manufacture a highly sensitive magnetic sensor by utilizing the EIT phenomenon.

In addition, in order to improve the signal-to-noise ratio (S/N) of the light output signal under the EIT phenomenon, it is only necessary to increase the number of atoms of the alkali metal interacting with the resonant light. For example, in Patent Document 1, for the purpose of improving the S/N of the output signal of an atomic oscillator, methods such as increasing the thickness of a gas cell (cell) in which gaseous alkali metal atoms are enclosed, or increasing the incident The beam diameter of the laser to the gas cell. Regardless of the method, in order to increase the area where the alkali metal atoms are in contact with the resonant light, as shown in Figure 24(b) or Figure 24(c), the thickness or height of the gas cell is increased. As for the laser beams used here, only one pair of laser beams with two wavelengths satisfying the generation condition (recognition condition) of the EIT phenomenon was used.

In addition, Patent Document 2 (1) discloses a technique for improving the sensitivity of an EIT (CPT) system atomic oscillator. That is, it is characterized in that the D1 line is used as a light source. Compared with the previous D2 line, the EIT (CPT) signal strength can theoretically be improved. As a result, sensitivity/frequency stability is improved. (2) In addition, using a 4-wave light source, the P1/2 excitation level (hyperfine structure) formed by splitting the energy into two by double Λ-type transitions interacts simultaneously, thereby further improving the signal intensity, but it is disclosed here The technology involved in the mixing of 4 light waves does not belong to the scope of the technical field involved in the present invention.

Patent Document 1: Japanese Patent Laid-Open No. 2004-96410

Patent Document 2: USP6359916

Focusing on each atom constituting the gaseous alkali metal atomic group in the gas cell, it can be seen that there is a constant velocity distribution corresponding to each state of motion. If there are only 2 wavelengths (a pair) of laser light incident on the atomic group, under the influence of the Doppler effect (Doppler frequency shift) of atomic motion, the atoms that can actually interact are only multiple atoms in the gas chamber. Among the atoms, a very small portion of atoms having a specific velocity component value in the laser incident direction has an extremely low ratio of atoms contributing to EIT. The prior art disclosed in Patent Document 1 has the following problem. Since the atomic oscillator is configured in such a state where EIT generation efficiency is low, in order to obtain a desired signal-to-noise ratio (S/N) For the absorption spectrum, either the thickness or the height of the gas cell must be increased, and it is difficult to achieve miniaturization while maintaining the signal-to-noise ratio. That is, the number of atoms contributing to the EIT phenomenon per unit volume in the gas cell remains constant. In addition, the technique disclosed in Patent Document 2-(1) also has the same problem.

That is, both Patent Documents 1 and 2-(1) use only two types of light waves. Alkaline atoms in the gas cell have a velocity distribution, and there is a Doppler spread of energy associated with this. Therefore, in the Λ-type transition with only 2 kinds of light waves, only a very small part of the atoms are interacted with, and therefore, the yield of EIT generation per unit volume is extremely poor. Therefore, there is a problem that the EIT signal strength is weak.

The actual excited energy level of the alkali atom has a hyperfine structure, and is split into energy levels having different energies from each other as shown in FIG. 20 . Therefore, the simple Λ-type 3-energy state system shown in Fig. 24(a) cannot be used to explain the EIT phenomenon targeting alkali atoms, and therefore, in practice, it is necessary to consider such multiple energy levels in order to efficiently generate EIT. However, there is a problem that studies considering the relationship between the presence of multiple energy levels and the energy Doppler spread accompanying the above-mentioned atomic velocity distribution have been insufficient.

In particular, from the viewpoint of optimization of driving conditions of a quantum interference device to which the EIT phenomenon is applied, as in the present invention, the center of the light source (laser light) is determined in consideration of the energy state of the excitation level in the case of using a plurality of resonant light pairs. The frequency or modulation conditions that determine the laser are important.

Contents of the invention

The present invention has been accomplished in view of the above-mentioned problems, and its object is to provide a quantum interference device that efficiently causes more gaseous alkali metal atoms in a gas chamber to generate an EIT phenomenon by generating multiple pairs of resonant light pairs with different wavelengths, and By using this quantum interference device, a small atomic oscillator, a magnetic sensor, or a quantum interference sensor can be provided.

An advantage of some aspects of the invention is to solve at least a part of the problems described above, and the invention can be implemented as the following forms or application examples.

[Application example 1] The quantum interference device has at least: a gaseous alkali metal atom; and a light source for generating a resonant light pair of different frequencies that maintains an energy difference between two ground states of the alkali metal atom The corresponding frequency difference causes the alkali metal atoms to interact with the resonant light pairs to produce electromagnetically induced transparency (EIT), which is characterized in that the number of the resonant light pairs is multiple pairs, and the center of each resonant light pair The frequencies are different from each other.

The quantum interference device of the present invention is characterized in that the number of excitation laser pairs is two or more pairs, and the center frequencies of the respective laser pairs are different from each other. Thus, more gaseous alkali metal atoms can be caused to generate the EIT phenomenon per unit volume.

[Application example 2] is characterized in that the resonant light pair interacting with the alkali metal atom is linearly polarized light.

When a resonant light pair emitted from a light source draws a straight line at the ends of an in-plane electric vector perpendicular to the propagation direction of the light, the light is called linearly polarized light. Therefore, if no polarization is applied to the resonant light pair emitted from the light source, it is linearly polarized light. In addition, the polarization state of light can be considered as the superposition of two perpendicular linearly polarized lights. Therefore, since the resonant light from the light source is linearly polarized light originally, no means for polarizing is required, and the structure of the light source can be simplified.

[Application example 3] is characterized in that the resonant light pair interacting with the alkali metal atom is circularly polarized light.

When a circle is drawn at the end of an in-plane electric vector perpendicular to the propagation direction of the light of the resonant light pair emitted from the light source, the light is called circularly polarized light. It has been confirmed by experiments that when the resonant light pair is converted into circularly polarized light, the light transmission intensity at the wavelength λ0 increases to about 6 times that of the usual one. Thereby, the S/N of the optical output signal under the EIT phenomenon can be improved.

[Application example 4] is characterized in that the resonant light pair interacting with the alkali metal atom is elliptically polarized light.

When the resonant light pair emitted from the light source draws an ellipse at the end of an in-plane electric vector perpendicular to the propagation direction of the light, the light is called elliptical polarized light. And it can be seen that there is such elliptically polarized light, that is, when a wavelength plate is arranged perpendicular to the optical path on the optical path of the resonant light pair and its surface is rotated, the polarization state of the elliptically polarized light changes and is in the vertical There is a continuous change between polarized light and circularly polarized light. Therefore, even with elliptically polarized light, the S/N of the optical output signal under the EIT phenomenon can be improved.

[Application Example 5] A wavelength plate is provided on an optical path between the light source and the gas cell enclosing the alkali metal atoms.

The wave plate refers to a multi-refraction element that produces a phase difference between vertically polarized light components. A wavelength plate that produces a phase difference of π (180°) is called a λ/2 plate or a half-wavelength plate, which is used to change the polarization direction of linearly polarized light. A wavelength plate that produces a phase difference of π/2 (90°) is called a λ/4 plate or a quarter-wave plate, which is used to convert linearly polarized light into circularly polarized light (楕 circularly polarized light), or vice versa Convert circularly polarized light (o-circularly polarized light) into linearly polarized light. In the invention, since it is necessary to convert linearly polarized light into circularly polarized light or elliptic polarized light, it is necessary to use a λ/4 plate and use a wavelength plate 40 to convert the resonant light pair of linearly polarized light emitted from the light source into circularly polarized light Or ellipse circularly polarized light, incident on the gas cell. Accordingly, the S/N of the optical output signal under the EIT phenomenon can be improved with a simple structure.

[Application example 6] is characterized in that the multiple pairs of resonant light pairs meet the conditions for the generation of electromagnetically induced transparency, and the light intensity of each resonant light pair is near the maximum value P0 in the region where the EIT signal intensity increases linearly.

By adopting such a light intensity distribution of multiple pairs of resonant light pairs, light utilization efficiency can be improved.

[Application example 7] is characterized in that the intensity distribution of the multiple pairs of resonant light pairs is Gaussian distribution relative to the center frequency of each pair, and the resonant light pair corresponding to the maximum light intensity satisfies that the velocity component of the light direction is 0 The vicinity of the atomic group of the alkali metal corresponds to the generation condition of the electromagnetically induced transparency phenomenon, the intensity of which is the maximum value P0 in the linear region.

Since the velocity distribution of the alkali metal atoms is a Gaussian distribution, as long as the light intensity distribution of the resonant light pair is set to a Gaussian distribution in advance, a simple light drive circuit can be used to achieve high light utilization efficiency.

[Application example 8] is characterized in that the plurality of resonant light pairs are generated by combining amplitude modulation with frequency modulation or phase modulation.

This modulation method can control the light intensity distribution of the resonant light pair with a high degree of freedom.

[Application example 9] is characterized in that the plurality of resonant light pairs are generated by modulation of a signal having any one of a sine wave, a triangular wave, a sawtooth wave, and a rectangular wave.

This modulation method can use a simple optical drive circuit to control the light intensity distribution of the resonant light pair with a high degree of freedom.

[Application example 10] is characterized in that it has a drive circuit unit for modulating the light source, the drive circuit unit is separated from other components, and can be arbitrarily controlled, A constant of the drive circuit section is set.

Various applications are conceivable for "quantum interference devices" that utilize the EIT phenomenon, such as high-precision oscillators, high-precision measurement devices such as clocks, and quantum interference sensors represented by magnetic sensors and fine particle detection sensors such as pollen and smoke etc., by adopting such a structure, it is possible to obtain an optimal EIT signal curve suitable for the purpose.

[Application example 11] is characterized in that when the nuclear spin quantum number of the alkali metal atom is 1, the hyperfine structure in the P1/2 excitation level or P3/2 excitation level of the alkali metal atom The quantum number is F', the minimum energy is E1, and the maximum energy is E2 in the area where the two energy ranges of the Doppler expansion of F'=I-1/2 and F'=I+1/2 overlap each other. When , the excitation target energy Eend of any one of the multiple pairs of resonant light pairs that causes the electromagnetically induced transparency (EIT) phenomenon satisfies E1<Eend<E2.

For the resonant light pair corresponding to Eend that satisfies this condition, atoms with velocity components in opposite directions can simultaneously generate EIT, so power broadening (power broadening: the stronger the optical power, the larger the linewidth of the EIT signal) is not likely to occur. phenomenon), therefore, increasing the Q value (reciprocal of the half-value width of the EIT signal), thereby improving the performance index (defined later).

[Application example 12] is characterized in that, if the nuclear spin quantum number of the alkali metal atom is I, and the quantum number of the hyperfine structure of the excitation energy level of the alkali metal atom is F', then considering F'= In the state where the two energy ranges of the Doppler spread of I-1/2 and F'=I+1/2 do not overlap with each other, when the F'=I-1/ The energy range of 2 is from E11 to E12 (where E11<E12), and the energy range of F'=I+1/2 considering the Doppler spread is from E21 to E22 (where E21<E22 ), the excitation target energy Eend of any one of the multiple pairs of resonant light pairs that causes the electromagnetically induced transparency phenomenon only satisfies one of the conditions of E11<Eend<E12 or E21<Eend<E22.

When this condition is satisfied, the EIT based on multiple resonant light pairs can be realized while maintaining the pure Λ-type transition of the three-level system, so the enhancement effect of the EIT signal based on the overlapping effect can be increased.

[Application example 13] The quantum interference device allows multiple pairs of resonant light to pass through the alkali metal atoms one or more times, and detects the electromagnetically induced transparency phenomenon from the alkali metal atoms. When the energy of the excitation level considering the Doppler width is E10, and the excitation target energy of the plurality of resonant light pairs is Eend 0, the Eend 0 satisfies E10<Eend 0 or Eend 0<E10.

In this case, one pair of resonant light can be caused to generate EIT with the alkali metal atom group having the velocity components in opposite directions in the gas cell, respectively, on the outward path and the return path. Therefore, when EIT is generated by multiple resonant light pairs under such conditions, the same effect can be obtained by using half the number of resonant light pairs or half the light modulation width compared to the case of the non-reflective type.

[Application example 14] The quantum interference device allows multiple pairs of resonant light to pass through the alkali metal atoms one or more times, and detects the electromagnetically induced transparency phenomenon from the alkali metal atoms. When the excitation target energy of any one of the plurality of resonant light pairs in the electromagnetically induced transparency phenomenon is Eend, the Eend only satisfies either the condition of Eend<E10 or E10<Eend.

In this case, all resonant light pairs contribute to EIT, and since it is a reflective type, only half the number of resonant light pairs is required compared with the case of a non-reflective type, and the efficiency is higher.

[Application Example 15] is characterized in that the number of times of reentry is an odd number (total optical path lengths of going and returning are substantially equal).

If the optical path lengths of the outward path and the return path of light are substantially equal, the number of atoms contributing to EIT in different velocity groups is substantially equal, which is advantageous from the viewpoint of EIT generation efficiency.

[Application example 16] An atomic oscillator includes the quantum interference device.

Since the atomic oscillator has the quantum interference device of the present invention, the EIT phenomenon can be generated in a high S/N state, and thus the miniaturization of the atomic oscillator can be realized.

[Application example 17] A magnetic sensor is characterized in that it has the above-mentioned quantum interference device of the present invention.

The oscillation frequency of the atomic oscillator is based on the energy difference (ΔE12) between the two ground state energy levels of the atom. The value of ΔE12 changes with the strength or fluctuation of the external magnetic field. Therefore, the gas chamber of the atomic oscillator is shielded from the magnetic field so as not to be affected by the external magnetic field. Therefore, a magnetic sensor that measures the strength and fluctuation of an external magnetic field can be manufactured by removing the magnetic field shield and reading the change in ΔE12 according to the change in oscillation frequency. By having the quantum interference device of the present invention, the EIT phenomenon can be generated in a state with a high S/N, and thus the magnetic sensor can be miniaturized.

[Application example 18] The quantum interference sensor has the quantum interference device of the present invention.

By having the quantum interference device of the present invention, it is possible to achieve improvement in sensitivity and accuracy and miniaturization of various sensors for detecting external disturbances that affect the EIT signal curve.

Description of drawings

Fig. 1 is a schematic diagram of the velocity distribution of gaseous alkali metal atoms.

FIG. 2 is a diagram showing the configuration of an atomic oscillator according to the first embodiment of the present invention.

3( a ) and ( b ) are graphs showing the spectrum of resonance light incident on a gas cell.

FIG. 4 is a diagram showing the state of resonant light incident on the gas cell and the direction of movement of gaseous alkali metal atoms.

FIG. 5 is a schematic diagram illustrating the relationship between energy Doppler spread based on atomic motion and resonant light of the present invention.

FIG. 6 is a diagram showing the configuration of an atomic oscillator according to a second embodiment of the present invention.

FIG. 7 is a diagram showing the configuration of an atomic oscillator according to a third embodiment of the present invention.

FIG. 8 is a diagram showing a configuration of a magnetic sensor according to an embodiment of the present invention.

Fig. 9(a) is a graph showing the light transmission intensity of the EIT phenomenon caused by the pair of two resonance lights with different wavelengths, and (b) is the light transmission intensity of the EIT phenomenon when the pair of two resonance lights with different wavelengths is modulated strength graph.

FIG. 10 is a diagram showing the configuration of an atomic oscillator according to a fourth embodiment of the present invention.

FIG. 11 is a diagram showing the configuration of an atomic oscillator according to a fifth embodiment of the present invention.

Fig. 12(a) is a graph showing the "velocity (one-dimensional projection)" distribution of atoms (Maxwell Boltzmann distribution), and (b) is a graph showing the "velocity" distribution of atoms (Maxwell Boltzmann distribution) diagram.

13( a ) is a diagram showing the distribution of higher harmonics (+ components) during sine wave modulation, (b) is a diagram showing the distribution of higher harmonics (+ components) during typical square wave modulation, (c) is a figure which shows the distribution of a harmonic (+ component) at the time of typical triangular wave modulation.

14( a ) is a graph showing a linear-nonlinear branch point of light intensity, and ( b ) is a graph showing laser frequency distribution.

15( a ) is a graph showing the laser intensity dependence of the EIT signal line width, and ( b ) is a graph showing a comparison between the conventional and the present invention regarding the relationship between the EIT signal intensity and the EIT signal line width.

Fig. 16 is a graph showing laser frequency distribution near the CsD2 line.

FIG. 17 is a graph showing the relationship between EIT signal strength and line width.

FIG. 18 is a graph showing a comparison of EIT signal strengths at the same line width.

FIG. 19 is a diagram showing the configuration of an experimental system.

20( a ) is an energy diagram corresponding to line D2 , ( b ) is an energy diagram corresponding to line D1 , and ( c ) is an energy diagram near the excitation level in consideration of Doppler spread.

FIG. 21( a ) is an energy diagram around the excitation level in consideration of Doppler spread, and FIG. 21( b ) is an energy diagram around the excitation level in consideration of Doppler spread.

Fig. 22(a) is an energy diagram near the excitation level, (b) is an energy diagram near the excitation level, and (c) shows a gas cell and a light source in which alkali metal atoms are enclosed according to the sixth embodiment of the present invention. , the optical path and the configuration diagram of the detector.

Fig. 23(a) is an energy diagram near the excitation level, (b) is an energy diagram near the excitation level, and (c) shows a gas cell and a light source in which alkali metal atoms are enclosed according to the seventh embodiment of the present invention. , the optical path and the configuration diagram of the detector.

24( a ) is a diagram illustrating the principle of the conventional EIT method, and (b) and (c) are diagrams showing the relationship between the conventional gas cell and resonance light.

Label description

1 Central wavelength generation unit; 2LD; 3EOM; 4EOM; 5 gas chamber; 6 photodetector; 7 frequency control unit; 8 voltage-controlled quartz oscillator; 9 oscillator; 10 oscillator; 11, 12, 13 resonance light; 14, 15, 16 gaseous cesium atom; 17 mixer; 18, 19 modulated signal; 40 wavelength plate; 41 linearly polarized waveform without modulation; 42 circularly polarized waveform without modulation ; 43 implements the waveform that is linearly polarized when modulation is implemented; 44 implements the waveform that is elliptically polarized when modulation is implemented; 45 implements the waveform that is circularly polarized when modulation is implemented; 50, 51, 52, 53 , 54 atomic oscillators.

Detailed ways

Hereinafter, the present invention will be described in detail using embodiments shown in the drawings. However, unless otherwise specified, the structural elements, types, combinations, shapes, relative arrangements, etc. described in this embodiment are merely illustrative examples, and are not intended to limit the scope of the present invention thereto.

Here, "performance index" which will appear several times below is defined in advance. The performance index is defined as the product of the reciprocal of the line width of the EIT signal (ie, the Q value) and the EIT signal-to-noise ratio (ie, S/N). For example, since S/N is proportional to EIT signal strength, if the EIT signal strength increases, the performance index increases. The main purpose of the present invention is to improve this performance index.

FIG. 1 is a schematic diagram showing the velocity distribution of gaseous alkali metal radicals enclosed in a container.

The horizontal axis of FIG. 1 represents the velocity of gaseous alkali metal atoms, and the vertical axis represents the ratio of the number of gaseous alkali metal atoms having the velocity. As shown in FIG. 1 , gaseous alkali metal atoms have a certain velocity distribution centered on velocity 0 corresponding to temperature. Here, the velocity represents an atomic velocity component parallel to the irradiation direction when the gaseous alkali metal radical is irradiated with laser light, and the value of the velocity at rest relative to the light source is set to zero. Here, the present inventors have noticed that the velocity of gaseous alkali metal atoms greatly affects the EIT phenomenon. When there is a distribution in the velocity of gaseous alkali metal atoms, due to the Doppler effect of light (Doppler shift), distribution occurs in the apparent wavelength of resonance light, that is, the wavelength of resonance light observed from gaseous alkali metal atoms. Therefore, note that there are a considerable number of gaseous alkali metal atoms in the atomic group that will remain without generating the EIT phenomenon even if a pair of resonance lights 1 and 2 are irradiated at the same time. In the conventional method of simultaneously irradiating a pair of resonance lights 1 and 2 to an alkali metal radical, only a part of the alkali metal atoms that contribute to the EIT phenomenon are contained in the gaseous alkali metal radical enclosed in the gas cell. Therefore, the present inventors conducted research so that gaseous alkali metal atoms, which have not contributed to the EIT phenomenon due to the influence of the Doppler effect, can also contribute to the generation of the EIT phenomenon. Next, the present invention will be described in detail.

FIG. 2 is a diagram showing the configuration of an atomic oscillator according to the first embodiment of the present invention. This atomic oscillator 50 controls the oscillation frequency by utilizing the light absorption characteristics based on the quantum interference effect when resonant light composed of two or more pairs (three pairs as described later) of coherent light pairs with different wavelengths enters, and the atomic oscillator 50 The oscillator 50 is composed of: an LD (VCSEL) (coherent light source) 2 that emits each resonant light; a center wavelength generating unit 1 that generates the center wavelength of the LD 2; an oscillator 9 that oscillates to generate two different ground states. 1/2 (4.596GHz) of the frequency (9.2GHz) of the energy difference (ΔE12); oscillator 10, which oscillates to generate a frequency of about 25MHz; EOM (Electron Optical Modulation Element) 3, 4, which uses electrical signals to slave LD 2. The emitted resonance light 11 implements frequency modulation; the gas chamber 5, which changes the light absorption amount according to the wavelength of the light 12 modulated by the EOM 4, is sealed with gaseous cesium (Cs, alkali metal) atoms; the photodetector (light detection Unit) 6, which detects the light 13 transmitted from the gas cell 5; and a frequency control unit 7, which detects the EIT state of the gas cell 5 according to the output of the light detector 6, and controls the output voltage. In addition, the oscillation frequency of the oscillator 10 is set to 25 MHz, which is a value much smaller than the typical Doppler width of cesium atoms (for example, approximately 1 GHz at room temperature). Appropriate changes can be made to this frequency. In addition, regarding the output frequency of the oscillator 9, since the frequency corresponding to ΔE12 is approximately 9.2 GHz (4.596 GHz × 2) for cesium, the output frequency of the oscillator 9 is set to 4.596 GHz by the following The frequency obtained by means of frequency multiplication is generated by controlling the voltage-controlled quartz oscillator 8 according to the control voltage output from the frequency control unit 7 . In addition, EOM3 is modulated by the frequency of oscillator 10 (25MHz), EOM4 is modulated by the frequency of oscillator 9 (4.596GHz), and EOM3 and EOM4 are arranged in series on the emission side of LD2. Also, the order of the combination of EOM 3 and oscillator 10 and the combination of EOM 4 and oscillator 9 can be reversed.

That is, the structure of the atomic oscillator 50 of the present embodiment differs from conventional ones in that two or more pairs (three pairs) of different wavelengths are obtained for the resonant light 11 emitted from the LD 2 through the EOM 3 as a modulation unit. 2 pairs of resonant light. In conventional atomic oscillators, only one pair of two kinds of resonant light with different wavelengths is prepared, and the frequency is controlled so that the frequency difference (wavelength difference) of the two kinds of resonant light irradiated at the same time is different from that of each ground state energy level. The energy difference ΔE12 exactly coincides. However, due to the Doppler effect of the resonant light generated by the movement of atoms, the resonant light wavelengths of the cesium atomic clusters sealed in the gas cell 5 are distributed, and a pair of resonant light is only occasionally matched to satisfy the wavelength corresponding to the resonant light. Since a part of the cesium atoms moving at the velocity of the resonance condition interacts, the efficiency of generating the EIT phenomenon is poor. Therefore, in the present embodiment, the modulation unit is configured such that at least four (two resonant light pairs) of different wavelengths of resonant light interact with gaseous cesium atoms sealed in the gas cell 5 . Thereby, the number of cesium atoms contributing to the EIT phenomenon per unit volume of the gas cell 5 can be increased, and EIT signals can be acquired efficiently.

3( a ) and ( b ) are graphs showing the frequency spectrum of resonance light incident on the gas cell. FIG. 4 is a diagram showing the state of resonant light incident on the gas cell and the direction of movement of gaseous cesium atoms.

Next, the operation of this embodiment will be described with reference to FIGS. 3 and 4 . The central wavelength generating unit 1 generates the resonant light 11 of the LD 2 in such a manner that the central wavelength is λ0 (central frequency f0). When the EOMs 3 and 4 perform frequency modulation on the resonant light 11 of the LD 2, the resonant light 12 having the spectrum 30-32 shown in FIG. 3(a) is input into the gas cell 5. Here, in Fig. 3(a), the frequency difference of AA' is 9.2 GHz. For this pair of resonant lights, by setting λ0 to an appropriate value, the frequency in the direction of the incident light 12 shown in Fig. 4 The gaseous cesium atom 15 with a small velocity component produces the EIT phenomenon. Also, the frequency difference between BB' is 9.2 GHz, and the gaseous cesium atoms 14 having a velocity component in the opposite direction to that of the incident light 12 shown in Fig. 4 generate an EIT phenomenon with respect to this pair of resonant lights. In addition, in Fig. 3(a), the frequency difference of CC' is also 9.2 GHz. For this pair of resonant lights, the gaseous cesium atoms 16 having the velocity component in the same direction as the incident light 12 shown in Fig. 4 generate EIT Phenomenon. In this way, the atoms in the gas cell 5 have various velocity distributions. Therefore, when the resonant light 12 to which components of sidebands B, B', C, and C' are given enters the gas cell 5 as described above, AA', BB', and C- The frequency difference of C' is 9.2 GHz, and the three pairs of lasers all interact with gaseous cesium atoms with corresponding velocity components. As a result, the proportion of cesium atoms contributing to the EIT phenomenon increases. Thereby, a desired EIT signal with a large signal-to-noise ratio (S/N) can be obtained.

In addition, in this embodiment, although the modulation frequency of EOM 4 is set to 1/2 (4.596 GHz) of the frequency difference of gaseous cesium atoms, it may be set to a frequency difference of 9.2 GHz. The spectrum of the resonant light at this time is as shown in FIG. 3( b ). Spectrum 33 to 35 are generated, but for example, spectrum 33 is not used, but spectrum 34 and 35 are used (spectrum 33 and 34 may also be used). That is, the frequency difference of A-λ0 is 9.2 GHz. For this pair of resonant lights, by setting λ0 to an appropriate value, gaseous cesium atoms 15 with a small velocity component in the direction of incident light 12 shown in FIG. EIT phenomenon occurs. The frequency difference of B-λ1 is also 9.2 GHz, and the gaseous cesium atoms 14 having a velocity component in the opposite direction to that of the incident light 12 shown in FIG. 4 generate an EIT phenomenon for this pair of resonant lights. In addition, the frequency difference of C-λ2 is also 9.2 GHz, and the gaseous cesium atoms 16 having a velocity component in the same direction as the incident light 12 shown in FIG. 4 generate an EIT phenomenon for this pair of resonant lights. In this way, the atoms in the gas cell 5 have various velocity distributions. Therefore, when the resonant light 12 to which the components of sidebands B, λ1, C, and λ2 are given enters the gas cell 5 as described above, the frequency differences of A-λ0, B-λ1, and C-λ2 are all 9.2 GHz. , the three pairs of lasers all interact with gaseous cesium atoms with corresponding velocity components, and as a result, the proportion of cesium atoms that contribute to the EIT phenomenon increases. Accordingly, a desired EIT signal having a large signal-to-noise ratio (S/N) can be obtained.

That is, in order to generate at least two resonant light pairs (here, three pairs) of resonant light, it is considered that the resonant light emitted from the LD 2 overlaps to generate sidebands and utilize the spectrum thereof. In addition, the frequency for modulating the resonant light needs to be modulated with the following two frequencies, namely: 4.596 GHz corresponding to 1/2 of the frequency (9.2 GHz) of the energy difference (ΔE12) of two different ground states; and A frequency (here 25 MHz) of a value much smaller than the typical Doppler width of cesium atoms (eg about 1 GHz at room temperature). In addition, it is necessary to utilize the EOM for modulating the light. Therefore, in the present embodiment, the oscillators 9 and 10 that oscillate and generate two kinds of frequencies are prepared, and the EOMs 3 and 4 arranged in series at the injection side of the LD 2 are modulated with each frequency. Thereby, based on the resonant light 11 emitted from the LD 2, it is possible to generate resonant light having three pairs of spectrums, and these three pairs of spectrums maintain a frequency difference of 9.2 GHz.

In addition, in this embodiment, one EOM 3 and one EOM 4 are respectively provided, but it is also possible to arrange EOM 4 and at least two EOM 3 in series on the injection side of LD 2. As a result, the number of resonant light pairs can be set arbitrarily and generated at comb-tooth-like frequency intervals.

FIG. 5 is a schematic diagram illustrating the relationship between energy Doppler spread based on atomic motion and resonant light of the present invention. The energy state diagram of a gaseous alkali metal atomic group enclosed in a container can be expressed by replacing the excitation level of the energy state diagram for one atom shown in FIG. 24 with an energy band equivalent to Doppler spread. The respective energy levels 20, 21, and 22 in FIG. 5 are excitation energy levels corresponding to the atoms respectively indicated by 16, 15, and 14 in FIG. 4 . It can be seen that, for gaseous alkali metal atomic groups with velocity distribution, the use of multiple resonant light pairs increases the proportion of atoms that contribute to the EIT phenomenon. Therefore, for example, if the power allocated to one pair of resonant lights is set to be substantially equal to the conventional power, the saturation limit of absorption becomes higher and the total power increases, so that a high-contrast EIT signal can be obtained. In addition, when the total light irradiation power is substantially equal to the conventional one, the power of each pair of resonant light in the present invention is reduced, so the power broadening of the EIT signal (the phenomenon in which the line width of the EIT signal becomes larger as the optical power is stronger) is suppressed. ), it is possible to obtain a good EIT signal with a narrower half-value width than conventional ones. Therefore, when this is applied to an oscillator, frequency stability can be improved compared to conventional ones.

FIG. 6 is a diagram showing the configuration of an atomic oscillator according to a second embodiment of the present invention. The same constituent elements will be described with the same reference numerals as in FIG. 2 . The difference between Fig. 6 and Fig. 2 is that EOM 4 is deleted, and a mixer 17 that mixes the output signals of oscillator 10 and oscillator 9 is set, and the output signal 18 of mixer 17 is used to drive EOM 3, and the EOM 3 is placed on the injection side of LD 2. As a result, the resonant light 12 emitted from the EOM 3 has the same spectrum as that shown in Figure 3(a).

That is, EOMs are used to modulate light, but there are problems in that if the number of spectrums is increased, the number of EOMs must be increased accordingly, which increases the cost and the number of parts. Therefore, in this embodiment, the signal for modulating the EOM is mixed in advance by the mixer 17, and one EOM 3 is modulated by the output signal 18 thereof. Accordingly, the number of EOMs can be minimized and the number of parts can be reduced.

FIG. 7 is a diagram showing the configuration of an atomic oscillator according to a third embodiment of the present invention. The same reference numerals as in FIG. 6 are attached to the same constituent elements and described. The difference between Fig. 7 and Fig. 6 is that the EOM 3 is deleted, and the output signal 19 of the mixer 17 is used to directly modulate and drive the LD 2 . Thus, the resonant light 11 emitted from the LD 2 has the same spectrum as that shown in Fig. 3(a).

That is, the central wavelength generating unit 1 generates the resonant light 11 emitted from the LD 2 so that the central wavelength is λ0. In addition, in order to modulate the center wavelength, there is a method of modulating the LD 2 itself besides the method of modulating the resonant light 11 emitted from the LD 2 by the EOM. Therefore, in this embodiment, the mixer 17 mixes the output frequencies of the oscillator 10 and the oscillator 9, and uses the signal 19 mixed by the mixer 17 to modulate and drive the LD 2 itself. Thus, EOM may not be required. In addition, the output frequency of the oscillator 10 can also be generated from the pressure-controlled quartz oscillator 8 via a PLL or the like (a part of the circuit of the oscillator 9 can also be used). In this case, the oscillator 10 is also unnecessary.

In addition, although illustration is omitted, the LD provided in a conventional EIT-type atomic oscillator may be formed in a structure in which surface-emitting laser beams of different wavelengths are arranged in an array.

FIG. 8 is a diagram showing a configuration of a magnetic sensor according to an embodiment of the present invention. The same constituent elements will be described with the same reference numerals as in FIG. 7 . 8 is different from FIG. 7 in that a magnetic field generator 37 to be measured is arranged near the gas chamber 5 and a magnetic field measuring device 36 for measuring fluctuations in the output signal of the frequency control unit 7 is provided. The oscillation frequency of the atomic oscillator is based on the energy difference (ΔE12) between the two ground state energy levels of the atom. The value of ΔE12 changes with the strength or fluctuation of the external magnetic field. Therefore, the gas chamber of the atomic oscillator is shielded from the magnetic field so as not to be affected by the external magnetic field. Therefore, a magnetic sensor that measures the strength and fluctuation of an external magnetic field can be manufactured by removing the magnetic field shield and reading the change in ΔE12 according to the change in oscillation frequency. By employing the structure of the present invention, the EIT phenomenon can be generated in a state with a high S/N, and thus the size of the magnetic sensor can be reduced.

Fig. 9(a) is a graph of the light transmission intensity of the EIT phenomenon caused by two pairs of resonant lights with different wavelengths, and Fig. 9(b) is a graph of the EIT phenomenon when two pairs of resonant lights with different wavelengths are modulated. Plot of light transmission intensity. As can be seen from FIG. 9( a ), the waveform 41 is a waveform of the linearly polarized light transmission intensity from the VCSEL, and the waveform 42 shows the light transmission intensity when the resonant light pair is further passed through a wavelength plate to become circularly polarized light. It can be seen that waveform 42 has a level increased by about 20% relative to waveform 41 . In addition, when the resonant light pairs are modulated as shown in FIG. 9( b ), multiple resonant light pairs all interact with gaseous cesium atoms with corresponding velocity distributions, and a waveform 43 with multiple peaks appears. In this embodiment, for example, as shown in FIG. 10 , between the LD 2 and the gas chamber 5, a wavelength plate 40 is arranged perpendicular to the optical path, and when the wavelength plate surface is gradually rotated, the resonant light pair 11 becomes circularly polarized. When the light is turned on, a waveform 45 in which the light transmission intensity is maximum at the wavelength λ0 is confirmed. Therefore, it was confirmed that when the resonant light pair changes from linearly polarized light to circularly polarized light, the transmitted light intensity changes to waveform 43 (linearly polarized light), waveform 44 (elliptical polarized light), and waveform 45 (circularly polarized light). ).

That is, when the resonant light pair 11 emitted from the LD 2 draws a circle at the end of the in-plane electric vector perpendicular to the propagation direction of the light, the light is called circularly polarized light. It has been confirmed through experiments that when the resonant light pair is converted into circularly polarized light, the light transmission intensity at the wavelength λ0 increases to about 6 times that of normal light. Thereby, the S/N of the optical output signal under the EIT phenomenon can be improved.

In addition, when the resonant light pair 11 emitted from the LD 2 draws an ellipse at the end of the in-plane electric vector perpendicular to the propagation direction of the light, the light is called elliptical polarized light. There is such elliptically polarized light that the polarization state of the elliptically polarized light changes when the wavelength plate is arranged perpendicular to the optical path on the optical path of the resonant light pair and its surface is rotated, and is between the vertically polarized light and the Continuously change between circularly polarized light. Therefore, even with elliptically polarized light, the S/N of the optical output signal under the EIT phenomenon can be improved.

FIG. 10 is a diagram showing the configuration of an atomic oscillator according to a fourth embodiment of the present invention. The fourth embodiment is a configuration in which a wavelength plate 40 is added to the configuration of FIG. 7 . That is, between the LD 2 and the gas cell 5, the wavelength plate 40 is arranged perpendicular to the optical path. The resonant light pair 11 of linearly polarized light emitted from the LD 2 enters the wave plate 40 and is polarized at a 90-degree phase to become circularly polarized light 11a. In addition, the wavelength plate 40 can be arranged at any position between the LD 2 and the gas chamber 5, it can be located near the exit surface of the LD 2, or it can be located near the entrance of the gas chamber 5.

FIG. 11 is a diagram showing the configuration of an atomic oscillator according to a fifth embodiment of the present invention. The fifth embodiment is a configuration in which a wavelength plate 40 is added to the configuration of FIG. 6 . That is, between the EOM 3 and the gas cell 5, a wavelength plate 40 is provided perpendicular to the optical path. The resonant light pair 11 of the linearly polarized light emitted from the LD 2 is modulated by the EOM 3 to become a resonant light 12, which is incident on the wavelength plate 40 and is polarized at a 90-degree phase to become circularly polarized light 12a. In addition, the wavelength plate 40 can be disposed at any position between the EOM 3 and the gas chamber 5, can be disposed near the exit surface of the EOM 3, or can be disposed near the entrance of the gas chamber 5.

That is, the wave plate refers to a multi-refringence element that generates a phase difference between vertically polarized light components. A wavelength plate that produces a phase difference of π (180°) is called a λ/2 plate or a half-wavelength plate, which is used to change the polarization direction of linearly polarized light. A wavelength plate that produces a phase difference of π/2 (90°) is called a λ/4 plate or a quarter-wave plate, which is used to convert linearly polarized light into circularly polarized light (楕 circularly polarized light), or vice versa Convert circularly polarized light (o-circularly polarized light) into linearly polarized light. In this embodiment, since the linearly polarized light needs to be converted into circularly polarized light or elliptic polarized light, it is necessary to use a λ/4 plate to convert the resonant light pair 11 of the linearly polarized light emitted from the LD 2 by the wavelength plate 40. Circularly polarized light or elliptic polarized light is incident on the gas chamber 5 . Accordingly, the S/N of the optical output signal under the EIT phenomenon can be improved with a simple structure.

FIG. 14( a ) is a graph showing the relationship between the light intensity (horizontal axis) and the EIT signal intensity (vertical axis) of a 2-light wave resonance light pair satisfying the conditions for generating EIT. In areas where the light intensity is very weak, the EIT signal intensity maintains a proportional relationship with the light intensity and changes approximately linearly. However, when the light intensity exceeds a certain point (P0), even if the light intensity is increased, the EIT signal intensity does not change significantly (saturation region). Taking this into consideration, focusing on the ensemble with a specific velocity (as mentioned above, referring to the velocity component parallel to the incident light) among the alkali metal atoms in the gas cell, it is hoped that the incident light The light intensity was set to the maximum light intensity P0 (maximum light intensity in a region where the intensity increases linearly) at which the EIT signal intensity does not reach saturation with respect to the incident light intensity.

The clusters of alkali metal atoms (such as cesium, Cs) in the gas chamber as the EIT generation region have the velocity distribution (curve) shown in Fig. 12(b), which varies with environmental factors such as pressure and temperature, but if only one The distribution of velocity components in a fixed direction is basically Gaussian distribution as shown in Fig. 12(a). When a resonant light pair of two light waves is incident on this system to generate EIT, Doppler spread of energy is generated due to the velocity distribution, so the EIT signal intensity distribution corresponding to the center frequency of the frequency region where EIT is generated also exhibits a Gaussian distribution ( Typically, it has an extension of about 1 [GHz] after frequency conversion). Therefore, focusing on the above-mentioned light utilization efficiency, when the light intensity of each of the multiple resonant light pairs is set to be near P0, it is desirable that the distribution is as shown in Fig. 14(b), which is close to the Gaussian distribution of the velocity distribution of atoms shape.

A semiconductor laser or the like emits monochromatic light (coherent light) of a frequency (wavelength) corresponding to the current value (Ivias) when a direct current is applied thereto. If the central wavelength is set to about 852 [nm] and a "modulation" of 4.6 [GHz] is applied to Ivias (Imod (1) = 4.6 [GHz]), the distance between the two on both sides of the central wavelength is (4.6× 2=9.2[GHz]), when the 2 light waves enter the Cs atoms in the gas cell as resonant light, quantum interference occurs and the EIT phenomenon occurs. Here, it can be seen from the previous Doppler expansion that, for the resonant light pair (1 pair) of 2 light waves, the number of Cs atoms in the gas cell that contributes to the EIT phenomenon is very small. That is, conventional EIT generation efficiency is poor.

The state of the applied current for driving the semiconductor laser and the frequency distribution of the laser will be described in detail below using the drawings. FIG. 16 is a graph showing a frequency distribution observed when frequency modulation is performed on a monochromatic semiconductor laser having a center wavelength of about 852 [nm]. In order to generate EIT using an alkali metal atom (Cs) as the target atom, Ivias (DC bias current) is set so that the central wavelength becomes about 852 [nm] which is equivalent to the excitation energy of Cs, and then 4.6 [GHz] can be performed on Ivias ]’s frequency modulation Imod (1), or generate sidebands via EOM (Electron Optical Modulation Element), thereby generating a pair of resonant light pairs of 2 light waves with a frequency difference of 9.2 GHz. When the modulation Imod (2) (overlap modulation) of an arbitrary frequency (for example, 15 [MHz]) is further superimposed on it, the 2 light waves are respectively modulated by the superposition frequency 15 [MHz] to generate the Comb (Comb) tooth-shaped frequency distribution. Each of the original 2 light waves with this comb-shaped frequency distribution can be regarded as multiple pairs of resonant light pairs. Therefore, as long as they interact with the Cs atoms in the gas chamber, they can simultaneously interact with the Cs atomic groups moving at different speeds. EIT is generated, and the efficiency of EIT generation is further improved (the present invention).

FIG. 16( a ) shows one of two light waves that are not superimposed and modulated as in the past. (b) and (c) are the frequency spectrum when the sine wave is used to overlap Imod (2). The modulated frequencies are all equal to 15 [MHz], but the modulation amplitude conditions of (b) and (c) are different. Both exhibit a comb-shaped frequency distribution, and it can be seen that (c) with a modulation amplitude of 0.2 [V] has a wider frequency expansion range than (b) with a modulation amplitude of 0.2 [V].

Fig. 17 is a graph comparing the relationship between the intensity (vertical axis) and line width (horizontal axis) of the EIT signal of Cs by using the overlapping modulation Imod(2) in consideration of the present invention with the existing method The laser is driven to irradiate multiple resonant light pairs, and the data is obtained by changing the laser power irradiated to Cs. (a), (b), and (c) of FIG. 17 correspond to (a), (b), and (c) of FIG. 16 , respectively. It can be seen that compared with the past, under the same line width, the EIT signal strength of the present invention is far greater than that of the past, and the previously defined "performance index" (=Q×(S/N)) is improved. In the method of the present invention, it can also be understood that, compared with (b), the EIT signal intensity of (c) is greater because: according to the distribution of each laser spectrum shown in Fig. With more Cs atoms, the efficiency of the interaction with the resonant light pair increases, which contributes to the generation of EIT. It was also confirmed that in the conventional method (a), since the EIT signal strength cannot be obtained, it is difficult to achieve an EIT linewidth below 120 [kHz], and it is difficult to improve the Q value (the reciprocal of the EIT signal linewidth), but in In (b) and (c) of the present invention, the line width can be further refined, so the performance index can be greatly improved.

FIG. 18 is a diagram comparing individual EIT signals at a full width at half maximum (line width) of 127 [kHz]. It was confirmed that in (c) of the present invention, the EIT signal intensity is about 14 times larger than that of the conventional method (a).

Summarizing the results so far, the following conclusions can be clarified. When the line width of power broadening is to be refined, if the laser power is reduced (Fig. 15(a)), the EIT signal intensity is proportionally weakened (Fig. 15(b)), and in the existing method, at point A The EIT signal strength becomes 0. That is, a signal line width narrower than that at point A cannot be obtained.

However, in the method of the present invention, the number of atoms (density) in the gas cell that contributes to the generation of the EIT signal is greatly increased, so sufficient signal strength can be obtained at the EIT signal width where the signal strength has disappeared in the conventional method (point B). That is, the value obtained by dividing the EIT signal strength at point B by the EIT signal strength at point A represents the maximum amplification ratio of the method of the present invention relative to the conventional method, and is an index of the improvement effect of S/N. If the S/N is improved, the performance index is improved, so that the performance of various devices utilizing the EIT phenomenon can be improved in proportion to their size. It is clear that, for example, in an atomic oscillator utilizing the EIT phenomenon, the frequency stability increases proportionally to S/N, and if it is applied to a magnetic sensor (the frequency of the atomic oscillator utilizing the EIT responds sensitively to an external magnetic field In quantum interference sensors such as the nature of the change), it can produce effects such as high sensitivity. In addition, in the present invention, even if the size of the air cell causing the EIT phenomenon is reduced in accordance with the improvement in S/N, the same signal strength as in the past can be obtained, so that further miniaturization of the device can be realized. and so on.

In addition, as shown in Figure 15(b), if sufficient EIT signal intensity is obtained at point B, the signal linewidth can be further refined by further reducing the laser intensity (excluding the influence of power broadening). For example, the minimum signal strength line as the target is represented by a dotted line, and the signal line width at point C can be realized for the method of the present invention. As in the previous discussion about S/N, the smaller the line width value, the larger the Q value, and therefore the larger the value of the performance index, which can improve the performance of various devices using the EIT phenomenon. For example, in an atomic oscillator using the EIT phenomenon, the frequency stability is improved by thinning the EIT signal, and if it is applied to a magnetic sensor (the frequency of the atomic oscillator using EIT responds sensitively to an external magnetic field and Quantum interference sensors such as the nature of the change) bring effects such as high precision.

From the above discussion, it can be seen that according to the present invention, by properly selecting the laser modulation method, EIT signal strength and EIT linewidth that cannot be achieved by existing methods can be obtained. The EIT signal curve. Taking advantage of this advantage, for example, in the EIT device design and manufacturing stages, if a laser drive circuit IC is used to independently set up a unit capable of controlling the above-mentioned laser modulation parameters (modulation waveform, intensity, etc., including modulation on/off), and A considerable number of other structural elements can be used as common components, and special-purpose EIT devices can be easily separately manufactured, which has the effect of reducing costs and the like. In addition, it is also possible to pre-install such a unit, that is, the product user can use this unit to properly control and set the above-mentioned laser modulation parameters according to the use environment and the like.

FIG. 13 shows the relationship between the modulation method of laser light and Fourier components. (a) is the Fourier component when performing amplitude modulation (AM) with a sine wave, (b) is the Fourier component when performing amplitude modulation (AM) with a rectangular wave, and (c) is when performing amplitude modulation (AM) with a triangular wave Fourier components. The horizontal axis is frequency. Rectangular wave modulation has higher-order Fourier components than triangular wave modulation. If these synthesized waves are further overlap-modulated by frequency modulation (FM) or phase modulation (PM), and the laser beam is overlap-modulated as Imod (2), arbitrary modulation waveforms can be obtained and can be controlled with a high degree of freedom Intensity distribution and adjacent frequency spacing of multiple resonant light pairs. As a result, it is possible to obtain the effects that the EIT signal control required for device performance required for each application can be easily realized, and the accuracy can also be improved.

Fig. 19 is a diagram showing the configuration of an experimental system of the present invention. It is an example where instead of modulating the laser light with Imod(1), EOM (Electron Optical Modulation Element) is used.

Fig. 20 is an energy diagram of electron states of alkali metals. Fig. 20(a) is an energy diagram corresponding to the excitation level P3/2, that is, the so-called D2 line, and Fig. 20(b) is an energy diagram corresponding to the so-called D1 line at the excitation level P1/2. Figure 20(c) shows the interaction between a conventional resonant light pair based on two light waves or multiple resonant light pairs of the present invention and an alkali metal atom in consideration of Doppler spread, which satisfies the requirement to generate the EIT phenomenon The energy diagram around the excitation level for the condition.

The excitation energy level P3/2 is composed of a hyperfine structure, and within the normal operating temperature range of a device utilizing the EIT phenomenon, the energy related to the EIT generation F'=I+1/2, I-1/2 is reduced by the Doppler spread coincident (Fig. 20(c)). In addition, in a high-temperature region, even in a hyperfine structure with an excitation level P1/2, energy overlapping may occur due to Doppler spreading. The laser center frequency (central wavelength) is set so that the excitation target energy Eend of as many resonant light pairs as possible among the multiple resonant light pairs in the present invention enters the overlapping region. That is, as shown in FIG. 20( c ), E1<Eend<E2 is satisfied. Here, the F' represents the quantum number of the hyperfine structure, and the I represents the nuclear spin quantum number.

A pair of resonant light beams incident on this energy overlapping region causes the EIT phenomenon of two kinds of alkali metal atoms corresponding to different F' (quantum number of hyperfine structure). That is, EIT is simultaneously generated for alkali metal atoms of two different velocity groups (ensembles: atomic groups) having velocity components in opposite directions. When such conditions are satisfied, the light intensity (number of photons) of the resonant light pair is dispersed in each atomic group, so the EIT signal intensity is less likely to be saturated, and stronger laser light can be irradiated, improving S/N. Especially, the effect is better when the miniaturization of the air chamber needs to enhance the EIT signal strength. In addition, if the total irradiated light intensity is constant, the number of photons in the overlapping region is dispersed in such a manner that the alkali metal atoms of the two different velocity groups interact with the photons as described above, so the result Yes, for one speed group, the power broadening is suppressed, and the line width of the EIT signal is refined (the Q value is increased). That is, performance index can be improved.

Figure 21 is an energy diagram of a typical P1/2 level. In general, the hyperfine structure energy splitting width of the D1 line is larger than that of the D2 line (typically 0.5-1 GHz), and the two energy bands of Doppler expansion do not overlap. As mentioned above, in the case of the D2 line (the excitation target energy level is P3/2), since the energy splitting width of the hyperfine structure is small, the energy band overlap occurs due to Doppler expansion, and it is possible to make multiple pairs of resonant light Pairs interact with the same atom at the same time. In this case, 4-wave mixing occurs, and the Λ-type transition of the pure 3-level system suffers from problems, and the EIT efficiency decreases. However, in general, the hyperfine structure energy splitting width of the D1 line is larger than that of the D2 line (typically 0.5 to 1 GHz), and the two energy bands of the Doppler extension do not overlap. Therefore, if the D1 line is used, it is possible to realize EIT based on multiple pairs of resonant light pairs while maintaining a pure 3-level system Λ-type transition, thus increasing the enhancement effect of the EIT signal based on the superposition effect. In this case, there are two methods of E11<EENd<E12 ( FIG. 21( a )) and E21<Eend<E22 ( FIG. 21( b )).

FIG. 22( c ) is a diagram showing an arrangement structure of a gas cell in which alkali metal atoms are enclosed, a light source, an optical path, and a detector according to a sixth embodiment of the present invention. Here, the light emitted by the laser light source enters the gas cell, and the EIT phenomenon occurs with the alkali metal atoms, and then the light returned by means of reflection travels in the opposite direction, thereby generating the EIT phenomenon with the alkali metal atoms in the gas cell again, It is then directed into a photodetector. This is the so-called reflective type. At this time, as shown in Figure 22 (a) and (b), when the energy of the excitation level without considering the Doppler width is set as E10, if the excitation target energy Eend0 and E10 of the monochromatic light of the above light source are If the mode of unequal (E10<Eend0 or Eend0<E10) is selected, then a pair of resonant light can generate EIT with the alkali metal atomic group with the velocity component in the opposite direction in the gas chamber on the outgoing path and the return path respectively. Therefore, when EIT is generated by a plurality of resonant light pairs under such conditions, the same effect of the present invention can be obtained with half the number of resonant light pairs or half the light modulation width compared to the case of the non-reflective type. Therefore, according to this configuration, the design of a mechanism for generating a plurality of resonant light pairs such as a laser driver becomes easier, power consumption during device driving is reduced, and energy saving is utilized.

FIG. 23( c ) is a diagram showing an arrangement structure of a gas cell in which alkali metal atoms are enclosed, a light source, an optical path, and a detector according to a seventh embodiment of the present invention. Here, the light emitted from the laser light source enters the gas cell, and the EIT phenomenon occurs with the alkali metal atoms. After that, the light passes through the gas cell many times by reflection or other means, and is introduced into the photodetector every time the EIT phenomenon is caused. . This is the so-called multiple reflection type. At this time, as shown in Figure 23(a) and (b), if all the excitation target energies Eend of multiple resonant light pairs that can cause the EIT phenomenon only satisfy any one of the conditions of Eend<E10 or E10<Eend If the method is selected, a pair of resonant light can generate EIT with the alkali metal atom group with the velocity component in the opposite direction in the gas chamber on the outgoing path and the return path respectively. In addition, by adopting the multiple reflection type, the optical path length becomes longer, so that the coherence time is increased, the EIT signal strength is stronger, and the line width is thinner. This is beneficial to improve the performance index. In addition, when the number of reflections of light is set to an odd number and the optical path lengths of the outgoing path and the return path of light are approximately equal, the number of atoms that contribute to EIT is approximately equal in the different velocity groups, and therefore, the generation efficiency from EIT It is beneficial from the point of view. Therefore, when EIT is caused by a plurality of resonant light pairs under this condition, the same effect can be obtained with half the number of resonant light pairs or half the light modulation width compared to the case of the non-reflective type. Therefore, according to this configuration, the design of a mechanism for generating multiple pairs of resonant light, such as a laser driver, becomes easier, and power consumption during device driving is reduced, which contributes to energy saving.

Claims (18)

1. A quantum interference device, the quantum interference device has: gaseous alkali metal atoms; and a light source for generating resonant light pairs of different frequencies that maintain a frequency difference corresponding to the energy difference between the 2 ground states of the alkali metal atom, causing said alkali metal atoms to interact with said resonant light pair to produce electromagnetically induced transparency, The quantum interference device is characterized in that, There are multiple resonant light pairs, and the center frequencies of the resonant light pairs are different from each other. 2. The quantum interference device according to claim 1, characterized in that, The resonant light pair interacting with the alkali metal atom is linearly polarized light. 3. The quantum interference device according to claim 1, characterized in that, The resonant light pair interacting with the alkali metal atom is circularly polarized light. 4. The quantum interference device according to claim 1, characterized in that, The resonant light pair interacting with the alkali metal atom is elliptically polarized light. 5. The quantum interference device according to claim 1, characterized in that, A wavelength plate is provided on an optical path between the light source and the gas cell enclosing the alkali metal atoms. 6. The quantum interference device according to any one of claims 1 to 5, characterized in that, The multiple pairs of resonant light pairs meet the conditions for the electromagnetically induced transparency phenomenon, and the light intensity of each resonant light pair is near the maximum value P0 in the region where the EIT signal intensity increases linearly. 7. The quantum interference device according to any one of claims 1 to 5, characterized in that, The intensity distribution of the multiple pairs of resonant light pairs is a Gaussian distribution relative to the center frequency of each pair, and the resonant light pair corresponding to the maximum light intensity satisfies the atomic group of the alkali metal whose velocity component in the light direction is near 0 Corresponding to the generation condition of the electromagnetically induced transparency phenomenon, its intensity is the maximum value P0 in the linear region. 8. The quantum interference device according to claim 1, characterized in that, The multiple pairs of resonant light pairs are generated by combining amplitude modulation and frequency modulation or phase modulation. 9. The quantum interference device according to claim 1, characterized in that, The multiple pairs of resonant light pairs are generated by modulation of a signal having any one of a sine wave, a triangular wave, a sawtooth wave, and a rectangular wave. 10. The quantum interference device according to any one of claims 1 to 9, characterized in that, The quantum interference device has a drive circuit part for modulating the light source, the drive circuit part is separated from other structural components, and the drive circuit part can be arbitrarily controlled and set during the manufacturing process or in the state after commercialization. Constants of the drive circuit section. 11. The quantum interference device according to any one of claims 1 to 10, characterized in that, When the nuclear spin quantum number of the alkali metal atom is assumed to be I, and the quantum number of the hyperfine structure in the P1/2 excitation level or P3/2 excitation level of the alkali metal atom is F', considering F When the minimum energy is E1 and the maximum energy is E2 in the area where the two energy ranges of the Doppler extension of '=I-1/2 and F'=I+1/2 overlap with each other, the electromagnetically induced transparency phenomenon is caused The excitation target energy Eend of any one of the multiple pairs of resonant light pairs satisfies E1<Eend<E2. 12. The quantum interference device according to any one of claims 1 to 10, characterized in that, Assuming that the nuclear spin quantum number of the alkali metal atom is I, and the quantum number of the hyperfine structure of the excited energy level of the alkali metal atom is F', then considering F'=I-1/2 and F' In the state where the two energy ranges of the Doppler spread of =I+1/2 do not overlap with each other, when the range of energy of the F'=I-1/2 of the Doppler spread is considered to be from E11 To E12, when the energy range of F'=I+1/2 considering the Doppler spread is from E21 to E22, and E11<E12, E21<E22, the multiple pairs that cause the electromagnetically induced transparency phenomenon The excitation target energy Eend of any one of the resonant light pairs only satisfies one of the conditions of E11<Eend<E12 or E21<Eend<E22. 13. The quantum interference device according to any one of claims 1 to 12, wherein the quantum interference device makes multiple pairs of resonant light pairs pass through the alkali metal atom one or more times, and detects from the alkali metal atom The electromagnetically induced transparency phenomenon, the quantum interference device is characterized in that, When the energy of the excitation level without considering the Doppler width is E10, and the excitation target energy of the multiple resonant light pairs is Eend0, the Eend0 satisfies E10<Eend0 or Eend0<E10. 14. The quantum interference device according to any one of claims 1 to 12, wherein the quantum interference device makes multiple pairs of resonant light pairs pass through the alkali metal atom once or more times, and detects from the alkali metal atom The electromagnetically induced transparency phenomenon, the quantum interference device is characterized in that, When the excitation target energy of any one of the multiple pairs of resonant light pairs causing the electromagnetically induced transparency phenomenon is set as Eend, the Eend only satisfies the condition of Eend<E10 or E10<Eend. 15. The quantum interference device according to claim 13 or 14, characterized in that, The number of turns is an odd number. 16. An atomic oscillator, characterized in that the atomic oscillator has the quantum interference device according to any one of claims 1 to 15. 17. A magnetic sensor, characterized in that the magnetic sensor has the quantum interference device according to any one of claims 1-15. 18. A quantum interference sensor, characterized in that the quantum interference sensor has the quantum interference device according to any one of claims 1-15.

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