Atomic oscillator and frequency signal generation system

An atomic oscillator includes a light emitting element, an atomic cell, and a light receiving element that receives the light passing through the atomic cell. The atomic cell has a first chamber containing alkali metal atoms in a gas state and having a first wall through which the light from the light emitting element passes, a second chamber containing alkali metal atoms in a liquid state and having a second wall, a passage connecting the first chamber and the second chamber to each other, and a part which is disposed between the first chamber and the second chamber and has a thermal conductivity lower than the thermal conductivity of a material forming the first wall and the thermal conductivity of a material forming the second wall.

The present application is based on and claims priority from JP Application Serial Number 2018-087840, filed Apr. 27, 2018, the disclosure of which is hereby incorporated by reference herein in its entirety.

BACKGROUND

1. Technical Field

The present disclosure relates to an atomic oscillator and a frequency signal generation system.

2. Related Art

As an oscillator having high precision oscillation characteristics in the long term, an atomic oscillator oscillating based on energy transition of alkali metal atoms such as cesium is known. The atomic oscillator includes a light source, an atomic cell in which alkali metal atoms such as cesium or the like are sealed, and a light receiving element for receiving a light passing through the atomic cell.

For example, JP-A-2015-53304 discloses an atomic oscillator including an atomic cell in which a gas container containing metal atoms in a gas state and a metal accumulator containing metal atoms in a liquid or solid state. Generally, the temperature of the metal accumulator is lower than the temperature of the gas container.

However, in the atomic oscillator of JP-A-2015-53304, the gas container and the metal accumulator are formed by forming through holes in a main body portion configured of a glass material, a silicon material, or the like. Therefore, if a thermal conductivity of a material forming the main body portion is high, one of the temperatures of the gas container and the metal accumulator is influenced by the other, thereby, for example, alkali metal atoms is precipitated in the gas container, and an oscillation frequency of the atomic oscillator fluctuates in some cases.

On the other hand, if a thermal conductivity of a material forming the main body portion is low, it is difficult for a temperature distribution to become uniform in the gas container. Therefore, a light having various temperature dependencies is received by a light receiving element, and the oscillation frequency varies in some cases.

SUMMARY

An atomic oscillator according to an aspect of the present disclosure includes a light emitting element that emits a light, an atomic cell, and a light receiving element that receives the light passing through the atomic cell, in which the atomic cell has a first chamber containing alkali metal atoms in a gas state and having a first wall through which the light emitted from the light emitting element passes, a second chamber containing alkali metal atoms in a liquid state and having a second wall, a passage connecting the first chamber and the second chamber to each other, and a part which is disposed between the first chamber and the second chamber and has a thermal conductivity lower than the thermal conductivity of a material forming the first wall and the thermal conductivity of a material forming the second wall.

In the atomic oscillator according to the aspect of the present disclosure, the part may have a slit structure or a hollow structure.

In the atomic oscillator according to the aspect of the present disclosure, the part may include a wall, and a low thermal conductivity member disposed on the wall and having the thermal conductivity lower than the thermal conductivity of the material forming the first wall and the thermal conductivity of the material forming the second wall.

In the atomic oscillator according to the aspect of the present disclosure, a high thermal conductivity member having the thermal conductivity higher than the thermal conductivity of the material forming the first wall may be disposed on an outer surface of the first wall.

In the atomic oscillator according to the aspect of the present disclosure, the part may have the slit structure or the hollow structure, and the high thermal conductivity member may be disposed on a wall of the part on a side of the first chamber.

In the atomic oscillator according to the aspect of the present disclosure, the first wall may have a window through which the light emitted from the light emitting element passes, the high thermal conductivity member may be disposed on an outer surface of the window, and the high thermal conductivity member may be provided with a through hole through which the light emitted from the light emitting element passes.

In the atomic oscillator according to the aspect of the present disclosure, the part may have the slit structure, and a wall of the part may include a first part connecting the first chamber and the second chamber to each other, a second part configuring the slit structure on one side of the first part, and a third part configuring the slit structure on the other side of the first part.

In the atomic oscillator according to the aspect of the present disclosure, the second wall may include a fourth part, a fifth part having a temperature lower than the temperature of the fourth part, and a sixth part configuring the slit structure between the fourth part and the fifth part.

A frequency signal generation system according to an aspect of the present disclosure includes an atomic oscillator, in which the atomic oscillator includes a light emitting element that emits a light, an atomic cell, and a light receiving element that receives the light passing through the atomic cell, the atomic cell has a first chamber containing alkali metal atoms in a gas state and having a first wall through which the light emitted from the light emitting element passes, a second chamber containing alkali metal atoms in a liquid state and having a second wall, a passage connecting the first chamber and the second chamber to each other, and a part which is disposed between the first chamber and the second chamber and has a thermal conductivity lower than the thermal conductivity of a material forming the first wall and the thermal conductivity of a material forming the second wall.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

Hereinafter, preferred embodiments of the present disclosure will be described in detail with reference to the drawings. Note that the embodiments described below do not unduly limit the contents of the present disclosure described in the appended claims. Also, not all of the configurations described below are necessarily essential components of the present disclosure.

1. First Embodiment

First, an atomic oscillator according to a first embodiment will be described with reference to the drawings.FIG. 1is a schematic view showing an atomic oscillator100according to the first embodiment.

The atomic oscillator100is an atomic oscillator using a quantum interference effect (CPT: Coherent Population Trapping) in which, when alkali metal atoms are simultaneously irradiated with two resonance lights of specific wavelengths different each other, a phenomenon occurs where the two resonant lights are transmitted without being absorbed by the alkali metal atoms. Note that the phenomenon due to the quantum interference effect is also referred to as an electromagnetically induced transparency (EIT) phenomenon. Further, the atomic oscillator according to the present disclosure may be an atomic oscillator using a double resonance phenomenon by a light and a microwave.

As shown inFIG. 1, the atomic oscillator100includes a light source unit10, an optical system unit20, an atomic cell unit30, and a control unit50for controlling the light source unit10and the atomic cell unit30. Hereinafter, an outline of the atomic oscillator100will be described first.

The light source unit10has a Peltier element11, a light emitting element12, and a temperature sensor13.

The light emitting element12emits a linearly polarized light LL containing two kinds of lights having different frequencies. The light emitting element12is, for example, a vertical cavity surface emitting laser (VCSEL). The temperature sensor13detects the temperature of the light emitting element12. The Peltier element11controls the temperature of the light emitting element12.

The optical system unit20is disposed between the light source unit10and the atomic cell unit30. The optical system unit20has a neutral density filter21, a lens22, and a quarter wavelength plate23.

The neutral density filter21reduces the intensity of the light LL emitted from the light emitting element12. The lens22adjusts a radiation angle of the light LL. Specifically, the lens22makes the light LL into a parallel light. The quarter wavelength plate23converts the two kinds of lights having different frequencies included in the light LL from a linearly polarized light to a circularly polarized light.

The atomic cell unit30includes an atomic cell31, a light receiving element32, a first temperature control element37a, a second temperature control element37b, a first temperature detection element38a, a second temperature detection element38b, and a coil39.

The atomic cell31contains alkali metal atoms. The alkali metal atom has an energy level of a three-level system configured with two ground levels different from each other and an excitation level. The light LL emitted from the light emitting element12is incident on the atomic cell31via the neutral density filter21, the lens22, and the quarter wavelength plate23.

The light receiving element32receives and detects the light LL passed through the atomic cell31. The light receiving element32is, for example, a photodiode.

The first temperature control element37aheats the alkali metal atoms contained in the atomic cell31and brings at least a part of the alkali metal atoms into a gas state. The first temperature control element37ais, for example, a heater. The first temperature detection element38adetects the temperature of the atomic cell31. The second temperature control element37b, for example, heats the atomic cell31to a temperature lower than the temperature of the first temperature control element37a. The second temperature control element37bis, for example, a Peltier element. The second temperature detection element38bdetects the temperature of the atomic cell31. The temperature detection elements38aand38b, and the temperature sensor13are, for example, thermistors or the like.

The coil39applies a magnetic field in a predetermined direction to the alkali metal atoms contained in the atomic cell31and Zeeman splits an energy level of the alkali metal atoms. When the alkali metal atoms are irradiated with a pair of circularly polarized resonance light in a state where the alkali metal atoms are Zeeman split, the number of alkali metal atoms having a desired energy level is relatively larger than the number of alkali metal atoms having other energy levels among a plurality of levels of the alkali metal atoms that are Zeeman split. Therefore, the number of atoms that develops a desired EIT phenomenon increases, and a desired EIT signal increases. As a result, the oscillation characteristics of the atomic oscillator100can be improved.

The control unit50includes a first temperature controller51a, a second temperature controller51b, a light source controller52, a magnetic field controller53, and a third temperature controller54. Based on a detection result of the first temperature detection element38a, the first temperature controller51acontrols carrying of electricity to the first temperature control element37aso that an inside of the atomic cell31becomes a desired temperature. Based on a detection result of the second temperature detection element38b, the second temperature controller51bcontrols carrying of electricity to the second temperature control element37bso that the inside of the atomic cell31becomes a desired temperature. The magnetic field controller53controls carrying of electricity to the coil39so that the magnetic field generated by the coil39is constant. Based on a detection result of the temperature sensor13, the third temperature controller54controls carrying of electricity to the Peltier element11so that the temperature of the light emitting element12becomes a desired temperature.

Based on a detection result of the light receiving element32, the light source controller52controls frequencies of two kinds of lights included in the light LL emitted from the light emitting element12so that the EIT phenomenon occurs. Here, the EIT phenomenon occurs when the two kinds of lights become a pair of resonant lights of a frequency difference corresponding to an energy difference between two ground levels of the alkali metal atoms contained in the atomic cell31. The light source controller52includes a voltage controlled oscillator (not shown) in which an oscillation frequency is controlled so as to be stabilized in synchronization with the control of the frequencies of the two kinds of lights, and outputs an output signal of the voltage controlled oscillator (VOC) as an output signal (clock signal) of the atomic oscillator100.

1.1.2. Specific Configuration

Next, a specific configuration of the atomic oscillator100will be described.FIGS. 2 and 3are cross-sectional views schematically showing the atomic oscillator100. Note thatFIG. 2is a cross-sectional view taken along the line II-II inFIG. 3. InFIGS. 2 and 3, andFIGS. 4 and 5to be described later, X, Y, and Z axes are shown as three axes orthogonal to each other.

As shown inFIGS. 2 and 3, the atomic oscillator100includes the light source unit10, the optical system unit20, the atomic cell unit30, a supporting member40, the control unit50, and an outer container60.

Here, the Z axis is an axis along the perpendicular P of an inner surface62aof a base body62of the outer container60, and the Z axis+direction is a direction from the inner surface62ato a component disposed on the inner surface62a. The X axis is an axis along the light emitted from the light source unit10and the X axis+direction is a direction in which the light emitted from the light source unit10advances. The Y axis is an axis perpendicular to the X axis and the Z axis and the Y axis+direction is a direction from the front to the back when the Z axis+direction is up and the X axis+direction is directed to the right.

The light source unit10is disposed on the supporting member40. The light source unit10includes the Peltier element11, the light emitting element12, the temperature sensor13, a light source container14which contains the Peltier element11, the light emitting element12, and the temperature sensor13, and a light source substrate15on which the light source container14is disposed. The light source substrate15is, for example, fixed to the supporting member40. The Peltier element11, the light emitting element12, and the temperature sensor13are electrically connected to the control unit50.

The optical system unit20is disposed on the supporting member40. The optical system unit20has the neutral density filter21, the lens22, the quarter wavelength plate23, and a holder24which holds the neutral density filter21, the lens22, and the quarter wavelength plate23. The holder24is, for example, fixed to the supporting member40.

The holder24is provided with a through hole25. The through hole25is a passing area of the light LL. In the through hole25, the neutral density filter21, the lens22, and the quarter wavelength plate23are arranged in the order from the light source unit10side.

The atomic cell unit30includes the atomic cell31, the light receiving element32, a first holding member33, a second holding member34, a first atomic cell container35, a second atomic cell container36, the first temperature control element37a, the second temperature control element37b, the first temperature detection element38a, and the second temperature detection element38b.

FIG. 4is a cross-sectional view schematically showing the atomic cell31of the atomic cell unit30.FIG. 5is a perspective view schematically showing the atomic cell31of the atomic cell unit30. As shown inFIGS. 4 and 5, the atomic cell31includes a first chamber112, a second chamber114, a passage116, and a low thermal conductivity portion118, through which the light emitted from the light emitting element12passes.

The first chamber112contains alkali metal atoms in a gas state. The first chamber112has a first space102and a first wall122defining the first space102. The alkali metal atoms in a gas state are present in the first space102. The first wall122has a first window122aand a second window122bthrough which the light emitted from the light emitting element12passes. The light emitted from the light emitting element12is incident on the first chamber112from the first window122a, and emitted from the second window122b. In the illustrated example, the first window122ais a part of the X axis − side of the first wall122. The second window122bis a part of the X axis+side of the first wall122. Although not shown, the second window122bmay be integrally provided with a part other than the first window122aof the first wall122.

The second chamber114contains alkali metal atoms M in a liquid state. Therefore, when the alkali metal atoms in a gas state contained in the first chamber112are reduced due to a reaction with the first wall122or the like, the liquid alkali metal atoms M are vaporized and a concentration of the alkali metal atoms in a gas state present in the first chamber112can be kept constant. The second chamber114has a second space104and a second wall124defining the second space104. In the illustrated example, the alkali metal atoms M in a liquid state are present in contact with the second wall124at a corner portion opposite to the first chamber112side of the second space104. The length along the X axis of the second space104of the second chamber114is, for example, the same as the length along the X axis of the first space102of the first chamber112.

The passage116connects the first chamber112and the second chamber114to each other. The passage116is disposed between the first chamber112and the second chamber114. The passage116has a third space106and a third wall126defining the third space106. The third space106connects the first space102and the second space104to each other. The third wall126connects to the first wall122and the second wall124to each other. The length along the X axis of the passage116is smaller than the length along the X axis of the chambers112and114.

The shape of the inner wall surface of the first chamber112, the second chamber114, and the passage116is, for example, a cylinder shape. The outer shape of the first wall122, the second wall124, and the third wall126is, for example, a rectangular parallelepiped shape. The material of the walls122,124and126is, for example, a glass, more specifically an aluminosilicate glass. Note that the material of a part other than the windows122aand122bamong the walls122,124, and126may be a silicon.

The low thermal conductivity portion118is disposed between the first chamber112and the second chamber114. In the illustrated example, the low thermal conductivity portion118is a slit structure having a fourth space108and a fourth wall128defining the fourth space108. In the illustrated example, the low thermal conductivity portion118is a slit structure in which the −X axial direction side, the +Z axial direction side, and the −Z axial direction side of the space108are opened. In the illustrated example, a part of the fourth wall128on the −Y axis direction side is a part of the first wall122. A part of the fourth wall128on the +Y axis direction side is a part of the second wall124. A part of the fourth wall128on the +X axis direction side is a part of the third wall126.

The low thermal conductivity portion118is a part having a lower thermal conductivity than the thermal conductivity of the material forming the first wall122and the thermal conductivity of the material forming the second wall124. The low thermal conductivity portion118may be such that the thermal conductivity of at least a part of the low thermal conductivity portion118is lower than the thermal conductivity of the materials forming the walls122and124. In the illustrated example, the thermal conductivity of the space108is lower than the thermal conductivity of the materials forming the walls122,124, and126. Nitrogen may be present in the space108. Air may be present in the space108. The space108may be in a vacuum state that is in a state where a pressure is lower than the atmospheric pressure. When gas is present in the space108, the thermal conductivity of the gas is the thermal conductivity of the space108.

Note that the magnitude of the thermal conductivity may be determined, for example, by specifying the material and comparing a value known as the thermal conductivity of the material, or by measuring the thermal conductivity by a hot wire method or the like and comparing a measurement result.

Regarding a manufacturing method of the atomic cell31, for example, firstly, a rectangular parallelepiped member to be the walls122,124, and126are prepared, and the space108is formed by cutting, etching, or the like. Next, a through hole is formed from one side of the rectangular parallelepiped member with a drill or the like to form the first space102and the second space104. Next, a hole is formed from the other side of the rectangular parallelepiped member to form the third space106. Next, the windows122aand122bare connected to the rectangular parallelepiped member. In this manner, the atomic cell31can be manufactured.

As shown inFIGS. 2 and 3, the light receiving element32receives the light that has passed through the first chamber112. The light receiving element32is disposed on the side opposite to the light emitting element12with respect to the first chamber112. In the illustrated example, the light receiving element32is disposed in the first atomic cell container35. The light receiving element32is electrically connected to the control unit50.

The first holding member33and the second holding member34hold the atomic cell31. The holding members33and34are disposed on an outer surface of the atomic cell31. The thermal conductivity of a material forming the holding members33and34is higher than the thermal conductivity of a material forming the walls122,124, and126and the thermal conductivity of a material forming the first atomic cell container35. A material of the holding members33and34is, for example, an aluminum, a titanium, a copper, a brass, or the like.

The first holding member33transmits a heat of the first temperature control element37ato the alkali metal atoms in a gas state contained in the first chamber112. The first holding member33is disposed on the first wall122. The first holding member33is disposed so as to surround the first chamber112, for example. The first holding member33is also disposed on a part of the third wall126and the second wall124, for example.

The second holding member34transmits a heat of the second temperature control element37bto the alkali metal atoms M in a liquid state contained in the second chamber114. The second holding member34is disposed so as to surround the alkali metal atoms M in a liquid state, for example. The temperature of the second holding member34is lower than the temperature of the first holding member33. The second holding member34is disposed apart from the first holding member33. The holding members33and34have a structure allowing the light emitted from the light emitting element12to pass therethrough.

The first atomic cell container35contains the atomic cell31, the light receiving element32, and the holding members33and34. The first atomic cell container35has a substantially rectangular parallelepiped outer shape. The first atomic cell container35is provided with a through hole35athrough which the light emitted from the light emitting element12passes. A material of the first atomic cell container35is, for example, a permalloy, a silicon iron, or the like. By using such a material, the first atomic cell container35can shield a magnetic field from the outside. As a result, the first atomic cell container35can inhibit the alkali metal atoms in the atomic cell31from being influenced by the magnetic field from the outside and stabilize the oscillation characteristics of the atomic oscillator100.

The first temperature control element37aand the first temperature detection element38aare disposed on the outer surface of the first atomic cell container35, for example. In the illustrated example, the first temperature control element37aand the first temperature detection element38aare disposed on the outer surface of a part in contact with the first holding member33of the first atomic cell container35. The first temperature control element37aheats the first chamber112via the first atomic cell container35and the first holding member33.

The second temperature control element37band the second temperature detection element38bare disposed on the outer surface of the first atomic cell container35. Specifically, the second temperature control element37band the second temperature detection element38bare disposed on the outer surface of a part in contact with the second holding member34of the first atomic cell container35. The second temperature control element37bheats the second chamber114via the first atomic cell container35and the second holding member34. Alternatively, the second temperature control element37b, for example, dissipates the heat of the second chamber114to the outside via the first atomic cell container35and the second holding member34, and cools the second chamber114.

The second atomic cell container36contains the first atomic cell container35, the temperature control elements37aand37b, and the temperature detection elements38aand38b. The second atomic cell container36is provided with a through hole36athrough which the light emitted from the light emitting element12passes. A material of the second atomic cell container36is, for example, the same as the material of the first atomic cell container35. The second atomic cell container36can shield the magnetic field from the outside. The first atomic cell container35and the second atomic cell container36are disposed, for example, apart from each other. Therefore, compared with a case where, for example, the first atomic cell container35and the second atomic cell container36are in contact with each other, a function of shielding the magnetic field from the outside can be enhanced.

Note that, although not shown inFIGS. 2 and 3, for example, the coil39may be a solenoid type coil wound around the outer circumference of the atomic cell31, or a pair of Helmholtz type coils facing each other via the atomic cell31. The coil39generates a magnetic field in the atomic cell31in a direction along an optical axis A of the light. Thereby, a gap between different degenerate energy levels of the alkali metal atoms contained in the atomic cell31can be expanded by Zeeman split, a resolution can be improved, and a line width of the EIT signal can be reduced.

As shown inFIG. 2, the supporting member40is cantilevered and fixed to the base body62of the outer container60. In the illustrated example, the supporting member40is fixed to a pedestal portion63of the base body62. A material of the supporting members40is, for example, an aluminum, or a copper. The supporting member40may be a carbon sheet using a carbon fiber.

The supporting member40is provided with a through hole42. The through hole42passes through the supporting member40in the Z axis direction. When viewed from the Z axis direction, the atomic cell unit30is disposed so as to overlap with the through hole42. The atomic cell unit30is supported by the supporting member40. In the illustrated example, the first atomic cell container35is supported by the supporting member40via a spacer44. A material of the spacer44is, for example, a resin such as an engineering plastic, a liquid crystal polymer (LCP) resin, a polyether ether ketone (PEEK), or the like.

The control unit50has a circuit substrate55. The circuit substrate55is fixed to the base body62of the outer container60via a plurality of lead pins59. An integrated circuit (IC) chip (not shown) is disposed on the circuit substrate55, and the IC chip functions as the temperature controllers51a,51b, and54, the light source controller52, and the magnetic field controller53. The IC chip is electrically connected to the light source unit10and the atomic cell unit30. The circuit substrate55is provided with a through hole56through which the supporting member40is inserted.

The outer container60contains the light source unit10, the optical system unit20, the atomic cell unit30, the supporting member40, and the control unit50. The outer container60has the base body62and a lid body64that is a separate body from the base body62. A material of the outer container60is, for example, the same as the material of the first atomic cell container35. Therefore, the outer container60can shield a magnetism from the outside, and inhibit the alkali metal atoms in the atomic cell31from being influenced by the magnetism from the outside. The inside of the outer container60may be a nitrogen atmosphere or a vacuum.

The atomic oscillator100has, for example, the following effects.

In the atomic oscillator100, the atomic cell31is disposed between the first chamber112and the second chamber114, and includes a low thermal conductivity portion118having a thermal conductivity lower than the thermal conductivity of the material forming the first wall122and the thermal conductivity of the material forming the second wall124. Therefore, in the atomic oscillator100, as compared with the case where the thermal conductivity of the part defined by the fourth wall is the same as the thermal conductivity of the first wall and the second wall, it is difficult for the first chamber112to be influenced by the temperature of the second chamber114. Therefore, in the atomic oscillator100, for example, it is difficult for the alkali metal atoms to be precipitated in the first chamber112by the temperature of the second chamber114, and the oscillation frequency of the atomic oscillator100is hard to fluctuate. Alternatively, since it is difficult for the second chamber114to be influenced by the temperature of the first chamber112, the concentration of the alkali metal atoms in a gas state contained in the first chamber112can be easily set to a desired value and the oscillation frequency of the atomic oscillator100is hard to fluctuate.

Furthermore, since the thermal conductivity of the material forming the walls122and124is higher than the thermal conductivity of the low thermal conductivity portion118, for example, the heat of the temperature control elements37aand37bis easily transmitted to the chambers112and114respectively, as compared with the case where the entire wall of the atomic cell31is made of a material having a low thermal conductivity. Therefore, a uniformity of the temperature distribution in the chambers112and114is good, and a temperature controllability of the chambers112and114is good. Accordingly, the oscillation frequency of the atomic oscillator100hardly varies.

As described above, in the atomic oscillator100, it is possible to stabilize the oscillation frequency.

Here,FIG. 6is a graph schematically showing a relationship between a position along a way from the second chamber114of the atomic cell31toward the first chamber112and the temperature of the atomic cell31. InFIG. 6, a solid line indicates the atomic cell31of the atomic oscillator100, a broken line indicates the atomic cell in a case where the thermal conductivity of a part defined by the fourth wall is the same as the thermal conductivity of the first wall and the second wall. In the atomic oscillator100, as shown inFIG. 6, the temperature difference between the first chamber112and the second chamber114is large, and the uniformity of the temperature distribution is good in the first chamber112and the second chamber114.

Note that, although not shown, the atomic oscillator100may not have the second temperature control element37band the second temperature detection element38b. In this case, the second chamber114can be cooled by natural cooling. In the atomic oscillator100, since the thermal conductivity of the second wall124is higher than the thermal conductivity of the part defined by the fourth wall128, for example, as compared with the case where the thermal conductivity of the second wall is the same as the thermal conductivity of the part defined by the fourth wall, the heat of the second chamber114is easily dissipated via the second wall124and the temperature controllability of the second chamber114is good.

In the atomic oscillator100, the low thermal conductivity portion118has a slit structure. Therefore, in the atomic oscillator100, for example, the low thermal conductivity portion118can be formed more easily as compared with the case where the low thermal conductivity portion has a hollow structure.

1.2. Modification Example of Atomic Oscillator

1.2.1. First Modification Example

Next, an atomic oscillator110according to a modification example of the first embodiment will be described with reference to the drawings.FIG. 7is a cross-sectional view schematically showing an atomic cell31of the atomic oscillator110according to the first modification example of the first embodiment. InFIG. 7, andFIGS. 8 and 9to be described later, X, Y, and Z axes are shown as three axes orthogonal to each other.

Hereinafter, in the atomic oscillator110according to the first modification example of the first embodiment, differences from the example of the atomic oscillator100according to the above-described first embodiment will be described, and description of similar points will be omitted. This is the same in atomic oscillators according to second and third modification examples of the first embodiment described later.

In the atomic oscillator100described above, as shown inFIG. 4, the low thermal conductivity portion118has a slit structure. In contrast to this, in the atomic oscillator110, as shown inFIG. 7, the low thermal conductivity portion118has a hollow structure. In the illustrated example, the fourth wall128has a part positioned on the −X axis direction side of the fourth space108and surrounds the fourth space108.

In the atomic oscillator110, since the low thermal conductivity portion118has a hollow structure, the atomic cell31is robust as compared with the case where the thermal conductivity portion has a slit structure, for example.

1.2.2. Second Modification Example

Next, an atomic oscillator120according to a second modification example of the first embodiment will be described with reference to the drawings.FIG. 8is a cross-sectional view schematically showing the atomic cell31of the atomic oscillator120according to the second modification example of the first embodiment.

In the atomic oscillator100described above, as shown inFIG. 4, the low thermal conductivity portion118has the fourth space108. In contrast to this, in the atomic oscillator120, as shown inFIG. 8, the low thermal conductivity portion118has a low thermal conductivity member119having a lower thermal conductivity than the thermal conductivity of the material forming the first wall122and the thermal conductivity of the material forming the second wall124. The low thermal conductivity member119is disposed on the fourth wall128.

Specifically, a thermal conductivity of the material forming the low thermal conductivity member119is lower than the thermal conductivity of the material forming the walls122,124, and126. In the illustrated example, the low thermal conductivity member119is filled in the space defined by the fourth wall128. The material of the low thermal conductivity member119is, for example, a polytetrafluoroethylene, a polyetheretherketone (PEEK), or the like.

In the atomic oscillator120, the low thermal conductivity portion118is disposed between the fourth wall128and the fourth wall128, and includes the low thermal conductivity member119having a thermal conductivity lower than the thermal conductivity of the material forming the first wall122and the thermal conductivity of the material forming the second wall124. Therefore, in the atomic oscillator120, for example, the atomic cell31is robust as compared with the case where the low thermal conductivity portion118does not have the low thermal conductivity member119and the fourth wall128defines only a space.

1.2.3. Third Modification Example

Next, an atomic oscillator130according to a third modification example of the first embodiment will be described with reference to the drawings.FIG. 9is a cross-sectional view schematically showing the atomic cell31of the atomic oscillator130according to the third modification example of the first embodiment.

In the atomic oscillator100described above, as shown inFIG. 4, the length along the X axis of the second space104of the second chamber114is the same as the length along the X axis of the first space102of the first chamber112. In contrast to this, in the atomic oscillator130, as shown inFIG. 9, the length along the X axis of the second space104of the second chamber114is smaller than the length along the X axis of the first space102of the first chamber112.

The atomic oscillator130does not have the second temperature control element37band the second temperature detection element38b. The second chamber114may not be surrounded by the second holding member34shown inFIG. 3.

In the atomic oscillator130, the length along the X axis of the second space104of the second chamber114is smaller than the length along the X axis of the first space102of the first chamber112. Therefore, in the atomic oscillator130, as compared with the case where the length along the X axis of the second space104of the second chamber114is the same as the length along the X axis of the first space102of the first chamber112, the second chamber114is easily kept at a constant temperature by the first temperature control element37awhich heats the first chamber112and is hardly influenced by the temperature outside the atomic oscillator130.

2. Second Embodiment

Next, an atomic oscillator200according to a second embodiment will be described with reference to the drawings.FIG. 10is a plan view schematically showing an atomic cell31of the atomic oscillator200according to the second embodiment.FIG. 11is a side view schematically showing the atomic cell of the atomic oscillator200according to the second embodiment. InFIGS. 10 and 11, X, Y, and Z axes are shown as three axes orthogonal to each other.

Hereinafter, in the atomic oscillator200according to the second embodiment, differences from the example of the atomic oscillator100according to the above-described first embodiment will be described, and description of similar points will be omitted.

The atomic oscillator200is different from the atomic oscillator100described above in that a high thermal conductivity member202having a thermal conductivity higher than the thermal conductivity of the material forming the first wall122is disposed on the outer surface123of the first wall122.

The high thermal conductivity member202is disposed, for example, so as to surround the first wall122. In the illustrated example, the high thermal conductivity member202is disposed on the outer surface123facing in the +Z axis direction of the first wall122, the outer surface123facing in the +Y axis direction of the first wall122, the outer surface123facing in the −Z axis direction of the first wall122, and the outer surface123facing in the −Y axis direction of the first wall122.

The high thermal conductivity member202is disposed on the fourth wall128of the first chamber112side. In the illustrated example, the high thermal conductivity member202is disposed on a surface facing the +Y axis direction side of the fourth wall128. The high thermal conductivity member202is, for example, in contact with the first holding member33shown inFIG. 3. The high thermal conductivity member202is disposed, for example, between the first wall122and the first holding member33.

A material of the high thermal conductivity member202is, for example, a graphite, a copper, or the like. The high thermal conductivity member202may be a graphite sheet. The high thermal conductivity member202may be a copper wire. Preferably, the high thermal conductivity member202has low magnetic permeability so that the magnetic field of the coil39shown inFIG. 1is applied to the alkali metal atoms contained in the first chamber112. The high thermal conductivity member202, for example, is not transparent with respect to the light emitted from the light emitting element12. The high thermal conductivity member202may be darkly colored so as not to transmit the light emitted from the light emitting element12.

The atomic oscillator200has, for example, the following effects.

In the atomic oscillator200, the high thermal conductivity member202having a thermal conductivity higher than the thermal conductivity of the material forming the first wall122is disposed on the outer surface123of the first wall122. Therefore, in the atomic oscillator200, as compared with the case where the high thermal conductivity member202is not disposed, the temperature gradient is small in the first chamber112, and a uniformity of the temperature distribution can be improved. Therefore, in the atomic oscillator200, for example, it is difficult for the alkali metal atoms to be precipitated in the first window122aof the first wall122by the temperature of the second chamber114.

Here,FIG. 12is a graph schematically showing a relationship between a position in a direction from the second chamber114of the atomic cell31toward the first chamber112and the temperature of the atomic cell31. InFIG. 12, the solid line indicates the atomic cell31of the atomic oscillator200, and the broken line indicates the atomic cell in which the high thermal conductivity member202is not disposed. In the atomic oscillator200, as shown inFIG. 12, the temperature gradient in the first chamber112is small, and the uniformity of the temperature distribution in the first chamber112is good.

In the atomic oscillator200, the high thermal conductivity member202is disposed on the fourth wall128of the first chamber112side. Therefore, in the atomic oscillator200, the uniformity of the temperature distribution of the first chamber112is good as compared with the case where the high thermal conductivity member202is not disposed on the fourth wall128.

In the atomic oscillator200, the high thermal conductivity member202is not transparent with respect to the light emitted from the light emitting element12. Therefore, in the atomic oscillator200, the amount in which the light emitted from the light emitting element12acts on the alkali metal atoms in a gas state, is difficult to change.

For example, when the high thermal conductivity member is not disposed, the light emitted from the light emitting element is scattered on the first wall. The scattered light detected by the light receiving element becomes noise with respect to the light with which the alkali metal atoms in a gas state is directly irradiated. In the atomic oscillator200, since the high thermal conductivity member202is not transparent with respect to the light emitted from the light emitting element12, the light emitted from the light emitting element12is hard to scatter on the first wall122, and it is possible to make the above problems less likely to occur.

Although not shown, in the atomic oscillator200, the low thermal conductivity portion118may have a hollow structure, as in the atomic oscillator110described above. In addition, the atomic oscillator200may include the low thermal conductivity member119, as in the atomic oscillator120described above. Further, in the atomic oscillator200, the length along the X axis of the second space104of the second chamber114may be smaller than the length along the X axis of the first space102of the first chamber112, as in the atomic oscillator130.

2.2. Modification Example of Atomic Oscillator

2.2.1. First Modification Example

Next, an atomic oscillator210according to a first modification example of the second embodiment will be described with reference to the drawings.FIG. 13is a plan view schematically showing the atomic cell31of the atomic oscillator210according to the first modification example of the second embodiment. Note that inFIG. 13, andFIGS. 14 to 18to be described later, X, Y, and Z axes are shown as three axes orthogonal to each other.

Hereinafter, in the atomic oscillator210according to the first modification example of the second embodiment, differences from the example of the atomic oscillator200according to the above-described second embodiment will be described, and description of similar points will be omitted. This is the same in atomic oscillators according to second and third modification examples of the second embodiment described later.

In the atomic oscillator200described above, as shown inFIG. 10, the high thermal conductivity member202is disposed only on the first wall122. In contrast to this, in the atomic oscillator210, as shown inFIG. 13, the high thermal conductivity member202is also disposed on a part of the second wall124.

In the illustrated example, the high thermal conductivity member202is disposed on a part connected to the third wall126of the second wall124. Further, the high thermal conductivity member202is disposed on the third wall126.

In the atomic oscillator210, the high thermal conductivity member202is disposed on a part of the second wall124. Therefore, in the atomic oscillator210, as compared with the case where the high thermal conductivity member202is not disposed on the second wall124, the volume of a part of the second chamber114in which the temperature is lower than the temperature of the first chamber112can be reduced, and it is easy to control the position of the alkali metal atoms M in a liquid state.

2.2.2. Second Modification Example

Next, an atomic oscillator220according to a second modification example of the second embodiment will be described with reference to the drawings.FIG. 14is a plan view schematically showing the atomic cell31of the atomic oscillator220according to the second modification example of the second embodiment.FIG. 15is a side view schematically showing the atomic cell31of the atomic oscillator220according to the second modification example of the second embodiment.

In the atomic oscillator200described above, as shown inFIGS. 10 and 11, corners of the first wall122are covered with the high thermal conductivity member202. In contrast to this, in the atomic oscillator220, as shown inFIGS. 14 and 15, corners222of the first wall122are not covered with the high thermal conductivity member202.

The high thermal conductivity members202are disposed on the first wall122avoiding the corners222of the first wall122. In the illustrated example, four high thermal conductivity members202are disposed. A shape of the high thermal conductivity member202is, for example, a flat plate shape.

In the atomic oscillator220, since the high thermal conductivity members202are disposed on the first wall122avoiding the corners222, for example, as compared with the case where the high thermal conductivity member202covers the corners222, fluctuation in the oscillation frequency of the atomic oscillator220can be suppressed by changing the thermal conductivity of the high thermal conductivity member202over time.

For example, in a case where the material of the high thermal conductivity member202is a graphite, when the high thermal conductivity members202are bent so as to cover the corners222, a structure of the bent part is broken and the thermal conductivity is lowered, and the thermal conductivity of the part bent over time is changed in some cases. Therefore, there may be a case that the oscillation frequency of the atomic oscillator fluctuates. In the atomic oscillator220, it is possible to make the above problem less likely to occur.

2.2.3. Third Modification Example

Next, an atomic oscillator230according to a third modification example of the second embodiment will be described with reference to the drawings.FIG. 16is a plan view schematically showing the atomic cell31of the atomic oscillator230according to the third modification example of the second embodiment.FIG. 17is a side view schematically showing the atomic cell31of the atomic oscillator230according to the third modification example of the second embodiment.

In the atomic oscillator200described above, as shown inFIGS. 10 and 11, the high thermal conductivity member202is not disposed on the first window122aof the first wall122. In contrast to this, in the atomic oscillator230, as shown inFIGS. 16 and 17, the high thermal conductivity member202is disposed on an outer surface123aof the first window122a. In the illustrated example, the outer surface123ais a surface facing the Z axis minus direction.

As shown inFIG. 17, the high thermal conductivity member202is provided with a through hole202athrough which the light LL emitted from the light emitting element12passes. In the illustrated example, the shape of a wall surface defining the through hole202ais a circular shape. When viewed from the X axis direction, the diameter of the through hole202ais larger than the diameter of the light LL. The high thermal conductivity member202is not irradiated with the light LL.

In the atomic oscillator230, the high thermal conductivity member202is disposed on the outer surface123aof the first window122aand the high thermal conductivity member202is provided with the through hole202athrough which the light LL emitted from the light emitting element12passes. Therefore, in the atomic oscillator230, as compared with the case where the high thermal conductivity member202is not disposed on the outer surface123aof the first window122a, the uniformity of the temperature distribution in the first chamber112can be improved, for example, and it is difficult for the alkali metal atoms to be further precipitated in the first window122aof the first wall122by the temperature of the second chamber114.

As shown inFIG. 18, the diameter of the through hole202amay be smaller than the diameter of the light LL when viewed from the X axis direction. The high thermal conductivity member202may shield a part of the light LL. In this case, for example, the diameter of the light LL passing through the first chamber112can be reduced by the high thermal conductivity member202, and the light LL can be separated from the first wall122defining a direction orthogonal to the X axis of the first space102. Therefore, it is possible to reduce the possibility that a frequency difference corresponding to an energy difference between the two ground levels of the alkali metal atoms in a gas state gets deviated. The alkali metal atoms in a gas state in the vicinity of the first wall122do not ideally resonate and there is a possibility that the frequency difference corresponding to the energy difference between the two ground levels of the alkali metal atoms in a gas state gets deviated.

Next, an atomic oscillator300according to a third embodiment will be described with reference to the drawings.FIG. 19is a perspective view schematically showing an atomic cell31of the atomic oscillator300according to the third embodiment.FIG. 20is a plan view schematically showing the atomic cell31of the atomic oscillator300according to the third embodiment.FIG. 21is a side view schematically showing the atomic cell31of the atomic oscillator300according to the third embodiment. Note that inFIGS. 20 and 21, the holding members33and34are also shown. Further, inFIGS. 19 to 21, X, Y, and Z axes are shown as three axes orthogonal to each other.

Hereinafter, in the atomic oscillator300according to the third embodiment, differences from the example of the atomic oscillator100according to the above-described first embodiment will be described, and description of similar points will be omitted.

In the atomic oscillator100described above, as shown inFIGS. 4 and 5, the low thermal conductivity portion118has one fourth space108. In contrast to this, in the atomic oscillator300, as shown inFIGS. 19 to 21, the low thermal conductivity portion118has a fifth space108aand a sixth space108bwhich are separated from each other. The fourth wall128defines the spaces108aand108b.

The fourth wall128has a first part128a, a second part128b, and a third part128c. The first part128aconnects the first chamber112and the second chamber114to each other. Specifically, the first part128aconnects the first wall122of the first chamber112and the second wall124of the second chamber114to each other.

The second part128bconfigures the low thermal conductivity portion118having a slit structure on one side of the first part128a. In the illustrated example, the second part128bconfigures the low thermal conductivity portion118on the Z axis minus direction of the first part128a. The second part128bdefines the fifth space108a.

The third part128cconfigures the low thermal conductivity portion118having a slit structure on the other side of the first part128a. In the illustrated example, the third part128cconfigures the low thermal conductivity portion118on the Z axis plus direction of the first part128a. The third part128cdefines the sixth space108b.

In the illustrated example, parts on the Y axis minus side of the second part128band the third part128care a part of the first wall122. Parts on the Y axis plus side of the second part128band the third part128care a part of the second wall124. Parts on the X axis plus side of the second part128band the third part128care a part of the third wall126. A part on the Z axis plus side of the second part128bis the first part128a. A part on the Z axis minus side of the third part128cis the first part128a.

The atomic oscillator300has, for example, the following effects.

In the atomic oscillator300, the fourth wall128includes the first part128aconnecting the first chamber112and the second chamber114to each other, the second part128bconfiguring the low thermal conductivity portion118which has a slit structure in one side of the first part128a, and the third part128cconfiguring the low thermal conductivity portion118which has a slit structure in the other side of the first part128a. Therefore, in the atomic oscillator300, the atomic cell31is more robust as compared with the case where the fourth wall128does not have the first part128a.

Note that, although not shown, the atomic oscillator300may include a low thermal conductivity member119, as in the atomic oscillator120described above. Further, in the atomic oscillator300, the length along the X axis of the second space104of the second chamber114may be smaller than the length along the X axis of the first space102of the first chamber112, as in the atomic oscillator130described above. In addition, the atomic oscillator300may include the high thermal conductivity member202, as in the atomic oscillator200,210,220, and230described above.

3.2. Modification Example of Atomic Oscillator

Next, an atomic oscillator310according to a modification example of the third embodiment will be described with reference to the drawings.FIG. 22is a perspective view schematically showing the atomic cell31of the atomic oscillator310according the modification example of to the third embodiment.FIG. 23is a plan view schematically showing the atomic cell31of the atomic oscillator310according to the modification example of the third embodiment. Note that inFIG. 23, the holding members33and34are also shown. Further, inFIGS. 22 and 23, X, Y, and Z axes are shown as three axes orthogonal to each other.

Hereinafter, in the atomic oscillator310according to the modification example of the third embodiment, differences from the example of the atomic oscillator300according to the above-described third embodiment will be described, and description of similar points will be omitted.

As shown inFIGS. 22 and 23, the atomic oscillator310is different from the atomic oscillator300described above in that the second wall124defines a seventh space312and an eighth space314.

In the atomic oscillator310, the second wall124has a fourth part124a, a fifth part124b, and a sixth part124c. The temperature of the fifth part124bis lower than the temperature of the fourth part124a. The fourth part124ais a part covered with a first holding member33shown inFIG. 3. The fifth part124bis a part covered with a second holding member34shown inFIG. 3.

The sixth part124cdefines the spaces312and314between the fourth part124aand the fifth part124b. The sixth part124cand the spaces312and314configure a slit structure316. In the illustrated example, a part on the X axis plus side of the sixth part124cis a part common to the fourth part124a. A part on the X axis minus side of the sixth part124cis a part common to the fifth part124b. The sixth part124chas a part connecting the fourth part124aand the fifth part124bto each other. In the illustrated example, the slit structure316is a slit structure in which the Z axis minus side of the seventh space312, the Z axis plus side of the eighth space314, and the Y axis plus side of the spaces312and314, are opened.

The spaces312and314are provided between the fourth part124aand the fifth part124b. In the illustrated example, the seventh space312is continuous with the fifth space108a. The eighth space314is continuous with the sixth space108b. In the illustrated example, the spaces108aand108bare directed from the X axis minus side of the atomic cell31toward the passage116side, and the spaces312and314are directed from the spaces108aand108balong the passage116toward the Y axis plus side of the atomic cell31.

In the atomic oscillator310, the second wall124has a fourth part124a, a fifth part124bhaving a temperature lower than the temperature of the fourth part124a, and the sixth part124cconfiguring the slit structure316between the fourth part124aand the fifth part124b. Therefore, in the atomic oscillator310, as compared with the case where the sixth part124cconfiguring the slit structure316between the fourth part124aand the fifth part124bis not provided, the first chamber112is less likely to be influenced by the temperature of the second chamber114.

Next, a frequency signal generation system according to a fourth embodiment will be described with reference to the drawings. The following clock transmission system as a timing server is an example of a frequency signal generation system.FIG. 24is a schematic configuration diagram showing a clock transmission system900.

The clock transmission system according to the present disclosure includes the atomic oscillator according to the present disclosure. In the following, the clock transmission system900including the atomic oscillator100will be described as an example.

The clock transmission system900is to synchronize a clock of each device in a time division multiplexing network, and is a system having a redundant configuration of a normal (N) system and an emergency (E) system.

As shown inFIG. 24, the clock transmission system900includes a clock supply device901and a synchronous digital hierarchy (SDH) device902of an A station (upper level (N system)), a clock supply device903and SDH device904of a B station (upper level (E system)), and a clock supply device905and SDH devices906and907of a C station (lower level). The clock supply device901has the atomic oscillator100and generates an N system clock signal. The atomic oscillator100in the clock supply device901generates a clock signal in synchronization with a more accurate clock signal from master clocks908and909including the atomic oscillator using a cesium.

Based on the clock signal from the clock supply device901, the SDH device902transmits and receives a main signal, superimposes the N system clock signal on the main signal, and transmits the signal to the lower level clock supply device905. The clock supply device903has the atomic oscillator100and generates an E system clock signal. The atomic oscillator100in the clock supply device903generates a clock signal in synchronization with a more accurate clock signal from master clocks908and909including the atomic oscillator using a cesium.

Based on the clock signal from the clock supply device903, the SDH device904transmits and receives a main signal, superimposes the E system clock signal on the main signal, and transmits the signal to the lower level clock supply device905. The clock supply device905receives the clock signal from the clock supply devices901and903, and generates a clock signal in synchronization with the received clock signal.

The clock supply device905normally generates a clock signal in synchronization with the N system clock signal from the clock supply device901. Then, when an abnormality occurs in the N system, the clock supply device905generates a clock signal in synchronization with the E system clock signal from the clock supply device903. By switching from the N system to the E system like this, a stable clock supply can be guaranteed, and the reliability of the clock path network can be enhanced. The SDH device906transmits and receives the main signal based on the clock signal from the clock supply device905. Similarly, the SDH device907transmits and receives the main signal based on the clock signal from the clock supply device905. In this way, it is possible to synchronize the device of the station C with the device of the station A or the station B.

The frequency signal generation system according to the fourth embodiment is not limited to the clock transmission system. The frequency signal generation system is equipped with the atomic oscillator, and includes various devices using the frequency signal of the atomic oscillator and a system configured with a plurality of devices. The frequency signal generation system includes a terminal to which a frequency signal from the atomic oscillator is input and a controller to control the atomic oscillator.

The frequency signal generation system according to the fourth embodiment may be, for example, a smart phone, a tablet terminal, a timepiece, a portable phone, a digital still camera, a liquid ejecting apparatus such as an ink jet printer, a personal computer, a television, a video camera, a video tape recorder, a car navigation device, a pager, an electronic notebook, an electronic dictionary, a calculator, an electronic game machine, a word processor, a workstation, a video phone, a security television monitor, an electronic binoculars, a point of sales (POS) terminal, a medical machine, a fish finder, a global navigation satellite system (GNSS) frequency standard, various measuring machines, instruments, a flight simulator, a terrestrial digital broadcasting system, a portable phone base station, and a moving object.

Examples of the medical machine include, for example, an electronic clinical thermometer, a blood pressure manometer, a blood glucose meter, an electrocardiogram measurement device, an ultrasonic diagnostic device, an electronic endoscope, and a magnetocardiograph. Examples of the instruments include, for example, instruments such as a vehicle, an aircraft, and a ship. Examples of the moving object include, for example, a vehicle, an aircraft, a ship, or the like.

The present disclosure may omit a part of the configuration within a range having the features and effects described in this application, or combine each embodiment and modification.

The present disclosure includes a configuration (for example, a configuration having the same function, a method, and a result, or a configuration having the same object and effect) that is substantially the same as the configuration described in the embodiment. Further, the present disclosure includes a configuration in which non-essential parts of the configuration described in the embodiments are replaced. Further, the present disclosure includes a configuration that achieves the same operation and effect as the configuration described in the embodiments, or a configuration that can achieve the same object. Further, the present disclosure includes a configuration in which a known technique is added to the configuration described in the embodiments.