JP7473319B2 - Atomic oscillator and frequency signal generating system - Google Patents

Description

The present invention relates to an atomic oscillator and a frequency signal generating system.

Atomic oscillators that oscillate based on the energy transition of alkali metal atoms such as rubidium and cesium are known as oscillators that have high-precision oscillation characteristics over a long period of time.
In an atomic oscillator, alkali metal atoms are sealed in a gas cell, and the gas cell is heated to a specified temperature by a heater to keep the alkali metal atoms in a gaseous state. However, the gaseous alkali metal atoms in the gas cell decrease with age, so there is a problem that the performance of the atomic oscillator deteriorates after long-term use.
For example, in Patent Document 1, a heat dissipation part is arranged at a position separated from a heat transfer part that heats the gas cell, and instead of gasifying all of the alkali metal atoms in the gas cell, some of them are precipitated in the heat dissipation part, which is a low-temperature part of the gas cell, and enclosed as a liquid. Therefore, the decrease in gaseous alkali metal atoms due to aging is compensated for by vaporizing the liquid alkali metal atoms.

JP 2015-122597 A

However, the atomic oscillator described in Patent Document 1 has a heat dissipation section that releases heat from the gas cell to the outside, thereby lowering the temperature of part of the gas cell. This means that the degree of cooling of the gas cell is easily affected by the outside air temperature, making it difficult to stabilize the temperature distribution of the gas cell.

The atomic oscillator includes a light-emitting element, an atomic cell that contains alkali metal atoms and receives the light emitted from the light-emitting element, a heater that covers the atomic cell and heats the atomic cell to a first temperature, a first portion that is heated to the first temperature by the heater, and a second portion that is in contact with the atomic cell and is controlled to a second temperature lower than the first temperature by the Peltier effect, and includes a temperature control element disposed between the heater and the atomic cell, and a light-receiving element that detects the light that has passed through the atomic cell.

In the above atomic oscillator, it is preferable to include a constant current source connected to the temperature control element.

In the above atomic oscillator, it is preferable that the temperature of the surface of the atomic cell where the light enters and the temperature of the surface of the atomic cell where the light exits are higher than the second temperature.

In the above atomic oscillator, the temperature control element is a Peltier element including a first temperature control surface, a second temperature control surface, and a semiconductor layer connecting the first temperature control surface and the second temperature control surface, and the first part is the first temperature control surface of the Peltier element, and the second part is the second temperature control surface of the Peltier element, and it is preferable that the first part, the semiconductor layer, and the second part are arranged in this order from the heater toward the atomic cell.

In the above atomic oscillator, it is preferable that the temperature control element includes a first metal and a second metal different from the first metal, and the second portion is a junction between the first metal and the second metal.

In the above atomic oscillator, it is preferable that the first portion is a portion of the first metal that contacts the heater and a portion of the second metal that contacts the heater.

In the above atomic oscillator, it is preferable that the oscillator includes a shield that is disposed between the heater and the atomic cell and is heated to the first temperature by the heater, and the first portion is a portion of the first metal that contacts the shield.

In the above atomic oscillator, it is preferable that the temperature control element is a coil that generates a magnetic field.

In the above atomic oscillator, it is preferable that the first portion of the temperature control element and the constant current source are connected by a third metal.

The frequency signal generating system includes an atomic oscillator and a processing unit that processes a frequency signal from the atomic oscillator. The atomic oscillator includes a light-emitting element, an atomic cell that contains alkali metal atoms and into which light emitted from the light-emitting element is incident, a heater that covers the atomic cell and heats the atomic cell to a first temperature, a first portion that is heated to the first temperature by the heater, and a second portion that is in contact with the atomic cell and is controlled to a second temperature lower than the first temperature by the Peltier effect. The system also includes a temperature control element disposed between the heater and the atomic cell, and a light-receiving element that detects light that has passed through the atomic cell.

FIG. 1 is a schematic diagram showing an atomic oscillator according to a first embodiment. FIG. 1 is a cross-sectional view illustrating an atomic oscillator according to a first embodiment. FIG. 2 is a cross-sectional view illustrating an atomic cell unit according to the first embodiment. FIG. 4 is a cross-sectional view taken along line AA in FIG. FIG. 11 is a cross-sectional view illustrating an atomic cell unit according to a second embodiment. FIG. 13 is a cross-sectional view illustrating an atomic cell unit according to a third embodiment. FIG. 13 is a cross-sectional view illustrating an atomic cell unit according to a fourth embodiment. FIG. 13 is a cross-sectional view illustrating an atomic cell unit according to a fifth embodiment. FIG. 13 is a cross-sectional view illustrating an atomic cell unit according to a sixth embodiment. FIG. 13 is a cross-sectional view illustrating an atomic cell unit according to a seventh embodiment. FIG. 23 is a cross-sectional view illustrating an atomic cell unit according to the eighth embodiment. FIG. 13 is a schematic configuration diagram showing a frequency signal generating system according to a ninth embodiment.

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

The atomic oscillator 1 is an atomic oscillator that utilizes the quantum interference effect (CPT: Coherent Population Trapping), a phenomenon that occurs when two resonant lights of specific different wavelengths are simultaneously irradiated onto an alkali metal atom, and the two resonant lights are transmitted through the alkali metal atom without being absorbed. Note that this phenomenon caused by the quantum interference effect is also called the electromagnetically induced transparency (EIT) phenomenon. The atomic oscillator 1 according to this embodiment may also be an atomic oscillator that utilizes the double resonance phenomenon caused by light and microwaves.

As shown in FIG. 1, the atomic oscillator 1 includes a light-emitting element 10, an optical system unit 20, an atomic cell unit 30, and a control unit 40 that controls the light-emitting element 10 and the atomic cell unit 30.

The light-emitting element 10 emits linearly polarized light LL that contains two types of light with different frequencies. The light-emitting element 10 is, for example, a vertical cavity surface-emitting laser (VCSEL).

The optical system unit 20 is disposed between the light-emitting element 10 and the atomic cell unit 30. The optical system unit 20 has a neutral density filter 21, a lens 22, and a quarter-wave plate 23.

The neutral density filter 21 reduces the intensity of the light LL emitted from the light emitting element 10. The lens 22 adjusts the radiation angle of the light LL. Specifically, the lens 22 converts the light LL into parallel light. The quarter-wave plate 23 converts the two types of light with different frequencies contained in the light LL from linearly polarized light to circularly polarized light.

The atomic cell unit 30 has an atomic cell 31, a light receiving element 32, a heater 33, a temperature sensor 34, a coil 35, and a temperature control element 36.

The atomic cell 31 transmits the light LL emitted from the light receiving element 32. The atomic cell 31 contains an alkali metal atom. The alkali metal atom has a three-level energy level system consisting of two mutually different ground levels and an excited level. The light LL emitted from the light emitting element 10 enters the atomic cell 31 via the neutral density filter 21, the lens 22, and the quarter-wave plate 23.

The light receiving element 32 receives and detects the light LL that has passed through the atomic cell 31. The light receiving element 32 is, for example, a photodiode.

The heater 33 controls the atomic cell 31 to a first temperature T1. The heater 33 heats the alkali metal atoms contained in the atomic cell 31, causing at least a portion of the alkali metal atoms to become gaseous. The first temperature T1 is, for example, 60°C or higher and 70°C or lower.

The temperature sensor 34 detects the temperature of the atomic cell 31. The temperature sensor 34 is, for example, one of various temperature sensors such as a thermistor or a thermocouple.
The coil 35 applies a magnetic field in a predetermined direction to the alkali metal atoms contained in the atomic cell 31, and Zeeman-splits the energy levels of the alkali metal atoms.

When an alkali metal atom is irradiated with a circularly polarized resonant light pair in a state where the alkali metal atom has undergone Zeeman splitting, the number of alkali metal atoms at the desired energy level among the multiple levels at which the alkali metal atom has undergone Zeeman splitting becomes relatively large compared to the number of alkali metal atoms at other energy levels. Therefore, the number of atoms that exhibit the desired EIT phenomenon increases, and the desired EIT signal becomes larger. As a result, the oscillation characteristics of the atomic oscillator 1 can be improved.

The temperature control element 36 utilizes the Peltier effect to cool a portion of the atomic cell 31 to a second temperature T2 that is lower than the first temperature T1. The second temperature T2 is, for example, a temperature that is 1° C. or more lower than the first temperature T1. The temperature control element 36 is, for example, a Peltier element.

The control unit 40 has a temperature control circuit 41, a constant current source 42, a magnetic field control circuit 43, and a light source control circuit 44.

The temperature control circuit 41 controls the power supply to the heater 33 based on the detection result of the temperature sensor 34 so that the inside of the atomic cell 31 reaches the desired temperature.

The constant current source 42 passes a direct current through the temperature control element 36, controlling a portion of the atomic cell 31 to a second temperature T2.

The magnetic field control circuit 43 controls the current flow to the coil 35 so that the magnetic field generated by the coil 35 is constant.

Based on the detection result of the light receiving element 32, the light source control circuit 44 controls the frequency of the two types of light contained in the light LL emitted from the light receiving element 32 so that the EIT phenomenon occurs. Here, when these two types of light become a resonant light pair with a frequency difference corresponding to the energy difference between the two ground levels of the alkali metal atom contained in the atomic cell 31, the EIT phenomenon occurs. The light source control circuit 44 is equipped with a voltage controlled oscillator (not shown) whose oscillation frequency is controlled so as to be stabilized in synchronization with the control of the frequency of the two types of light, and outputs the output signal of this voltage controlled oscillator (VCO: Voltage Controlled Oscillator) as the clock signal CLK, which is the output signal of the atomic oscillator 1.

Next, a specific configuration of the atomic oscillator 1 will be described.
Fig. 2 is a cross-sectional view that typically shows the atomic oscillator 1 according to the first embodiment. Fig. 3 is a cross-sectional view that typically shows the atomic cell unit 30 according to the first embodiment. Fig. 4 is a cross-sectional view taken along line AA in Fig. 3. In addition, in Figs. 2 to 4 and Figs. 5 to 11 described below, an X-axis, a Y-axis, and a Z-axis are illustrated as three mutually orthogonal axes.

As shown in FIG. 2, the atomic oscillator 1 includes a light-emitting element 10, an optical system unit 20, an atomic cell unit 30, a control unit 40, and an outer container 50.

The light emitting element 10 is arranged on the light source substrate 11. The light source substrate 11 is arranged on a heat insulating member 53 provided on an outer base 51, and is fixed to the outer base 51 together with the heat insulating member 53 by, for example, a screw (not shown). The light emitting element 10 is electrically connected to the light source control circuit 44 of the control unit 40.

The optical system unit 20 is disposed on the outer base 51 via a heat insulating member 53. The optical system unit 20 has a neutral density filter 21, a lens 22, a quarter-wave plate 23, and a holder 24 that holds these. The holder 24 is fixed to the outer base 51 together with the heat insulating member 53, for example, by a screw (not shown).

The holder 24 has a through hole, which is an area through which the light LL passes. In the through hole, a neutral density filter 21, a lens 22, and a quarter-wave plate 23 are arranged in this order from the light-emitting element 10 side.

The atomic cell unit 30 is disposed on the outer base 51 via a heat insulating member 53, and is fixed to the outer base 51 together with the heat insulating member 53 by, for example, screws (not shown).
3 and 4, the atom cell unit 30 includes an atom cell 31, a light receiving element 32, a heater 33, a temperature sensor 34, a coil 35, a temperature control element 36, and a shield 37 serving as an inner container. The atom cell 31, the heater 33, and the shield 37 are cylindrical in shape with the longitudinal direction along the X-axis, and the shield 37 is disposed inside the heater 33, and the atom cell 31, the light receiving element 32, the temperature sensor 34, the coil 35, and the temperature control element 36 are disposed inside the shield 37.

The atomic cell 31 contains an alkali metal such as gaseous rubidium, cesium, or sodium. If necessary, the atomic cell 31 may contain a rare gas such as argon or an inert gas such as nitrogen as a buffer gas together with the alkali metal atoms.

The light LL emitted from the light emitting element 10 is incident on the atomic cell 31. The material of the wall of the atomic cell 31 is, for example, glass. The wall of the atomic cell 31 defines the internal space S of the atomic cell 31. The internal space S of the atomic cell 31 is, for example, saturated vapor pressure of alkali metal atoms. The light LL emitted from the light emitting element 10 passes through the internal space S. For example, liquid alkali metal atoms 60 are present on the surface of the atomic cell 31 on the internal space S side at the position where the atomic cell 31 and the temperature control element 36 are in contact. As a result, when the gaseous alkali metal atoms in the internal space S are reduced due to a reaction with the wall of the atomic cell 31, the liquid alkali metal atoms 60 are vaporized, and the concentration of the gaseous alkali metal atoms in the internal space S can be kept constant.

The light receiving element 32 detects the light LL that has passed through the atomic cell 31, and is disposed on the opposite side of the atomic cell 31 from the light emitting element 10 side. The light receiving element 32 is electrically connected to the light source control circuit 44 of the control unit 40.

The heater 33 houses the atom cell 31, the light receiving element 32, the temperature sensor 34, the coil 35, the temperature control element 36, and the shield 37, and covers the atom cell 31. The heater 33 is electrically connected to a temperature control circuit 41 of the control unit 40.
The heater 33 heats the atom cell 31 to a first temperature T1 based on temperature information from a temperature sensor 34 disposed in the atom cell 31. The heater 33 may be, for example, a sheet heater that covers the entire atom cell 31, or may be a combination of a heating element and a metal with high thermal conductivity such as copper.

A plurality of temperature sensors 34 are arranged in the atom cell 31 and detect the temperature of the atom cell 31. The number and arrangement of the temperature sensors 34 are not limited as long as the heater 33 can heat the atom cell 31 to the first temperature T1. For example, the number of the temperature sensors 34 may be one, and the temperature sensor 34 may be arranged outside the shield 37.
The coil 35 is, for example, a solenoid coil wound around the outer periphery of the atomic cell 31, or a pair of Helmholtz coils facing each other across the atomic cell 31. The coil 35 generates a magnetic field in a direction along the optical axis LA of the light LL inside the atomic cell 31. This makes it possible to widen the gap between different degenerate energy levels of the alkali metal atoms contained in the atomic cell 31 by Zeeman splitting, thereby improving the resolution and reducing the linewidth of the EIT signal.
The temperature sensor 34 and the coil 35 are electrically connected to a temperature control circuit 41 and a magnetic field control circuit 43 of the control unit 40 .

The temperature control element 36 is a Peltier element arranged between the atom cell 31 and the heater 33 that heats the atom cell 31 to a first temperature T1, and includes a first temperature control surface P1 as a first portion 361, a second temperature control surface P2 as a second portion 363, and a semiconductor layer 362 that connects the first temperature control surface P1 and the second temperature control surface P2. The first portion 361, the semiconductor layer 362, and the second portion 363 are arranged in this order from the heater 33 toward the atom cell 31. The temperature control element 36 is electrically connected to the constant current source 42 of the control unit 40 from the first portion 361 by two wirings (not shown).
The first portion 361 of the temperature control element 36 is heated to a first temperature T1 by the heater 33, and the second portion 363 in contact with the atom cell 31 is controlled to a second temperature T2 lower than the first temperature T1 by the Peltier effect. Therefore, a part of the atom cell 31 in contact with the second portion 363 of the temperature control element 36 is cooled to a second temperature T2 lower than the first temperature T1. This is because a temperature difference can be generated between the first temperature control surface P1 and the second temperature control surface P2 by the Peltier effect by passing a direct current from the constant current source 42 to the temperature control element 36, and the second temperature control surface P2 in contact with the atom cell 31 can be made to absorb heat.
Therefore, in the internal space S of the cooled atom cell 31, the gaseous alkali metal atoms are cooled and liquefied to generate liquid alkali metal atoms 60.

The temperature control element 36 may be positioned anywhere along the optical axis LA, but is preferably located near the center of the atomic cell 31. For example, it may be positioned within a range of 1/3 to 2/3 of the length along the optical axis LA of the atomic cell 31. Since the portion at the second temperature T2 can be separated from both the surface M1 where the light LL of the atomic cell 31 is incident and the surface M2 where the light of the atomic cell 31 is emitted, it is possible to make it difficult for liquid alkali metal atoms 60 to adhere to the surfaces M1 and M2. This makes it difficult for the intensity of the light LL incident on the atomic cell 31 and the intensity of the light LL emitted from the atomic cell 31 to decrease, thereby suppressing a decrease in the frequency accuracy of the atomic oscillator 1.

The atomic cell 31 is heated by the heater 33 so that the temperature of the surface M1 and the temperature of the surface M2 become a first temperature T1 that is higher than the second temperature T2.

The shield 37 houses the atomic cell 31, the light receiving element 32, the temperature sensor 34, the coil 35, and the temperature control element 36, and is disposed inside the heater 33. A transparent member 37a such as glass is disposed on the wall of the shield 37 on the side of the light emitting element 10. Therefore, the light LL emitted from the light emitting element 10 can be incident on the atomic cell 31.

The material of the shield 37 is, for example, iron, silicon iron, permalloy, supermalloy, sendust, copper, etc. By using such materials, the atomic cell 31 can block external magnetism. This makes it possible to suppress the influence of external magnetism on the alkali metal atoms in the atomic cell 31, and stabilize the oscillation characteristics of the atomic oscillator 1. Here, "suppress" includes cases where an event is completely stopped from occurring, and cases where the severity of an event is reduced.

As shown in FIG. 2, the control unit 40 has a circuit board 45. The circuit board 45 is fixed to the outer base 51 via a plurality of lead pins 54. An IC (Integrated Circuit) chip (not shown) is arranged on the circuit board 45, and the IC chip functions as a temperature control circuit 41, a magnetic field control circuit 43, and a light source control circuit 44. The IC chip is electrically connected to the light-emitting element 10 and the atomic cell unit 30.

The outer container 50 houses the light emitting element 10, the optical system unit 20, the atomic cell unit 30, and the control unit 40. The outer container 50 has an outer base 51 and an outer lid 52 that is separate from the outer base 51. The material of the outer container 50 is, for example, the same as that of the shield 37. Therefore, the outer container 50 can block external magnetic fields and can prevent the alkali metal atoms in the atomic cell 31 from being affected by external magnetic fields.

In this embodiment, four temperature control elements 36 are arranged, but this is not limited to this and one or more temperature control elements 36 may be arranged.

In the atomic oscillator 1 of this embodiment, the atomic cell 31 is placed inside the heater 33, whose temperature is stabilized, so that the temperature of the atomic cell 31 is less susceptible to the effect of the outside air temperature. In addition, by using the Peltier effect for cooling to create a constant temperature difference between the first part 361 and the second part 363 based on the temperature of the heater 33, the temperature of the heater 33 is less likely to fluctuate even if part of the atomic cell 31 is cooled inside the heater 33, so that the temperature distribution of the atomic cell 31 can be stabilized. As a result, a highly accurate atomic oscillator 1 can be obtained.

In addition, because the temperature control element 36 is connected to the constant current source 42, the temperature difference caused by the Peltier effect is kept constant. Therefore, the second part 363 of the temperature control element 36 that contacts the atomic cell 31 can be stably controlled to the second temperature T2.

In addition, since the temperature of the surface M1 where the light LL of the atomic cell 31 is incident and the temperature of the surface M2 where the light LL of the atomic cell 31 is emitted are higher than the second temperature T2, the gaseous alkali metal atoms do not precipitate as a liquid on the two surfaces, so the light is not blocked and stable oscillation characteristics can be obtained.

In addition, since the temperature control element 36 is arranged from the heater 33 toward the atomic cell 31 in the order of the first portion 361, the semiconductor layer 362, and the second portion 363, a temperature difference can be generated between the first temperature control surface P1, which is at the first temperature T1, and the second temperature control surface P2 by the Peltier effect, and heat can be absorbed by the second temperature control surface P2 that is in contact with the atomic cell 31. Therefore, a part of the atomic cell 31 can be cooled while maintaining a stable temperature distribution of the atomic cell 31.

2. Second Embodiment Next, an atomic oscillator 1a according to a second embodiment will be described with reference to FIG.
FIG. 5 is a cross-sectional view that illustrates a schematic diagram of an atom cell unit 30a according to the second embodiment.

The atomic oscillator 1a of this embodiment is similar to the atomic oscillator 1 of the first embodiment, except that the configuration of the atomic cell unit 30a is different from that of the atomic oscillator 1 of the first embodiment. Note that the following description will focus on the differences from the first embodiment described above, and similar items will be given the same reference numerals and their description will be omitted.

As shown in FIG. 5, in the atomic cell unit 30a of the atomic oscillator 1a, the temperature control element 36 is arranged in the order of a first portion 361, a semiconductor layer 362, and a second portion 363 from the light-emitting element 10 side, and the first portion 361 is heated to a first temperature T1, and the second portion 363 is cooled to a second temperature T2 by the Peltier effect.
Between the atom cell 31 and the coil 35 and between the light receiving element 32 and the shield 37 , a heat transfer member 70 for transferring heat from the heater 33 is disposed.
A heat transfer member 71 is disposed on the light receiving element 32 side of the temperature control element 36, in contact with the second portion 363 and the atom cell 31. The heat transfer member 71 is separated from the heat transfer member 70 and the shield 37. The heat transfer member 71 transfers heat from the second portion 363 cooled to the second temperature T2 to the atom cell 31, and can cool a part of the atom cell 31 in contact with the heat transfer member 71. Therefore, liquid alkali metal atoms 60 can be generated in the internal space S of the atom cell 31 in contact with the heat transfer member 71, in which the gaseous alkali metal atoms are cooled and liquefied.

The material of the heat transfer member 70 and the heat transfer member 71 is preferably a material that does not impede the magnetic field from the coil 35 to the atomic cell 31 and has high thermal conductivity, such as a metal such as aluminum.

By adopting such a configuration, the temperature distribution of the atomic cell 31 can be stabilized while a portion of the atomic cell 31 is cooled. In addition, since the portion to be cooled is the light receiving element 32 side of the atomic cell 31, i.e., near the surface M2, the intensity of the light LL irradiated to the gaseous alkali metal atoms in the atomic cell 31 is unlikely to fluctuate. Therefore, the deterioration of the frequency accuracy of the atomic oscillator 1 can be suppressed.

3. Third Embodiment Next, an atomic oscillator 1b according to a third embodiment will be described with reference to FIG.
FIG. 6 is a cross-sectional view that illustrates a schematic diagram of an atom cell unit 30b according to the third embodiment.

The atomic oscillator 1b of this embodiment is similar to the atomic oscillator 1 of the first embodiment, except that the atomic cell unit 30b has a different configuration compared to the atomic oscillator 1 of the first embodiment. Note that the following description will focus on the differences from the first embodiment described above, and similar items will be given the same reference numerals and their description will be omitted.

6, the atomic cell unit 30b of the atomic oscillator 1b includes temperature control elements 36 arranged in the order of the first portion 361, the semiconductor layer 362, and the second portion 363 from the light-emitting element 10 side, and temperature control elements 36 arranged in the order of the first portion 361, the semiconductor layer 362, and the second portion 363 from the light-receiving element 32 side, which are disposed between the atomic cell 31 and the coil 35, and a heat transfer member 72 is disposed between the two temperature control elements 36. Since the two second portions 363 are cooled to the second temperature T2 by the Peltier effect, the heat transfer member 72 is cooled to the second temperature T2, and a part of the atomic cell 31 in contact with the heat transfer member 72 can be cooled. Therefore, in the internal space S of the atomic cell 31 in contact with the heat transfer member 72, the gaseous alkali metal atoms are cooled and liquefied to generate liquid alkali metal atoms 60.
In addition, a heat transfer member 70 for retaining the heat of the heater 33 is disposed between the atom cell 31 and the coil 35 and the shield 37 .

By using this configuration, the temperature distribution of the atomic cell 31 can be stabilized while a portion of the atomic cell 31 is cooled.

4. Fourth Embodiment Next, an atomic oscillator 1c according to a fourth embodiment will be described with reference to FIG.
FIG. 7 is a cross-sectional view that illustrates a schematic diagram of an atom cell unit 30c according to the fourth embodiment.

The atomic oscillator 1c of this embodiment is similar to the atomic oscillator 1 of the first embodiment, except that the configuration of the atomic cell unit 30c and the configuration of the temperature control element 36c are different from those of the atomic oscillator 1 of the first embodiment. Note that the following description will focus on the differences from the first embodiment described above, and similar items will be given the same reference numerals and their description will be omitted.

7, in the atomic cell unit 30c of the atomic oscillator 1c, a through hole 33c is provided in the heater 33, and a through hole 37c is also provided in the shield 37 at a position overlapping with the through hole 33c. A temperature control element 36c composed of a first metal 38a and a second metal 38b different from the first metal 38a is disposed in the through holes 33c and 37c.
In the temperature control element 36c, the second portion 392, which is a junction between the first metal 38a and the second metal 38b, is disposed in contact with the atomic cell 31, and the portion of the first metal 38a in contact with the heater 33 and the first portions 391 and 393, which are portions of the second metal 38b in contact with the heater 33, are disposed in contact with the heater 33. The first portions 391 and 393 are electrically connected to the constant current source 42 by the third metals 38c and 38d, which serve as wiring. In this embodiment, a part of the wiring from the first metal 38a and the second metal 38b to the constant current source 42 is not shown. In addition, the first portions 391 and 393 may be covered by the first metal 38a and the second metal 38b, and may not be directly in contact with the heater 33.

Generally, when two different metal wires are connected at both ends and a temperature difference is applied between the two junctions, an electromotive force is generated. Conversely, when a current or voltage is passed through the two junctions, a temperature difference can be generated between the two junctions, resulting in the Peltier effect.
Therefore, the temperature control element 36c can provide a certain temperature difference with the second portion 392 based on the first portions 391, 393 heated to the first temperature T1 by the heater 33 due to the Peltier effect. Therefore, the second portion 392 can be cooled to the second temperature T2 and a part of the atomic cell 31 in contact with the second portion 392 can be cooled by absorbing heat.
Combinations of the first metal 38a and the second metal 38b include chromel and alumel, chromel and constantan, platinum-rhodium alloy and platinum, nichrome and iron-gold alloy, and the like.

According to this configuration, by contacting the second part 392, which is the junction between the first metal 38a and the second metal 38b of the temperature control element 36c, with the atomic cell 31, the second part 392 absorbs heat from the atomic cell 31 due to the Peltier effect, and a part of the atomic cell 31 can be cooled while maintaining a stable temperature distribution of the atomic cell 31.

In addition, by having the first parts 391, 393, which are the part of the first metal 38a that contacts the heater 33 and the part of the second metal 38b that contacts the heater 33, it is possible to utilize the Peltier effect to create a constant temperature difference between the second part 392 and the temperature of the first parts 391, 393 as a reference, and therefore it is possible to cool the part of the atomic cell 31 that contacts the second part 392 while maintaining a stable temperature distribution of the atomic cell 31.

In addition, since the first parts 391 and 393 are connected to the constant current source 42 by the third metals 38c and 38d, the cost of the atomic oscillator 1c can be reduced by using an inexpensive material for the third metals 38c and 38d.

5. Fifth Embodiment Next, an atomic oscillator 1d according to a fifth embodiment will be described with reference to FIG.
FIG. 8 is a cross-sectional view that illustrates a schematic diagram of an atom cell unit 30d according to the fifth embodiment.

The atomic oscillator 1d of this embodiment is similar to the atomic oscillator 1 of the first embodiment, except that the configuration of the atomic cell unit 30d and the configuration of the temperature control element 36d are different from those of the atomic oscillator 1 of the first embodiment. Note that the following description will focus on the differences from the first embodiment described above, and similar items will be given the same reference numerals and their description will be omitted.

As shown in FIG. 8, the atomic cell unit 30d of the atomic oscillator 1d is arranged such that the second part 392 of the temperature control element 36d is in contact with the atomic cell 31, and the first parts 391 and 393 of the temperature control element 36d are in contact with the shield 37.

According to this configuration, the first portion 391 of the first metal 38a is in contact with the shield 37 that is heated to the first temperature T1 by the heater 33, so that the Peltier effect can be used to set the temperature of the first portion 391 in contact with the shield 37 as the reference temperature, and a certain temperature difference can be created between the first portion 391 and the second portion 392. Therefore, the portion of the atomic cell 31 in contact with the second portion 392 can be cooled while maintaining a stable temperature distribution in the atomic cell 31.

6. Sixth Embodiment Next, an atomic oscillator 1e according to a sixth embodiment will be described with reference to FIG.
FIG. 9 is a cross-sectional view that illustrates a schematic diagram of an atom cell unit 30e according to the sixth embodiment.

The atomic oscillator 1e of this embodiment is similar to the atomic oscillator 1 of the first embodiment, except that the configuration of the atomic cell unit 30e and the configuration of the temperature control element 36e are different from those of the atomic oscillator 1 of the first embodiment. Note that the following description will focus on the differences from the first embodiment described above, and similar items will be given the same reference numerals and their description will be omitted.

As shown in FIG. 9, in the atomic cell unit 30e of the atomic oscillator 1e, the second part 392 of the temperature control element 36e is arranged in contact with the atomic cell 31, and the first parts 391 and 393 of the temperature control element 36e are arranged in contact with the shield 37. The third metals 38c and 38d, which are the wiring from the first metal 38a and the second metal 38b to the constant current source 42, are twisted together and arranged between the coil 35 and the shield 37.

This configuration provides the same effects as the fifth embodiment. In addition, because the third metals 38c and 38d that form the wiring are twisted together, it is possible to suppress the generation of a current magnetic field due to the wiring, and stable oscillation characteristics can be obtained.

7. Seventh Embodiment Next, an atomic oscillator 1f according to a seventh embodiment will be described with reference to FIG.
FIG. 10 is a cross-sectional view that illustrates a schematic view of an atom cell unit 30f according to the seventh embodiment.

The atomic oscillator 1f of this embodiment is similar to the atomic oscillator 1 of the first embodiment, except that the configuration of the atomic cell unit 30f and the configuration of the temperature control element 36f are different from those of the atomic oscillator 1 of the first embodiment. Note that the following description will focus on the differences from the first embodiment described above, and similar items will be given the same reference numerals and their description will be omitted.

As shown in FIG. 10, the atomic cell unit 30f of the atomic oscillator 1f is provided with a temperature control element 36f composed of a cylindrical first metal 70a covering the atomic cell 31 and a cylindrical second metal 70b covering the atomic cell 31 and the light receiving element 32. The first metal 70a and the second metal 70b are joined at the center of the atomic cell 31 in the longitudinal direction, and this joint is in contact with the atomic cell 31 as the second part 392. The end of the first metal 70a opposite to the second part 392 is the first part 391, and the end of the second metal 70b opposite to the second part 392 is the first part 393, which are in contact with the shield 37 heated by the heater 33, respectively, so that a certain temperature difference can be created between the first part 391 and the second part 392 by utilizing the Peltier effect and the temperature of the first part 391 and 393 in contact with the shield 37 as a reference.

With this configuration, the atomic cell 31 is covered with the first metal 70a and the second metal 70b, which have a shape with a larger heat capacity than wire material or the like, so that the portion of the atomic cell 31 that contacts the second portion 392 can be cooled while maintaining a stable temperature distribution of the atomic cell 31.

8. Eighth Embodiment Next, an atomic oscillator 1g according to an eighth embodiment will be described with reference to FIG.
FIG. 11 is a cross-sectional view that illustrates a schematic diagram of an atomic cell unit 30g according to the eighth embodiment.

The atomic oscillator 1g of this embodiment is similar to the atomic oscillator 1 of the first embodiment, except that the atomic cell unit 30g and the temperature control element 36g are different in configuration compared to the atomic oscillator 1 of the first embodiment. Note that the following description will focus on the differences from the first embodiment described above, and similar items will be given the same reference numerals and their description will be omitted.

As shown in FIG. 11, the atomic cell unit 30g of the atomic oscillator 1g has a temperature control element 36g, which is composed of a coil, arranged between the atomic cell 31 and the heater 33. The temperature control element 36g is composed of a coil made of a first metal 35a, a second metal 35b, and third metals 35c and 35d. The first metal 35a and the second metal 35b are joined at the center of the longitudinal direction of the atomic cell 31, and this joint becomes the second part 392. A heat transfer member 74 is arranged between the second part 392 and the atomic cell 31, which contacts the second part 392 and the atomic cell 31. The third metal 35c is joined to the first part 391 at the end opposite the second part 392 of the first metal 35a, and the third metal 35d is joined to the first part 393 at the end opposite the second part 392 of the second metal 35b. Since the first parts 391 and 393 are heated by the heater 33 to a first temperature T1, the Peltier effect can be used to set the temperature of the first parts 391 and 393 as a reference and create a certain temperature difference with the second part 392. Therefore, the heat transfer member 74 in contact with the second part 392 can be cooled, and the part of the atomic cell 31 in contact with the heat transfer member 74 can be cooled.

With this configuration, the temperature control element 36g forms a coil that generates a magnetic field, so that a magnetic field in a predetermined direction can be applied to the alkali metal atoms in the atomic cell 31, and stable oscillation characteristics can be obtained. In addition, the number of parts can be reduced compared to when the temperature control element 36g and the coil are separate, which allows the atomic oscillator 1g to be made smaller and less expensive.

9. Ninth Embodiment Next, a frequency signal generation system according to a ninth embodiment will be described with reference to Fig. 12. A clock transmission system (timing server) 90 described below is an example of a frequency signal generation system.
FIG. 12 is a schematic configuration diagram showing a frequency signal generating system according to the ninth embodiment.

The clock transmission system 90 includes atomic oscillators 1 to 1g according to this embodiment. Below, as an example, a clock transmission system 90 including atomic oscillator 1 will be described.

The clock transmission system 90 synchronizes the clocks of each device in a time division multiplexing network, and is a system with a redundant configuration of an N (Normal) system and an E (Emergency) system.

As shown in FIG. 12, the clock transmission system 90 includes an N-system clock supply device 901 and an SDH (Synchronous Digital Hierarchy) device 902 that are higher-level devices owned by station A, an E-system clock supply device 903 and an SDH device 904 that are higher-level devices owned by station B, and a lower-level clock supply device 905 and SDH devices 906 and 907 that are lower-level devices owned by station C. The clock supply device 901 has an atomic oscillator 1 and generates an N-system clock signal. The atomic oscillator 1 in the clock supply device 901 generates a clock signal in synchronization with a more accurate clock signal from master clocks 908 and 909 that include atomic oscillators using cesium. The clock supply devices 901 and 903 correspond to processing units that process the frequency signal from the atomic oscillator 1.

The SDH device 902 transmits and receives a main signal based on the clock signal from the clock supply device 901, and also superimposes an N-system clock signal onto the main signal and transmits it to the subordinate clock supply device 905. The clock supply device 903 has an atomic oscillator 1 and generates an E-system clock signal. The atomic oscillator 1 in the clock supply device 903 generates a clock signal in synchronization with a more accurate clock signal from master clocks 908 and 909, which include atomic oscillators using cesium.

The SDH device 904 transmits and receives the main signal based on the clock signal from the clock supply device 903, and also superimposes the E-system clock signal onto the main signal and transmits it to the downstream clock supply device 905. The clock supply device 905 receives the clock signals from the clock supply devices 901 and 903, and generates a clock signal in synchronization with the received clock signal.

The clock supply device 905 normally generates a clock signal in synchronization with the N system clock signal from the clock supply device 901. If an abnormality occurs in the N system, the clock supply device 905 generates a clock signal in synchronization with the E system clock signal from the clock supply device 903. By switching from the N system to the E system in this way, a stable clock supply is ensured and the reliability of the clock path network can be improved. The SDH device 906 transmits and receives the main signal based on the clock signal from the clock supply device 905. Similarly, the SDH device 907 transmits and receives the main signal based on the clock signal from the clock supply device 905. This allows the equipment at station C to be synchronized with the equipment at stations A and B.

The frequency signal generation system according to this embodiment is not limited to the clock transmission system 90. The frequency signal generation system includes various devices and systems that are equipped with an atomic oscillator 1 and use the frequency signal of the atomic oscillator 1, and are composed of multiple devices.

The frequency signal generating system according to this embodiment may be, for example, a smartphone, a tablet terminal, a watch, a mobile phone, a digital still camera, a liquid ejection device (e.g., an inkjet printer), a personal computer, a television, a video camera, a video tape recorder, a car navigation device, a pager, an electronic organizer, an electronic dictionary, a calculator, an electronic game device, a word processor, a workstation, a videophone, a security television monitor, an electronic binoculars, a POS (point of sales) terminal, a medical device (e.g., an electronic thermometer, a blood pressure monitor, a blood glucose meter, an electrocardiogram measuring device, an ultrasonic diagnostic device, an electronic endoscope, a magnetocardiograph), a fish finder, a GNSS (Global Navigation Satellite System) frequency standard, various measuring instruments, instruments (e.g., instruments in automobiles, aircraft, ships), a flight simulator, a terrestrial digital broadcasting system, a mobile phone base station, a moving object (automobiles, aircraft, ships, etc.).

The following is a summary of what can be derived from the embodiment:

The atomic oscillator includes a light-emitting element, an atomic cell that contains alkali metal atoms and receives the light emitted from the light-emitting element, a heater that covers the atomic cell and heats the atomic cell to a first temperature, a first portion that is heated to the first temperature by the heater, and a second portion that is in contact with the atomic cell and is controlled to a second temperature lower than the first temperature by the Peltier effect, and includes a temperature control element disposed between the heater and the atomic cell, and a light-receiving element that detects the light that has passed through the atomic cell.

With this configuration, the atomic cell is placed inside the heater, where the temperature is stabilized, so the temperature of the atomic cell is less susceptible to the effects of the outside air temperature. In addition, by using the Peltier effect for cooling to create a constant temperature difference between the first and second parts based on the heater temperature, the heater temperature is less likely to fluctuate even if part of the atomic cell is cooled inside the heater, so the temperature distribution of the atomic cell can be stabilized. As a result, a highly accurate atomic oscillator can be obtained.

In the above atomic oscillator, it is preferable to include a constant current source connected to the temperature control element.

With this configuration, since the temperature control element is connected to a constant current source, the second part of the temperature control element that contacts the atomic cell can be stably controlled to the second temperature by utilizing the Peltier effect.

In the above atomic oscillator, it is preferable that the temperature of the surface of the atomic cell where the light enters and the temperature of the surface of the atomic cell where the light exits are higher than the second temperature.

With this configuration, the temperature of the surface of the atomic cell where the light enters and the temperature of the surface of the atomic cell where the light exits are higher than the second temperature, so the gaseous alkali metal atoms do not liquefy and adhere to the two surfaces, and stable oscillation characteristics can be obtained without blocking the light.

In the above atomic oscillator, the temperature control element is a Peltier element including a first temperature control surface, a second temperature control surface, and a semiconductor layer connecting the first temperature control surface and the second temperature control surface, and the first part is the first temperature control surface of the Peltier element, and the second part is the second temperature control surface of the Peltier element, and it is preferable that the first part, the semiconductor layer, and the second part are arranged in this order from the heater toward the atomic cell.

According to this configuration, the temperature control element is arranged from the heater toward the atomic cell in the order of the first portion, the semiconductor layer, and the second portion, so that a temperature difference can be generated between the first temperature control surface, which is at the first temperature, and the second temperature control surface by the Peltier effect, and heat can be absorbed by the second temperature control surface that is in contact with the atomic cell. Therefore, a part of the atomic cell can be cooled while maintaining a stable temperature distribution in the atomic cell.

In the above atomic oscillator, it is preferable that the temperature control element includes a first metal and a second metal different from the first metal, and the second portion is a junction between the first metal and the second metal.

According to this configuration, by contacting the second part, which is the junction between the first metal and the second metal of the temperature control element, with the atomic cell, the second part absorbs heat from the atomic cell due to the Peltier effect, and a part of the atomic cell can be cooled while maintaining a stable temperature distribution of the atomic cell.

In the above atomic oscillator, it is preferable that the first portion is a portion of the first metal that contacts the heater and a portion of the second metal that contacts the heater.

With this configuration, the Peltier effect can be used in the portion of the first metal that contacts the heater and the first portion, which is the portion of the second metal that contacts the heater, to create a constant temperature difference between the second portion and the temperature of the first portion on the heater side as the reference temperature, so that the portion of the atomic cell that contacts the second portion can be cooled while maintaining a stable temperature distribution in the atomic cell.

In the above atomic oscillator, it is preferable that the oscillator includes a shield that is disposed between the heater and the atomic cell and is heated to the first temperature by the heater, and the first portion is a portion of the first metal that contacts the shield.

With this configuration, the first portion of the first metal is in contact with the shield that is heated to the first temperature by the heater, so that the Peltier effect can be used to set the temperature of the first portion in contact with the shield as the reference temperature and create a constant temperature difference with the second portion. Therefore, the portion of the atomic cell in contact with the second portion can be cooled while maintaining a stable temperature distribution of the atomic cell.

In the above atomic oscillator, it is preferable that the temperature control element is a coil that generates a magnetic field.

With this configuration, by configuring a coil that generates a magnetic field with the temperature control element, a magnetic field in a specified direction can be applied to the alkali metal atoms in the atomic cell, resulting in stable oscillation characteristics. In addition, the number of parts can be reduced compared to when the temperature control element and the coil are separate, making it possible to reduce the size and cost of the atomic oscillator.

In the above atomic oscillator, it is preferable that the first portion of the temperature control element and the constant current source are connected by a third metal.

With this configuration, the first portion and the constant current source are connected by the third metal, so that the cost of the atomic oscillator can be reduced by using an inexpensive material for the third metal.

The frequency signal generating system includes an atomic oscillator and a processing unit that processes a frequency signal from the atomic oscillator. The atomic oscillator includes a light-emitting element, an atomic cell that contains alkali metal atoms and receives light emitted from the light-emitting element, a heater that covers the atomic cell and heats the atomic cell to a first temperature, a first portion that is heated to the first temperature by the heater, and a second portion that is in contact with the atomic cell and is controlled to a second temperature lower than the first temperature by the Peltier effect. The system also includes a temperature control element disposed between the heater and the atomic cell, and a light-receiving element that detects light that has passed through the atomic cell.

This configuration provides a high-performance frequency signal generation system because it is equipped with a high-precision atomic oscillator.

1, 1a, 1b, 1c, 1d, 1e, 1f, 1g... atomic oscillator, 10... light emitting element, 11... light source substrate, 20... optical system unit, 21... neutral density filter, 22... lens, 23... quarter wave plate, 24... holder, 30... atomic cell unit, 31... atomic cell, 32... light receiving element, 33... heater, 34... temperature sensor, 35... coil, 36... temperature control element, 37... shield, 40... control unit, 41... temperature control circuit, 42... constant current source, 43... magnetic field control control circuit, 44...light source control circuit, 45...circuit board, 50...outer container, 51...outer base, 52...outer lid, 53...insulating material, 54...lead pin, 60...liquid alkali metal atoms, 90...clock transmission system as frequency signal generation system, 361...first part, 362...semiconductor layer, 363...second part, LA...optical axis, LL...light, M1...surface, M2...surface, P1...first temperature control surface, P2...second temperature control surface, S...internal space, T1...first temperature, T2...second temperature.

Claims (10)

A light-emitting element;
an atomic cell that contains alkali metal atoms and into which the light emitted from the light-emitting element is incident;
a heater covering the atomic cell and heating the atomic cell to a first temperature;
a temperature control element including a first portion heated to the first temperature by the heater and a second portion in contact with the atomic cell and controlled to a second temperature lower than the first temperature by a Peltier effect, the temperature control element being disposed between the heater and the atomic cell;
a light receiving element that detects light transmitted through the atomic cell ,
At least a portion of the alkali metal atoms are present in the atomic cell in a liquid state . The atomic oscillator of claim 1, including a constant current source connected to the temperature control element. The atomic oscillator according to claim 1 or 2, wherein the temperature of the surface of the atomic cell on which the light enters and the temperature of the surface of the atomic cell from which the light exits are higher than the second temperature. the temperature control element is a Peltier element including a first temperature control surface, a second temperature control surface, and a semiconductor layer connecting the first temperature control surface and the second temperature control surface,
the first portion being the first temperature control surface of the Peltier element;
the second portion being the second temperature control surface of the Peltier element;
4. The atomic oscillator according to claim 1, wherein the first portion, the semiconductor layer, and the second portion are arranged in this order from the heater toward the atomic cell. the temperature control element includes a first metal and a second metal different from the first metal;
The atomic oscillator according to claim 2 , wherein the second portion is a junction between the first metal and the second metal. The atomic oscillator of claim 5, wherein the first portion is a portion of the first metal that contacts the heater and a portion of the second metal that contacts the heater. a shield disposed between the heater and the atomic cell and heated to the first temperature by the heater;
6. The atomic oscillator according to claim 5, wherein the first portion is a portion of the first metal that contacts the shield. The atomic oscillator of claim 5, wherein the temperature control element is a coil that generates a magnetic field. The atomic oscillator according to any one of claims 5 to 8, wherein the first portion of the temperature control element and the constant current source are connected by a third metal. An atomic oscillator;
A processing unit that processes a frequency signal from the atomic oscillator,
The atomic oscillator comprises:
A light-emitting element;
an atomic cell that contains alkali metal atoms and into which light emitted from the light-emitting element is incident;
a heater covering the atomic cell and heating the atomic cell to a first temperature;
a temperature control element including a first portion heated to the first temperature by the heater and a second portion in contact with the atomic cell and controlled to a second temperature lower than the first temperature by a Peltier effect, the temperature control element being disposed between the heater and the atomic cell;
a light receiving element that detects light transmitted through the atomic cell ,
At least a portion of the alkali metal atoms are present in the atomic cell in a liquid state .

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