JP7473326B2 - 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.
For example, in Patent Document 1, alkali metal atoms and a buffer gas are enclosed in a gas cell in order to miniaturize the gas cell. The buffer gas is a mixed gas of nitrogen and argon, and the mole fraction of argon gas in the mixed gas is set to 15% or more and 40% or less, thereby disclosing an atomic oscillator that has excellent temperature characteristics when miniaturized.

JP 2015-119443 A

However, in the atomic oscillator described in Patent Document 1, when the gas cell is affected by a temperature change in the external environment, the temperature gradient inside the gas cell changes, and the density distribution of the buffer gas changes. As a result, there is a risk that the frequency of collisions between the alkali metal atoms and the buffer gas molecules will change, causing a change in the oscillation frequency of the atomic oscillator.

The atomic oscillator includes a light-emitting element, a first portion that contains gaseous cesium and has a surface on which light from the light-emitting element is incident along the X-axis, a second portion that contains liquid or solid cesium, and a third portion that connects the first portion and the second portion and has two walls that face each other along the Y-axis perpendicular to the X-axis, and in the third portion, the distance between the two walls decreases at a constant rate from the first portion to the second portion along the Y-axis, and includes an atomic cell that contains a buffer gas that is made of argon and nitrogen and has a mole fraction of argon of 64.1%, a heater that heats the first portion, a light detection element that is arranged on the opposite side of the atomic cell from the light-emitting element, and a temperature detection element that is arranged closer to the heater and the surface than the light detection element and is used to control the temperature of the heater.

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, a first portion that contains gaseous cesium and has a surface on which light from the light emitting element is incident along the X-axis, a second portion that contains liquid or solid cesium, and a third portion that connects the first portion and the second portion and has two wall portions that face each other along the Y-axis perpendicular to the X-axis. In the third portion, the distance between the two wall portions decreases at a constant rate from the first portion to the second portion along the Y-axis. The third portion includes an atomic cell that contains a buffer gas that is made of argon and nitrogen and has a mole fraction of argon of 64.1%, a heater that heats the first portion, a light detection element that is arranged on the opposite side of the atomic cell from the light emitting element, and a temperature detection element that is arranged closer to the heater and the surface than the light detection element and is used to control the temperature of the heater.

FIG. 1 is a schematic diagram showing an atomic oscillator according to an embodiment. FIG. 2 is a cross-sectional view taken along the XZ plane, which illustrates a schematic view of the atomic oscillator. FIG. 2 is a cross-sectional view taken along the XY plane, which illustrates a schematic diagram of an atomic oscillator. FIG. 2 is a cross-sectional view along the XY plane that illustrates a schematic view of an atomic cell of the atomic oscillator. 5 is a cross-sectional view taken along line AA in FIG. 4 . 4 is a graph showing the relationship between the mole fraction of argon in a buffer gas made of argon and nitrogen and the rate of frequency change. FIG. 4 is a plan view illustrating a mounting state of a light detection element. FIG. 1 is a schematic configuration diagram showing a frequency signal generating system according to an embodiment.

1. Atomic Oscillator First, an atomic oscillator 10 according to this embodiment will be described with reference to FIG.

The atomic oscillator 10 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. This phenomenon caused by the quantum interference effect is also called the electromagnetically induced transparency (EIT) phenomenon. The atomic oscillator 10 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 10 includes a light source unit 100, an optical system unit 200, an atomic cell unit 300, and a control unit 500 that controls the light source unit 100 and the atomic cell unit 300.

The light source unit 100 has a Peltier element 110, a light-emitting element 120, and a temperature sensor 130.

The light-emitting element 120 emits linearly polarized light LL, which contains two types of light with different frequencies, in a direction along the optical axis LA. The light-emitting element 120 is a Vertical Cavity Surface Emitting Laser (VCSEL) or the like. The temperature sensor 130 detects the temperature of the light-emitting element 120. The temperature sensor 130 is, for example, a thermistor, a thermocouple, or the like. The Peltier element 110 controls the temperature of the light-emitting element 120 to, for example, a temperature between 25°C and 35°C.

The optical system unit 200 is disposed between the light source unit 100 and the atomic cell unit 300. The optical system unit 200 has a neutral density filter 210, a lens 220, and a quarter-wave plate 230.

The neutral density filter 210 reduces the intensity of the light LL emitted from the light emitting element 120. The lens 220 adjusts the radiation angle of the light LL. Specifically, the lens 220 converts the light LL into parallel light. The quarter-wave plate 230 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 300 has an atomic cell 310, a light detection element 320, a heater unit 380, a temperature detection element 322, and a coil 324.

The atomic cell 310 transmits the light LL emitted from the light-emitting element 120. The atomic cell 310 contains cesium, an alkali metal atom, and a buffer gas made of argon and nitrogen. Cesium has a three-level energy level system consisting of two different ground levels and an excited level. The light LL emitted from the light-emitting element 120 enters the atomic cell 310 through the neutral density filter 210, the lens 220, and the quarter-wave plate 230. In addition, the atomic oscillator 10 uses a buffer gas made of argon and nitrogen to suppress interactions between alkali metal atoms and changes in the state of alkali metal atoms caused by collisions of alkali metal atoms with the inner wall of the atomic cell 310, thereby improving the frequency characteristics.

The light detection element 320 receives and detects the light LL that has passed through the atomic cell 310. The light detection element 320 is, for example, a photodiode.

The heater unit 380 controls the temperature of the atomic cell 310 to, for example, 60° C. or higher and 75° C. or lower. The heater unit 380 heats the alkali metal atoms contained in the atomic cell 310, causing at least a portion of the alkali metal atoms to enter a gaseous state.

The temperature detection element 322 detects the temperature of the atomic cell 310. The temperature detection element 322 is, for example, a thermistor, a thermocouple, or the like.
The coil 324 applies a magnetic field in a predetermined direction to the alkali metal atoms contained in the atomic cell 310, causing Zeeman splitting of the energy levels of the alkali metal atoms.

When an alkali metal atom is Zeeman split and a circularly polarized resonant light pair is irradiated onto the alkali metal atom, the number of alkali metal atoms at the desired energy level among the multiple levels into which the alkali metal atom is Zeeman split 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 10 can be improved.

The control unit 500 has a temperature control circuit 510, a light source control circuit 520, a magnetic field control circuit 530, and a temperature control circuit 540.

The temperature control circuit 510 controls the supply of electricity to the heater unit 380 based on the detection result of the temperature detection element 322 so that the inside of the atomic cell 310 reaches the desired temperature. The magnetic field control circuit 530 controls the supply of electricity to the coil 324 so that the magnetic field generated by the coil 324 is constant. The temperature control circuit 540 controls the supply of electricity to the Peltier element 110 based on the detection result of the temperature sensor 130 so that the temperature of the light-emitting element 120 reaches the desired temperature.

Based on the detection result of the light detection element 320, the light source control circuit 520 controls the frequency of the two types of light contained in the light LL emitted from the light emitting element 120 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 310, the EIT phenomenon occurs. The light source control circuit 520 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 output signal of the atomic oscillator 10, i.e., the clock signal Clk.

Next, the specific configuration of the atomic oscillator 10 will be described with reference to Figures 2 to 7. Note that in Figures 2 to 5 and 7, the X-axis, Y-axis, and Z-axis are illustrated as three mutually perpendicular axes. The X-axis is an axis along a line segment connecting the light-emitting element 120 and the light detection element 320, and the light LL emitted from the light-emitting element 120 travels along the X-axis, which is the optical axis LA. The Y-axis is an axis along which the first part 312 and the second part 314 of the atomic cell 310, which will be described later, are aligned.

As shown in Figures 2 and 3, the atomic oscillator 10 includes a light source unit 100, an optical system unit 200, an atomic cell unit 300, a support member 400, a control unit 500, and an outer container 600.

The light source unit 100 is arranged on a support member 400. The light source unit 100 has a Peltier element 110, a light emitting element 120, a temperature sensor 130, a light source container 140 that houses these, and a light source board 150 on which the light source container 140 is arranged. The light source board 150 is fixed to the support member 400, for example, by screws (not shown). The Peltier element 110, the light emitting element 120, and the temperature sensor 130 are electrically connected to the control unit 500.

The optical system unit 200 is disposed on a support member 400. The optical system unit 200 has a neutral density filter 210, a lens 220, a quarter-wave plate 230, and a holder 240 that holds these. The holder 240 is fixed to the support member 400, for example, by a screw (not shown).

The holder 240 has a through hole 250. The through hole 250 is an area through which the light LL passes. In the through hole 250, a neutral density filter 210, a lens 220, and a quarter-wave plate 230 are arranged in this order from the light source unit 100 side.

The atomic cell unit 300 includes an atomic cell 310, a light detection element 320, a first member 330, a second member 332, a first atomic cell container 340, a second atomic cell container 370, a heater unit 380, and a Peltier element 390.

The atomic cell 310 contains cesium and a buffer gas consisting of argon and nitrogen.

Light LL emitted from the light emitting element 120 is incident on the atomic cell 310. The material of the wall of the atomic cell 310 is, for example, glass. The internal space S of the atomic cell 310 includes a first portion 312, a second portion 314, and a third portion 316, as shown in Figures 4 and 5.

The inner surfaces that define the internal space S of the atomic cell 310 are arc-shaped, the inner surface 310A on the -Y axis side and the inner surface 310B on the +Y axis side. In addition, the inner surface 310C on the +Z axis side and the inner surface 310D on the -Z axis side that connect these arcs are linear and inclined with respect to the Y axis. Therefore, the internal space S of the atomic cell 310 can be divided into three areas: the area included in the first portion 312, the area included in the second portion 314, and the area included in the third portion 316.

The first portion 312 is, for example, a portion filled with gaseous alkali metal atoms, through which the light LL passes, and includes the inner surface 310A. The first portion 312 is also a portion that is heated by the heater 381 via the first member 330. The region of the internal space S included in the first portion 312 is the region inside the circle surrounded by the inner surface 310A and a virtual arc F1 of the same curvature from the arc of the inner surface 310A. The first portion 312 includes a part of the surface 311 on which the light LL is incident.

The second portion 314 is a portion that contains liquid or solid alkali metal atoms. The second portion 314 is a portion that dissipates heat, i.e., is cooled, by the second member 332. A portion of the second portion 314 is covered by the second member 332. If a portion is covered by the second member 332, the temperature of that portion will be the lowest in the atomic cell 310, and liquid or solid alkali metal atoms can be collected in that portion. The region of the internal space S included in the second portion 314 is the region inside the circle surrounded by the inner surface 310B and a virtual arc F2 of the same curvature from the arc of the inner surface 310B.

The third portion 316 is located between the first portion 312 and the second portion 314 and connects them. It has inner surfaces 310C and 310D as two walls facing each other along the Y axis, and the distance between the inner surfaces 310C and 310D decreases at a constant rate from the first portion 312 to the second portion 314 along the Y axis. This third portion 316 is a portion through which the excess alkali metal atoms of the first portion 312 pass when moving toward the second portion 314. The third portion 316 is an area surrounded by the virtual arc F1, the virtual arc F2, the inner surface 310C, and the inner surface 310D. The rate of decrease in the distance between the inner surfaces 310C and 310D is preferably 5%/mm or more and 50%/mm or less. This makes it easier for the alkali metal atoms to move to the second portion 314.

Here, the relationship between the mole fraction of argon in the buffer gas contained in the atomic cell 310 and the frequency change rate will be described with reference to FIG.
6, the horizontal axis indicates the mole fraction of argon in the buffer gas, and the vertical axis indicates the frequency change rate (ΔF/F)/°C of the atomic oscillator 10 per 1°C of environmental temperature. An approximate straight line C1 from the actual measurement values is a characteristic when the temperature detection element 322 is arranged near the atomic cell 310 and at a position close to the light detection element 320. An approximate straight line C2 from the actual measurement values is a characteristic when the temperature detection element 322 is arranged near the atomic cell 310 and at a position closer to the heater 381 or the surface 311 on which the light LL of the atomic cell 310 is incident than the light detection element 320, as shown in FIG. That is, the approximate straight line C2 is a characteristic of this embodiment.

When the temperature detection element 322 is positioned close to the light detection element 320, the approximated straight line C1 has a substantially constant frequency change rate of 6.0E-11/°C even when the molar fraction of argon in the buffer gas changes. In contrast, when the temperature detection element 322 of this embodiment is positioned close to the surface 311, the approximated straight line C2 changes from positive to negative as the molar fraction of argon in the buffer gas increases, and becomes zero at an argon molar fraction of 64.1%. Therefore, by setting the argon molar fraction of the buffer gas to 64.1%, the frequency change rate in response to changes in environmental temperature can be minimized.

Note that the above mole fraction of argon allows for some error. It is preferable for the error to be small, but for example, the following ranges are acceptable. If the mole fraction of argon is 64.1% ±1.5%, the frequency change rate will be ±1.0E-11/°C or less; if the mole fraction of argon is 64.1% ±3.0%, the frequency change rate will be ±2.0E-11/°C or less; and if the mole fraction of argon is 64.1% ±4.5%, the frequency change rate will be ±3.0E-11/°C or less.

The pressure of the buffer gas contained together with the alkali metal atoms in the atomic cell 310 is set to 13.3 kPa or more and 18.6 kPa or less. If the buffer gas pressure is less than 13.3 kPa, the line width of the EIT signal tends to increase, and if the buffer gas pressure is more than 18.6 kPa, the intensity of the EIT signal tends to decrease. Therefore, by setting the buffer gas pressure to 13.3 kPa or more and 18.6 kPa or less, stable oscillation characteristics can be realized.
In addition, since the buffer gas contains argon gas, which has temperature characteristics opposite to those of nitrogen gas, the temperature characteristics of the two gases can be offset, thereby achieving excellent temperature characteristics.

The light detection element 320 is disposed on the opposite side of the atomic cell 310 from the light emitting element 120 side. In the illustrated example, the light detection element 320 is disposed in the first atomic cell container 340. As shown in FIG. 7, the light detection element 320 is mounted on a printed circuit board 321 and electrically connected to a wiring 323 provided on the printed circuit board 321. Therefore, at least a part of the heat of the light detection element 320 is dissipated through the wiring 323 and the printed circuit board 321. In addition, the wiring 323 is electrically connected to the light source control circuit 520 through a flexible board on which wiring (not shown) is provided. Therefore, the heat of the light detection element 320 is further dissipated through the flexible board. Therefore, the temperature near the light detection element 320 of the atomic cell 310 is more likely to fluctuate due to heat dissipation through the wiring 323 and the printed circuit board 321 than the temperature of the part far from the light detection element 320.

The first member 330 holds the atom cell 310 in the first atom cell container 340. The first member 330 is disposed between the first portion 312 and the heater 381, and is in contact with, for example, the wall of the atom cell 310 that defines the first portion 312. In the illustrated example, the first member 330 is fixed to the first atom cell container 340 by a screw 331. The first member 330 transfers heat from the heater unit 380 to the alkali metal atoms in the first portion 312. Therefore, the first portion 312 can contain gaseous alkali metal atoms. The material of the first member 330 is, for example, aluminum, titanium, copper, brass, etc.

The first member 330 has through holes 330a and 330b. The light LL emitted from the light emitting element 120 passes through the through hole 330a and enters the atomic cell 310. The light LL that passes through the atomic cell 310 passes through the through hole 330b and enters the photodetector element 320. A member that transmits the light LL may be disposed in the through holes 330a and 330b.

The second member 332 holds the atomic cell 310 in the first atomic cell container 340. The second member 332 is disposed on the second portion 314 side, and is in contact with, for example, the wall of the atomic cell 310 that defines the second portion 314. In the illustrated example, the second member 332 is fixed to the first atomic cell container 340 by a screw 333. The second member 332, for example, transfers heat from the second portion 314 to the Peltier element 390. The second member 332 is provided at a distance from the first member 330. This allows the second portion 314 to be adjusted to a lower temperature than the first portion 312, and allows liquid or solid alkali metal atoms to be contained in the second portion 314. The material of the second member 332 is, for example, the same as that of the first member 330. The first member 330 and the second member 332 may be in direct contact with the atomic cell 310, or may be in contact with the atomic cell 310 via a thermally conductive adhesive or the like.

The first atomic cell container 340 contains the atomic cell 310, the photodetector element 320, the first member 330, and the second member 332. The first atomic cell container 340 is arranged on the support member 400. The first atomic cell container 340 has an approximately rectangular parallelepiped outer shape. The material of the first atomic cell container 340 is, for example, iron, silicon iron, permalloy, supermalloy, sendust, copper, etc. By using such materials, the first atomic cell container 340 can shield from external magnetism. This can prevent the alkali metal atoms in the atomic cell 310 from being affected by external magnetism, and stabilize the oscillation characteristics of the atomic oscillator 10.

The first atom cell container 340 is provided with a through hole 340a. The light LL emitted from the light emitting element 120 passes through the through hole 340a and enters the atom cell 310. The through hole 340a may be provided with a member that transmits the light LL.

The second atomic cell container 370 contains the first atomic cell container 340 and is fixed to the support member 400. The material of the second atomic cell container 370 is, for example, the same as that of the first atomic cell container 340. The second atomic cell container 370 can shield against magnetic fields from the outside.

The second atom cell container 370 is provided with a through hole 370a. The light LL emitted from the light emitting element 120 passes through the through hole 370a and enters the atom cell 310. The through hole 370a may be provided with a member that transmits the light LL.

The heater unit 380 is in contact with the first atom cell container 340 and is fixed to the second atom cell container 370 with screws or the like. The heater unit 380 has a heater 381, a heater container 382, and a heat insulating member 385.

The heater container 382 has a heater lid 383 and a heater base 384, and contains the heater 381 and a heat insulating member 385. The material of the heater container 382 is, for example, the same as that of the first atomic cell container 340. The heater container 382 can shield the magnetic field generated by the heater 381.

The heater 381 is placed on the outer surface of the first atom cell container 340 while being housed in a heater container 382. The heater 381 heats the alkali metal atoms in the first portion 312 of the atom cell 310 to a predetermined temperature. The heater 381 is, for example, a heating resistor. Note that a Peltier element may be used as the heater 381 instead of the heating resistor or in combination with the heating resistor.

The temperature detection element 322 is disposed near the atomic cell 310, and is disposed closer to the heater 381 and the surface 311 on which the light LL of the atomic cell 310 is incident than the light detection element 320. In other words, the distance between the temperature detection element 322 and the surface 311 and the distance between the temperature detection element 322 and the heater 381 are smaller than the distance between the temperature detection element 322 and the light detection element 320. By disposing the temperature detection element 322 at a position away from the light detection element 320 that dissipates heat, it becomes difficult to detect temperature changes due to heat dissipation, so that the temperature of the first part 312 of the atomic cell 310, more precisely, the temperature of the first part 312 of the atomic cell 310 due to heating by the heater 381, can be detected with high accuracy. As a result, the temperature control of the heater 381 is less susceptible to temperature changes due to heat dissipation, so the temperature of the first part 312 can be stably controlled. In addition, by disposing the temperature detection element 322 at a position close to the surface 311, it is easy to stably control the temperature of the surface 311. If the temperature of the surface 311 changes, there is a risk that cesium will adhere to the surface 311, causing a change in the intensity of the light LL incident on the atomic cell 310 and a change in the oscillation frequency of the atomic oscillator 10. By stabilizing the temperature of the surface 311, it is possible to reduce fluctuations in the oscillation frequency of the atomic oscillator 10. Furthermore, although not shown, if the temperature detection element 322 is placed at a position overlapping with the optical axis LA in a plan view along the Z axis or Y axis, the temperature of the most stable part of the atomic cell 310 of the light LL and cesium gas can be further stabilized, thereby further stabilizing the oscillation characteristics of the atomic oscillator 10.

Although the coil 324 is not shown in Figs. 2 and 3, it is, for example, a solenoid coil wound around the outer periphery of the atomic cell 310, or a pair of Helmholtz coils facing each other across the atomic cell 310. The coil 324 generates a magnetic field inside the atomic cell 310 in a direction along the optical axis LA of the light LL. This allows the gap between the different degenerate energy levels of the alkali metal atoms contained in the atomic cell 310 to be widened by Zeeman splitting, improving the resolution and reducing the linewidth of the EIT signal.

Although not shown, a flexible substrate equipped with wiring for supplying power to the heater 381 from the outside may be disposed on the side of the heat insulating member 385 opposite the heater 381. This makes it possible to prevent the heat of the heater 381 from being transmitted to the flexible substrate, and allows the heat of the heater 381 to be transmitted efficiently to the atomic cell 310.

The Peltier element 390 is disposed in the second atom cell container 370 as shown in FIG. 2. In the illustrated example, the Peltier element 390 is disposed on the outer surface on the +Z axis direction side of the second atom cell container 370. The Peltier element 390 is controlled by the temperature control circuit 510, for example, to transfer heat from the second atom cell container 370 to the outer lid portion 620 of the outer container 600.

A heat transfer member 392 is disposed between the Peltier element 390 and the outer lid portion 620 of the outer container 600. The thermal conductivity of the heat transfer member 392 is, for example, higher than the thermal conductivity of the outer lid portion 620. The heat transfer member 392 is, for example, plate-shaped or sheet-shaped. The material of the heat transfer member 392 is, for example, aluminum, titanium, copper, or silicone with high heat dissipation properties. The heat transfer member 392 transfers the heat released from the heat dissipation surface of the Peltier element 390 to the outer lid portion 620.

The support member 400 is fixed in a cantilever manner to the outer base 610 of the outer container 600 as shown in FIG. 2. The support member 400 is fixed, for example, to the base portion 611 of the outer base 610 by two screws as shown in FIG. 3. The support member 400 includes a fixed end 402 and a free end 404. The material of the support member 400 may be, for example, aluminum or copper, or the support member 400 may be, for example, a carbon sheet using carbon fiber.

As shown in Figures 2 and 3, the light source unit 100, the optical system unit 200, and the atomic cell unit 300 are arranged on the support member 400.

The light source unit 100 is disposed on the fixed end 402 side of the support member 400. The light source unit 100 is fixed to the surface on the -X axis direction side of the light source support part 420, for example, by a screw (not shown) so that the light source container 140 is positioned in the through hole 422. In the illustrated example, the light emitting element 120 is disposed on the fixed end 402 side of the support member 400 via the light source container 140 and the light source board 150. The optical system unit 200 is fixed to the surface on the +X axis direction side of the light source support part 420, for example, by a screw (not shown).

The atom cell unit 300 is arranged on the free end 404 side of the support member 400. The atom cell unit 300 is arranged on the free end 404 side so as to overlap with the through hole 412 when viewed from the Z-axis direction. In the illustrated example, the atom cell unit 300 is fixed to the atom cell support part 410 by a screw.

In this way, by fixing the support member 400 to the outer base 610 in a cantilever manner, it is possible to prevent the support member 400 from being deformed due to stress caused by, for example, the difference between the thermal expansion coefficient of the support member 400 and the thermal expansion coefficient of the outer base 610.

The control unit 500 has a circuit board 502, as shown in FIG. 2. The circuit board 502 is fixed to the outer base 610 via a plurality of lead pins 504. An IC (Integrated Circuit) chip (not shown) is arranged on the circuit board 502, and the IC chip functions as a temperature control circuit 510, a light source control circuit 520, a magnetic field control circuit 530, and a temperature control circuit 540. The IC chip is electrically connected to the light source unit 100 and the atomic cell unit 300. The circuit board 502 has a through hole 503 through which the support member 400 is inserted.

The outer container 600 houses the light source unit 100, the optical system unit 200, the atomic cell unit 300, the support member 400, and the control unit 500. The outer container 600 has an outer base 610 and an outer lid 620 that is separate from the outer base 610. The material of the outer container 600 is, for example, the same as that of the first atomic cell container 340. Therefore, the outer container 600 can shield against external magnetic fields, and can prevent the alkali metal atoms in the atomic cell 310 from being affected by external magnetic fields.

In the atomic oscillator 10 of this embodiment, the internal space S of the atomic cell 310 has a first portion 312, a second portion 314, and a third portion 316, and the distance between the two walls connecting the first portion 312 and the second portion 314 of the third portion 316 decreases at a constant rate from the first portion 312 to the second portion 314. Since the volume of the third portion 316 is smaller than the volume of the first portion 312, the amount of alkali metal atoms and buffer gas affected by temperature changes due to cooling is smaller than when the volume of the first portion 312 and the volume of the third portion 316 are the same. Therefore, even if the atomic cell 310 is affected by temperature changes in the external environment, the effect of density changes of the alkali metal atoms and buffer gas of the gas present in the third portion 316 on the density changes of the alkali metal atoms in the first portion 312 can be reduced, so that the change in the oscillation frequency of the atomic oscillator 10 due to temperature changes can be reduced.

In addition, by arranging the temperature detection element 322 used to control the temperature of the heater 381 in a position close to the surface 311 on which the light LL is incident, it can be separated from the light detection element 320 that dissipates heat, so that the temperature of the first portion 312 of the atomic cell 310 can be detected with high accuracy, and the temperature of the first portion 312 can be stably controlled.

In addition, by setting the mole fraction of argon in the buffer gas to 64.1%, the frequency change rate of the atomic oscillator 10 in response to changes in environmental temperature can be minimized in the atomic cell 310 having the above-mentioned internal space S.

2. Frequency Signal Generation System Next, a frequency signal generation system including the atomic oscillator 10 according to this embodiment will be described with reference to Fig. 8. A clock transmission system (timing server) 90 described below is an example of the frequency signal generation system.

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. 8, 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 10 and generates an N-system clock signal. The atomic oscillator 10 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 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 10 and generates an E-system clock signal. The atomic oscillator 10 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 clock supply devices 901 and 903 correspond to processing units that process the frequency signal from the atomic oscillator 10.

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 composed of multiple devices that are equipped with an atomic oscillator 10 and use the frequency signal of the atomic oscillator 10.

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 such as 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, an electronic thermometer, a blood pressure monitor, a blood glucose meter, an electrocardiogram measuring device, an ultrasound diagnostic device, an electronic endoscope, a magnetocardiograph, or other medical equipment, a fish finder, a GNSS (Global Navigation Satellite System) frequency standard, various measuring instruments, instruments such as instruments for automobiles, aircraft, and ships, a flight simulator, a terrestrial digital broadcasting system, a mobile phone base station, an automobile, an aircraft, a ship, or other moving object.

10... atomic oscillator, 90... clock transmission system as a frequency signal generating system, 100... light source unit, 110... Peltier element, 120... light emitting element, 130... temperature sensor, 140... light source container, 150... light source substrate, 200... optical system unit, 210... neutral density filter, 220... lens, 230... quarter wave plate, 240... holder, 250... through hole, 300... atomic cell unit 310...atom cell, 310A, 310B, 310C, 310D...inner surface, 311...surface, 312...first part, 314...second part, 316...third part, 320...light detection element, 321...printed circuit board, 322...temperature detection element, 323...wiring, 324...coil, 330...first member, 330a, 330b...through hole, 331...screw, 332...second member, 333...screw, 340...first atom Cell container, 340a...through hole, 370...second atomic cell container, 370a...through hole, 380...heater unit, 381...heater, 382...heater container, 383...heater lid, 384...heater base, 385...insulating member, 390...peltier element, 392...heat transfer member, 400...support member, 402...fixed end, 404...free end, 410...atom cell support, 412...through hole, 420... Light source support, 422...through hole, 500...control unit, 502...circuit board, 503...through hole, 504...lead pin, 510...temperature control circuit, 520...light source control circuit, 530...magnetic field control circuit, 540...temperature control circuit, 600...outer container, 610...outer base, 611...pedestal, 620...outer lid, C1, C2...approximate straight line, F1, F2...virtual arc, LA...optical axis, LL...light, S...internal space.

Claims (6)

A light-emitting element;
a first portion containing gaseous cesium and having a surface on which light from the light emitting device is incident along an X-axis;
a second portion in which liquid or solid cesium is accommodated; and a third portion connecting the first portion and the second portion and having two walls facing each other along a Y axis perpendicular to the X axis,
In the third portion, the distance between the two walls decreases at a constant rate from the first portion to the second portion along the Y axis;
an atomic cell containing a buffer gas consisting of argon and nitrogen, the mole fraction of the argon being 64.1%;
A heater that heats the first portion;
a light detection element disposed on an opposite side of the atomic cell from the light emitting element;
a temperature detection element that is disposed closer to the heater and the surface than the light detection element is, and is used to control the temperature of the heater. The atomic oscillator of claim 1, having wiring connected to the photodetector element. The atomic oscillator of claim 2, which has a printed circuit board on which the wiring is mounted. a first member disposed between the first portion and the heater;
4. The atomic oscillator according to claim 1, further comprising: a second member disposed on a side of the first member facing the second portion and spaced apart from the first member. The atomic oscillator according to any one of claims 1 to 4, wherein the pressure of the buffer gas is 13.3 kPa or more and 18.6 kPa or less. An atomic oscillator;
A processing unit that processes a frequency signal from the atomic oscillator,
The atomic oscillator comprises:
A light-emitting element;
a first portion containing gaseous cesium and having a surface on which light from the light emitting device is incident along an X-axis;
a second portion in which liquid or solid cesium is contained;
a third portion connecting the first portion and the second portion and having two walls facing each other along a Y axis perpendicular to the X axis;
In the third portion, the distance between the two walls decreases at a constant rate from the first portion to the second portion along the Y axis;
an atomic cell containing a buffer gas consisting of argon and nitrogen, the mole fraction of said argon being 64.1%;
A heater that heats the first portion;
a light detection element disposed on an opposite side of the atomic cell from the light emitting element;
a temperature detection element disposed closer to the heater and the surface than the light detection element and used to control the temperature of the heater.

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