JP2007324818A - Atomic oscillator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an atomic oscillator stabilizing the temperature of a gas cell by a simple constitution and being capable of easily collecting a rubidium metal at one place. <P>SOLUTION: The atomic oscillator 100 includes a cavity resonator 3 resonating in the vicinity of the resonance frequency of rubidium atoms, the gas cell 4 sealing rubidium atoms, a hollow cylindrical high dielectric substance 8 having a high thermal conductivity, a rubidium light source 1, and an antenna 6 exciting microwaves in the cavity resonator 3. The atomic oscillator further includes a photodetector 7 detecting the quantity of a light from the rubidium light source 1 transmitted through the gas cell 4, a temperature control circuit 10 keeping the cavity resonator 3 at a fixed temperature by heating by a heater 9, and a movable plate 2 for adjusting a frequency notching a thread groove so as to be able to adjust the length of the cavity resonator 3 for adjusting the resonance frequency of the cavity resonator 3. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

The present invention relates to an atomic oscillator, and more particularly to a configuration of an atomic oscillator in which the influence of thermal fluctuation outside the cavity resonator on the gas cell inside the cavity resonator is eliminated.

In recent years, digital networks such as communication networks and broadcast networks have progressed, and as a result, highly accurate and highly stable oscillators are indispensable as clock sources used to generate clock signals for transmission equipment and reference frequencies for broadcast stations. It has become a thing. As an oscillator that satisfies such a demand, a rubidium atomic oscillator having high oscillation frequency accuracy and stability is often used. In recent years, the demand for miniaturization of atomic oscillators has increased, and there is an urgent need to miniaturize the whole including the optical microwave unit (OMU unit). Along with this miniaturization, the cavity resonators are also forced to be miniaturized.

FIG. 8 shows a configuration example of a conventional rubidium atomic oscillator. As shown in the figure, the rubidium atomic oscillator is provided in a pumping light source 31, a cavity resonator 33 having a light passage hole to which the pumping light source 31 is incident, and inside the cavity resonator 33, and encloses a gas of rubidium atoms. Gas pump 38, antenna 36 for exciting microwaves inside cavity resonator 33, photodetector 37 for detecting the amount of light from pumping light source 31 that has passed through gas cell 38, and excitation for the excitation according to the output of photodetector 37. The frequency control circuit 41 that controls the frequency of the microwave, the temperature control circuit 40 that heats the cavity resonator 33 to keep it at a constant temperature, and the length of the cavity resonator 33 to adjust the resonance frequency of the cavity resonator 33 A frequency adjusting movable plate 32 in which a screw groove is engraved so as to adjust the height is provided.

When the cavity resonator 33 is excited at the resonance frequency of the rubidium atom (6.834682 ... MHz), the rubidium atom in the gas cell 38 absorbs the light incident from the pumping light source 31 in the largest amount. This phenomenon is observed by a decrease in the output of the photodetector 37, and the frequency control circuit 41 is a microwave that excites the cavity resonator 33 (a microwave radiated from the antenna 36).
Is controlled to a frequency at which the output value of the photodetector 37 is the lowest. By doing so, the frequency control circuit 41 causes the resonance frequency of the rubidium atom (6.834682... MHz
The oscillator output signal with high accuracy synchronized with () can be taken out, and this output signal can be used as a highly accurate and highly stable clock source or a reference frequency signal source.

Further, downsizing of the rubidium atomic oscillator often depends on downsizing of the cavity resonator 33 in which microwaves having a rubidium atomic resonance frequency are constant, and the resonance mode is set to TE111 using the cavity resonator 33 as a cylindrical resonator. In this basic mode, the size of the gas cell 38 built in the cavity resonator 33 is optimized by optimizing the glass thickness and shape.
Actually, as a technique for miniaturization, in Patent Document 1, as shown in FIG. 9, a high dielectric material 58 having high thermal conductivity is disposed in close contact with the inner wall surface of the cavity 53, and this high dielectric By shortening the wavelength of the microwave radiated from the antenna 56 by the substance 58, the cavity resonator 53 is obtained.
The total length (the total length: the length between the frequency adjusting movable plate 52 and the photodetector 57) is shortened, the high dielectric material 58 is made of a material having high thermal conductivity, and the cavity resonator 53 is manufactured. A technique that enables the rubidium cell to be heated quickly by the heater 59 installed outside the cavity resonator 53 by being disposed in close contact with the cavity resonator 53, thereby shortening the time for the gas cell 54 to reach an appropriate operating temperature condition. Is disclosed.
JP 2001-308416 A

However, in the technique disclosed in Patent Document 1, the high dielectric material 58 is replaced with the cavity resonator 53.
Since the thermal coupling between the cavity resonator 58 and the gas cell 54 becomes high due to the close contact, the temperature change outside the cavity resonator is easily transmitted to the gas cell 54. Therefore, there is a problem that the temperature of the gas cell 54 is likely to fluctuate and the output frequency as an atomic oscillator fluctuates in a short period.

The main cause of the change in the temperature outside the cavity resonator is a change in the external temperature of the atomic oscillator main body. For example, when the ambient temperature of the atomic oscillator body changes suddenly in a short time, the change in the outside air temperature is transmitted to the cavity resonator 53 and thus to the gas cell 54, and the temperature of the gas cell 54 is likely to fluctuate. Another cause of the temperature change outside the cavity resonator is that a cooling fan is used in the vicinity of the atomic oscillator when another device or circuit that operates the atomic oscillator as a reference oscillation source is also provided. There is a possibility that air disturbance occurs around the atomic oscillator due to the influence of the air blown from the fan, and non-uniform heat dissipation occurs from the oscillator due to the disturbance (if there is no disturbance, the atomic oscillator itself Heat is released by stable air convection due to heat generation). There is a problem that the temperature of the casing is not stabilized by this non-uniform heat radiation, and the change in temperature is transmitted to the cavity resonator 53 and thus to the gas cell 54, and the temperature of the gas cell 54 fluctuates.
In particular, since the method of Patent Document 1 is aimed at miniaturization, the physical distance between the casing and the gas cell 54 is inevitably shortened, and as a measure for preventing temperature fluctuation of the gas cell 54, there is sufficient space between the casing and the gas cell 54. It is considered difficult to dispose a heat insulating material.

Further, rubidium metal is sealed in the gas cell 54, and by heating the gas cell 54, part of the rubidium metal is gasified to function as a rubidium gas cell. Since rubidium gas is vaporized at the vapor pressure at the current temperature of the rubidium gas cell, not all of the enclosed metal is vaporized. Therefore, the metal that does not evaporate remains in the gas cell. The metal that does not evaporate becomes a loss for the resonance of the microwave in the cavity resonator 53 and lowers the resonance Q. Therefore, it is necessary to collect the metal that does not evaporate at a position where it is difficult to lose the microwave. For this purpose, it is necessary to collect a metal that does not evaporate by intentionally cooling a part of the temperature of the gas cell 54 by a mechanical device. If the structure is such that the heat fluctuation is easily transmitted to the inside, the temperature of the cooling point 61 for collecting the metal becomes unstable.

In view of such a problem, the present invention provides a gap between the cavity resonator and the high dielectric material, and uses the low thermal conductivity of air as the coupling between the cavity resonator and the high dielectric material as a rough coupling. An object of the present invention is to provide an atomic oscillator that can stabilize the temperature of a gas cell with a simple configuration and can easily collect rubidium metal in one place by blocking the influence of temperature fluctuation outside the cavity resonator. .

In order to solve such a problem, the present invention is an atomic oscillator that controls an oscillation frequency by using a light absorption characteristic according to a microwave frequency of incident light from a rubidium light source, and resonates near the resonance frequency of the rubidium atom. A cavity resonator, a gas cell encapsulating the rubidium atoms, and a high thermal conductivity disposed inside the cavity resonator on the outer diameter side of the gas cell so that the optical axis of the incident light is parallel to the axis A hollow cylindrical high-dielectric material, and an air gap is provided between the inner surface of the cavity resonator and the outer surface of the high-dielectric material.
When the cavity resonator and the hollow cylindrical high dielectric material having high thermal conductivity are disposed in close contact with each other,
When the ambient temperature of the atomic oscillator body changes suddenly in a short period, the change in the outside air temperature is transmitted to the cavity resonator and thus to the gas cell, and the temperature of the gas cell is likely to fluctuate. Therefore, in the present invention, an air gap is provided between the inner surface of the cavity resonator and the outer surface of the high dielectric material to block the influence of external temperature changes. Thereby, the fluctuation | variation of the temperature of a gas cell can be reduced and rubidium metal can be easily collected in one place.

The air gap is formed by circulating at least two narrow spacers around the surface of the high dielectric material.
If the air gap is made too wide, the heat of the cavity resonator becomes difficult to transfer to the high dielectric material. Therefore, in the present invention, a tape-shaped spacer having a certain thickness is circulated around the surface of the high dielectric material, thereby forming a gap corresponding to the thickness of the spacer. As a result, the air is sealed, so that the temperature of the air once heated is not easily changed.

In addition, the gap is configured by disposing at least two piece-like spacers on the surface of the high dielectric material.
In this configuration, voids are formed on almost the surface of the high dielectric material, and many voids can be secured with a small number of spacers.

Further, the gap is formed by providing at least two narrow spacers along the axial direction of the surface of the high dielectric material.
In this configuration, since air gaps are formed between the spacers and the air gaps are not sealed by the spacers, air convection is performed smoothly. Further, since the narrow spacer is provided along the axial direction of the surface of the high dielectric material, the high dielectric material can be easily inserted into the cavity resonator.

The gap may be formed by partially circulating at least two narrow spacers around the surface of the high dielectric material.
When the spacer is rotated around the outer periphery of the surface of the high dielectric material without any gap, the gap is sealed. In the present invention, it is configured not to form a gap as a closed space by circling without a gap, but to form a non-continuous configuration by partially cutting each spacer or the like so that the gap is not sealed. It promotes air convection.

Further, the gap is configured by providing at least two narrow spacers on the surface of the high dielectric material so as to cross the axial direction.
The spacers can be dispersed without concentrating the voids on the surface of the high dielectric material without concentrating them on the surface of the high dielectric material without being parallel to the axial direction. The temperature gradient on the surface of the body material can be reduced.

Further, the gap is configured by providing at least one narrow spacer in a spiral shape on the surface of the high dielectric material.
By providing the spacer in a spiral on the surface of the high dielectric material, a gap can be easily formed by one spacer, and the temperature gradient on the surface of the high dielectric material can be reduced.

The spacer may be made of a material having a thermal conductivity lower than that of the high dielectric material.
The spacer needs to prevent the cavity resonator heat from being transferred directly to the high dielectric material. For this purpose, it is necessary to be made of a material having a lower thermal conductivity than that of the high dielectric material.

The spacer may be Teflon (registered trademark) or Kapton.
The spacer is preferably made of a material having low thermal conductivity and heat resistance. In that sense, Teflon (registered trademark) or Kapton is optimal.

Hereinafter, the present invention will be described in detail with reference to embodiments shown in the drawings. However, the components, types, combinations, shapes, relative arrangements, and the like described in this embodiment are merely illustrative examples and not intended to limit the scope of the present invention only unless otherwise specified. .
FIG. 1 is a diagram showing a main configuration of an atomic oscillator according to an embodiment of the present invention. The atomic oscillator 100 includes a cavity resonator 3 that resonates in the vicinity of a resonance frequency of rubidium atoms, a gas cell 4 in which rubidium atoms are sealed, a hollow cylindrical high dielectric material 8 having high thermal conductivity, a rubidium light source 1, and the like. The antenna 6 for exciting the microwave inside the cavity resonator 3, the photodetector 7 for detecting the light quantity of the rubidium light source 1 transmitted through the gas cell 4, and the cavity resonator 3 are heated by the heater 9 at a constant temperature. A temperature control circuit 10 for maintaining the cavity resonator 3 and a frequency adjusting movable plate 2 in which a screw groove is engraved so that the length of the cavity resonator 3 can be adjusted in order to adjust the resonance frequency of the cavity resonator 3. It is prepared for. In addition, a hollow cylindrical high dielectric material 8 having a high thermal conductivity disposed inside the cavity resonator 3 on the outer diameter side of the gas cell 4 so that the optical axis of the incident light is parallel to the axis, In the present embodiment, at least two strip-shaped spacers 11 circulate around the outer periphery of the high dielectric material 8 in order to provide the air gap 12 between the inner surface 3 a of the cavity resonator 3 and the outer surface 8 a of the high dielectric material 8. Provided.

That is, the high dielectric material 8 is made smaller than the inner dimension of the cavity resonator 3, and the heat-resistant tape 11, for example, thinly cut with a width of about 1 mm is wound around the both ends of the high dielectric material 8 one or more times.
By doing in this way, the thickness of the tape between the high dielectric material 8 and the cavity resonator 3 (0.1 mm to
A gap 12 of 0.2 mm) can be provided (details will be described later). Air is contained in the gap, and the high dielectric material 8 and the cavity resonator 3 can be thermally coarsely coupled by utilizing the low thermal conductivity of the air. However, it is difficult for heat fluctuation outside the cavity resonator 3 to be transmitted. In addition, it is more effective to use a tape substrate having a relatively low thermal conductivity such as Teflon (registered trademark) or Kapton. Thereby, since the temperature of the gas cell 4 is stabilized, it becomes easy to collect the rubidium metal which is not vaporized in the rubidium reservoir part 13.

FIG. 2 is a schematic view of a high dielectric material according to the first embodiment of the present invention. The same components will be described with the same reference numerals as in FIG. The same shall apply hereinafter. (A) is a perspective view of a high dielectric material, and (b) is a view of the high dielectric material as viewed from the A side. In this embodiment, at least two belt-like spacers 11 a and 11 b are formed around the surface of the high dielectric material 8. Therefore, the spacers 11a, 1b are in the range B surrounded by the spacers 11a, 11b.
A gap having a thickness of 1b is formed. In this configuration, since the air gap is surrounded by the spacers 11a and 11b and the air is sealed, the temperature of the air once heated is not easily changed. For this reason, once a predetermined temperature is reached, for example, even when air disturbance occurs in the surroundings, the temperature can be kept stable without being immediately affected. In this embodiment,
Although there are two spacers, it may be more than this. However, in order to secure a large area of the gap, it is preferable that the spacer is a minimum.

FIG. 3 is a schematic view of a high dielectric material according to the second embodiment of the present invention. (A) is a perspective view of a high dielectric material, and (b) is a view of the high dielectric material as viewed from the A side. In this embodiment, at least two narrow spacers 21 a, 21 b, and 21 c are provided along the axial direction of the high dielectric material 8. In this configuration, since air gaps are formed between the spacers and the air gaps are not completely sealed by the spacers, air convection is smoothly performed. However, since the spacer portion provided along the axial direction of the high dielectric material 8 is difficult to transmit heat at all times, a constant temperature gradient is likely to be generated in the axial direction. Further, since the narrow spacers 21 a, 21 b, and 21 c are provided along the axial direction of the surface of the high dielectric material 8, the high dielectric material 8 can be easily inserted into the cavity resonator 3. In this embodiment, the number of spacers is three, but it may be more. However, in order to secure a large area of the gap, it is preferable that the spacer is a minimum.

FIG. 4 is a schematic view of a high dielectric material according to the third embodiment of the present invention. (A) is a perspective view of a high dielectric material, and (b) is a view of the high dielectric material as viewed from the A side. In this embodiment, at least two piece-like spacers 22A to 22C and 22a to 22c are combined with the high dielectric material 8.
It is comprised by arrange | positioning on the surface of. In this configuration, voids are formed on almost the surface of the high dielectric material, and the widest voids can be secured. Further, since the area where the spacer is disposed is small and dispersed, a temperature gradient hardly occurs on the surface of the high dielectric material. In this embodiment, the spacers are arranged symmetrically, but the present invention is not limited to this and may be arranged at random positions. However, in order to secure a large area of the gap, it is preferable that the spacer is a minimum.

FIG. 5 is a schematic view of a high dielectric material according to the fourth embodiment of the present invention. (A) is a perspective view of a high dielectric material, and (b) is a view of the high dielectric material as viewed from the A side. In this embodiment, at least two narrow spacers 23 a, 23 b, 23 A, and 23 B are configured to partially circulate around the surface of the high dielectric material 8. When the spacers circulate around the outer periphery of the surface of the high dielectric material 8 without gaps, the gaps are sealed, and there are some advantages when sealed,
In this embodiment, air convection is promoted by opening a part of the spacer so as not to seal the air gap, instead of circulating around without a gap. In this embodiment,
Although four spacers are provided, it may be more than this. However, in order to secure a large area of the gap, it is preferable that the spacer is a minimum.

FIG. 6 is a schematic view of a high dielectric material according to the fifth embodiment of the present invention. (A) is a perspective view of a high dielectric material, and (b) is a view of the high dielectric material as viewed from the A side. In this embodiment, at least two narrow spacers 24a, 24b, and 24c are provided on the surface of the high dielectric material 8 so as to cross the axial direction. The spacers 24a, 24b, and 24c are configured not to be parallel to the axial direction on the surface of the high dielectric material 8 but to be crossed obliquely, so that the voids on the surface of the high dielectric material 8 are not concentrated in one place. And the temperature gradient of the surface of the high dielectric material 8 can be reduced. In this embodiment,
Although the number of spacers is three, it may be more than this. However, in order to secure a large area of the gap, it is preferable that the spacer is a minimum.

FIG. 7 is a schematic view of a high dielectric material according to the sixth embodiment of the present invention. (A) is a perspective view of a high dielectric material, and (b) is a view of the high dielectric material as viewed from the A side. In this embodiment, at least one narrow spacer 25 is provided on the surface of the high dielectric material 8 in a spiral shape. By providing the spacer 25 spirally on the surface of the high dielectric material 8,
The space can be easily formed by the spacers 25, and the temperature gradient of the surface of the high dielectric material 8 can be reduced. Moreover, many voids can be secured by blocking the density of the spiral.

It is a figure which shows the principal part structure of the atomic oscillator which concerns on one Embodiment of this invention. It is a schematic diagram of the high dielectric material which concerns on the 1st Embodiment of this invention. It is a schematic diagram of the high dielectric material which concerns on the 2nd Embodiment of this invention. It is a schematic diagram of the high dielectric material which concerns on the 3rd Embodiment of this invention. It is a schematic diagram of the high dielectric material which concerns on the 4th Embodiment of this invention. It is a schematic diagram of the high dielectric material which concerns on the 5th Embodiment of this invention. It is a schematic diagram of the high dielectric material which concerns on the 6th Embodiment of this invention. It is a figure which shows the structural example of the conventional rubidium atomic oscillator. It is a figure which shows the structural example at the time of using the high dielectric material of the conventional rubidium atomic oscillator.

Explanation of symbols

1 rubidium light source, 2 movable plate for frequency adjustment, 3 cavity resonator, 4 gas cell, 5
Cavity resonator, 6 antenna, 7 photodetector, 8 high dielectric material, 9 heater, 10 temperature control circuit, 11 spacer, 12 air gap, 13 rubidium metal reservoir, 100 atomic oscillator

Claims (9)

An atomic oscillator that controls an oscillation frequency by utilizing a light absorption characteristic according to a microwave frequency of incident light from a rubidium light source,
A cavity resonator that resonates near the resonance frequency of the rubidium atom;
A gas cell enclosing the rubidium atoms;
A hollow cylindrical high-dielectric material having high thermal conductivity disposed inside the cavity resonator and on the outer diameter side of the gas cell so that the optical axis of the incident light is parallel to the axis,
An atomic oscillator characterized in that a gap is provided between an inner surface of the cavity resonator and an outer surface of the high dielectric material. 2. The atomic oscillator according to claim 1, wherein the gap is formed by circulating at least two narrow spacers around the surface of the high dielectric material. 2. The atomic oscillator according to claim 1, wherein the air gap is configured by disposing at least two piece-like spacers on the surface of the high dielectric material. 2. The atomic oscillator according to claim 1, wherein the air gap is configured by providing at least two narrow spacers along an axial direction of the surface of the high dielectric material. 2. The atomic oscillator according to claim 1, wherein the air gap is configured by partially circling at least two narrow spacers around the surface of the high dielectric material. 2. The atomic oscillator according to claim 1, wherein the gap is configured by providing at least two narrow spacers on the surface of the high dielectric material so as to cross the axial direction. 2. The atomic oscillator according to claim 1, wherein the air gap is configured by providing at least one narrow spacer in a spiral shape on the surface of the high dielectric material. The atomic oscillator according to any one of claims 2 to 7, wherein the spacer is made of a material having a thermal conductivity lower than that of the high dielectric material. 3. The spacer is Teflon (registered trademark) or Kapton.
The atomic oscillator as described in any one of thru | or 8.

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