JP2009176852A - Optical system and atomic oscillator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical system of an atomic oscillator, which reduces the number of components, miniaturizes a gas cell, makes temperature distribution of the gas cell to be uniform and improves deterioration of a light absorption characteristic. <P>SOLUTION: The gas cell 3 includes a silicon substrate 11 having an opening part 13 penetrating in a thickness direction for sealing at least a metal atom, and glass (transparent members) 10 and 12 sealing the opening part 13. Heating elements 14, 15 and 16 heating the silicon substrate 11 are arranged on the silicon substrate 11 as shown in Fig.3(b). Although a bipolar transistor 14, a MOS transistor 15 and a resistor 16 are shown as the heating elements in Fig.3(b), the substrate can be constituted only by one type among them or a plurality of types can be mixed. Since it is important that the silicon substrate 11 is uniformly heated, it is desirable that the heating elements are arranged to be uniformly distributed on a part on the silicon substrate 11 without being biased. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an optical system of an atomic oscillator, and more particularly to a heating technique for heating a gas cell constituting the optical system.

An atomic oscillator using an alkali metal such as rubidium or cesium needs to keep atoms in a gas state when utilizing energy transition of atoms. Therefore, the gas cell in which atoms are hermetically sealed is kept operating at a constant temperature. ing. The principle of operation of an atomic oscillator is roughly divided into a double resonance method using light and microwaves, and a method using a quantum interference effect (hereinafter referred to as CPT: Coherent Population Trapping) by two types of laser light. In both cases, the amount of the light incident on the gas cell is detected by the detector provided on the opposite side to detect how much light has been absorbed by the atomic gas, so that the atomic resonance is detected and a reference signal from a crystal oscillator or the like is sent to the control system. Output is obtained in synchronization with atomic resonance.
Patent Document 1 discloses a gas cell structure of an atomic oscillator using CPT. As described above, since it is necessary to keep atoms in a gas state when using energy transition of atoms, the gas cell in which atoms are hermetically sealed is kept operating at a constant temperature. In FIG. 6, in order to maintain the gas cell 200 at a constant temperature, layers 210, 220, and 230 are arranged around the cavity 240, and heated by the heater 215 so as to sandwich the layers 210 and 220, Is kept constant.
US2006 / 0022761A1

However, in the conventional configuration disclosed in Patent Document 1, the heater 215 is required to heat the gas cell, and the entire gas cell becomes large, and a portion near the heater 215 is excessively heated. There is a problem that light absorption loss occurs due to a problem and a heater.
In view of such problems, the present invention arranges a heat generating element on a substrate constituting the gas cell and heats the substrate itself, thereby reducing the number of parts and reducing the size of the gas cell and making the temperature distribution of the gas cell uniform. It is an object of the present invention to provide an optical system for an atomic oscillator that can improve the deterioration of light absorption characteristics.

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

[Application Example 1]
In order to solve such a problem, the present invention is an optical system of an atomic oscillator that controls an oscillation frequency by utilizing a light absorption characteristic due to a quantum interference effect when two types of resonant light as coherent lights having different wavelengths are incident. A coherent light source that emits the resonance light, a gas cell that is disposed on the emission side of the coherent light source, encloses gaseous metal atoms, and passes the resonance light into the metal atom gas, and passes through the gas cell. A light detection means for detecting the light, and the gas cell includes a silicon substrate having an opening penetrating in the thickness direction to enclose the metal atoms, and a transparent member for sealing both ends of the opening. And a heating element for heating the silicon substrate is disposed on the silicon substrate.

  The atomic oscillator of the present invention utilizes the quantum interference effect of coherent light such as laser light. In this method, two ground levels of two resonant lights irradiated simultaneously in a three-level system (for example, a Λ-type level system) in which two ground levels receive resonant light and are resonantly coupled with a common excitation level. When the frequency exactly matches the energy difference between the ground level 1 and the ground level 2, the three-level system becomes a superposition state of the two ground levels, and the excitation to the excitation level 3 stops. CPT uses this principle to detect and use a state in which light absorption in the gas cell stops when the wavelength of one or both of the two resonance lights is changed. In the optical system of the present invention, the resonance light emitted from the coherent light source passes through the gas cell, and the light emitted from the gas cell is detected by the light detection means. Here, a conventional atomic oscillator using an alkali metal such as rubidium or cesium needs to keep atoms in a gas state when utilizing energy transition of atoms, so a gas cell in which atoms are hermetically sealed is kept at a constant temperature. To keep it running. Therefore, in order to keep the gas cell at a constant temperature, a layer is arranged around the cavity, and the temperature of the cavity is kept constant by heating with a heater so as to sandwich the layer. As a result, in order to heat the gas cell, there is a problem that a heater is required and the entire gas cell becomes large, a problem that a portion close to the heater is excessively heated, and a problem that light absorption characteristics are deteriorated. Therefore, in the present invention, by disposing a heat generating element on the silicon substrate constituting the gas cell and heating the silicon substrate itself, the number of components is reduced, the gas cell is downsized, and the temperature distribution of the gas cell is made uniform. Can do.

[Application Example 2]
Further, a temperature detecting element for detecting the temperature of the silicon substrate is further arranged on the silicon substrate.

  In order to maintain the temperature on the silicon substrate at a constant value, the temperature on the silicon substrate must be detected. Therefore, in the present invention, a temperature detecting element is further arranged on the silicon substrate. Thereby, the temperature information can be fed back to control the temperature of the silicon substrate to be constant.

[Application Example 3]
In addition, a temperature control circuit for controlling an operating state of the heat generating element based on temperature information from the temperature detecting element is provided outside the silicon substrate.

  The temperature information from the temperature detecting element changes following the temperature change of the silicon substrate. Therefore, if the relationship between temperature and temperature information is known in advance, the temperature of the silicon substrate can be determined from the temperature information. Therefore, in the present invention, when temperature information with respect to the upper limit temperature is received, the heating element is deactivated and heating is stopped, and when temperature information with respect to the lower limit temperature is received, a temperature control circuit that operates the heating element to start heating, Alternatively, a temperature control circuit for keeping the temperature constant by continuous operation is provided outside the silicon substrate. Thereby, the temperature control circuit is not affected by the substrate temperature, and the control method can be changed flexibly.

[Application Example 4]
Further, the temperature control circuit is arranged on the silicon substrate together with the heating element and the temperature detecting element.

  Since the heat generating element and the temperature detecting element are arranged on the silicon substrate, if a temperature control circuit for controlling them is also arranged on the silicon substrate, only the power source needs to be supplied from the outside. Thereby, the whole optical system can be reduced in size.

[Application Example 5]
In addition, a plurality of the heating elements are dispersedly arranged so as to have a uniform distribution on the surface of the silicon substrate.

  Since the silicon substrate has a certain area, in order to heat the entire substrate, the uniform temperature distribution can reach a certain temperature in a shorter time than the heating at one place. Further, the temperature gradient can be eliminated by uniformly disposing the layers.

[Application Example 6]
The plurality of heating elements are arranged at positions along the outer periphery of the silicon substrate.

  Since the outer periphery of the substrate is exposed to the outside air, the temperature is greatly reduced. Therefore, in the present invention, the heating element is arranged at a position along the outer periphery of the substrate. Thereby, the temperature fall by external air can be minimized.

[Application Example 7]
Further, a heat generating element having a large power is disposed at a position along the outer periphery of the silicon substrate, and a heat generating element having a small power is disposed inside the heat generating element group having a large power.

  The outer periphery of the substrate has a large temperature drop, and becomes smaller as it goes to the inner periphery. Therefore, in the present invention, a heating element having a large power is disposed at a position along the outer periphery of the substrate, and a heating element having a small power is disposed on the inner periphery. Thereby, while increasing a heating rate, a temperature gradient can be reduced.

[Application Example 8]
The coherent light is laser light.

  Ordinary light is light in which various wavelengths are mixed and the phase is random. On the other hand, laser light has good monochromaticity in wavelength and is light with a uniform phase. Coherence is defined as a measure of the stability of the wavelength and phase of light. Light with good coherence, that is, with stable wavelength and phase, can cause a quantum interference effect. In that respect, laser light is optimal.

[Application Example 9]
The gaseous metal atom is rubidium or cesium.

  If cesium atoms are used, a highly accurate atomic oscillator can be realized. In addition, rubidium atoms are widely spread easily. Therefore, any metal atom can be selected in consideration of the required performance and cost of the atomic oscillator.

[Application Example 10]
Further, the optical system having the above configuration is provided in an atomic oscillator.

  The gas cell can be made smaller by reducing the number of parts, the temperature distribution of the gas cell can be made uniform, and the deterioration of light absorption characteristics can be improved. An oscillator can be provided.

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 configuration diagram of a main part of an optical system of an atomic oscillator according to an embodiment of the present invention. This optical system 1 is an optical system 1 of an atomic oscillator 50 that controls an oscillation frequency by utilizing a light absorption characteristic due to a quantum interference effect when two types of resonant light as coherent lights having different wavelengths are incident. A coherent light source 2 that emits resonance light 2a, a gas cell 3 that is disposed on the emission side of the coherent light source 2 and encloses gaseous metal atoms, and that passes the resonance light 2a into the metal atom gas, and has passed through the gas cell 3. And a light detector (light detection means) 4 for detecting the light 3a. The atomic oscillator 50 further includes a frequency control circuit 8 that controls the oscillation frequency based on the output signal of the photodetector 4. In the present embodiment, a temperature control circuit 5 is provided for controlling the operation of the heating element disposed in the gas cell 3 based on the information 6 of the temperature sensor (temperature detection element) disposed in the gas cell 3 (for details, see FIG. Will be described later). Since the gist of the present invention is the configuration of the optical system that constitutes the atomic oscillator, a detailed description of the frequency control of the atomic oscillator is omitted.

  That is, the atomic oscillator 50 of the present invention utilizes the quantum interference effect of coherent light such as laser light. In this method, two ground levels of two resonant lights irradiated simultaneously in a three-level system (for example, a Λ-type level system) in which two ground levels receive resonant light and are resonantly coupled with a common excitation level. When the frequency exactly matches the energy difference between the ground level 1 and the ground level 2, the three-level system becomes a superposition state of the two ground levels, and the excitation to the excitation level 3 stops. CPT uses this principle to detect and use a state in which light absorption in the gas cell stops when the wavelength of one or both of the two resonance lights is changed. In the optical system 1 of the present invention, the resonance light 2 a emitted from the coherent light source 2 passes through the gas cell 3, and the light 3 a emitted from the gas cell 3 is detected by the photodetector 4. Here, a conventional atomic oscillator using an alkali metal such as rubidium or cesium needs to keep atoms in a gas state when utilizing energy transition of atoms, so a gas cell in which atoms are hermetically sealed is kept at a constant temperature. To keep it running. Therefore, in order to keep the gas cell at a constant temperature, a layer is arranged around the cavity, and the temperature of the cavity is kept constant by heating with a heater so as to sandwich the layer. As a result, in order to heat the gas cell, there is a problem that a heater is required and the entire gas cell becomes large, a problem that a portion close to the heater is excessively heated, and a problem that light absorption characteristics are deteriorated. Therefore, in the present embodiment, a heating element that generates heat is arranged on the silicon substrate that constitutes the gas cell 3 to heat the substrate itself, thereby reducing the number of components and reducing the size of the gas cell 3, and the temperature distribution of the gas cell 3. Can be made uniform, and degradation of light absorption characteristics can be improved.

Further, laser light is used as the coherent light. In other words, ordinary light (lamp light source or the like) is light in which various wavelengths are mixed and the phase is random. On the other hand, laser light has good monochromaticity in wavelength and is light with a uniform phase. Coherence is defined as a measure of the stability of the wavelength and phase of light. Light with good coherence, that is, with stable wavelength and phase, can cause a quantum interference effect. In that respect, laser light is optimal.
As the gaseous metal atom, rubidium or cesium is used. If cesium atoms are used, a highly accurate atomic oscillator can be realized. In addition, rubidium atoms are widely spread easily. Therefore, any metal atom can be selected in consideration of the required performance and cost of the atomic oscillator.
In addition, by providing the optical system 1 with the above configuration in the atomic oscillator, the number of components can be reduced, the gas cell 3 can be downsized, the temperature distribution of the gas cell can be made uniform, and the deterioration of the light absorption characteristics can be improved. Therefore, it is possible to provide a high-performance atomic oscillator that is small and has high temperature stability of the gas cell 3.

  FIG. 2 is an example for explaining a three-level system of atoms by the CPT method. The rubidium and cesium ground levels used in the atomic oscillator are divided into two kinds of ground levels by the hyperfine structure due to the nuclear spin-electron spin interaction. These ground level atoms absorb light and excite to higher energy levels. A state in which two ground levels receive light and are resonantly coupled to a common excitation level as shown in FIG. 2 is called two-photon resonance. In FIG. 2, since the ground level 1 (23) and the ground level 2 (24) have slightly different levels of energy, the resonant light also has a wavelength slightly different from that of the resonant light 1 (20) and the resonant light 2 (22), respectively. Different. When the frequency difference (wavelength difference) between the resonant light 1 (20) and the resonant light 2 (22) irradiated at the same time exactly matches the energy difference between the ground level 1 (23) and the ground level 2 (24), The system shown in FIG. 2 enters a superposition state of two ground levels, and excitation to the excitation level 21 stops. The CPT utilizes this principle to absorb light in the gas cell 3 (that is, to the excitation level 21) when the wavelength of one or both of the resonant light 1 (20) and the resonant light 2 (22) is changed. This is a method of detecting and using a state where the conversion is stopped. The light 3a that passes through the gas cell 3 in a state where the light absorption is stopped is called an EIT signal.

  FIG. 3A is a diagram schematically showing the configuration of the gas cell according to the first embodiment of the present invention. FIG. 3B is a view showing a heating element arranged on the silicon substrate. The gas cell 3 includes a silicon substrate 11 having an opening 13 penetrating in the thickness direction so as to enclose at least metal atoms, and glasses (transparent members) 10 and 12 for sealing the opening 13. As shown in FIG. 3B, heating elements 14, 15, and 16 for heating the silicon substrate 11 were arranged on the silicon substrate 11. In FIG. 3B, the bipolar transistor 14, the MOS transistor 15, and the resistor 16 are shown as the heating elements. However, any one of these may be used, or they may be mixed. . In addition, since it is important that the silicon substrate 11 is heated uniformly, it is preferable that the heating elements be arranged so as to have a uniform distribution without being biased to a part on the silicon substrate 11.

Further, a temperature sensor for detecting the temperature of the silicon substrate 11 is further arranged on the silicon substrate 11. That is, in order to keep the temperature of the silicon substrate 11 at a constant value, the temperature of the silicon substrate 11 must be detected. Therefore, in this embodiment, a temperature sensor is further arranged on the silicon substrate 11. Thereby, the temperature information can be fed back to control the temperature of the substrate to be constant. For example, the temperature sensor may detect a change in resistance value or may be provided with a thermistor.
In addition, a temperature control circuit for controlling the operation of the heating element is provided outside the silicon substrate 11 based on temperature information from the temperature sensor. That is, the temperature information from the temperature sensor changes following the temperature change of the silicon substrate 11. Therefore, if the relationship between temperature and temperature information is known in advance, the temperature of the silicon substrate 11 can be determined from the temperature information. Therefore, in this embodiment, when the temperature information for the upper limit temperature is received, the heating element is deactivated and heating is stopped, and when the temperature information for the lower limit temperature is received, the temperature control circuit starts operating the heating element to start heating. Alternatively, a temperature control circuit for keeping the temperature constant by continuous operation is provided outside the silicon substrate 11. Thereby, the temperature control circuit is not affected by the substrate temperature, and the control method can be changed flexibly. The temperature control circuit may be controlled so as to change the value of the current flowing through the heat generating element in an analog manner, in addition to a control method for operating or disabling the heat generating element. Further, the current may be digitally controlled by modulating the pulse width.

In addition, the temperature control circuit is arranged on the silicon substrate 11 together with the heating element and the temperature sensor. That is, since the heat generating element and the temperature sensor are arranged on the silicon substrate 11, if a temperature control circuit for controlling them is also arranged on the substrate, only the power source needs to be supplied from the outside. Thereby, the whole optical system can be reduced in size.
In the above description, the substrate is described as silicon, but the substrate may be made of glass. That is, the substrate can be made of glass and a circuit can be formed on the glass. Thereby, the selection range of a circuit formation process can be expanded.

  FIG. 4 is a view showing a layout of the heat generating elements arranged on the silicon substrate. FIG. 4A is a diagram in which the heating elements 17 are arranged so as to have a uniform distribution without being biased to a part of the silicon substrate 11. In this case, the types of the heat generating elements 17 are the same, and are arranged approximately in the middle between the silicon substrate 11 and the opening 13. FIG. 4B is a diagram in which the heat generating element 17 is arranged at a position along the outer periphery of the silicon substrate 11. Since the outside of the silicon substrate 11 is exposed to the outside air, the temperature is the lowest as the temperature distribution. Therefore, the heat generating element 17 is arranged close to the position along the outer periphery of the silicon substrate 11 to reduce the temperature drop. In FIG. 4C, a heating element 17 having high power is arranged at a position along the outer periphery of the silicon substrate 11, and a heating element 18 having low power is arranged inside. Thereby, the heating temperature is increased on the outside where the temperature drop is large, and the heating temperature is lowered on the inside where the temperature drop is small, so that the temperature can be made uniform efficiently as a whole.

As described above, since the heating element can be freely arranged on the silicon substrate 11, an optimum heating element can be arranged according to the size of the gas cell and the use environment. This arrangement is an example, and other arrangements may be used.
In other words, since the silicon substrate 11 has a certain area, in order to heat the entire silicon substrate, the temperature of the silicon substrate 11 reaches a constant temperature in a shorter time if it is distributed and distributed so as to be distributed uniformly rather than heating at one location. Moreover, a temperature gradient can be eliminated by arranging them uniformly. Moreover, since the outer periphery of the silicon substrate 11 is exposed to the outside air, the temperature is greatly reduced. Therefore, in the present embodiment, the heating element 17 is arranged at a position along the outer periphery of the silicon substrate 11. Thereby, the temperature fall by external air can be minimized. Moreover, the temperature decrease is large at the outer periphery of the silicon substrate 11 and becomes smaller toward the inner periphery. Therefore, in the present embodiment, the heat generating element 17 having a large power is disposed at a position along the outer periphery of the silicon substrate 11, and the heat generating element 18 having a small power is disposed on the inner periphery. Thereby, while increasing a heating rate, a temperature gradient can be reduced.

  FIG. 5 is a view showing a layout of the temperature sensor arranged on the silicon substrate. FIG. 5A is a diagram in which the temperature sensors 19 are arranged at four locations on the silicon substrate 11. A predetermined time is required for the temperature of the silicon substrate to reach a constant temperature as a whole. Therefore, the temperature sensors 19 are evenly arranged at four locations on the silicon substrate 11, and the heating elements around the temperature sensors are controlled based on the temperature information from each temperature sensor. Thereby, useless heating can be reduced and the silicon substrate can be efficiently heated. FIG. 5B is a diagram in which the temperature sensor 19 is arranged in the vicinity of the opening 13. The opening 13 is filled with gaseous metal atoms. Since it is necessary to keep the metal atoms in a gas state, the gas cell in which the metal atoms are hermetically sealed is operated at a constant temperature. Therefore, it is important that the temperature of the opening 13 becomes a predetermined temperature. Therefore, the temperature sensor 19 is disposed in the vicinity of the opening 13. Thereby, a metal atom can be efficiently made into a gas state.

It is a principal part block diagram of the optical system of the atomic oscillator which concerns on embodiment of this invention. It is a figure explaining the 3 level system of an atom by a CPT system. It is the figure which modeled the structure of the gas cell which concerns on the 1st Embodiment of this invention. It is a figure which shows the layout of the heat generating element arrange | positioned on the silicon substrate. It is a figure which shows the layout of the temperature sensor arrange | positioned on a silicon substrate. It is a block diagram of the conventional gas cell.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Optical system, 2 Coherent light source, 2a Resonant light, 3 Gas cell, 4 Photo detector, 5 Temperature control circuit, 6 Temperature information, 7 Control signal, 8 Frequency control circuit 10, 12 Glass, 11 Silicon substrate, 13 Aperture 14, 15, 16 Heating element, 50 Atomic oscillator

Claims (10)

An optical system of an atomic oscillator that controls an oscillation frequency by utilizing a light absorption characteristic due to a quantum interference effect when two types of resonance light as coherent light having different wavelengths are incident,
A coherent light source that emits the resonant light;
A gas cell that is disposed on the emission side of the coherent light source and encloses gaseous metal atoms, and allows resonance light to pass through the metal atom gas; and
A light detection means for detecting light that has passed through the gas cell;
With
The gas cell includes a silicon substrate having an opening that penetrates in the thickness direction to enclose the metal atoms, and a transparent member that seals both ends of the opening,
An optical system of an atomic oscillator, wherein a heating element for heating the silicon substrate is disposed on the silicon substrate.   2. The atomic oscillator optical system according to claim 1, wherein a temperature detecting element for detecting the temperature of the silicon substrate is further arranged on the silicon substrate.   3. The atomic oscillator optical device according to claim 1, further comprising: a temperature control circuit that controls an operating state of the heat generating element based on temperature information from the temperature detecting element. system.   3. The atomic oscillator optical system according to claim 1, wherein the temperature control circuit is disposed on the silicon substrate together with the heating element and the temperature detecting element.   5. The optical system of an atomic oscillator according to claim 1, wherein a plurality of the heat generating elements are dispersedly arranged so as to have a uniform distribution on the surface of the silicon substrate.   5. The atomic oscillator optical system according to claim 1, wherein the plurality of heating elements are arranged at positions along an outer periphery of the silicon substrate.   5. A heating element having a high power is arranged at a position along the outer periphery of the silicon substrate, and a heating element having a low power is arranged inside the heating element group having a large power. The optical system of the atomic oscillator according to any one of the above.   The optical system for an atomic oscillator according to claim 1, wherein the coherent light is laser light.   2. The optical system of an atomic oscillator according to claim 1, wherein the gaseous metal atom is rubidium or cesium.   An atomic oscillator comprising the optical system according to claim 1.

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