U.S. patent application number 15/867969 was filed with the patent office on 2018-07-26 for atom cell, method of manufacturing atom cell, quantum interference device, atomic oscillator, electronic apparatus, and moving object.
The applicant listed for this patent is Seiko Epson Corporation. Invention is credited to Naoki ISHIHARA.
Application Number | 20180212613 15/867969 |
Document ID | / |
Family ID | 57130044 |
Filed Date | 2018-07-26 |
United States Patent
Application |
20180212613 |
Kind Code |
A1 |
ISHIHARA; Naoki |
July 26, 2018 |
ATOM CELL, METHOD OF MANUFACTURING ATOM CELL, QUANTUM INTERFERENCE
DEVICE, ATOMIC OSCILLATOR, ELECTRONIC APPARATUS, AND MOVING
OBJECT
Abstract
An atom cell is provided with an internal space including a
space formed of a through hole housing gaseous alkali metal, a
space formed of a through hole housing a compound as an alkali
metal emission material, and a space formed of a through hole
housing liquid or solid alkali metal.
Inventors: |
ISHIHARA; Naoki; (Chino,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Seiko Epson Corporation |
Tokyo |
|
JP |
|
|
Family ID: |
57130044 |
Appl. No.: |
15/867969 |
Filed: |
January 11, 2018 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
15097659 |
Apr 13, 2016 |
|
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15867969 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G04F 5/14 20130101; H01S
1/06 20130101; H03L 7/26 20130101; G04F 5/145 20130101; H03B 17/00
20130101 |
International
Class: |
H03L 7/26 20060101
H03L007/26; H03B 17/00 20060101 H03B017/00; G04F 5/14 20060101
G04F005/14; H01S 1/06 20060101 H01S001/06 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 15, 2015 |
JP |
2015-083450 |
Claims
1. An atom cell comprising: a side wall having top and bottom
openings; first and second window substrates that are airtightly
fixed to the first and second openings, respectively, so as to form
an internal space; and alkali metal atoms that are housed in the
internal space; wherein the internal space includes: a first region
housing the alkali metal atoms in a gas state; a second region
housing the alkali metal atoms in one of a liquid state and a solid
state; and a connection path that is spacially-coupled between the
first and second regions, and a combined part of the side wall and
the first window substrate, which are located directly adjacent to
the second region, has a groove.
2. The atom cell according to claim 1, wherein the combined part
has a projection, and the projection outwardly projects from an
outer surface of the side wall.
3. The atom cell according to claim 1, wherein partial pressure of
a gas other than the gaseous alkali metal atoms in the internal
space is equal to or lower than 10.sup.-4 Pa.
4. A method of manufacturing an atom cell, the method comprising:
preparing an airtightly-formed cell container having an internal
space, the internal space including: a first region; a second
region that is spacially connected to the first region via a first
connection path; and a third region that is spacially connected to
the second region via a second connection path so that the first,
second, and third regions are spacially connected to each other,
the third region having a solid compound including alkali metal;
heating the solid compound so as to emit alkali metal atoms,
wherein the first and second regions have the alkali metal atoms in
a gas state; adjusting a temperature of the second region to a
level lower than a temperature of the first region so that the
second region houses the alkali metal atoms in one of a liquid
state and a solid state; melting a material of the
airtightly-formed cell container, which is located directly
adjacent to the second connection path, so that the second
connection path is sealed by the melted material; and cutting part
of the airtightly-formed cell container including the third region
so that the melted material of the airtightly-formed cell container
is part of a periphery of the atom cell.
5. The method of manufacturing an atom cell according to claim 4,
wherein partial pressure of a gas other than the gaseous alkali
metal atoms in the internal space is equal to or lower than
10.sup.-4 Pa.
6. The method of manufacturing an atom cell according to claim 4,
wherein in the preparing, a plurality of the airtightly-formed cell
containers are connected to one another.
7. A quantum interference device comprising: the atom cell
according to claim 1; and a light source that emits light to the
atom cell.
8. The quantum interference device according to claim 7, wherein
the first region is higher in temperature than the second
region.
9. A quantum interference device comprising: the atom cell
according to claim 2; and a light source that emits light to the
atom cell.
10. The quantum interference device according to claim 9, wherein
the first region is higher in temperature than the second
region.
11. A quantum interference device comprising: the atom cell
according to claim 3; and a light source that emits light to the
atom cell.
12. The quantum interference device according to claim 11, wherein
the first region is higher in temperature than the second
region.
13. An atomic oscillator comprising: the atom cell according to
claim 1; a light source that emits light to the atom cell; and a
light detector that receives light which passes through the atomic
cell.
14. An atomic oscillator comprising: the atom cell according to
claim 2; a light source that emits light to the atom cell; and a
light detector that receives light which passes through the atomic
cell.
15. An atomic oscillator comprising: the atom cell according to
claim 3; a light source that emits light to the atom cell; and a
light detector that receives light which passes through the atomic
cell.
16. An electronic apparatus comprising: the atom cell according to
claim 1; and a signal receiver that receive a signal form an
external device, wherein the atom cell is located in the signal
receiver.
17. An electronic apparatus comprising: the atom cell according to
claim 2; and a signal receiver that receive a signal form an
external device, wherein the atom cell is located in the signal
receiver.
18. An electronic apparatus comprising: the atom cell according to
claim 3; and a signal receiver that receive a signal form an
external device, wherein the atom cell is located in the signal
receiver.
19. A moving object comprising: the atom cell according to claim 1;
and a movable body that houses the atom cell.
20. A moving object comprising: the atom cell according to claim 2;
and a movable body that houses the atom cell.
Description
CROSS REFERENCE
[0001] This application is a divisional of U.S. patent application
Ser. No. 15,097,659, filed on Apr. 13, 2016, which claims the
benefit of Japanese Application No. JP 2015-083450, filed on Apr.
15, 2015. The disclosures of the above applications are hereby
incorporated by reference herein in their entireties.
BACKGROUND
1. Technical Field
[0002] The present invention relates to an atom cell, a method of
manufacturing an atom cell, a quantum interference device, an
atomic oscillator, an electronic apparatus, and a moving
object.
2. Related Art
[0003] As an oscillator having long-term accurate oscillation
characteristics, there has been known an atomic oscillator, which
oscillates based on the energy transition of an atom of alkali
metal such as rubidium or cesium.
[0004] In general, the operation principles of atomic oscillators
are roughly classified into a system using a double resonance
phenomenon by light and microwave, and a system using the quantum
interference effect (coherent population trapping (CPT)) due to two
types of light different in wavelength from each other. Both of the
atomic oscillators are generally provided with an atom cell (gas
cell) having alkali metal encapsulated.
[0005] As a method of manufacturing such an atom cell, there has
been known a method of sealing a hollow section housing a compound
including the alkali metal, and then heating to react the compound
to thereby generate an alkali metal gas inside the hollow section
as disclosed in JP-A-2013-007720 (Document 1). According to such a
method, an unwanted gas in the hollow section can be reduced.
[0006] However, in the gas cell obtained by the method described in
Document 1, there is a problem that an amount of alkali metal gas
in the hollow section sealed decreases with time, and as a result,
the frequency stability degrades.
SUMMARY
[0007] An advantage of the invention is to provide an atom cell and
a method of manufacturing the atom cell, and further provide a
quantum interference device, an atomic oscillator, an electronic
apparatus, and a moving object each equipped with such an atom
cell.
[0008] The invention is implemented as the following aspects or
application examples.
APPLICATION EXAMPLE 1
[0009] An atom cell according to this application example of the
invention includes alkali metal atoms, an alkali metal emission
material having emitted the alkali metal atoms, and an internal
space housing the alkali metal atoms and the alkali metal emission
material, the internal space includes a first region housing the
alkali metal atoms in a form of a gas, a second region housing the
alkali metal emission material, and a third region housing the
alkali metal atoms in a form of one of a liquid and a solid.
[0010] According to such an atom cell, since the liquid or solid
alkali metal atoms exist in the third region of the internal space
as an excess, it is possible to reduce chances for the amount (the
partial pressure) of the gaseous alkali metal atoms existing in the
first region of the internal space sealed to decrease. Therefore,
it is possible to realize the excellent frequency stability for a
long period of time.
APPLICATION EXAMPLE 2
[0011] In the atom cell according to the application example of the
invention, it is preferable that the third region is located
between the first region and the second region.
[0012] According to this application example of the invention, even
if the second region is removed, the first region and the third
region can be made to be communicated with each other, and thus, it
is possible to reduce the chances for the amount of the gaseous
alkali metal atoms located in the first region to decrease.
APPLICATION EXAMPLE 3
[0013] In the atom cell according to the application example of the
invention, it is preferable that the first region is located
between the second region and the third region.
[0014] According to this application example of the invention, when
heating the second region to emit the alkali metal atoms from the
alkali metal emission material, the temperature of the third region
can easily be set to a level lower than the temperature of the
second region. Therefore, the liquid or solid alkali metal atoms
can easily be housed in the third region.
APPLICATION EXAMPLE 4
[0015] In the atom cell according to the application example of the
invention, it is preferable that there is further included a
communication hole communicating the first region and the second
region with each other, and a width of the communication hole is
smaller than a width of the alkali metal emission material.
[0016] According to this application example of the invention, it
is possible to reduce the chances for the alkali metal emission
material to move from the second region to the first region.
APPLICATION EXAMPLE 5
[0017] In the atom cell according to the application example of the
invention, it is preferable that there is further included a getter
material disposed in the second region.
[0018] According to this application example of the invention, it
is possible to make the getter material adsorb the unwanted gas
existing in the internal space to make the characteristics of the
atom cell excellent.
APPLICATION EXAMPLE 6
[0019] In the atom cell according to the application example of the
invention, it is preferable that partial pressure of a gas other
than the gaseous alkali metal atoms in the internal space is one of
equal to and lower than 10.sup.-4 Pa.
[0020] Such an atom cell small in the amount of unwanted gas has
excellent characteristics.
APPLICATION EXAMPLE 7
[0021] A method of manufacturing an atom cell according to this
application example of the invention includes preparing a cell
container having an internal space including a first region, a
second region, and a third region, and housing a solid compound
including alkali metal in the second region of the internal space,
heating the second region to emit the alkali metal from the
compound, and adjusting a temperature of the third region to a
level lower than a temperature of the first region.
[0022] According to such a method of manufacturing an atom cell, it
is possible to obtain the atom cell having the liquid or solid
alkali metal atoms existing in the third region of the internal
space as an excess. According to the atom cell thus obtained, it is
possible to prevent the amount (the partial pressure) of the
gaseous alkali metal atoms located in the first region of the
internal space sealed from decreasing, and thus the excellent
frequency stability can be realized for a long period of time.
APPLICATION EXAMPLE 8
[0023] In the method of manufacturing an atom cell according to the
application example of the invention, it is preferable that the
preparing includes sealing the internal space.
[0024] According to this application example of the invention, the
amount of unwanted gas in the internal space of the atom cell
obtained can be reduced.
APPLICATION EXAMPLE 9
[0025] In the method of manufacturing an atom cell according to the
application example of the invention, it is preferable that there
is further included removing the second region after the heating
for emitting.
[0026] According to this application example of the invention, the
compound having emitted the alkali metal can be eliminated in the
atom cell obtained, and it is possible to reduce the influence of
the compound to enhance the frequency stability.
APPLICATION EXAMPLE 10
[0027] In the method of manufacturing an atom cell according to the
application example of the invention, it is preferable that the
removing is performed after the adjusting.
[0028] According to this application example of the invention, the
compound having been emitted the alkali metal can be eliminated in
the atom cell obtained.
APPLICATION EXAMPLE 11
[0029] In the method of manufacturing an atom cell according to the
application example of the invention, it is preferable that in the
preparing, the first region and the second region are communicated
with each other via a communication hole, and the removing includes
blocking the communication hole.
[0030] According to this application example of the invention, the
internal space from which the second region has been removed can
easily be sealed.
APPLICATION EXAMPLE 12
[0031] In the method of manufacturing an atom cell according to the
application example of the invention, it is preferable that in the
preparing, a plurality of the cell containers is connected to one
another.
[0032] According to this application example of the invention, the
plurality of atom cells can efficiently be manufactured.
APPLICATION EXAMPLE 13
[0033] A quantum interference device according to this application
example of the invention includes the atom cell according to the
application example of the invention.
[0034] With the quantum interference device according to this
application example of the invention, the excellent frequency
stability can be exerted.
APPLICATION EXAMPLE 14
[0035] In the quantum interference device according to the
application example of the invention it is preferable that the
first region is higher in temperature than the third region.
[0036] According to this application example of the invention, it
is possible to make the gaseous alkali metal atoms and the liquid
or solid alkali metal stably exist in the first region and the
third region, respectively.
APPLICATION EXAMPLE 15
[0037] An atomic oscillator according to this application example
of the invention includes the atom cell according to the
application example of the invention.
[0038] With the atomic oscillator according to this application
example of the invention, the excellent frequency stability can be
exerted.
APPLICATION EXAMPLE 16
[0039] An electronic apparatus according to this application
example of the invention includes the atom cell according to the
application example of the invention.
[0040] With the electronic apparatus according to this application
example of the invention, the frequency stability of the atom cell
can be made excellent.
APPLICATION EXAMPLE 17
[0041] A moving object according to this application example of the
invention includes the atom cell according to the application
example of the invention.
[0042] With the moving object according to this application example
of the invention, the frequency stability of the atom cell can be
made excellent.
BRIEF DESCRIPTION OF THE DRAWINGS
[0043] The invention will be described with reference to the
accompanying drawings, wherein like numbers reference like
elements.
[0044] FIG. 1 is a schematic diagram showing an atomic oscillator
(a quantum interference device) according to a first embodiment of
the invention.
[0045] FIG. 2 is a diagram for describing the energy state of
alkali metal.
[0046] FIG. 3 is a graph showing a relationship between a
difference in frequency between two types of light emitted from a
light emitting section, and the intensity of the light detected in
a light detection section.
[0047] FIG. 4A is a vertical cross-sectional view of an atom cell
provided to the atomic oscillator shown in FIG. 1, and FIG. 4B is a
cross-sectional view (a horizontal cross-sectional view) along the
line A-A in FIG. 4A.
[0048] FIG. 5 is a diagram showing a member used for a preparatory
process in a method of manufacturing the atom cell shown in FIGS.
4A and 4B.
[0049] FIGS. 6A through 6C are diagrams for describing the
preparatory process, an emission process, a temperature adjustment
process, and a segmenting process in the method of manufacturing
the atom cell shown in FIGS. 4A and 4B.
[0050] FIGS. 7A and 7B are diagrams for describing a modified
example of the atom cell according to the first embodiment of the
invention.
[0051] FIG. 8A is a vertical cross-sectional view of an atom cell
provided to an atomic oscillator according to a second embodiment
of the invention, and FIG. 8B is a cross-sectional view (a
horizontal cross-sectional view) along the line A-A in FIG. 8A.
[0052] FIGS. 9A and 9B are diagrams for describing a modified
example of the atom cell according to the second embodiment of the
invention.
[0053] FIG. 10 is a horizontal cross-sectional view showing an atom
cell provided to an atomic oscillator according to a third
embodiment of the invention.
[0054] FIG. 11 is a diagram showing a schematic configuration in
the case of using the atomic oscillator according to the invention
to a positioning system using GPS satellites.
[0055] FIG. 12 is a diagram showing an example of a moving object
according to the invention.
DESCRIPTION OF EXEMPLARY EMBODIMENTS
[0056] Hereinafter, an atom cell, a method of manufacturing the
atom cell, a quantum interference device, an atomic oscillator, an
electronic apparatus, and a moving object according to the
invention will be described in detail based on the embodiments
shown in the accompanying drawings.
1. An Atomic Oscillator (Quantum Interference Device)
[0057] Firstly, the atomic oscillator (atomic oscillator equipped
with the atom cell according to the invention) according to the
invention will be described. It should be noted that although an
example of applying the quantum interference device according to
the invention to the atomic oscillator will hereinafter be
described, the quantum interference device according to the
invention can be applied not only to the atomic oscillator, but
also to, for example, a magnetic sensor or a quantum memory.
First Embodiment
[0058] FIG. 1 is a schematic diagram showing the atomic oscillator
(quantum interference device) according to a first embodiment of
the invention. Further, FIG. 2 is a diagram for describing the
energy state of alkali metal, and FIG. 3 is a graph showing a
relationship between a difference in frequency between two types of
light emitted from a light emitting section, and the intensity of
the light detected in a light detection section.
[0059] The atomic oscillator 1 shown in FIG. 1 is an atomic
oscillator using coherent population trapping. As shown in FIG. 1,
the atomic oscillator 1 is provided with an atom cell 2 (a gas
cell), a light emitting section 3, optical components 41, 42, 43,
and 44, a light detection section 5, a heater 6, a temperature
sensor 7, a magnetic field generation section 8, and a control
section 10.
[0060] Firstly, the principle of the atomic oscillator 1 will
briefly be described.
[0061] As shown in FIG. 1, in the atomic oscillator 1, the light
emitting section 3 emits excitation light LL toward the atom cell
2, and the light detection section 5 detects the excitation light
LL having been transmitted through the atom cell 2.
[0062] In the atom cell 2, there is encapsulated gaseous alkali
metal (metal atoms), and as shown in FIG. 2, the alkali metal has
energy levels in the three-level system, and can take three states,
namely two ground states (first and second ground states) different
in energy level and an excited state. Here, the first ground state
is an energy state lower than the second ground state.
[0063] The excitation light LL having been emitted from the light
emitting section 3 includes two types of resonance light, namely
first and second resonance light, different in frequency, and when
irradiating the gaseous alkali metal described above with the two
types of resonance light, namely the first resonance light and the
second resonance light, the light absorptance (the light
transmittance) of the first and second resonance light in the
alkali metal varies in accordance with a difference
(.omega..sub.1-.omega..sub.2) between the frequency .omega..sub.1
of the first resonance light and the frequency .omega..sub.2 of the
second resonance light.
[0064] Then, when the difference (.omega..sub.1-.omega..sub.2)
between the frequency .omega..sub.1 of the first resonance light
and the frequency .omega..sub.2 of the second resonance light
coincides with the frequency corresponding to the energy difference
between the first ground state and the second ground state, the
excitation from the first and second ground states to the excited
state stops, respectively. On this occasion, both of the first
resonance light and the second resonance light are transmitted
without being absorbed by the alkali metal. Such a phenomenon is
called a CPT phenomenon or electromagnetically induced transparency
(EIT).
[0065] For example, in the case in which the light emitting section
3 fixes the frequency .omega..sub.1 of the first resonance light
and varies the frequency .omega..sub.2 of the second resonance
light, the detection intensity of the light detection section 5
rapidly rises as shown in FIG. 3 when the difference
(.omega..sub.1-.omega..sub.2) between the frequency .omega..sub.1
of the first resonance light and the frequency .omega..sub.2 of the
second resonance light coincides with the frequency .omega..sub.0
corresponding to the energy difference between the first ground
state and the second ground state. Such a rapid signal as described
above is detected as an EIT signal. The EIT signal has a
characteristic value determined by the type of the alkali metal.
Therefore, by using such an EIT signal, an oscillator can be
configured.
[0066] Hereinafter, constituents of the atomic oscillator 1 will
briefly be described.
Atom Cell
[0067] In the atom cell 2, there is encapsulated the alkali metal
such as rubidium, cesium, or sodium in the form of a gas. Further,
in the atom cell 2, there can also be encapsulated a noble gas such
as argon or neon, or an inert gas such as nitrogen as a buffer gas
together with the alkali metal gas if needed.
[0068] Further, in the atom cell 2, there are disposed an alkali
metal compound, a getter material, and so on besides the above. It
should be noted that this point will be described later in detail
together with the configuration of the atom cell 2.
Light Emitting Section
[0069] The light emitting section 3 (a light source) has a function
of emitting the excitation light LL for exciting the alkali metal
atoms in the atom cell 2.
[0070] More specifically, the light emitting section 3 is for
emitting the two types of light (the first resonance light and the
second resonance light) different in frequency from each other as
described above as the excitation light LL. The first resonance
light is the light which can excite (resonate) the alkali metal
located inside the atom cell 2 from the first ground state
described above to the excited state. In contrast, the second
resonance light is the light which can excite (resonate) the alkali
metal located inside the atom cell 2 from the second ground state
described above to the excited state.
[0071] The light emitting section 3 is not particularly limited
providing such excitation light as described above can be emitted,
and for example, a semiconductor laser such as a vertical cavity
surface emitting laser (VCSEL) can be used as the light emitting
section 3.
[0072] It should be noted that the light emitting section 3 is
adjusted in temperature to a predetermined temperature using a
temperature control element (e.g., a heating resistive element and
a Peltier element) not shown.
Optical Components
[0073] The plurality of optical components 41, 42, 43, and 44 is
disposed on a light path of the excitation light LL between the
light emitting section 3 described above and the atom cell 2. Here,
the optical component 41, the optical component 42, the optical
component 43, and the optical component 44 are arranged in this
order from the light emitting section 3 side to the atom cell 2
side.
[0074] The optical component 41 is a lens. Thus, the atom cell 2
can be irradiated with the excitation light LL with no waste.
[0075] Further, the optical component 41 has a function of changing
the excitation light LL to parallel light. Thus, it is possible to
easily and reliably prevent the excitation light LL from being
reflected by an inside wall of the atom cell 2. Therefore, it is
possible to preferably generate the resonance of the excitation
light inside the atom cell 2, and as a result, improve the
oscillation characteristics of the atomic oscillator 1.
[0076] The optical component 42 is a polarization plate. Thus, it
is possible to adjust the polarization direction of the excitation
light LL from the light emitting section 3 to a predetermined
direction.
[0077] The optical component 43 is a neutral density filter (ND
filter). Thus, it is possible to adjust (decrease) the intensity of
the excitation light LL entering the atom cell 2. Therefore, even
in the case in which the output of the light emitting section 3 is
high, it is possible to set the intensity of the excitation light
entering the atom cell 2 to a predetermined intensity. In the
present embodiment, the intensity of the excitation light LL, which
has passed through the optical component 42 described above, and is
provided with the predetermined polarization direction, is
controlled using the optical component 43.
[0078] The optical component 44 is a .lamda./4 wave plate. Thus, it
is possible to convert the excitation light LL from the light
emitting section 3 from linearly polarized light to circularly
polarized light (right circularly polarized light or left
circularly polarized light).
[0079] As described later, if the alkali metal atoms are irradiated
with the excitation light as the linearly polarized light in the
state in which the alkali metal atoms located in the atom cell 2
are Zeeman-split due to the magnetic field by the magnetic field
generation section 8 as described later, it results that the alkali
metal atoms exist dispersing evenly at a plurality of levels, at
which the alkali metal atoms are Zeeman-split, due to a mutual
action between the excitation light and the alkali metal atoms. As
a result, since the number of the alkali metal atoms at a desired
energy level becomes relatively small to the number of the alkali
metal atoms at other energy levels, the number of atoms developing
the desired EIT phenomenon decreases, and the intensity of the
desired EIT signal decreases. As a result, degradation of the
oscillation characteristics is caused in the atomic oscillator
1.
[0080] In contrast, in the case of irradiating the alkali metal
atoms with the excitation light as the circularly polarized light
in the state in which the alkali metal atoms located in the atom
cell 2 are Zeeman-split due to the magnetic field by the magnetic
field generation section 8 as described later, the number of the
alkali metal atoms at the desired energy level out of the plurality
of levels, at which the alkali metal atoms are Zeeman-split, can be
made relatively large to the number of the alkali metal atoms at
other energy levels due to a mutual action between the excitation
light and the alkali metal atoms. Therefore, the number of the
atoms developing the desired EIT phenomenon increases to increase
the intensity of the desired EIT signal, and as a result, the
oscillation characteristics of the atomic oscillator 1 can be
improved.
Light Detection Section
[0081] The light detection section 5 has a function of detecting
the intensity of the excitation light LL (the first resonance light
and the second resonance light) having been transmitted through the
atom cell 2.
[0082] The light detection section 5 is not particularly limited
providing such excitation light as described above can be detected,
and for example, a photo detector (a light receiving element) such
as a solar cell or a photodiode can be used as the light detection
section 5.
Heater
[0083] The heater 6 (a heating section) has a function of heating
the atom cell 2 (more specifically the alkali metal in the atom
cell 2) described above. Thus, the alkali metal located in the atom
cell 2 can be kept in the form of a gas with an appropriate
density.
[0084] The heater 6 is configured including, for example, a heating
resistive element for generating heat in accordance with power
distribution. The heating resistive element can be disposed so as
to have contact with the atom cell 2, or can also be disposed so as
not to have contact with the atom cell 2.
[0085] For example, in the case of disposing the heating resistive
element so as to have contact with the atom cell 2, the heating
resistive element is disposed on each of a pair of windows of the
atom cell 2. Thus, it is possible to prevent the alkali metal atoms
from condensing on the windows of the atom cell 2. As a result, the
characteristics (the oscillation characteristics) of the atomic
oscillator 1 can be made excellent for a long period of time. Such
a heating resistive element is formed of a material having
permeability with respect to the excitation light, specifically a
transparent electrode material such as an oxide such as ITO (indium
tin oxide), IZO (indium zinc oxide), In.sub.3O.sub.3, SnO.sub.2,
Sb-doped SnO.sub.2, and Al-doped ZnO. Further, the heating
resistive element can be formed using, for example, a chemical
vapor deposition (CVD) such as a plasma CVD or a thermal CVD, a dry
plating method such as a vacuum deposition, or a sol-gel
method.
[0086] Further, in the case of disposing the heating resistive
element so as not to have contact with the atom cell 2, it is
sufficient to conduct the heat from the heating resistive element
to the atom cell 2 via a member made of metal, ceramics, or the
like superior in heat conductivity.
[0087] It should be noted that the heater 6 is not limited to the
configuration described above providing the atom cell 2 can be
heated, and a variety of types of heaters can be used as the heater
6. Further, it is also possible to heat the atom cell 2 using a
Peltier element instead of, or together with the heater 6.
Temperature Sensor
[0088] The temperature sensor 7 is for detecting the temperature of
the heater 6 or the atom cell 2. Further, an amount of the heat
generated by the heater 6 described above is controlled based on
the detection result of the temperature sensor 7. Thus, it is
possible to keep the alkali metal atoms in the atom cell 2 at a
desired temperature.
[0089] It should be noted that the installation position of the
temperature sensor 7 is not particularly limited, and can also be,
for example, a place on the heater 6 or a place on an outside
surface of the atom cell 2.
[0090] The temperature sensor 7 is not particularly limited, and a
variety of known temperature sensors such as a thermistor or a
thermocouple can be used as the temperature sensor 7.
Magnetic Field Generation Section
[0091] The magnetic field generation section 8 has a function of
generating the magnetic field for Zeeman-splitting the degenerate
energy levels of the alkali metal in the atom cell 2. Thus, it is
possible to enlarge the degenerate gap between the energy levels
different from each other of the alkali metal using the Zeeman
split to thereby improve the resolution. As a result, the accuracy
of the oscillation frequency of the atomic oscillator 1 can be
improved.
[0092] The magnetic field generation section 8 is formed of, for
example, a Helmholtz coil disposed so as to sandwich the atom cell
2, or a solenoid coil disposed so as to cover the atom cell 2.
Thus, it is possible to generate a unidirectional and uniform
magnetic field in the atom cell 2.
[0093] Further, the magnetic field generated by the magnetic field
generation section 8 is a constant magnetic field (direct-current
magnetic field), but can also be superimposed with an
alternating-current magnetic field.
Control Section
[0094] The control section 10 has a function of controlling each of
the light emitting section 3, the heater 6, and the magnetic field
generation section 8.
[0095] The control section 10 has an excitation light control
section 12 for controlling the frequencies of the first resonance
light and the second resonance light of the light emitting section
3, a temperature control section 11 for controlling the temperature
of the alkali metal in the atom cell 2, and a magnetic field
control section 13 for controlling the magnetic field generated by
the magnetic field generation section 8.
[0096] The excitation light control section 12 controls the
frequencies of the first resonance light and the second resonant
light emitted from the light emitting section 3 based on the
detection result of the light detection section 5 described above.
More specifically, the excitation light control section 12 controls
the frequencies of the first resonance light and the second
resonance light emitted from the light emitting section 3 so that
the frequency difference (.omega..sub.1-.omega..sub.2) described
above becomes equal to the frequency .omega..sub.0 inherent in the
alkali metal described above.
[0097] Here, the excitation light control section 12 is provided
with a voltage controlled quartz crystal oscillator (an oscillation
circuit) although not shown, and outputs an output signal of the
voltage controlled quartz crystal oscillator as an output signal
while synchronizing and adjusting the oscillation frequency of the
voltage controlled quartz crystal oscillator based on the detection
result of the light detection section 5.
[0098] For example, although not shown, the excitation light
control section 12 is provided with a frequency multiplier for
multiplying the frequency of the output signal from the voltage
controlled quartz crystal oscillator, superimposes a signal (a
high-frequency signal) obtained by the multiplication by the
frequency multiplier on a direct-current bias current, and then
input the result to the light emitting section 3 as a drive signal.
Thus, it results that the signal with the desired frequency is
output from the voltage controlled quartz crystal oscillator by
controlling the voltage controlled quartz crystal oscillator so
that the EIT signal is detected by the light detection section 5.
The multiplication ratio of the frequency multiplier is
.omega..sub.0/(2.times.f) assuming that, for example, the desired
frequency of the output signal from the atomic oscillator 1 is f.
Therefore, it is possible to modulate the light emitting element
such as a semiconductor laser included in the light emitting
section 3 to emit the two types of light having the frequency
difference (.omega..sub.1-.omega..sub.2) equal to .omega..sub.0
using the signal from the frequency multiplier when the oscillation
frequency of the voltage controlled quartz crystal oscillator is
f.
[0099] Further, the temperature control section 11 controls
distribution of the power to the heater 6 based on the detection
result of the temperature sensor 7. Thus, the atom cell 2 can be
kept within the desired temperature range. For example, the atom
cell 2 is controlled in temperature by the heater 6 to, for
example, around 70.degree. C.
[0100] Further, the magnetic field control section 13 controls the
distribution of the power to the magnetic field generation section
8 so that the magnetic field generated by the magnetic field
generation section 8 becomes constant.
[0101] Such a control section 10 is disposed in, for example, an IC
chip mounted on a substrate.
[0102] Hereinabove, the configuration of the atomic oscillator 1 is
briefly described.
Detailed Description of Atom Cell
[0103] FIG. 4A is a vertical cross-sectional view of the atom cell
provided to the atomic oscillator shown in FIG. 1, and FIG. 4B is a
cross-sectional view (a horizontal cross-sectional view) along the
line A-A in FIG. 4A.
[0104] It should be noted that the upper side of FIG. 4A is
referred to as an "upper side," and the lower side thereof is
referred to as a "lower side" in the following descriptions for the
sake of convenience of explanation.
[0105] As shown in FIG. 4A, the atom cell 2 has a body section 21,
and a pair of window sections 22, 23 disposed sandwiching the body
section 21. In the atom cell 2, the body section 21 is disposed
between the pair of windows 22, 23, and the body section 21 and the
pair of window sections 22, 23 compartment (form) an internal space
S in which the gaseous alkali metal is encapsulated.
[0106] The body section 21 has a plate-like shape having a vertical
direction as the thickness direction, and is provided with through
holes 211, 212, and 213 penetrating in the thickness direction of
the body section 21 (the vertical direction), a groove 214 opening
on an upper surface of the body section 21 to communicate the
through hole 211 and the through hole 213 with each other, and a
groove 215 opening on the upper surface of the body section 21 to
communicate the through hole 212 and the through hole 213. It
should be noted that it is also possible to form a recessed section
opening on the upper surface of the body section 21 instead of the
through hole 212. Similarly, it is also possible to form a recessed
section opening on the upper surface of the body section 21 instead
of the through hole 213.
[0107] The constituent material of the body section 21 is not
particularly limited, and there can be cited a glass material, a
quartz crystal, a metal material, a resin material, a silicon
material, and so on as the constituent material of the body section
21. Among these materials, either of the glass material, the quartz
crystal, and the silicon material is preferably used, and the
silicon material is further preferably used. Thus, even in the case
of forming a small atom cell 2 with the width and the height equal
to or smaller than 10 mm, it is possible to easily form the body
section 21 high in accuracy using a microfabrication technology
such as etching. In particular, the microfabrication by etching can
be performed on silicon. Therefore, by forming the body section 21
using silicon, even in the case of achieving miniaturization of the
atom cell 2, the body section 21 can easily and accurately be
formed. Further, in the case in which the window sections 22, 23
are formed of glass, the body section 21 and the window sections
22, 23 can airtightly be bonded to each other with ease using
anodic bonding, and thus the reliability of the atom cell 2 can be
made excellent.
[0108] To the lower surface of such a body section 21, there is
bonded the window section 22 having a plate-like shape, and on the
other hand, to the upper surface of the body section 21, there is
bonded the window 23 having a plate-like shape. Thus, the lower-end
side opening of each of the through holes 211, 212, and 213 is
blocked by the window 22, and at the same time, the upper-end side
opening of each of the through holes 211, 212, and 213 and the
opening of each of the grooves 214, 215 are blocked by the window
23. Further, the internal space S constituted by the through holes
211, 212, and 213 and the grooves 214, 215 is formed as an airtight
space.
[0109] The bonding method between the body section 21 and the
window sections 22, 23 is determined in accordance with the
constituent materials of these sections, and is not particularly
limited providing the body section 21 and the window sections 22,
23 can airtightly be bonded to each other. As the bonding method,
there can be used, for example, a bonding method using an adhesive,
a direct bonding method, an anodic bonding method, and a surface
activated bonding method, and the direct bonding method or the
anodic bonding method is preferably used. Thus, the body section 21
and the window sections 22, 23 can airtightly be bonded to each
other with ease, and the reliability of the atom cell 2 can be made
excellent.
[0110] The window sections 22, 23 bonded to such a body section 21
each have permeability with respect to the excitation light from
the light emitting section 3. Further, one of the window sections,
namely the window section 22, is an entrance side window section
through which the excitation light LL enters the internal space S
of the atom cell 2, and the other of the window sections, namely
the window section 23, is an exit side window section through which
the excitation light LL is emitted from the internal space S of the
atom cell 2.
[0111] The constituent material of the window sections 22, 23 is
not particularly limited providing such permeability with respect
to the excitation light as described above is provided, and as the
constituent material of the window sections 22, 23, there can be
cited, for example, a glass material and a quartz crystal, and the
glass material is preferably used. Thus, there can be realized the
window sections 22, 23 having the permeability with respect to the
excitation light. Further, in the case in which the body section 21
is formed of silicon, by forming the window sections 22, 23 using
glass, the body section 21 and the window sections 22, 23 can
airtightly be bonded to each other with ease using anodic bonding,
and thus the reliability of the atom cell 2 can be made excellent.
It should be noted that depending on the thickness of the window
sections 22, 23 and the intensity of the excitation light, the
window sections 22, 23 can be formed of silicon. In this case, the
body section 21 and the window sections 22, 23 can directly be
bonded to each other.
[0112] In the internal space S formed as a compartment by such a
body section 21 and such window sections 22, 23, there is housed
the gaseous alkali metal. The gaseous alkali metal housed in the
internal space S is excited by the excitation light LL in the
through hole 211. Specifically, at least a part of the space in the
through hole 211 constitutes a "light passing space" (a first
region) through which the excitation light LL passes. In the
present embodiment, the cross-sectional surface of the through hole
211 has a circular shape, and in contrast, the cross-sectional
surface of the light passing space has a similar shape (i.e., a
circular shape) to the cross-sectional surface of the through hole
211 although not shown, and is set to be slightly smaller than the
cross-sectional surface of the through hole 211. It should be noted
that the cross-sectional shape of the through hole 211 is not
limited to the circular shape, but can also be a polygonal shape
such as a quadrangular shape or a pentangular shape, an elliptical
shape, or the like.
[0113] Further, the space in the through hole 213 out of the
internal space S is communicated with a space in the through hole
211 via a space in the groove 214, and is also communicated with a
space in the through hole 212 via a space in the groove 215. In the
present embodiment, the cross-sectional surfaces of the through
holes 212, 213 each have a rectangular shape. It should be noted
that the cross-sectional shapes of the through holes 212, 213 are
not limited to a rectangular shape, but can also be a polygonal
shape such as a pentangular shape, a circular shape, an elliptical
shape, or the like.
[0114] In the space in the through hole 213, there is housed alkali
metal M in the form of a liquid or a solid. In other words, the
space in the through hole 213 is a space constituting a part of the
internal space S or communicated with the internal space S, and
constitutes a "metal storage section" (a third region) in which the
liquid or solid alkali metal M is disposed. The liquid or solid
alkali metal M is held in equilibrium with the gaseous alkali metal
in the internal space S at the saturated vapor pressure, and thus,
the gaseous alkali metal in the internal space S can be kept at a
predetermined density. Further, by disposing the alkali metal M in
the space in the through hole 213 separated from the space in the
through hole 211, it is possible to reduce the chances for the
alkali metal M to affect the frequency characteristics.
[0115] Further, in the space in the through hole 212, there are
disposed the compound P and the getter material G. The compound
Pisan "alkali metal emission material" having emitted the gaseous
alkali metal and the solid alkali metal M described above, and is a
residual dross of a decomposition reaction of a metal compound P1
used for the production of the atom cell 2 described later, and is
an unreacted part of the metal compound P1, for example. Further,
the compound P includes a product other than the alkali metal
produced by the decomposition reaction of the metal compound P1 in
some cases. Further, by disposing the compound P in the space in
the through hole 212 separated from the space in the through hole
211, it is possible to reduce the chances for the compound P to
affect the frequency characteristics.
[0116] It should be noted that in the case in which the product
other than the alkali metal produced by the decomposition reaction
of the metal compound P1 is an inert gas such as nitrogen, such a
product can be used as a part of the buffer gas.
[0117] The getter material G has a function of adsorbing or
absorbing a gas other than the desired alkali metal gas or the
buffer gas. Thus, it is possible to make the getter material G
adsorb or absorb at least a part of the unwanted material other
than the alkali metal atoms existing in the internal space S.
Therefore, an amount of the unwanted material suspended in the atom
cell 2 can be reduced, and as a result, it is possible to prevent
or reduce the degradation of the frequency stability due to the
influence exerted on the EIT signal caused by a change in behavior
of the alkali metal atoms due to the unwanted material in the atom
cell 2. Therefore, the frequency stability can be improved.
Further, by disposing the getter material G in the space in the
through hole 212 separated from the space in the through hole 211,
it is possible to reduce the chances for the getter material G to
affect the frequency characteristics.
[0118] It should be noted that the compound P, the metal compound
P1, the getter material G will be described in detail together with
a method of manufacturing the atom cell 2 described later.
[0119] As described above, the internal space S of the atom cell 2
includes the first region (the space formed of the through hole
211) housing the gaseous alkali metal (the alkali metal atoms), a
second region (the space formed of the through hole 212) housing
the compound P as the alkali metal emission material, and the third
region (the space formed of the through hole 213) housing the
liquid or solid alkali metal M. According to such an atom cell 2,
since the liquid or solid alkali metal M exists in the third region
of the internal space S as an excess, it is possible to prevent the
amount (partial pressure) of the gaseous alkali metal existing in
the first region of the internal space S sealed from decreasing.
Therefore, it is possible to realize the excellent frequency
stability for a long period of time.
[0120] Here, the temperature in the through hole 211 is higher than
the temperature in the through hole 213. Thus, it is possible to
make the gaseous alkali metal atoms and the liquid or solid alkali
metal stably exist in the through hole 211 and the through hole
213, respectively.
[0121] Further, in the present embodiment, the space formed of the
through hole 213 is located between the space formed of the through
hole 211 and the space formed of the through hole 212. Thus, as
described later, even in the case of separating and then removing
the space formed of the through hole 212, it is possible to
communicate the space formed of the through hole 211 and the space
formed of the through hole 213 with each other, and the amount of
the gaseous alkali metal atoms existing in the space formed of the
through hole 211 can be prevented from decreasing.
[0122] Further, the width of the grooves 214, 215 constituting the
communication holes communicating the space formed of the through
hole 211 and the space formed of the through hole 212 with each
other is smaller than the width of the compound P. Thus, it is
possible to prevent the compound P from moving from the inside of
the through hole 212 to the inside of the through hole 211.
[0123] Such an atom cell 2 as described above provided to the
atomic oscillator 1 can be manufactured in such a manner as
described below. Thus, the partial pressure of the gas other than
the gaseous alkali metal atoms in the internal space S can be set
to a level equal to or lower than 10.sup.-4 Pa. Such an atom cell 2
small in the amount of unwanted gas has excellent
characteristics.
Method of Manufacturing Atom Cell
[0124] Hereinafter, a method of manufacturing the atom cell
according to the invention will be described citing the case of
manufacturing the atom cell 2 described above as an example. It
should be noted that the description is hereinafter presented
citing the case in which the body section 21 is formed of silicon,
and the window sections 22, 23 are each formed of glass as an
example.
[0125] FIG. 5 is a diagram showing a member used for a preparatory
process in the method of manufacturing the atom cell shown in FIGS.
4A and 4B. FIGS. 6A through 6C are diagrams for describing the
preparatory process, an emission process, a temperature adjustment
process, and a segmenting process in the method of manufacturing
the atom cell shown in FIGS. 4A and 4B.
[0126] The method of manufacturing the atom cell 2 includes [1]
preparatory process, [2] emission process, [3] temperature
adjustment process, and [4] segmenting process. Hereinafter, each
of the processes will sequentially be described.
1 Preparatory Process
[0127] 1-1.
[0128] Firstly, as shown in FIG. 5, there are prepared a body
section forming substrate 210 and window section forming substrates
220, 230.
[0129] The body section forming substrate 210 is a silicon
substrate used for forming the body section 21 described above, and
has the through holes 211, 212, and 213, and the grooves 214, 215.
Further, the window section forming substrate 220 is a glass
substrate used for forming the window section 22 described above.
Similarly, the window section forming substrate 230 is a glass
substrate used for forming the window section 23 described
above.
[0130] As described above, since the body section forming substrate
210 includes silicon, and the window section forming substrates
220, 230 each include glass, it is possible to manufacture the atom
cell 2 small in size and high in accuracy using an etching
technology and a photolithography technology.
[0131] In the present embodiment, the body section forming
substrate 210 has a plurality of sets of the through holes 211,
212, and 213, and the grooves 214, 215, and is then segmented into
the body sections 21 in the segmenting process [4] described later.
Further, the window section forming substrates 220, 230 are
segmented into the window sections 22, 23 in the segmenting process
[4] described later.
1-2.
[0132] Then, as shown in FIG. 6A, the body section forming
substrate 210 and the window section forming substrates 220, 230
are bonded to each other (a first bonding process) in the state in
which the metal compound P1 and the getter material G are disposed
in the internal space S.
[0133] In the detailed description, firstly, the body section
forming substrate 210 and the window section forming substrate 220
are bonded to each other. Thus, there can be obtained a bonded body
(a laminated body) having the body section forming substrate 210
and the window section forming substrate 220 bonded to each
other.
[0134] Bonding between the body section forming substrate 210 and
the window section forming substrate 220 is preferably achieved by
anodic bonding as a kind of heating bonding. Thus, the body section
forming substrate 210 and the window section forming substrate 220
can airtightly be bonded to each other with relative ease.
[0135] It should be noted that it is also possible to bond the body
section forming substrate 210 and the window section forming
substrate 230 to each other. In this case, it is sufficient to bond
the body section forming substrate 210 and the window section
forming substrate 220 to each other after disposing the metal
compound P1 and the getter material G, and before the emission
process [2].
[0136] Then, the metal compound P1 and the getter material G are
disposed in the recessed section formed of the through hole 212 (a
disposition process). Further, on this occasion, although not shown
in the drawings, a reducing agent necessary for the decomposition
reaction of the metal compound P1 is disposed in the recessed
section if needed.
[0137] The metal compound P1 is a compound including the alkali
metal, and is a compound (an alkali metal emission material) for
generating (emitting) the alkali metal as a simple substance by a
decomposition reaction (reduction). The metal compound P1 is not
particularly limited providing the compound generates the alkali
metal as a simple substance by a decomposition reaction
(reduction), and for example, cesium chloride (CsCl), cesium azide
(CsN.sub.3), and cesium chromate (CsCr.sub.2O.sub.7) can be cited
as the metal compound P1. Here, it is preferable for the metal
compound P1 to be a compound not substantially developing the
decomposition reaction under the heat when performing bonding (a
second bonding process) between the body section forming substrate
210 and the window section forming substrate 230 described later,
in other words, to be a compound developing the decomposition
reaction at a temperature higher than the temperature at which the
body section forming substrate 210 and the window section forming
substrate 230 are heated when bonding the body section forming
substrate 210 and the window section forming substrate 230 to each
other. Thus, it is possible to prevent the alkali metal from
adhering to the bonding surfaces of the body section forming
substrate 210 and the window section forming substrate 230, or to
reduce the chances for the alkali metal to adhere to the bonding
surfaces of the body section forming substrate 210 and the window
section forming substrate 230.
[0138] Further, the reducing agent used for the decomposition
reaction of the metal compound P1 is not particularly limited, and
in the case in which, for example, the metal compound P1 is cesium
chloride, calcium is used as the reducing agent. It should be noted
that the reducing agent can be a separated body from the metal
compound P1, or can be integrated with the metal compound P1 as a
mixture or an aggregate with the metal compound P1.
[0139] Further, the getter material G has a function of adsorbing
or absorbing a gas other than the desired alkali metal gas or the
buffer gas. The getter material G is not particularly limited
providing such a function is provided, and as the getter material
G, there can be cited, for example, an alloy including at least one
of titanium, barium, tantalum, zirconium, aluminum, vanadium,
indium, and calcium, or an Al--Zr--V--Fe series alloy. By using
such a getter material G, it is possible to make the getter
material G adsorb or absorb the gaseous unwanted materials in the
internal space S after the second bonding process described later.
It should be noted that the getter material G can be a separated
body from the metal compound P1, or can be integrated with the
metal compound P1 as a mixture or an aggregate with the metal
compound P1.
[0140] Then, the body section forming substrate 210 (one surface
side of the first substrate) and the window section forming
substrate 230 are bonded to each other (the second bonding process;
a sealing process). Thus, the recessed sections respectively formed
of the through holes 211, 212, and 213 and the grooves 214, 215 are
sealed, and thus, the internal space S is formed.
[0141] As the bonding method between the body section forming
substrate 210 and the window section forming substrate 230, there
can be used substantially the same method as the bonding method
between the body section forming substrate 210 and the window
section forming substrate 220 described above.
[0142] In the anodic bonding, the body section forming substrate
210 and the window section forming substrates 220, 230 become high
in temperature on the one hand, and the alkali metal as a simple
substance, for example, is relatively low in melting point and
boiling point on the other hand. Therefore, if the alkali metal as
a simple substance exists in the heating bonding, the alkali metal
adheres to the bonding surfaces of the body section forming
substrate 210 and the window section forming substrate 230 to incur
degradation of the bonding strength. In contrast, in the second
bonding process (the sealing process), since the metal compound P1
disposed in the recessed section formed of the through hole 212
keeps the solid state even under the heat in the anodic bonding, it
is possible to prevent the alkali metal from adhering to the
bonding surfaces of the body section forming substrate 210 and the
window section forming substrate 230, or to reduce the chances for
the alkali metal to adhere to the bonding surfaces of the body
section forming substrate 210 and the window section forming
substrate 230.
[0143] As described above, in the preparatory process [1], there is
prepared a bonded body formed of the body section forming substrate
210 and the window section forming substrates 220, 230. The bonded
body is a plurality of "cell containers" each having the internal
space S including the through holes 211, 212, and 213 communicated
with each other, and housing the solid compound including the
alkali metal in the through hole 212 of the internal space S.
[0144] Here, since the plurality of cell containers is connected to
one another, a plurality of atom cells 2 can efficiently be
manufactured through the segmenting process [4] described
later.
[0145] Further, since the preparatory process [1] includes a step
of sealing the internal space S as described above, the amount of
the unwanted gas in the internal space S of the atom cell 2
obtained can be reduced.
2 Emission Process (Compound Decomposition Process)
[0146] Then, as shown in FIG. 6B, the metal compound P1 is
irradiated with a laser beam (an energy beam). Thus, by making the
metal compound P1 develop the decomposition reaction, the alkali
metal simple substance is taken out.
[0147] On this occasion, due to the decomposition reaction of the
metal compound P1, a reaction product other than the alkali metal
occurs, and at the same time, the unreacted part of the metal
compound P1 remains as the residual dross to form the compound
P.
[0148] In the specific description, in the case in which, for
example, the metal compound P1 is cesium chloride, and calcium is
used as the reducing agent, in the present process, there occurs
the following reaction.
2CsCl+Ca.fwdarw.2Cs.uparw.+CaCl.sub.2
[0149] As described above, by reducing cesium chloride using
calcium as the reducing agent, cesium can be taken out as a simple
substance. Therefore, the cesium atoms can be encapsulated in the
atom cell 2.
[0150] Further, in the case in which the metal compound P1 is
cesium azide, the following reaction develops in the present
process.
2CsN.sub.3.fwdarw.2Cs+3N.sub.2
[0151] As described above, by reducing cesium azide, cesium can be
taken out as a simple substance. Therefore, the cesium atoms can be
encapsulated in the atom cell 2.
[0152] In the present process, since the decomposition reaction is
caused by irradiating the metal compound P1 with the energy beam,
the metal compound P1 disposed in the internal space S thus sealed
can be made to develop the decomposition reaction. It should be
noted that although in FIG. 6B, there is illustrated the case of
causing the decomposition reaction of the metal compound P1 using
the laser beam as an example, besides the laser beam, there can be
cited, for example, a light beam other than the laser beam, an
electromagnetic ray such as an X ray or a .gamma. ray, a particle
beam such as an electron beam or an ion beam, or a beam obtained by
combining two or more of these energy beams with each other
providing the decomposition reaction of the metal compound P1 is
caused. Further, it is also possible to heat the metal compound P1
using electromagnetic induction to cause the decomposition
reaction.
[0153] In such a manner as described above, by heating the inside
of the through hole 212, there is performed the emission process of
emitting the alkali metal from the metal compound P1.
3 Temperature Adjustment Process
[0154] The temperature in the vicinity of the through hole 213 is
decreased to a level lower than the temperature in the vicinity of
the through hole 211 at the same time as or after the emission
process [2]. In the emission process [2] described above, the
gaseous alkali metal equal to or more than the saturated amount is
emitted from the metal compound P1. Therefore, by decreasing the
temperature in the vicinity of the through hole 213 to a level
lower than the temperature in the vicinity of the through hole 211,
it is possible to condense the liquid or solid alkali metal M
inside the through hole 213.
[0155] It should be noted that although in FIGS. 6A through 6C,
there is illustrated the case of performing the temperature
adjustment process [3] at the same time as (in the period
overlapping) the emission process [2] as an example, the
temperature adjustment process [3] can also be performed after the
emission process [2] or after the segmenting process [4] described
later. Further, although in FIGS. 6A through 6C, there is
illustrated the case of cooling the vicinity of the through hole
213 as an example, the invention is not limited to this
configuration providing there is provided a relationship in which
the temperature in the vicinity of the through hole 213 becomes
lower than the temperature in the vicinity of the through holes
211, 212, and it is also possible to, for example, heat the
vicinity of the through hole 211.
[0156] In such a manner as described above, there is performed the
temperature adjustment process of decreasing the temperature in the
through hole 211 to a level lower than the temperature in the
through hole 213.
4 Segmenting Process
[0157] Then, the layered structure (the bonded body) formed of the
body section forming substrate 210 and the window section forming
substrates 220, 230 is segmented by, for example, dicing. Thus, the
atom cell 2 can be obtained as shown in FIG. 6C.
[0158] According to such a method of manufacturing the atom cell 2
as described above, the atom cell 2 exerting such an advantage as
described above can be obtained. Specifically, it is possible to
obtain the atom cell 2 in which the liquid or solid alkali metal M
exists as an excess in the through hole 213 of the internal space
S. According to the atom cell 2 thus obtained, it is possible to
prevent the amount (the partial pressure) of the gaseous alkali
metal atoms located inside the through hole 211 of the internal
space S sealed from decreasing, and thus the excellent frequency
stability can be realized for a long period of time.
[0159] Further, since the alkali metal atoms are encapsulated in
the internal space S using the solid alkali metal compound P1, it
is possible to prevent the alkali metal atoms from adhering to the
bonding surfaces of the body section forming substrate 210 and the
window section forming substrate 230. Therefore, the body section
forming substrate 210 and the window section forming substrate 230
can easily and firmly be bonded to each other. As a result, the
reliability of the atom cell 2 can be improved.
MODIFIED EXAMPLE
[0160] FIGS. 7A and 7B are diagrams for describing a modified
example of the atom cell according to the first embodiment of the
invention.
[0161] The atom cell 2 described above can be incorporated in the
atomic oscillator 1 with the configuration without modification,
but can also be used in the configuration in which the space (the
communication hole) formed of the groove 215 is blocked, or can
also be used in the configuration in which the space (the
communication hole) formed of the groove 215 is blocked, and at the
same time, the space formed of the through hole 212 is separated
and then removed.
[0162] In the case of such configurations, for example, in the
method of manufacturing the atom cell 2 described above, the window
section forming substrate 230 is melted in the vicinity of the
groove 215 to form a sealing section 216, and then the inside of
the groove 215 is blocked by the sealing section 216 as shown in
FIG. 7A after the temperature adjustment process [3] and before the
segmenting process [4]. Subsequently, the segmenting process is
performed, and at the same time the part corresponding to the
through hole 212 is removed by, for example, dicing. Thus, as shown
in FIG. 7B, the atom cell 2A having a body section 21A and window
sections 22A, 23A bonded to each other can be obtained. The atom
cell 2A corresponds to the configuration in which the space (the
communication hole) formed of the groove 215 is blocked and the
space formed of the through hole 212 is separated and then removed
in the atom cell 2 described above.
[0163] According to such an atom cell 2A as described hereinabove,
since the compound P and the getter material G do not exist in the
internal space S, there is no chance for the compound P and the
getter material G to, for example, adsorb the necessary gas
existing in the internal space S, and it is possible to reduce the
variation in the gas composition in the internal space S.
[0164] Here, by providing the removal process of removing the
through hole 212 after the emission process [2], the compound P
having emitted the alkali metal can be eliminated in the atom cell
2A thus obtained to reduce the influence of the compound P to
thereby enhance the frequency stability.
[0165] Further, by performing the removal process after the
temperature adjustment process [3], the compound P having emitted
the alkali metal can be eliminated in the atom cell 2A
obtained.
[0166] As described above, in the preparatory process [1], the
inside of the through hole 211 and the inside of the through hole
212 are communicated with each other via the grooves 214, 215, and
the removal process includes the step of blocking the groove 215.
Thus, the internal space S from which the through hole 212 has been
removed can easily be sealed.
Second Embodiment
[0167] Then, a second embodiment of the invention will be
described.
[0168] FIG. 8A is a vertical cross-sectional view of an atom cell
provided to an atomic oscillator according to the second embodiment
of the invention, and FIG. 8B is a cross-sectional view (a
horizontal cross-sectional view) along the line A-A in FIG. 8A.
FIGS. 9A and 9B are diagrams for describing a modified example of
the atom cell according to the second embodiment of the
invention.
[0169] The present embodiment is substantially the same as the
first embodiment except the point that a slit for making the
removal of the second region easy is provided to the atom cell.
[0170] It should be noted that in the description below, the second
embodiment will be described with a focus on the difference from
the embodiment described above, and the description for
substantially the same issues will be omitted.
[0171] In the atom cell 2B (the gas cell) shown in FIGS. 8A and 8B,
the slit 24 is formed in the periphery of the groove 215. In other
words, a weak section weaker than other portions is formed in the
periphery of the groove 215. Thus, it becomes easy to block the
space (the communication hole) formed of the groove 215, and at the
same time, separate the space formed of the through hole 212.
[0172] For example, as shown in FIG. 9A, the vicinity of the groove
215 of the window section 23 is melted to form a sealing section
217 to thereby block the groove 215 with the sealing section 217.
On this occasion, since the weak section is formed in the periphery
of the groove 215 as described above, the part corresponding to the
through hole 212 can be removed at the same time as melting the
vicinity of the groove 215. Thus, the atom cell 2C can be obtained
as shown in FIG. 9B. The atom cell 2C corresponds to the
configuration in which the space (the communication hole) formed of
the groove 215 is blocked and the space formed of the through hole
212 is separated and then removed in the atom cell 2B described
above.
Third Embodiment
[0173] Then, a third embodiment of the invention will be
explained.
[0174] FIG. 10 is a horizontal cross-sectional view showing an atom
cell provided to an atomic oscillator according to the third
embodiment of the invention.
[0175] The present embodiment is substantially the same as the
first embodiment described above except the point that the
positional relationship of the second region and the third region
with respect to the first region is different.
[0176] It should be noted that in the description below, the third
embodiment will be described with a focus on the difference from
the embodiment described above, and the description for
substantially the same issues will be omitted.
[0177] In a body section 21D of the atom cell 2D shown in FIG. 10,
the through hole 211 is disposed between the through hole 212 and
the through hole 213. In other words, the through hole 212 is
disposed on one side, and the through hole 213 is disposed on the
other side with respect to the through hole 211. Further, the
through hole 212 is communicated with the through hole 211 via a
groove 218, and the through hole 213 is communicated with the
through hole 211 via a groove 219.
[0178] According to such an atom cell 2D, since the space (the
first region) formed of the through hole 211 is located between the
space (the second region) formed of the through hole 212 and the
space (the third region) formed of the through hole 213, in the
case of heating the inside of the through hole 212 to emit the
alkali metal atoms from the alkali metal emission material, the
temperature in the through hole 213 can easily be set to a level
lower than the temperature in the through hole 212. Therefore, the
liquid or solid alkali metal M can easily be housed in the through
hole 213. It should be noted that the positional relationship
between the through holes 212, 213 in the circumferential direction
of the through hole 211 is not limited to the example shown in the
drawings, and it is also possible to dispose the through hole 212,
for example, on the upper side or the lower side in FIG. 10 with
respect to the through hole 211.
2. Electronic Apparatus
[0179] Such an atomic oscillator as described hereinabove can be
incorporated in a variety of electronic apparatuses.
[0180] The electronic apparatus according to the invention will
hereinafter be described.
[0181] FIG. 11 is a diagram showing a schematic configuration in
the case of using the atomic oscillator according to the invention
to a positioning system using GPS satellites.
[0182] The positioning system 100 shown in FIG. 11 is constituted
by GPS satellites 200, a base station device 300, and a GPS
receiving device 400.
[0183] The GPS satellites 200 each transmit positioning information
(a GPS signal).
[0184] The base station device 300 is provided with a receiving
device 302 for accurately receiving the positioning information
from the GPS satellites 200 via an antenna 301 installed at, for
example, an electronic reference point (a GPS continuous
observation station), and a transmitting device 304 for
transmitting the positioning information, which has been received
by the receiving device 302, via an antenna 303.
[0185] Here, the receiving device 302 is an electronic device
equipped with the atomic oscillator 1 according to the invention
described above as a reference frequency oscillation source for the
receiving device 302. Such a receiving device 302 has excellent
reliability. Further, the positioning information having been
received by the receiving device 302 is transmitted by the
transmitting device 304 in real time.
[0186] The GPS receiving device 400 is provided with a satellite
receiving section 402 for receiving the positioning information
from the GPS satellites 200 via an antenna 401, and a base station
receiving section 404 for receiving the positioning information
from the base station device 300 via an antenna 403.
3. Moving Object
[0187] FIG. 12 is a diagram showing an example of the moving object
according to the invention.
[0188] In the drawing, the moving object 1500 has a vehicle body
1501, and four wheels 1502, and is configured to rotate the wheels
1502 by a power source (an engine) not shown provided to the
vehicle body 1501. Such a moving object 1500 incorporates the
atomic oscillator 1.
[0189] It should be noted that, the electronic apparatus according
to the invention is not limited to those described above, and as
the electronic apparatus according to the invention, there can be
cited, for example, a cellular phone, a smartphone, a tablet
terminal, a timepiece, a digital still camera, an inkjet ejection
device (e.g., an inkjet printer), a personal computer (a mobile
personal computer and a laptop personal computer), a television
set, a video camera, a video cassette recorder, a car navigation
system, a pager, a personal digital assistance (including one with
a communication function), an electronic dictionary, an electric
calculator, a computerized game machine, a word processor, a
workstation, a video phone, a security video monitor, a pair of
electronic binoculars, a POS terminal, a medical device (e.g., an
electronic thermometer, an electronic manometer, an electronic
blood sugar meter, an electrocardiogram measurement instrument, an
ultrasonograph, and an electronic endoscope), a fish detector,
various types of measurement instruments, various types of gauges
(e.g., gauges for a vehicle, an aircraft, or a ship), a flight
simulator, digital terrestrial broadcasting equipment, a cellular
phone base station, and a GPS module.
[0190] Although the atom cell, the method of manufacturing the atom
cell, the quantum interference device, the atomic oscillator, the
electronic apparatus, and the moving object according to the
invention are hereinabove described based on the embodiments shown
in the accompanying drawings, the invention is not limited to the
embodiments.
[0191] Further, the configuration of each of the sections according
to the invention can be replaced with an arbitrary configuration
having substantially the same function, and further, it is also
possible to add an arbitrary constituent.
[0192] Further, the invention can be a combination of any of
configurations in each of the embodiments described above.
[0193] Further, although in the embodiments described above, there
is described, as an example, the case of using the atom cell
according to the invention for the quantum interference device for
making cesium or the like develop the resonance transition using
coherent population trapping by two types of light different in
wavelength from each other, the atom cell according to the
invention is not limited to this example, but can also be used for
a double resonance device for making rubidium or the like develop
the resonance transition using a double resonance phenomenon due to
light and microwave.
* * * * *