JP2018082108A - Quantum interference device, atomic oscillator, electronic apparatus and moving body - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a quantum interference device capable of improving frequency characteristics, an atomic oscillator including the quantum interference device, an electronic apparatus and a moving body.SOLUTION: The quantum interference device includes: an atom cell which has an internal space in which an alkali metal is sealed; a light source part that emits a beam of light for irradiating the atom cell; a light receiving part for receiving the light transmitting through the atom cell; a first optical element disposed between the light source part and the internal space; and a second optical element disposed between the light source part and the first optical element for focusing the light from the light source part to a position between the first optical element and the same.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a quantum interference device, an atomic oscillator, an electronic device, and a moving object.

  As an oscillator having high long-term frequency stability, an atomic oscillator that oscillates based on energy transition of alkali metal atoms such as rubidium and cesium is known (for example, see Patent Document 1).

  For example, the atomic oscillator described in Patent Document 1 includes a cell (atom cell) in which a gaseous alkali metal is sealed, a semiconductor laser element that emits light that irradiates the cell, and light detection that detects light transmitted through the cell. And a lens and a polarizer disposed between the cell and the semiconductor laser element, and controls the driving of the semiconductor laser element based on the detection result of the photodetector.

US Pat. No. 6,320,472

  In the atomic oscillator described in Patent Document 1, the light transmitted through the lens is reflected by the polarizer, and the reflected light is incident on the semiconductor laser element as return light with high intensity. The wavelength or intensity of the light from the semiconductor laser element As a result, the oscillation characteristics of the atomic oscillator are deteriorated.

  The objective of this invention is providing the quantum interference apparatus which can improve a frequency characteristic, and providing an atomic oscillator, an electronic device, and a moving body provided with this quantum interference apparatus.

The above object is achieved by the present invention described below.
The quantum interference device of the present invention includes an atomic cell having an internal space in which an alkali metal is enclosed;
A light source unit that emits light to irradiate the atomic cell;
A light receiving portion for receiving light transmitted through the atomic cell;
A first optical element disposed between the light source unit and the internal space;
A second optical element disposed between the light source unit and the first optical element and condensing light from the light source unit at a position between the first optical element and the second optical element. .

  According to the quantum interference device having such a feature, the second optical element disposed between the light source unit and the first optical element condenses the light from the light source unit between the first optical element ( Therefore, even if the light from the light source part is reflected by the first optical element, the reflected light can be diverged (diffused). Therefore, the amount of the reflected light incident on the light source unit as return light can be reduced, and output fluctuations (wavelength fluctuation, intensity fluctuation) of the light source part due to the return light can be reduced. As a result, the frequency characteristics of the quantum interference device can be improved.

In the quantum interference device according to the aspect of the invention, it is preferable that the second optical element is a biconvex lens.
Thereby, the focal distance of a 2nd optical element can be shortened, and the distance between a light source part and an atomic cell can also be shortened in connection with it. As a result, the size of the quantum interference device can be reduced. Further, since the surface of the second optical element on the light source unit side is a convex surface, even if light from the light source unit is reflected by the second optical element, the reflected light diverges (diffuses) and enters the light source unit. And fluctuations in the output of the light source unit due to return light can be further reduced.

  In the quantum interference device according to the aspect of the invention, it is preferable that an antireflection film is provided on a surface of the second optical element on the light source unit side.

  Thereby, it can reduce that the light from a light source part reflects in a 2nd optical element, and can further reduce the output fluctuation | variation of the light source part by return light.

In the quantum interference device according to the aspect of the invention, it is preferable that the first optical element is a condenser lens.
Thereby, the light incident on the atomic cell can be made into parallel light or a state close thereto. Therefore, the frequency characteristics of the quantum interference device can be further improved.

  In the quantum interference device according to the aspect of the invention, it is preferable that a surface of the first optical element on the second optical element side is a convex surface.

  Thereby, even if the light from the light source part is reflected by the first optical element, the reflected light can be diverged (diffused) at a wider radiation angle. Therefore, it is possible to reduce the amount of the reflected light that enters the light source unit as return light.

  In the quantum interference device according to the aspect of the invention, it is preferable that at least one of the first optical element and the second optical element includes a component that absorbs light.

  Thereby, at least one of the first optical element and the second optical element can be used as a neutral density filter. Therefore, it is not necessary to separately provide a neutral density filter, and the number of reflection surfaces that cause return light can be reduced.

  In the quantum interference device according to the aspect of the invention, it is preferable that at least one of a λ / 4 plate and a neutral density filter is disposed between the first optical element and the internal space.

  Thereby, the frequency characteristic of a quantum interference apparatus can be improved more. Further, since the λ / 4 plate or the neutral density filter is disposed on the atomic cell side with respect to the first optical element, the light from the light source unit is transmitted to the second optical element relative to the λ / 4 plate or the neutral density filter. The light can be diverged (diffused) by the element and incident. Therefore, even if the light from the light source unit is reflected by the λ / 4 plate or the neutral density filter, the reflected light can be reduced from entering the light source unit as incident light.

  In the quantum interference device according to the aspect of the invention, it is preferable that a third optical element that is a condensing lens is disposed between the internal space and the light receiving unit.

  Thereby, the light that has passed through the internal space of the atomic cell can be collected and incident on the light receiving unit. Therefore, the light receiving area of the light receiving unit can be reduced, and noise generated in the light receiving unit can be reduced. As a result, the S / N ratio of a signal (for example, an EIT signal) obtained using the light reception result of the light receiving unit can be increased, and the frequency characteristics of the quantum interference device can be further improved.

  In the quantum interference device according to the aspect of the invention, it is preferable that at least a part of the third optical element is configured integrally with the atomic cell.

  As a result, the number of parts can be reduced and the size of the quantum interference device can be reduced.

  In the quantum interference device according to the aspect of the invention, it is preferable that at least a part of the first optical element is configured integrally with the atomic cell.

  As a result, the number of parts can be reduced and the size of the quantum interference device can be reduced.

The atomic oscillator according to the present invention includes the quantum interference device according to the present invention.
According to the atomic oscillator having such characteristics, it is possible to enjoy the effects (for example, excellent frequency characteristics) of the quantum interference device and to exhibit excellent characteristics (for example, oscillation characteristics).

An electronic apparatus according to the present invention includes the quantum interference device according to the present invention.
According to the electronic device having such characteristics, it is possible to enjoy the effects (for example, excellent frequency characteristics) of the quantum interference device and exhibit the excellent characteristics.

The moving body of the present invention includes the quantum interference device of the present invention.
According to the moving body having such characteristics, it is possible to enjoy the effects (for example, excellent frequency characteristics) of the quantum interference device and exhibit the excellent characteristics.

1 is a schematic diagram showing an atomic oscillator (an example of a quantum interference device) according to a first embodiment of the present invention. It is a schematic diagram for demonstrating the optical element with which the atomic oscillator shown in FIG. 1 is provided. It is a schematic diagram for demonstrating the optical element with which the atomic oscillator (an example of a quantum interference apparatus) which concerns on 2nd Embodiment of this invention is provided. It is a figure which shows schematic structure at the time of using the atomic oscillator of this invention for the positioning system using a GPS satellite. It is a figure which shows an example of the moving body of this invention.

  Hereinafter, a quantum interference device, an atomic oscillator, an electronic device, and a moving body of the present invention will be described in detail based on embodiments shown in the accompanying drawings.

1. Atomic oscillator (quantum interference device)
First, the atomic oscillator of the present invention (the atomic oscillator including the quantum interference device of the present invention) will be described. In the following, a case where the present invention is applied to an atomic oscillator which is an example of a quantum interference device will be described as an example. However, the quantum interference device of the present invention is not limited to an atomic oscillator, and includes, for example, a magnetic sensor, a quantum memory, and the like. It is also applicable to devices such as.

  FIG. 1 is a schematic diagram showing an atomic oscillator (an example of a quantum interference device) according to the first embodiment of the present invention. FIG. 2 is a schematic diagram for explaining an optical element included in the atomic oscillator shown in FIG.

  The atomic oscillator 1 shown in FIG. 1 has a quantum phenomenon in which, when two resonant lights having specific different wavelengths are simultaneously irradiated to an alkali metal atom, the two resonant lights are transmitted without being absorbed by the alkali metal atom. It is an atomic oscillator that uses interference effects (CPT: Coherent Population Trapping). This phenomenon due to the quantum interference effect is also called an electromagnetically induced transparency (EIT) phenomenon. As illustrated in FIG. 1, the atomic oscillator 1 includes a package unit 2 and a control unit 10 that is electrically connected to the package unit 2.

  The package unit 2 includes a light source 22 (light source unit) that emits light, an atomic cell 21 (gas cell) in which alkali metal atoms such as rubidium atoms and cesium atoms are enclosed, a photodetector 23 (light receiving unit), Optical elements 24 to 27 (first to fourth optical elements), and these are housed in a package (not shown). Here, each of the optical elements 24, 25, and 27 (first to third optical elements) is a lens, and the optical element 26 is a λ / 4 plate. The package of the package unit 2 may be divided into two packages including a package for storing the light source 22 and a package for storing the atomic cell 21 and the photodetector 23. In this case, the optical element 27 May be housed in the same package as the atomic cell 21 and the photodetector 23, but the optical elements 24 to 26 may be housed in either one of the two packages or arranged between the two packages. May be.

  Here, the light source 22 is driven by a drive current in which a modulation current is superimposed on a bias current. The light source 22 includes light having a center wavelength corresponding to the current value of the bias current, and two sideband lights (seconds) having wavelengths shifted from both sides of the light by a wavelength corresponding to the frequency of the modulation current. 1 light and 2nd light) are radiate | emitted. The two sideband lights pass through the optical elements 24, 25 and 26, the atomic cell 21 and the optical element 27 in this order, and are detected by the photodetector 23.

  The control unit 10 includes a detection circuit 31, a modulation circuit 32, a low-frequency oscillator 33, a drive circuit 35, a detection circuit 42, a voltage controlled crystal oscillator 43 (VCXO), and a modulation circuit 44. And a low-frequency oscillator 45 and a phase locked loop 46 (PLL: phase locked loop), which are provided outside the package of the package unit 2. Note that at least a part of the control unit 10 may be housed in the package of the package unit 2.

  Here, the drive circuit 35 supplies the light source 22 with a drive current in which the modulation current is superimposed on the bias current. The detection circuit 31, the modulation circuit 32, and the low frequency oscillator 33 function as a “bias current adjustment unit 30” that adjusts the current value of the bias current of the drive circuit 35 based on the detection result of the photodetector 23. In addition, the detection circuit 42, the voltage-controlled crystal oscillator 43, the modulation circuit 44, the low-frequency oscillator 45, and the phase synchronization circuit 46 are based on two detection results of alkali metal atoms in the atomic cell 21 based on the detection result of the photodetector 23. It functions as a “signal generator 40” that generates a microwave signal corresponding to the transition frequency between the ground levels. The signal generation unit 40 adjusts the frequency of the microwave signal used as the modulation current so that the EIT phenomenon caused by the two sideband lights and the alkali metal atoms in the atomic cell 21 is generated, and the voltage controlled crystal oscillator The output signal of 43 (VCXO) is stabilized at a predetermined frequency, and the output signal is output as a clock signal of the atomic oscillator 1.

Hereinafter, each part of the atomic oscillator 1 will be described sequentially.
<Package part>
As described above, the package unit 2 illustrated in FIG. 1 includes the light source 22 (light source unit), the atomic cell 21 (gas cell), and the photodetector 23 (light detection unit).

(Light source)
The light source 22 (light source unit) is supplied with a drive current obtained by superimposing a modulation current on a bias current, and emits two sideband lights as described above as first light and second light having different frequencies (wavelengths). It has the function to do. Here, the light (first light and second light) emitted from the light source 22 is linearly polarized light. The light source 22 may be a light source having the above-described function, and is not particularly limited. Examples thereof include a light emitting element such as a semiconductor laser such as a vertical cavity surface emitting laser (VCSEL). . The light emitting element used for the light source 22 may directly emit linearly polarized light or may emit non-polarized light. In the case of using a light emitting element that emits non-polarized light, a polarizer may be disposed between the light emitting element and the optical element 26. In addition, “linearly polarized light” is light in which the vibration plane of electromagnetic waves (light) is in one plane, in other words, light in which the vibration direction of the electric field (or magnetic field) is constant.

(Atomic cell)
In the atomic cell 21 (internal space S), gaseous alkali metals (alkali metal atoms) such as rubidium, cesium, and sodium are enclosed. In addition, in the atomic cell 21, a rare gas such as argon or neon, or an inert gas such as nitrogen may be enclosed as a buffer gas together with a gaseous alkali metal, as necessary.

  As shown in FIG. 2, the atomic cell 21 forms a body portion 211 having a columnar through hole 212 and an internal space S that is hermetically sealed by sealing both openings of the through hole 212 of the body portion 211. A pair of windows 213, 214. Here, light LL incident on the internal space S is transmitted through one of the windows 213 and 214, and light LL emitted from the internal space S is transmitted through the other window 214. Is transparent. Accordingly, the constituent material of each of the windows 213 and 214 is not particularly limited as long as it has transparency to the light LL, and examples thereof include glass materials and crystal. On the other hand, the constituent material of the body portion 211 is not particularly limited, and examples thereof include a metal material, a resin material, a glass material, a silicon material, and a crystal. From the viewpoint of workability and bonding with the window portions 213 and 214, It is preferable to use a glass material or a silicon material. Further, the method for joining the body portion 211 and the window portions 213 and 214 is determined according to these constituent materials and is not particularly limited. For example, a direct joining method, an anodic joining method, or the like is used. Can do.

  In the present embodiment, the window portion 214 of the atomic cell 21 has a lens shape (plano-convex lens) and serves as the optical element 27. Thereby, the optical element 27 is configured integrally with the atomic cell 21.

The alkali metal atom accommodated in the atomic cell 21 has energy of a three-level system composed of two different ground levels (first ground level and second ground level) and an excited level. Has a level. The first ground level is an energy level lower than the second ground level. Here, the resonance light (first resonance light) having the frequency ω ₁ corresponding to the energy difference between the first ground level and the excitation level, and the energy difference between the second ground level and the excitation level. resonance light having a frequency omega ₂ of the (second resonant light) alone by the light absorption by irradiating the alkali metal atoms occurs. On the other hand, when the first resonance light and the second resonance light (resonance light pair) are irradiated at the same time, both the first resonance light and the second resonance light are not absorbed by the alkali metal atoms but are transmitted without being absorbed. ) Phenomenon occurs.

In this EIT phenomenon, the first resonance light and the second resonance light are simultaneously irradiated onto the alkali metal atom, and the frequency difference (ω ₁ −ω ₂₎ between the frequency ω ₁ of the first resonance light and the frequency ω ₂ of the second resonance light. ) Occurs at a frequency ω ₀ corresponding to the energy difference ΔE between the first ground level and the second ground level. Accordingly, the light absorption rate in the alkali metal atoms of the first resonant light and the second resonant light in response to the frequency difference (omega ₁ - [omega] ₂₎ (light transmittance) is changed, the frequency difference (omega ₁ - [omega] ₂₎ is When the frequency ω ₀ coincides, the EIT phenomenon occurs, and the intensities of the first resonance light and the second resonance light that have passed through the alkali metal atom rapidly increase. A steep signal generated in accordance with such an EIT phenomenon is called an EIT signal. This EIT signal has an eigenvalue determined by the type of alkali metal atom. Therefore, a highly accurate oscillator can be configured by using such an EIT signal as a reference.

For example, when the alkali metal atom is a cesium atom, the frequency ω ₀ corresponding to the energy difference ΔE is 9.1926 GHz. Therefore, the cesium atom has two types of frequency difference (ω ₁ −ω ₂ ) of 9.1926 GHz. The EIT signal is detected when the same light is irradiated simultaneously.

  The atomic cell 21 is heated by a heater (not shown) that is driven based on a detection result of a temperature sensor (not shown) that detects the temperature of the atomic cell 21. Thereby, the alkali metal in the atomic cell 21 can be maintained in a gaseous state with an appropriate concentration. Further, in the vicinity of the atomic cell 21, for example, a magnetic field generation unit (not shown) having a coil or the like for applying a magnetic field to an alkali metal by energization is provided. By the magnetic field from the magnetic field generation unit, the gap between a plurality of different energy levels in which alkali metal atoms are degenerated can be widened by Zeeman splitting to improve the resolution. As a result, the accuracy of the oscillation frequency of the atomic oscillator 1 can be increased.

(Light receiving section)
The photodetector 23 (light receiving unit) has a function of receiving and detecting light (first light and second light) transmitted through the atomic cell 21 and outputting a detection signal corresponding to the intensity of the detected light. Have. The photodetector 23 is not particularly limited as long as it can detect the above-described light intensity, and includes, for example, a photodetector (light receiving element) such as a photodiode.

(Optical element)
The plurality of optical elements 24 to 27 are provided on the optical path of the light LL between the light source 22 and the photodetector 23, respectively. Here, the optical elements 24 to 26 are arranged on the light source 22 side with respect to the internal space S of the atomic cell 21 and are arranged in this order from the light source 22 side to the atomic cell 21 side. The optical element 27 is disposed on the photodetector 23 side with respect to the internal space S of the atomic cell 21. Note that another optical element such as a neutral density filter may be provided between the optical element 25 and the optical element 26 or between the optical element 26 and the atomic cell 21. In the drawing, the surfaces of the optical elements 24 to 27 are arranged along a plane perpendicular to the optical axis of the light LL, but at least one of the optical elements 24 to 27 is an optical axis of the light LL. It may be arranged in a posture inclined with respect to a plane perpendicular to the.

  The optical element 24 (second optical element) is a biconvex lens, and particularly a ball lens in this embodiment. Accordingly, the surfaces of the optical element 24 on the atomic cell 21 side and the light source 22 side are respectively convex surfaces (curved convex surfaces). In particular, the optical element 24 is configured to condense (focus) the light LL from the light source 22 at a condensing point FP (beam waist) located between the optical element 24 and the optical element 25. . The optical element 24 condenses (converges) the light LL from the light source 22 at a condensing point FP (position where the beam diameter is the smallest) located between the optical element 24 and the optical element 25. If possible, the lens is not limited to a ball lens, and may be a biconvex lens other than a ball lens or a plano-convex lens. Furthermore, a combination of a plurality of lenses (biconvex lens, planoconvex lens, etc.) may be used.

  In the present embodiment, an antireflection film 241 (reflection reduction portion) that reduces reflection of light from the light source 22 is provided on the surface of the optical element 24 on the light source 22 side. The antireflection film 241 is composed of, for example, a dielectric multilayer film in which dielectric films such as a silicon dioxide film and a tantalum oxide film are laminated. The material (refractive index), thickness, and number of layers of each layer of the dielectric multilayer film By appropriately setting, the desired antireflection function is exhibited. An antireflection film similar to the antireflection film 241 may be provided on the surface of the optical element 24 on the atomic cell 21 side. In this case, by providing an antireflection film over almost the entire outer surface of the optical element 24, there is an advantage that when the optical element 24 is installed, it is not necessary to adjust the posture of the optical element 24 and the installation is easy. .

  The optical element 25 (first optical element) is a plano-convex lens having a convex surface on the light source 22 side and a flat surface on the atomic cell 21 side. In particular, the optical element 25 is configured to make the light LL from the light source 22 parallel light or a state close thereto. That is, the optical element 25 is configured to adjust (reduce) the radiation angle of the light LL that diverges (diffuses) from the condensing point FP toward the optical element 25. The optical element 25 only needs to be able to adjust the radiation angle of the light LL as described above, and may be a plano-convex lens having a convex surface on the atom cell 21 side or a biconvex lens. Furthermore, a combination of a plurality of lenses (biconvex lens, planoconvex lens, etc.) may be used. Further, an antireflection film similar to the above-described antireflection film 241 may be provided on at least one of the surfaces of the optical element 25 on the atomic cell 21 side and the light source 22 side.

  The optical element 26 is a λ / 4 plate. Thereby, the light LL from the light source 22 can be converted from linearly polarized light into circularly polarized light (right circularly polarized light or left circularly polarized light). As described above, when the alkali metal atom in the atomic cell 21 is Zeeman split, when the alkali-polarized resonance light pair is irradiated to the alkali metal atom, among the plurality of levels in which the alkali metal atom is Zeeman split, The number of alkali metal atoms at the energy level can be made relatively larger than the number of alkali metal atoms at other energy levels. Therefore, the number of atoms that express the desired EIT phenomenon increases and the desired EIT signal increases, and as a result, the oscillation characteristics of the atomic oscillator 1 can be improved.

  The optical element 27 (third optical element) is configured integrally with the atomic cell 21 as described above, and the inner space S side of the atomic cell 21 is a flat surface, and the opposite side (photodetector 23 side) is a convex surface. It is a plano-convex lens. In particular, the optical element 27 is a condensing lens configured to condense the light LL that has passed through the internal space S of the atomic cell 21 toward the photodetector 23. That is, the optical element 27 is configured to condense the light LL so that the spot diameter on the photodetector 23 becomes small. The optical element 27 may be a plano-convex lens having a convex surface on the inner space S side or a biconvex lens as long as the spot diameter of the light LL on the photodetector 23 can be reduced as described above. It may be. Further, the optical element 27 may be configured separately from the atomic cell 21 (window portion 214), or may be a combination of a plurality of lenses (biconvex lens, planoconvex lens, etc.). Good. Further, an antireflection film similar to the above-described antireflection film 241 may be provided on at least one of the inner space S side and the opposite surface of the optical element 27.

<Control part>
As described above, the control unit 10 includes the bias current adjustment unit 30, the drive circuit 35, and the signal generation unit 40.

(Bias current adjuster)
The bias current adjustment unit 30 includes a detection circuit 31, a modulation circuit 32, and a low frequency oscillator 33. The detection circuit 31 uses the output signal (oscillation signal) of the low-frequency oscillator 33 that oscillates at a low frequency of several Hz to several hundred Hz to synchronously detect the output signal of the photodetector 23 at that frequency. The modulation circuit 32 modulates the output signal of the detection circuit 31 using the output signal (oscillation signal) of the low frequency oscillator 33 as a modulation signal in order to enable detection by the detection circuit 31.

(Drive circuit)
The drive circuit 35 finely adjusts the bias current according to the output signal of the modulation circuit 32, and sets the bias current supplied to the light source 22 (sets the center wavelength of the light emitted from the light source 22). In this way, the center wavelength of the light emitted from the light source 22 is controlled (finely adjusted) by the feedback loop passing through the light source 22, the atomic cell 21, the photodetector 23, the detection circuit 31, the modulation circuit 32, and the drive circuit 35. Stabilize. The bias current may be adjusted without using such a feedback loop.

  The drive circuit 35 supplies the light source 22 with the modulation current from the signal generation unit 40 superimposed on the bias current finely adjusted as described above. When frequency modulation is applied to the light emitted from the light source 22 by this modulation current, a plurality of sets of light whose frequencies are shifted from each other by the frequency of the modulation current are generated on both sides of the light with the center frequency corresponding to the bias current. Generated as sideband light.

(Signal generator)
The signal generation unit 40 includes a detection circuit 42, a voltage control type crystal oscillator 43, a modulation circuit 44, a low frequency oscillator 45, and a phase synchronization circuit 46. The detection circuit 42 uses the oscillation signal of the low-frequency oscillator 45 that oscillates at a low frequency of about several Hz to several hundred Hz to synchronously detect the output signal of the photodetector 23 at that frequency (every first period). In the voltage controlled crystal oscillator 43 (VCXO), the oscillation frequency of the voltage controlled crystal oscillator 43 (VCXO) is finely adjusted according to the magnitude of the output signal of the detection circuit 42. The voltage controlled crystal oscillator 43 (VCXO) oscillates at a low frequency of about several tens Hz to several hundreds Hz, for example.

  The modulation circuit 44 modulates the output signal of the voltage controlled crystal oscillator 43 (VCXO) using the oscillation signal of the low frequency oscillator 45 as a modulation signal in order to enable detection by the detection circuit 42.

  The phase synchronization circuit 46 converts the output signal of the modulation circuit 44 at a constant frequency conversion rate (multiplication ratio) and outputs it. As a result, the phase synchronization circuit 46 multiplies the output of the modulation circuit 44 and generates a modulation current as a microwave signal. For example, the phase-locked loop circuit 46 has a frequency difference that is ½ of the frequency difference corresponding to the energy difference between the two ground levels of the alkali metal atom with the magnetic quantum number m = 0 enclosed in the atomic cell 21 (9 for the cesium atom). .1926 GHz / 2 = 4.5963 GHz). The phase synchronization circuit 46 uses the output signal of the modulation circuit 44 as a frequency difference (cesium atom) corresponding to the energy difference between the two ground levels of the alkali metal atom with the magnetic quantum number m = 0 enclosed in the atomic cell 21. In this case, the signal may be converted to a signal having a frequency equal to 9.1926 GHz.

  The output signal of the phase synchronization circuit 46 is input to the drive circuit 35 as a current having a modulation frequency fm (modulation current). Thus, the light source 22 emits by the feedback loop passing through the light source 22, the atomic cell 21, the photodetector 23, the detection circuit 42, the voltage control type crystal oscillator 43, the modulation circuit 44, the phase synchronization circuit 46, and the drive circuit 35. One set of sideband light is controlled (fine-tuned) to be a resonant light pair that causes an EIT phenomenon in an alkali metal atom.

  As described above, the EIT signal, which is a steep signal generated with the EIT phenomenon, is detected by the photodetector 23, and the output signal of the voltage controlled crystal oscillator 43 is used as a reference signal by using the EIT signal as a reference signal. Stabilize at a frequency of. The output signal of the voltage controlled crystal oscillator 43 is output to the outside. At that time, the output signal of the voltage controlled crystal oscillator 43 is frequency-converted to a desired frequency at a predetermined frequency conversion rate by a frequency conversion circuit (not shown) such as a DDS (Direct Digital Synthesizer), for example. May be.

  As described above, the atomic oscillator 1 which is a kind of “quantum interference device” includes an atomic cell 21 having an internal space S in which an alkali metal is sealed, and a light source unit that emits the light LL that irradiates the atomic cell 21. ”, A light detector 23 that is a“ light receiving unit ”that receives the light LL transmitted through the atomic cell 21, and a“ first optical element ”disposed between the light source 22 and the internal space S. The second optical element that is disposed between the optical element 25 and the light source 22 and the optical element 25 and collects the light LL from the light source 22 at a position (condensing point FP) between the optical element 25 and the second optical element. And an optical element 24.

  According to such an atomic oscillator 1, as shown in FIG. 2, the optical element 24 arranged between the light source 22 and the optical element 25 converts the light LL from the light source 22 into the optical element 24, the optical element 25, and Therefore, the light LL from the light source 22 is incident on the incident surface (the surface on the optical element 24 side) of the optical element 25 at a wide angle (not parallel light). Thereby, even if the light LL is reflected by the incident surface of the optical element 25, the reflected light LLR2 can be diverged (diffused). Therefore, the amount of the reflected light LLR2 incident on the light source 22 as return light can be reduced, and output fluctuation (wavelength fluctuation, intensity fluctuation) of the light source 22 due to the return light can be reduced. As a result, the frequency characteristics of the atomic oscillator 1 can be improved.

  In addition, it can be said that the atomic oscillator 1 which is a kind (example) of the quantum interference device includes the quantum interference device. The atomic oscillator 1 can enjoy the effects (for example, excellent frequency characteristics) of the quantum interference device and exhibit excellent characteristics (for example, oscillation characteristics).

  Further, since the return light to the light source 22 can be reduced without installing the optical element 25 in a posture inclined with respect to a plane perpendicular to the optical axis of the light LL, the atomic oscillator 1 can be easily reduced in size. There is also an advantage that can be achieved.

  Here, when the condensing point FP of the light LL by the optical element 24 is positioned between the optical element 24 and the optical element 25, the light source 22 is optically on the focal point of the optical element 24 on the light source 22 side or more optically than that. It is necessary to be disposed on the side opposite to the element 24. In order to reduce the size of the atomic oscillator 1, it is preferable that the focal point FP be as close as possible to the optical element 24 side (the focal point on the opposite side of the optical element 24 from the light source 22).

  The optical element 24 (second optical element) is a biconvex lens. Thereby, the focal distance of the optical element 24 can be shortened, and accordingly, the distance between the light source 22 and the atomic cell 21 can also be shortened. As a result, the atomic oscillator 1 can be reduced in size. Further, since the surface of the optical element 24 on the light source 22 side is a convex surface, even if the light LL from the light source 22 is reflected by the optical element 24, the reflected light LLR1 is diverged (diffused) and enters the light source 22. And fluctuations in the output of the light source 22 due to the return light can be further reduced.

  In particular, in the present embodiment, the optical element 24 is a ball lens. Thereby, the focal distance of the optical element 24 can be shortened effectively. Further, the optical element 24 can be easily installed. Here, the diameter of the optical element 24 which is a ball lens (in the case of a biconvex lens, the maximum length in the direction along the optical axis of the light LL) is not particularly limited, but from the viewpoint of miniaturization of the atomic oscillator 1 The width of the internal space S of the atomic cell 21 (the length in the direction perpendicular to the optical axis of the light LL) is preferably 0.3 times or more and 2 times or less, and more than 0.5 times 1 More preferably, it is 5 times or less.

  An antireflection film 241 is provided on the surface of the optical element 24 (second optical element) on the light source 22 (light source unit) side. Thereby, it can reduce that the light LL from the light source 22 reflects in the optical element 24, and can further reduce the output fluctuation of the light source 22 by return light.

  The optical element 25 (first optical element) is a condenser lens. Thereby, the light LL incident on the atomic cell 21 can be made into parallel light or a state close thereto. Therefore, the frequency characteristics of the atomic oscillator 1 can be further improved.

  In particular, the surface (incident surface) on the optical element 24 (second optical element) side of the optical element 25 (first optical element) is a convex surface. Thereby, even if the light LL from the light source 22 is reflected by the optical element 25, the reflected light LLR2 can be diverged (diffused) at a wider radiation angle than when the surface is a flat surface. Therefore, the amount of the reflected light LLR2 incident on the light source 22 as return light can be further reduced. As a result, output fluctuations of the light source 22 due to return light can be further reduced.

  Moreover, it is preferable that at least one of the optical element 24 (second optical element) and the optical element 25 (first optical element) includes a component that absorbs light. Thereby, at least one of the optical element 24 and the optical element 25 can be used as a neutral density filter. Therefore, it is not necessary to separately provide a neutral density filter, and the number of reflection surfaces that cause return light can be reduced. Here, the light absorbing component is not particularly limited as long as it is a material having an absorptivity with respect to the wavelength region of the light LL (in other words, a function of converting light into heat), and various organic materials and various inorganic materials are used. be able to.

  An optical element 26 that is a λ / 4 plate is disposed between the optical element 25 (first optical element) and the internal space S of the atomic cell 21. As a result, as described above, the light LL incident on the internal space S can be circularly polarized, and coupled with the fact that the alkali metal in the internal space S is Zeeman split, the frequency characteristics of the atomic oscillator 1 can be further improved. Can be improved. In addition, since the optical element 26 which is a λ / 4 plate is arranged on the atomic cell 21 side with respect to the optical element 25, the light LL from the light source 22 is diverged (diffused) by the optical element 26 with respect to the optical element 26. ). Therefore, even if the light LL from the light source 22 is reflected by the optical element 26 (λ / 4 plate), the reflected light can be reduced from entering the light source 22 as incident light. In place of or in addition to the optical element 26, a neutral density filter may be disposed between the optical element 25 and the internal space S of the atomic cell 21, and in this case, like the optical element 26 described above, It is possible to reduce the reflected light from the neutral density filter from returning to the light source 22.

  Furthermore, an optical element 27 that is a “third optical element” is disposed between the internal space S of the atomic cell 21 and the photodetector 23 (light receiving unit). This optical element 27 is a condenser lens. Thereby, the light that has passed through the internal space S of the atomic cell 21 can be collected and incident on the photodetector 23. For this reason, the light receiving area of the photodetector 23 can be reduced, and noise caused by the dark current generated in the photodetector 23 can be reduced. As a result, the S / N ratio of a signal (for example, EIT signal) obtained using the light reception result of the photodetector 23 can be increased, and the frequency characteristics of the atomic oscillator 1 can be further improved.

  Here, the diameter of the light LL on the light receiving surface of the photodetector 23 may be smaller than the diameter of the light LL in the internal space S of the atomic cell 21, but the light LL in the internal space S of the atomic cell 21 is sufficient. The diameter is preferably from 0.1 times to 0.8 times, and more preferably from 0.2 times to 0.6 times. Thereby, the intensity | strength of light LL is detected below the saturation point of the photodetector 23, and the effect which enlarges S / N ratio as mentioned above can be exhibited suitably.

  In the present embodiment, the optical element 27 (third optical element) is configured integrally with the atomic cell 21. Thereby, the number of parts can be reduced and the atomic oscillator 1 can be downsized.

  The first embodiment of the present invention has been described above. In the above-described embodiment, the optical element 25 is regarded as a “first optical element”, but the optical element 26 or the window portion 213 of the atomic cell 21 can also be regarded as a “first optical element”. Even if it catches in this way, there exists an effect similar to what was mentioned above in the relationship between a 1st optical element and a 2nd optical element. However, the optical element 25 closest to the optical element 24 among the optical elements 25 and 26 and the window portion 213 arranged between the atomic cell 21 and the optical element 24 has the largest amount of incident light LL. The effect of the optical element 25 is the highest. That is, when a plurality of optical elements are arranged between the second optical element and the internal space of the atomic cell, the optical element closest to the second optical element among the plurality of optical elements is defined as the first optical element. It can be said that it is preferable that the condensing point by the second optical element is located between the first optical element and the second optical element.

Second Embodiment
Next, a second embodiment of the present invention will be described.

  FIG. 3 is a schematic diagram for explaining an optical element included in an atomic oscillator (an example of a quantum interference device) according to the second embodiment of the present invention.

  This embodiment is the same as the first embodiment described above except that the arrangement of the optical elements and the configuration of the atomic cell are different.

  In the following description, the second embodiment will be described with a focus on differences from the first embodiment, and description of similar matters will be omitted. In FIG. 3, the same reference numerals are given to the same configurations as those in the above-described embodiment.

  The atomic oscillator 1A illustrated in FIG. 3 includes a light source 22 (light source unit), an atomic cell 21A, a photodetector 23 (light receiving unit), and optical elements 24 to 28.

  The atomic cell 21A includes a body portion 211 having a columnar through-hole 212 and a pair of window portions that form an airtightly sealed internal space S by sealing both openings of the through-hole 212 of the body portion 211. 213A, 214.

  In the present embodiment, the window portion 213A of the atomic cell 21 also has a lens shape (plano-convex lens). The window portion 213A serves as the optical element 25. Thus, the optical element 25 is configured integrally with the atomic cell 21A. As a result, the number of parts can be reduced and the atomic oscillator 1A can be downsized.

  In the present embodiment, the optical elements 26 and 28 are disposed between the optical element 24 and the optical element 25. Here, the optical element 28 is disposed between the optical element 24 and the optical element 26. This optical element 28 is a neutral density filter. Thereby, the dimmed light LL can be made incident on the optical element 26 which is a λ / 4 plate. Therefore, the reflected light from the optical element 26 can be reduced. The neutral density filter used for the optical element 28 may be either an absorption type or a reflection type, but from the viewpoint of reducing the return light to the light source 22, it is preferable to use an absorption type. In addition, when a reflection type neutral density filter is used as the optical element 28, it can be said that the effect of positioning a condensing point FP as described later between the optical element 24 and the optical element 28 becomes remarkable.

  As described above, the atomic oscillator 1A which is a kind of “quantum interference device” includes the atomic cell 21A having the internal space S in which the alkali metal is sealed, and the light source unit that emits the light LL that irradiates the atomic cell 21A. ”, A light detector 22 that is a“ light receiving unit ”that receives the light LL transmitted through the atomic cell 21 </ b> A, and a“ first optical element ”disposed between the light source 22 and the internal space S. The second optical element which is disposed between the optical element 28 and the light source 22 and the optical element 28 and condenses the light LL from the light source 22 at a position (condensing point FP) between the optical element 28 and the optical element 28. And an optical element 24.

  According to such an atomic oscillator 1A, as shown in FIG. 3, the optical element 24 disposed between the light source 22 and the optical element 28 converts the light LL from the light source 22 into the optical element 24, the optical element 28, and Therefore, the light LL from the light source 22 is incident on the incident surface of the optical element 28 (the surface on the optical element 24 side) at a wide angle. Thereby, even if the light LL is reflected by the incident surface of the optical element 28, the reflected light LLR2 can be diverged (diffused). Therefore, the amount of the reflected light LLR2 incident on the light source 22 as return light can be reduced, and output fluctuation (wavelength fluctuation, intensity fluctuation) of the light source 22 due to the return light can be reduced. As a result, the frequency characteristics of the atomic oscillator 1A can be improved.

  It can be said that the atomic oscillator 1A, which is an example (a type) of the quantum interference device, includes the quantum interference device. Then, the atomic oscillator 1A can enjoy the effects (for example, excellent frequency characteristics) of the quantum interference device and exhibit excellent characteristics (for example, oscillation characteristics).

  The second embodiment of the present invention has been described above. In the above-described embodiment, the optical element 28 is regarded as a “first optical element”, but the optical element 26 or the window 213A (optical element 25) of the atomic cell 21A may be regarded as a “first optical element”. it can. Even if it catches in this way, there exists an effect similar to what was mentioned above in the relationship between a 1st optical element and a 2nd optical element.

  When the window part 213 (optical element 25) is regarded as a “first optical element”, it can be said that the first optical element is configured integrally with the atomic cell 21A. As a result, the number of parts can be reduced and the atomic oscillator 1A can be downsized.

2. Electronic Device The atomic oscillator 1 or 1A as described above can be incorporated into various electronic devices. Hereinafter, the electronic apparatus of the present invention will be described.

  FIG. 4 is a diagram showing a schematic configuration when the atomic oscillator of the present invention is used in a positioning system using a GPS satellite.

  A positioning system 1100 shown in FIG. 4 includes a GPS satellite 1200, a base station device 1300, and a GPS receiver 1400.

The GPS satellite 1200 transmits positioning information (GPS signal).
The base station device 1300 receives the positioning information from the GPS satellite 1200 with high accuracy via, for example, the antenna 1301 installed at the electronic reference point (GPS continuous observation station), and the reception device 1302 receives the positioning information. A transmission apparatus 1304 that transmits positioning information via an antenna 1303.

  Here, the receiving device 1302 is an electronic device including the above-described atomic oscillator 1 of the present invention as its reference frequency oscillation source. In addition, the positioning information received by the receiving device 1302 is transmitted by the transmitting device 1304 in real time.

  The GPS receiver 1400 includes a satellite receiver 1402 that receives positioning information from the GPS satellite 1200 via the antenna 1401, and a base station receiver 1404 that receives positioning information from the base station device 1300 via the antenna 1403. Prepare.

  The receiving device 1302 that is an “electronic device” included in the positioning system 1100 as described above includes the atomic oscillator 1 that is a kind of “quantum interference device”. Thereby, the effect (for example, the excellent frequency characteristic) of the atomic oscillator 1 can be enjoyed and the excellent characteristic can be exhibited. Note that the receiving device 1302 may include an atomic oscillator 1A instead of the atomic oscillator 1.

  Note that the electronic apparatus of the present invention is not limited to the above-described ones. For example, a smartphone, a tablet terminal, a watch, a mobile phone, a digital still camera, an ink jet type ejection device (for example, an ink jet printer), a personal computer (a mobile personal computer). , Laptop personal computer), TV, video camera, video tape recorder, car navigation device, pager, electronic organizer (including communication function), electronic dictionary, calculator, electronic game device, word processor, workstation, video phone, TV monitor for crime prevention, electronic binoculars, POS terminal, medical equipment (for example, electronic thermometer, blood pressure monitor, blood glucose meter, electrocardiogram measuring device, ultrasonic diagnostic device, electronic endoscope), fish detector, various measuring devices, instruments ( Example If, vehicle, aircraft, gauges of a ship), flight simulators, terrestrial digital broadcasting, can be applied to a mobile phone base station or the like.

3. Mobile Object FIG. 5 is a diagram showing an example of the mobile object of the present invention.

  In this figure, a moving body 1500 has a vehicle body 1501 and four wheels 1502, and is configured to rotate the wheels 1502 by a power source (engine) (not shown) provided in the vehicle body 1501. In such a moving body 1500, the atomic oscillator 1 is built.

  The moving object 1500 as described above includes the atomic oscillator 1 which is a kind of “quantum interference device”. Thereby, the effect (for example, the excellent frequency characteristic) of the atomic oscillator 1 can be enjoyed and the excellent characteristic can be exhibited. Note that the moving object 1500 may include an atomic oscillator 1A instead of the atomic oscillator 1.

  As described above, the quantum interference device, the atomic oscillator, the electronic device, and the moving body of the present invention have been described based on the illustrated embodiments, but the present invention is not limited to these.

  Moreover, the structure of each part of this invention can be substituted by the thing of the arbitrary structures which exhibit the same function of embodiment mentioned above, and arbitrary structures can also be added.

DESCRIPTION OF SYMBOLS 1 ... Atomic oscillator, 1A ... Atomic oscillator, 2 ... Package part, 10 ... Control part, 21 ... Atomic cell, 21A ... Atomic cell, 22 ... Light source (light source part), 23 ... Photodetector (light-receiving part), 24 ... Optical element (second optical element), 25 ... Optical element (first optical element), 26 ... Optical element, 27 ... Optical element (third optical element), 28 ... Optical element (first optical element), 30 ... Bias Current adjustment unit 31 ... detection circuit 32 ... modulation circuit 33 ... low frequency oscillator 35 ... drive circuit 40 ... signal generation unit 42 ... detection circuit 43 ... voltage controlled crystal oscillator 44 ... modulation circuit 45 DESCRIPTION OF SYMBOLS ... Low frequency oscillator, 46 ... Phase synchronous circuit, 211 ... Body part, 212 ... Through-hole, 213 ... Window part, 213A ... Window part, 214 ... Window part, 241 ... Antireflection film, 1100 ... Positioning system, 1200 ... GPS Satellite, 1300 ... Base station equipment 1301 ... Antenna, 1302 ... Receiver, 1303 ... Antenna, 1304 ... Transmitter, 1400 ... GPS receiver, 1401 ... Antenna, 1402 ... Satellite receiver, 1403 ... Antenna, 1404 ... Base station receiver, 1500 ... Mobile, 1501 ... Car body, 1502 ... Wheel, FP ... Condensing point, LL ... Light, LLR1 ... Reflected light, LLR2 ... Reflected light, S ... Internal space

Claims (13)

An atomic cell having an internal space in which an alkali metal is enclosed;
A light source unit that emits light to irradiate the atomic cell;
A light receiving portion for receiving light transmitted through the atomic cell;
A first optical element disposed between the light source unit and the internal space;
A second optical element disposed between the light source unit and the first optical element and condensing light from the light source unit at a position between the first optical element and the second optical element. Quantum interference device.   The quantum interference device according to claim 1, wherein the second optical element is a biconvex lens.   The quantum interference apparatus according to claim 1, wherein an antireflection film is provided on a surface of the second optical element on the light source unit side.   The quantum interference device according to claim 1, wherein the first optical element is a condenser lens.   The quantum interference device according to claim 4, wherein a surface of the first optical element on the second optical element side is a convex surface.   The quantum interference device according to claim 1, wherein at least one of the first optical element and the second optical element includes a component that absorbs light.   7. The quantum interference device according to claim 1, wherein at least one of a λ / 4 plate and a neutral density filter is disposed between the first optical element and the internal space.   The quantum interference device according to claim 1, wherein a third optical element that is a condensing lens is disposed between the internal space and the light receiving unit.   The quantum interference device according to claim 8, wherein at least a part of the third optical element is configured integrally with the atomic cell.   The quantum interference device according to claim 1, wherein at least a part of the first optical element is configured integrally with the atomic cell.   An atomic oscillator comprising the quantum interference device according to claim 1.   An electronic apparatus comprising the quantum interference device according to claim 1.   A moving body comprising the quantum interference device according to claim 1.

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