JP4952603B2 - Atomic oscillator - Google Patents

Description

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

An atomic oscillator using an alkali metal such as rubidium or cesium needs to keep atoms in a gas state when utilizing energy transition of atoms, and therefore operates a gas cell in which atoms are hermetically sealed while maintaining a high temperature. . The principle of operation of an atomic oscillator is broadly divided into a double resonance method using light and microwaves, and a method using a quantum interference effect (hereinafter referred to as CPT: Coherent Population Trapping) by two types of laser light. In both cases, the amount of the light incident on the gas cell is detected by the detector provided on the opposite side to detect how much light has been absorbed by the atomic gas, so that the atomic resonance is detected and a reference signal from a crystal oscillator or the like is sent to the control system. Output is obtained in synchronization with atomic resonance. Here, in an atomic oscillator using CPT, a light emitting element, a gas cell, and a light receiving element are integrally formed to form an optical system (see Patent Document 1).
US6808064B2

  However, in the configuration of the conventional optical system disclosed in Patent Document 1, the light emitting element 33, the passive optical element 34, the gas cell 35, and the light receiving element 30 are vertically arranged as shown in FIG. For this reason, the bonding wire 31 for electrically connecting the light receiving element 30 arranged on the uppermost surface becomes long, and the mounting work of the module becomes complicated, and the signal obtained from the light receiving element 30 is weak. There is a problem that the S / N characteristic is not good because it is easily affected. Moreover, since each component is stacked, the height of the optical system is increased, which is disadvantageous for downsizing and thinning. Further, since each part is stacked and the optical system is adjusted after the bonding wire 31 is connected, when the optical axes of the light emitting element 33 and the light receiving element 30 are shifted, or when any part is defective. The bonding wire 31 must be removed again and the parts must be assembled from the beginning, and it took time and trouble to repair and replace the parts.

In order to solve such a conventional problem, as shown in FIG. 7, the light emitting element 42, the gas cell 43, and the light receiving element 48 are sequentially arranged along the plane direction on the same plane, and light is transmitted by the mirror 46 and the mirror 49. An optical system has been proposed in which the optical system is made thinner by bending the lens, and the repair and replacement of each component are facilitated. However, since the surface-emitting type VCSEL is generally used for the light emitting element 42, there is a high possibility that a failure called a sudden death inherent in the VCSEL occurs. In addition, since the light emission direction is not perpendicular to the incident surface of the gas cell, an optical element such as a mirror 46 is necessary, and accordingly, the height of the optical system is increased and the number of parts is increased. There is a problem that the accompanying adjustment time becomes long.
The present invention has been made in view of the above problems, and uses an edge-emitting laser diode as a light emitting element to improve the reliability of the light emitting element, and the light emitting element, the gas cell, and the light receiving element are arranged on the same plane. It is an object to provide an atomic oscillator including an optical system that is reduced in size and thickness by being sequentially arranged along the surface direction.

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

  Application Example 1 An optical system of an atomic oscillator that controls an oscillation frequency using light absorption characteristics due to a quantum interference effect when two types of resonance light as coherent light having different wavelengths are incident. A coherent light source that emits light, a gas cell that is disposed on the emission side of the coherent light source, encloses gaseous metal atoms, allows the resonance light to pass through the metal atom gas, and light that has passed through the gas cell. And a light detecting means for detecting, wherein the coherent light source is constituted by an edge-emitting laser diode, and the resonance light is directly irradiated onto the gas cell.

  The atomic oscillator of the present invention utilizes the quantum interference effect of coherent light such as laser light. In this method, two ground levels of two resonant lights irradiated simultaneously in a three-level system (for example, a Λ-type level system) in which two ground levels receive resonant light and are resonantly coupled with a common excitation level. When the frequency exactly matches the energy difference between the ground level 1 and the ground level 2, the three-level system becomes a superposition state of the two ground levels, and the excitation to the excitation level 3 stops. CPT uses this principle to detect and use a state in which light absorption in the gas cell stops when the wavelength of one or both of the two resonance lights is changed. The optical system of the present invention uses an edge emitting laser diode as a coherent light source. Since this laser diode has a horizontal light emission direction, an optical element such as a mirror is not necessary, and the optical system can be further reduced in size and thickness. In addition, since a failure such as a sudden death is reduced as compared with a VCSEL of a surface light emitting element, reliability is increased.

  Application Example 2 The optical detection means is constituted by a waveguide type light receiving element.

  Since the edge-emitting laser diode emits light in the horizontal direction, the light receiving surface of the light detection means must also be horizontal in order to sequentially arrange the light detection means along the plane direction on the same plane. It is. Therefore, in the present invention, the light detecting means is constituted by a waveguide type light receiving element. The waveguide type light receiving element is an element in which a waveguide for guiding light and a light detecting element are integrally formed, and light incident on the waveguide is guided to a light receiving surface of the light detecting element to detect light. Thereby, the optical system can be further reduced in size and thickness.

  Application Example 3 The coherent light source and the light detection unit are arranged to face each other.

  Since the emission surface of the edge emitting laser diode (coherent light source) and the light receiving surface of the waveguide type light receiving element (light detecting means) are arranged in the horizontal direction, they are arranged so as to face each other. As a result, the height of the optical system is the higher of the coherent light source and the light detection means, and the optical system can be made as thin as possible.

  Application Example 4 An optical system of an atomic oscillator that controls an oscillation frequency by using a light absorption characteristic due to a quantum interference effect when two types of resonance light as coherent light having different wavelengths are incident. A coherent light source that emits light, a gas cell that is disposed on the emission side of the coherent light source, encloses gaseous metal atoms, allows the resonance light to pass through the metal atom gas, and a light cell that has passed through the gas cell. An optical path conversion means for converting an optical path and a light detection means for detecting light converted by the optical path conversion means, wherein the coherent light source is constituted by an edge-emitting laser diode.

  In the present invention, an edge-emitting laser diode is used as a coherent light source, and a conventional surface-receiving photodiode that is lower in cost than a waveguide-type light-receiving element is used as a light detection means. Therefore, since the resonance light emitted in the horizontal direction cannot be received as it is, it is once bent by an optical path changing means such as a mirror and then received by the light detecting means. Thereby, one mirror can be reduced from the conventional configuration.

  Application Example 5 The light detection unit is arranged on the same side as the coherent light source, the light converted by the optical path conversion unit is incident on the gas cell again, and the light that has passed through the gas cell again is the light detection unit. It is characterized by having a configuration to detect by.

  The light that has passed through the gas cell has a higher S / N ratio due to the larger interaction between the atoms and light as the optical path of the gas cell is longer. Therefore, in the present invention, the light passing through the gas cell is bent by an optical path changing means such as a mirror, and the light is incident on the gas cell again. Thereby, the optical path of the gas cell is doubled, and the S / N of the signal can be improved.

  Application Example 6 A passive optical element that condenses light emitted from the coherent light source and corrects the light to parallel light is disposed between the coherent light source and the gas cell.

  In the optical system, a passive optical element such as a lens or a wave plate that changes the polarization state of the light is used in order to collect the light emitted from the coherent light source and correct it so as to become parallel light. This passive optical element may be disposed anywhere before entering the gas cell. Therefore, in the present invention, the passive optical element is disposed between the coherent light source and the gas cell. Thereby, light can be accurately incident on the light detection means.

  Application Example 7 The coherent light is laser light.

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

  Application Example 8 The gaseous metal atom is rubidium or cesium.

  If cesium atoms are used, a highly accurate atomic oscillator can be realized. In addition, rubidium atoms are easy to use because the microwave transition frequency is lower than 6.8 GHz and 9.2 GHz of cesium atoms. Therefore, any metal atom can be selected in consideration of the required performance and convenience of the atomic oscillator.

  Application Example 9 An optical oscillator having the above configuration is provided in an atomic oscillator.

  By using an edge-emitting laser diode as a coherent light source, the optical system can be further reduced in size and thickness. In addition, since a failure such as a sudden death is reduced as compared with a VCSEL of a surface light emitting element, an atomic oscillator with high reliability can be provided.

Hereinafter, the present invention will be described in detail with reference to embodiments shown in the drawings. However, the components, types, combinations, shapes, relative arrangements, and the like described in this embodiment are merely illustrative examples and not intended to limit the scope of the present invention only unless otherwise specified. .
FIG. 1 is a configuration diagram of a main part of an optical system of an atomic oscillator according to an embodiment of the present invention. This optical system 1 is an optical system 1 of an atomic oscillator 100 that controls an oscillation frequency by using a light absorption characteristic due to a quantum interference effect when two types of resonant light as coherent lights having different wavelengths are incident. A coherent light source 2 that emits each resonance light, a passive optical element 4 that performs processing such as condensing the light 3 emitted from the coherent light source 2 and correcting it to parallel light, and the output side of the passive optical element 4 A gas cell 6 that is disposed and encloses gaseous metal atoms and allows each resonance light to pass through the metal atom gas, a photodetector (light detection means) 8 that detects light 7 that has passed through the gas cell 6, and light detection And a frequency control circuit 9 for controlling the oscillation frequency based on the signal detected from the device 8. Since the gist of the present invention is the configuration of the optical system that constitutes the atomic oscillator, a detailed description of the frequency control of the atomic oscillator is omitted.

That is, the atomic oscillator 100 of this embodiment uses quantum interference of coherent light such as laser light. In this system, in a system in which two ground levels receive resonance light and are resonantly coupled with a common excitation level, the frequencies of the two resonance lights irradiated simultaneously are precisely the ground level 1 and the ground level. When the energy difference of level 2 coincides, the atom is in a superposition state of two ground levels, and excitation to excitation level 3 stops. CPT uses this principle to detect and use a state where light absorption in the gas cell stops when the wavelength of one or both of the two resonance lights is changed (details will be described later). . The optical system 1 of the present invention uses an edge-emitting laser diode as the coherent light source 2. Since this laser diode has a horizontal light emission direction, an optical element such as a mirror is not necessary, and the optical system 1 can be further reduced in size and thickness. In addition, since a failure such as a sudden death is reduced as compared with a VCSEL of a surface light emitting element, reliability is increased.
The coherent light in this embodiment uses laser light. Laser light has good monochromaticity in wavelength and has a uniform phase. Coherence is defined as a measure of the stability of the wavelength and phase of light. Light having good coherence, that is, light having a stable wavelength and phase can cause a quantum interference effect. In that respect, laser light is optimal. Moreover, the gaseous metal atom used for the gas cell 6 is rubidium or cesium. For example, a cesium atom used in a primary atom standard can be used to realize a highly accurate atomic oscillator. The rubidium atom used in the secondary standard is convenient because the microwave transition frequency is lower than that of the cesium atom. By using this, a small and low-priced atomic oscillator can be realized. Therefore, what is used for the metal atom may be selected according to the purpose of use. In this embodiment, rubidium and cesium are used. However, any atom having a three-level system may be used.

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

  FIG. 3A is a diagram schematically showing the configuration of the optical system 1a according to the first embodiment of the present invention. The same components will be described with the same reference numerals as in FIG. The optical system 1 a includes an edge-emitting laser diode (coherent light source) 2 installed on a pedestal 10, a passive optical element 4, a gas cell 6, and a photodiode installed on a pedestal 12 (waveguide-type light receiving element: Photodetectors) 8 are sequentially arranged along the surface direction on the substrate 11, and the respective elements are electrically connected to the substrate 11 by bonding wires (not shown). The passive optical element 4 is not necessarily required and may be omitted.

In other words, the optical system 1a of the present embodiment uses the edge emitting laser diode 2 as a coherent light source. Since the laser diode 2 has a horizontal light emission direction, an optical element such as a mirror is not necessary, so that the optical system can be further reduced in size and thickness. In addition, since a failure such as a sudden death is reduced as compared with a VCSEL of a surface light emitting element, reliability is increased. Further, since the edge emitting laser diode 2 emits the light 3 in the horizontal direction, in order to sequentially arrange the photodiodes 8 along the plane direction on the same plane, the light receiving surface of the photodiode 8 is also in the horizontal direction. It is necessary to be. Therefore, in the present embodiment, the photodiode 8 is constituted by a waveguide type light receiving element. The waveguide type light receiving element is an element in which a waveguide for guiding light and a light detecting element are integrally formed, and light incident on the waveguide is guided to a light receiving surface of the light detecting element to detect light. Thereby, the optical system can be further reduced in size and thickness. Further, since the emission surface of the edge-emitting laser diode 2 and the light receiving surface of the photodiode 8 are arranged in the horizontal direction, the height of the optical system 1a can be increased by arranging the surfaces to face each other. Thus, the height of the higher one of the edge-emitting laser diode 2 and the photodiode 8 is reached, and the optical system 1a can be made as thin as possible.
When a conventional surface-receiving photodiode 8a, which is lower in cost than the waveguide-type light-receiving element, is used for the photodiode 8, the photodiode 8a is attached to the substrate 13 as shown in FIG. 13 is installed at right angles to the base 12.

FIG. 4 is a diagram schematically showing the configuration of the optical system 1b according to the second embodiment of the present invention. The same components will be described with the same reference numerals as in FIG. The optical system 1b includes an edge-emitting laser diode (coherent light source) 2 installed on a pedestal 10, a photodiode (photodetector) 8a installed on the side of the same pedestal 10, a gas cell 6, a mirror ( Optical path conversion means) 14, and the light reflected by the mirror 14 is incident on the gas cell 6 again, and the light 3a that has passed through the gas cell 6 is detected by the photodiode 8a. Each element is electrically connected to the substrate 11 by a bonding wire (not shown). The passive optical element 4 is not shown.
That is, the photodiode 8a and the edge-emitting laser diode 2 are arranged on the same side with respect to the gas cell 6, the light whose path is changed by the mirror 14 is incident on the gas cell 6 again, and the light that has passed through the gas cell 6 again. 3a is detected by the photodiode 8a. The light 3 that has passed through the gas cell 6 has a higher S / N ratio because the longer the optical path of the gas cell 6, the greater the interaction between atoms and light. Therefore, in the present embodiment, the light 3 that has passed through the gas cell 6 is reflected by the mirror 14, and the light is incident on the gas cell 6 again. Thereby, the optical path of the gas cell 6 is doubled, and the S / N of the signal can be improved.

FIG. 5 is a diagram schematically showing the configuration of an optical system 1c according to the third embodiment of the present invention. The same components will be described with the same reference numerals as in FIG. The optical system 1c includes an edge-emitting laser diode (coherent light source) 2 installed on a pedestal 10, a gas cell 6, a mirror (optical path changing means) 14, and a photodiode (photodetector) installed on a substrate 11. ) 8a, and the light reflected by the mirror 14 is detected by the photodiode 8a. Each element is electrically connected to the substrate 11 by a bonding wire (not shown). The passive optical element 4 is not shown.
That is, the present invention uses the edge-emitting laser diode 2 as a coherent light source, and uses a conventional surface-receiving photodiode 8a, which is lower in cost than a waveguide-type light-receiving element, as a photodetector. Accordingly, since the resonance light emitted in the horizontal direction cannot be received as it is, it is once reflected by the mirror 14 and then received by the surface-receiving photodiode 8a. Thereby, one mirror can be reduced from the conventional configuration.

  FIG. 6 is a diagram schematically showing the configuration of an optical system 1d according to the fourth embodiment of the present invention. The same components will be described with the same reference numerals as in FIG. The optical system 1d is obtained by mounting the optical system 1a of FIG. 3A on a circuit board on which ICs 18, 19 and the like are mounted on a substrate 17 via a spacer 50. In other words, in the optical system 1a of FIG. Therefore, the height of the pedestals 10 and 12 is shortened, and the edge-emitting laser diode 2 and the photodiode 8 are installed on the substrates 15 and 16, respectively. It is possible to mount two boards on the board. By effectively using the space, the atomic oscillator can be miniaturized.

It is a principal part block diagram of the optical system of the atomic oscillator which concerns on embodiment of this invention. It is a figure explaining the 3 level system of an atom by a CPT system. It is the figure which modeled the structure of the optical system 1a which concerns on the 1st Embodiment of this invention. It is the figure which modeled the structure of the optical system 1b which concerns on the 2nd Embodiment of this invention. It is the figure which modeled the structure of the optical system 1c which concerns on the 3rd Embodiment of this invention. It is the figure which modeled the structure of the optical system 1d which concerns on the 4th Embodiment of this invention. It is a figure which shows the structure of the conventional optical system. It is a figure which shows the structure of the conventional optical system.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Optical system, 2 Coherent light source, 3 Resonant light, 4 Passive optical element, 5 Gas cell, 8 Photo detector, 9 Frequency control circuit, 100 Atomic oscillator

Claims (3)

An atomic oscillator using the quantum interference effect by resonant light,
A first substrate;
A first pedestal fixed to one surface side of the first substrate;
An end that is fixed to the first base and emits light in a direction along one surface of the first substrate.
A surface emitting laser diode;
Fixed from one surface of the first substrate and emitted from the edge-emitting laser diode
Gas that is incident as the resonance light and in which gaseous alkali metal atoms are sealed,
A second pedestal fixed to one surface side of the first substrate;
A light detection means fixed to the second pedestal for detecting the resonance light that has passed through the gas cell;
An atomic oscillator comprising: a light emitting surface of the edge-emitting laser diode; and a light receiving surface of the light detecting unit facing each other through the gas cell.   A spacer fixed to the one surface of the substrate;
  A second substrate supported by the spacer and to which the first pedestal is fixed;
  A third substrate supported by the spacer and to which the second pedestal is fixed;
The atomic oscillator according to claim 1, further comprising:   It is fixed to the one surface of the first substrate and supports the first pedestal and the second pedestal.
With a spacer to hold,
  2. The original according to claim 1, wherein the first pedestal and the second pedestal are substrates.
Child oscillator.

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