JP2018023095A - Atomic oscillator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an atomic oscillator which can be made small in size and have a simple configuration.SOLUTION: An atomic oscillator comprises: a light source; a filter element pulsating light emitted from the light source; a gas cell being filled with alkali metal atoms and irradiated with the light pulsated by the filter element; a photodetector part detecting quantity of light transmitted through the gas cell; and a power source supplying a current to the filter element. The filter element has first and second electrodes electrically connected to a power source, and a filter part interposed between the first and second electrodes. The filter part is constituted of a semiconductor material.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an atomic oscillator.

  An atomic oscillator using atomic transition energy as a reference frequency is widely used in communication base stations and the like as one of the most accurate oscillators. There are several types of atomic oscillators, but the microwave double resonance method using a rubidium (Rb) lamp is most commonly used.

  In recent years, an atomic oscillator using a phenomenon called CPT (Coherent Population Trapping), which is one of the quantum interference effects, has been proposed, and the atomic oscillator is expected to be smaller and consume less power than conventional ones. In the case of the CPT method, a coherent light source such as a laser is used as a light source, and a high frequency signal is superimposed to use the sideband for the CPT phenomenon. The CPT type atomic oscillator uses an electromagnetically induced transmission phenomenon (EIT phenomenon: Electromagnetically Induced Transparency) in which absorption of coherent light stops when an alkali metal atom is irradiated with coherent light having two different wavelengths (frequencies). It is.

  As such an atomic oscillator, Patent Document 1 discloses that Ramsey resonance can be generated by pulsing excitation laser light and irradiating the gas cell, thereby reducing the bandwidth of the resonance line and reducing the light shift. An atomic oscillator is disclosed. The atomic oscillator of Patent Document 1 uses an acousto-optic element (AOM, Acoustic-Optic Modulator) or a liquid crystal element in order to pulse laser light.

JP 2014-49886 A

  However, in an atomic oscillator, when an acousto-optic element or a liquid crystal element is used to pulse the excitation laser beam, the apparatus becomes large, the number of parts of the apparatus increases, and the apparatus becomes complicated. There's a problem.

  One of the objects according to some embodiments of the present invention is to provide an atomic oscillator that can be small and have a simple configuration.

The atomic oscillator according to the present invention is
A light source;
A filter element for pulsing the light emitted from the light source;
A gas cell in which alkali metal atoms are enclosed and irradiated with light pulsed by the filter element;
A light detection unit for detecting the amount of light transmitted through the gas cell;
A power supply for supplying current to the filter element,
The filter element is
A first electrode and a second electrode electrically connected to the power source;
A filter portion sandwiched between the first electrode and the second electrode,
The filter portion may be made of a semiconductor material.

  In such an atomic oscillator, the light emitted from the light source can be pulsed by utilizing the fact that the band gap of the filter portion made of a semiconductor material changes with temperature. Therefore, for example, light can be pulsed with a small and simple configuration as compared with the case where light is pulsed using an acousto-optic element or a liquid crystal element. Therefore, with such an atomic oscillator, a small and simple atomic oscillator can be realized.

In the atomic oscillator according to the present invention,
A power supply control unit for controlling the power supply,
The power control unit
A process of controlling the power supply so that the temperature of the filter unit becomes the first temperature;
You may repeatedly perform the process which controls the said power supply so that the temperature of the said filter part may become 2nd temperature higher than 1st temperature.

  In such an atomic oscillator, in the filter element, a state where the light emitted from the light source is absorbed by the filter unit and a state where the light passes through the filter unit can be repeatedly generated. The emitted light can be pulsed.

In the atomic oscillator according to the present invention,
The first electrode and the second electrode may transmit light emitted from the light source.

  In such an atomic oscillator, since the first electrode and the second electrode transmit light emitted from the light source, the first electrode and the second electrode are formed on the entire surface of the two surfaces of the filter portion facing in opposite directions. be able to. Therefore, a current can be uniformly applied to the filter part, and the filter part can be heated uniformly.

In the atomic oscillator according to the present invention,
The filter unit may include an n-type first semiconductor layer and a p-type second semiconductor layer.

  In such an atomic oscillator, since the filter portion includes the n-type first semiconductor layer and the p-type second semiconductor layer, a pn junction can be formed. Therefore, the filter unit can be heated by applying a current to the filter unit. Therefore, a heater or the like for heating the filter portion is unnecessary, and the filter element can be realized with a small and simple configuration.

In the atomic oscillator according to the present invention,
The light incident surface or the light emission surface of the filter element may be inclined with respect to a surface having the optical axis of the light as a normal line.

  In such an atomic oscillator, the light incident surface or the light exit surface of the filter element is inclined with respect to a plane whose normal is the optical axis of the light, so that the return light reflected by the filter element is Heading in a direction different from the optical axis. Thereby, the return light does not return to the light source, the output fluctuation of the light source due to the influence of the return light can be suppressed, and the deterioration of the accuracy of the atomic oscillator can be suppressed.

The functional block diagram of the atomic oscillator which concerns on 1st Embodiment. The figure which shows the frequency spectrum of resonant light. The figure which shows the relationship of the (LAMBDA) type | mold 3 level model of an alkali metal atom, a 1st sideband, and a 2nd sideband. The figure which shows an example of the light pulsed by the filter element. The figure which shows a filter element typically. The figure which shows the state whose temperature of a filter part is 1st temperature. The figure which shows the state which the temperature of a filter part is 2nd temperature higher than 1st temperature. The figure which shows typically the modification of the filter element in this embodiment. The functional block diagram of the atomic oscillator which concerns on 2nd Embodiment. The figure which shows the state of the reflected light of a filter element.

  DESCRIPTION OF EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. The embodiments described below do not unduly limit the contents of the present invention described in the claims. In addition, not all of the configurations described below are essential constituent requirements of the present invention.

(First embodiment)
1. Atomic oscillator 1.1. Configuration First, an atomic oscillator according to a first embodiment will be described with reference to the drawings. FIG. 1 is a functional block diagram of an atomic oscillator 100 according to the first embodiment.

  As shown in FIG. 1, the atomic oscillator 100 includes a light source 10, a filter element 12, a λ / 4 plate 14, a gas cell 16, a light detection unit 18, a power supply unit 20 as a power supply, and a power supply control unit 21. A center wavelength variable unit 22, a high frequency generation unit 24, an absorption detection unit 30, a sampling unit 26, an EIT detection unit 28, and a control unit 40. The control unit 40 includes a center wavelength control unit 42 and a high frequency control unit 44. The atomic oscillator 100 generates an EIT phenomenon in an alkali metal atom by a resonant light pair (first light and second light) having two different frequency components.

  The light source 10 generates light L. The light source 10 is, for example, a vertical cavity surface emitting laser (VCSEL) in which a resonator is formed perpendicular to a semiconductor substrate.

FIG. 2 is a diagram showing a frequency spectrum of resonant light. FIG. 3 is a diagram showing the relationship between the Λ-type three-level model of alkali metal atoms, the first sideband (first light) W1, and the second sideband (second light) W2. The light L emitted from the light source 10 includes a fundamental wave F having a center frequency f ₀ (= c / λ ₀ : c is the speed of light, and λ ₀ is the center wavelength of the laser beam), as shown in FIG. includes a first sideband W1 having a frequency f ₁ to the upper sideband with respect to the frequency f _0, and the second sideband wave W2 having a frequency f ₂ to the lower sideband with respect to the center frequency f _0, the. Frequency f ₁ of the first sideband W1 is _{f 1 = f 0 + f m} , the frequency f ₂ of the second sideband wave W2 is f ₂ = f ₀ -f _m.

As shown in FIG. 3, the energy difference between the frequency f ₁ of the first sideband wave W1 frequency difference between the frequency f ₂ of the second sideband wave W2 is the ground level GL1 and ground level GL2 alkali metal atom ΔE It matches the frequency corresponding to ₁₂ . Therefore, the alkali metal atom is, causing the first sideband W1 having a frequency f _1, a second sideband wave W2 having a frequency f _2, the EIT phenomenon by.

Here, the EIT phenomenon will be described. It is known that the interaction between alkali metal atoms and light can be explained by a Λ-type three-level model. As shown in FIG. 3, the alkali metal atom has two ground levels, a first sideband wave W1 having a wavelength (frequency f ₁ ) corresponding to the energy difference between the ground level GL1 and the excitation level, Alternatively, when the second sideband wave W2 having a wavelength (frequency f ₂ ) corresponding to the energy difference between the ground level GL2 and the excitation level is individually irradiated to the alkali metal atom, light absorption occurs. However, as shown in FIG. 2, the first sideband whose frequency difference f ₁ −f ₂ exactly coincides with the frequency corresponding to the energy difference ΔE ₁₂ between the ground level GL 1 and the ground level GL ₂ in this alkali metal atom. When W1 and the second sideband wave W2 are irradiated at the same time, a superposition state of two ground levels, that is, a quantum interference state occurs, and excitation to the excitation level stops and the first sideband wave W1 and the second sideband wave A transparency phenomenon (EIT phenomenon) occurs in which W2 transmits alkali metal atoms. Using this EIT phenomenon, the frequency difference f ₁ -f ₂ between the first sideband W1 and the second sideband W2 is shifted from the frequency corresponding to the energy difference ΔE ₁₂ between the base level GL1 and the base level GL2. By detecting and controlling steep changes in light absorption behavior over time, a highly accurate oscillator can be produced.

  The filter element 12 pulses the light L emitted from the light source 10. FIG. 4 is a diagram illustrating an example of light (pulse light) pulsed by the filter element 12. Here, pulsing light means making light (continuous light) into pulsed light, and pulsed light means light that lasts for a short time. The filter element 12 transmits the light L emitted from the light source 10 for the time t, absorbs the light for the time T, and transmits the light again for the time t, thereby pulsing the light L (with pulsed light). To do). As a result, as shown in FIG. 4, pulsed light having a pulse width of time t and a pulse interval of time T is obtained. The configuration of the filter element 12 will be described later. Here, as shown in FIG. 4, an example in which the pulsed light is a rectangular wave is shown, but the pulsed light is not limited to a rectangular wave.

  The λ / 4 plate 14 is a wave plate that gives an optical path difference of ¼ wavelength (90 ° phase difference) between linearly polarized light components orthogonal to each other. As the λ / 4 plate 14, for example, a crystal plate, a mica plate, or the like can be used. The λ / 4 plate 14 converts light (linearly polarized light) that has passed through the filter element 12 into circularly polarized light. That is, the light L emitted from the light source 10 is converted into circularly polarized light by the λ / 4 plate 14 and applied to the gas cell 16.

  In the state where the alkali metal atom in the gas cell is Zeeman split, when the circularly polarized excitation light is irradiated to the alkali metal atom, the interaction between the excitation light and the alkali metal atom causes the alkali metal atom to have multiple levels of Zeeman splitting. Of these, the number of alkali metal atoms at a desired energy level can be made relatively larger than the number of alkali metal atoms at other energy levels. Therefore, by using circularly polarized excitation light, the number of atoms that express the desired EIT phenomenon increases and the intensity of the desired EIT signal increases, and as a result, the oscillation characteristics of the atomic oscillator can be improved.

  The gas cell 16 is a container in which gaseous alkali metal atoms (sodium atom, rubidium atom, cesium atom, etc.) are sealed. The cesium atom is heated to, for example, about 80 ° C. and becomes gaseous. The atomic oscillator 100 includes a magnetic field generator (not shown) that generates a uniform magnetic field in one direction in the gas cell 16. The magnetic field generation unit is configured by, for example, a Helmholtz coil disposed so as to sandwich the gas cell 16 or a solenoid coil disposed so as to cover the gas cell 16.

  When the gas cell 16 is irradiated with two light waves (first light and second light) having a frequency (wavelength) corresponding to the energy difference between the two ground levels of the alkali metal atoms, the alkali metal atoms are subjected to EIT. Cause a phenomenon. For example, if the alkali metal atom is a cesium atom, the frequency corresponding to the energy difference between the ground level GL1 and the ground level GL2 in the D1 line is 9.19263... GHz, so the frequency difference is 9.19263. -When two light waves of GHz are irradiated, the EIT phenomenon occurs.

  In the present embodiment, the gas cell 16 is irradiated with pulsed light (pulsed light), so that Ramsey resonance occurs, and the resonance line width can be narrowed and the light shift can be reduced.

  Here, Ramsey resonance will be described. In order to solve the degeneracy of the order, a stationary magnetic field is applied to align the atomic states in a certain order. In this state, the atom is irradiated with an electromagnetic wave for a time a, waits for a time A, and is again irradiated with an electromagnetic wave for a time a. When the atom and electromagnetic wave interact in two steps in this way, the probability that the atom transitions to another state is not only the time a actually interacting but also the time A between the two interactions. Depends on the frequency, and how the quantum transition occurs becomes sensitive to frequency changes. This is called Ramsey resonance. By utilizing this phenomenon, the center frequency of the transition can be measured with high accuracy. The observed resonance line width narrows in proportion to time A.

  In the present embodiment, the filter element 12 irradiates the gas cell 16 with the light L for the time t, waits for the time T, and repeatedly irradiates the light L with the gas cell 16 for the time t (see FIG. 4). Thereby, Ramsey resonance can be generated.

  The time T is not particularly limited as long as the Ramsey resonance can be generated. The repetition frequency of the pulsed light L (pulse light) emitted from the filter element 12 is, for example, about 1 Hz to 10 Hz. Here, when the pulsed light repetition frequency is 1 Hz, it means that the light is turned on / off once per second, and when the pulsed light repetition frequency is 10 Hz, the light is turned on / off 10 times per second. To do. The duty ratio of the pulsed light is 50%, for example. The repetition frequency (that is, time T and time t) of the pulsed light is appropriately set according to the required performance (frequency stability, etc.) of the atomic oscillator.

  The light detection unit 18 detects the amount of light (intensity) that has passed through the gas cell 16 (transmitted through the alkali metal atoms sealed in the gas cell 16). The light detection unit 18 outputs a detection signal corresponding to the amount of light transmitted through the alkali metal atom. The light detection unit 18 includes, for example, a photodiode.

  A power supply unit 20 as a power supply supplies current to the filter element 12. The power supply unit 20 is, for example, a direct current power supply (DC power supply). The power supply unit 20 is controlled by the power supply control unit 21. The power supply control unit 21 may be configured to control the power supply unit 20 by being realized by a dedicated circuit, for example.

  The center wavelength variable unit 22 changes the center wavelength of the light L emitted from the light source 10 based on the signal from the center wavelength control unit 42. Thereby, the center wavelength of the resonant light pair (first light and second light) included in the light L can be changed.

  The high frequency generator 24 supplies a high frequency signal to the light source 10 based on a signal from the high frequency controller 44 to generate a resonant light pair. The high frequency generator 24 may be realized by a dedicated circuit.

The sampling unit 26 samples the detection signal of the light detection unit 18 in synchronization with the output signal of the power supply control unit 21. The sampling unit 26 acquires the detection signal of the light detection unit 18 while the gas L is being irradiated with the light L. In the example illustrated in FIG. 4, the sampling unit 26 acquires the detection signal of the light detection unit 18 at the timing when the time t ₀ (t ₀ <t) has elapsed immediately after the rise of the pulsed light. The sampling unit 26 may be realized by a dedicated circuit.

  The EIT detection unit 28 detects the EIT phenomenon by synchronously detecting the detection signal of the light detection unit 18 acquired by the sampling unit 26. The EIT detection unit 28 may be realized by a dedicated circuit.

  For example, the absorption detection unit 30 detects the minimum value (absorption bottom) of the signal intensity of the detection signal output by the light detection unit 18 when the center wavelength of the light L is changed. The absorption detection unit 30 may be realized by a dedicated circuit.

  The center wavelength control unit 42 changes the wavelength (center wavelength) of the light L emitted from the light source 10 by controlling the center wavelength variable unit 22 based on the signal from the absorption detection unit 30.

  The high frequency control unit 44 inputs a signal for generating a high frequency signal to the high frequency generation unit 24 based on the signal from the EIT detection unit 28.

  Note that the control unit 40 may be configured to perform the above-described control by being realized by a dedicated circuit. The control unit 40 functions as a computer by executing a control program stored in a storage device such as a ROM (Read Only Memory) or a RAM (Random Access Memory), for example, by a CPU (Central Processing Unit), and You may be comprised so that control may be performed.

  Next, the operation of the atomic oscillator 100 will be described. First, an initial operation when starting the atomic oscillator 100 in a stopped state will be described.

  The high frequency control unit 44 inputs a signal to the high frequency generation unit 24 and inputs a high frequency signal from the high frequency generation unit 24 to the light source 10. At this time, the frequency of the high frequency signal is slightly shifted so that the EIT phenomenon does not occur. For example, when cesium is used as the alkali metal atom of the gas cell 16, the value is shifted from a value of 4.596.

  Next, the center wavelength control unit 42 controls the center wavelength variable unit 22 to sweep the center wavelength of the light L. At this time, since the frequency of the high frequency signal is set so that the EIT phenomenon does not occur, the EIT phenomenon does not occur. The absorption detector 30 detects the minimum value (absorption bottom) of the detection signal output from the light detector 18 when the center wavelength of the light L is swept. For example, the absorption detecting unit 30 sets the bottom of absorption when the intensity change of the detection signal with respect to the center wavelength of the light L becomes constant.

  When the absorption detection unit 30 detects the bottom of absorption, the center wavelength control unit 42 controls the center wavelength variable unit 22 to fix (lock) the center wavelength. That is, the center wavelength control unit 42 fixes the center wavelength of the light L to a wavelength corresponding to the bottom of absorption.

  Next, the high frequency controller 44 controls the high frequency generator 24 to adjust the frequency of the high frequency signal to the frequency at which the EIT phenomenon occurs. Thereafter, the process shifts to a loop operation, and the EIT signal sampled by the sampling unit 26 is detected by the EIT detection unit 28.

  Next, the loop operation of the atomic oscillator 100 will be described.

The EIT detection unit 28 synchronously detects the detection signal output from the light detection unit 18, and the high frequency control unit 44 uses the frequency of the high frequency signal generated by the high frequency generation unit 24 based on the signal input from the EIT detection unit 28. Is controlled to have a frequency corresponding to half of ΔE ₁₂ of alkali metal atoms in the gas cell 16.

  The absorption detection unit 30 synchronously detects the detection signal output from the light detection unit 18, and the center wavelength control unit 42 determines that the center wavelength of the light L is based on the signal input from the absorption detection unit 30. The center wavelength variable section 22 is controlled so that the wavelength corresponds to the minimum value (absorption bottom) of the detection signal intensity output at 18.

  In the atomic oscillator 100, the temperature (drive temperature) of the light source 10 may be controlled to be constant.

1.2. Filter Element Next, the filter element 12 of the atomic oscillator 100 according to the present embodiment will be described with reference to the drawings. FIG. 5 is a diagram schematically showing the filter element 12.

  As shown in FIG. 5, the filter element 12 includes a filter portion 2 and a first electrode 4 a and a second electrode 4 b that sandwich the filter portion 2.

  The filter unit 2 is made of a semiconductor material. In the example shown in FIG. 5, the filter unit 2 includes a first semiconductor layer 2a and a second semiconductor layer 2b. The first semiconductor layer 2a is an n-type semiconductor layer doped with an n-type impurity (for example, silicon), and the second semiconductor layer 2b is a p-type semiconductor layer doped with a p-type impurity (for example, carbon). The first semiconductor layer 2a and the second semiconductor layer 2b may be formed by ion implantation. The first semiconductor layer 2a and the second semiconductor layer 2b are in contact with each other to form a pn junction.

  The first electrode 4 a and the second electrode 4 b are electrodes for applying a current to the filter unit 2. The first electrode 4a and the second electrode 4b are electrically connected to the power supply unit 20, and current is supplied from the power supply unit 20 to the first electrode 4a and the second electrode 4b.

  The first electrode 4a is provided on the first surface 3a (the surface of the first semiconductor layer 2a opposite to the surface in contact with the second semiconductor layer 2b) of the filter unit 2. The second electrode 4b is provided on the second surface 3b (surface opposite to the surface in contact with the first semiconductor layer 2a of the second semiconductor layer 2b) facing the direction opposite to the first surface 3a of the filter unit 2. It has been. The first electrode 4a is provided on the entire surface of the first surface 3a, and the second electrode 4b is provided on the entire surface of the second surface 3b.

  The first electrode 4 a and the second electrode 4 b transmit the light L emitted from the light source 10. That is, the first electrode 4 a and the second electrode 4 b are made of a material that is transparent to the light L. The material of the first electrode 4a and the second electrode 4b is, for example, ITO (Indium Tin Oxide).

  In the filter element 12, the light L emitted from the light source 10 is pulsed by utilizing the fact that the band gap of the filter unit 2 made of a semiconductor material changes with temperature.

  Next, control of the power supply unit 20 by the power supply control unit 21 will be described.

  FIG. 6 is a diagram illustrating a state in which the temperature of the filter unit 2 is the first temperature, and FIG. 7 is a diagram illustrating a state in which the temperature of the filter unit 2 is a second temperature higher than the first temperature.

  The light L emitted from the light source 10 enters the first electrode 4a, passes through the first electrode 4a, and enters the filter unit 2.

  The power supply control unit 21 controls the power supply unit 20 so that the filter unit 2 reaches the first temperature. Accordingly, a predetermined current is supplied from the power supply unit 20 to the first electrode 4a and the second electrode 4b, and the filter unit 2 becomes the first temperature. The first temperature is a temperature at which the band gaps of the semiconductor layers 2 a and 2 b constituting the filter unit 2 are larger than the energy of the light L. By setting the filter unit 2 to the first temperature, the band gaps of the semiconductor layers 2a and 2b become larger than the energy of the light L. As a result, the light L is not absorbed by the semiconductor layers 2a and 2b, Pass 2b. The light L that has passed through the filter unit 2 passes through the second electrode 4b and is emitted (see FIG. 6).

  Next, the power supply control unit 21 controls the power supply unit 20 so that the temperature of the filter unit 2 becomes the second temperature. Thus, a predetermined current is supplied from the power supply unit 20 to the first electrode 4a and the second electrode 4b, and the filter unit 2 becomes the second temperature. The second temperature is a temperature at which the band gap of the semiconductor layers 2 a and 2 b constituting the filter unit 2 becomes smaller than the energy of the light L. By setting the filter unit 2 to the second temperature, the band gap of the semiconductor layers 2a and 2b becomes smaller than the energy of the light L, and as a result, the light L is absorbed by the semiconductor layers 2a and 2b. That is, the light L does not pass through the semiconductor layers 2a and 2b (see FIG. 7).

  The power supply control unit 21 repeats the above process at a predetermined cycle to pulse the light L (see FIG. 4). The predetermined period is a period according to the repetition frequency (time T and time t) of the pulsed light set according to the required performance of the atomic oscillator.

For example, if the wavelength of the light L emitted from the light source 10 is 895 nm, the energy of the light L is 1.385475 eV. When the first semiconductor layer 2a and the second semiconductor layer 2b are Al _0.075 Ga _0.425 As _0.5 , the band gap at 301 ° C. of the first semiconductor layer 2a and the second semiconductor layer 2b is 1.385653113 eV, and the first semiconductor layer 2a The band gap of the second semiconductor layer 2b at 302 ° C. is 1.385149727 eV.

  Therefore, when the semiconductor layers 2a and 2b are set to 301 ° C. (first temperature), light L having a wavelength of 895 nm passes through the semiconductor layers 2a and 2b without being absorbed by the semiconductor layers 2a and 2b. Further, when the semiconductor layers 2a and 2b are set to 302 ° C. (second temperature), the light L having a wavelength of 895 nm is absorbed by the semiconductor layers 2a and 2b and cannot pass through the semiconductor layers 2a and 2b.

  In the above description, the example in which the material of the first semiconductor layer 2a and the second semiconductor layer 2b is AlGaAs has been described. However, the material of the first semiconductor layer 2a and the second semiconductor layer 2b is not particularly limited.

  In the above description, the example in which the filter unit 2 includes the first semiconductor layer 2a and the second semiconductor layer 2b has been described. However, the configuration of the filter unit 2 is not limited thereto. For example, the filter unit 2 may be composed of one semiconductor layer or may be composed of three or more semiconductor layers. For example, the filter unit 2 may be a pin diode in which an i-type semiconductor layer is sandwiched between an n-type semiconductor layer and a p-type semiconductor layer.

  Although not shown, the atomic oscillator 100 may include a cooling element for cooling the filter unit 2. By cooling the filter unit 2 with the cooling element, it is possible to shorten the time for the filter unit 2 to change from the second temperature to the first temperature.

  The atomic oscillator 100 has the following features, for example.

  In the atomic oscillator 100, the filter element 12 that pulsates the light L emitted from the light source 10 includes the filter portion 2 sandwiched between the first electrode 4a and the second electrode 4b, and the filter portion 2 is made of a semiconductor material. It is configured. Therefore, in the filter element 12, the light L emitted from the light source 10 can be pulsed by utilizing the fact that the band gap of the filter unit 2 made of a semiconductor material changes with temperature. Therefore, in the atomic oscillator 100, the light L can be pulsed with a small and simple configuration as compared with the case where the light L is pulsed using, for example, an acousto-optic element or a liquid crystal element. Therefore, according to this embodiment, the atomic oscillator 100 having a small and simple configuration can be realized.

  In the atomic oscillator 100, the power supply control unit 21 controls the power supply unit 20 so that the temperature of the filter unit 2 becomes the first temperature, and the temperature of the filter unit 2 becomes the second temperature higher than the first temperature. Thus, the process of controlling the power supply unit 20 is repeated. Thereby, in the filter element 12, the state where the light L emitted from the light source 10 is absorbed by the filter unit 2 and the state where the light L passes through the filter unit 2 can be repeated. The light L can be pulsed.

  Furthermore, since the filter element 12 can be operated by applying a current to the filter unit 2, there is no mechanically operated portion, and vibration or the like does not occur. Further, since the filter element 12 turns on and off light by utilizing the change in the band gap of the semiconductor, there is little light loss in the on state, and no light leaks in the off state. It can be completely blocked.

  In the atomic oscillator 100, since the first electrode 4a and the second electrode 4b transmit light emitted from the light source 10, the first electrode 4a and the second electrode 4b are separated from each other in two directions facing the filter unit 2 in opposite directions. It can be formed on the entire surface 3a, 3b. Therefore, a current and a voltage can be uniformly applied to the filter unit 2, and the filter unit 2 can be heated uniformly.

  In the atomic oscillator 100, since the filter unit 2 includes the n-type first semiconductor layer 2a and the p-type second semiconductor layer 2b, a pn junction can be formed. Therefore, the filter unit 2 can be heated by applying a current to the filter unit 2, and a heater or the like for heating the filter unit 2 is unnecessary. Therefore, the filter element 12 can be realized with a small and simple configuration.

  FIG. 8 is a diagram schematically showing a modification of the filter element 12 in the first embodiment described above. As shown in FIG. 8, the filter element 12 may include a temperature sensor 6 that measures the temperature of the filter unit 2. In the example illustrated in FIG. 8, the power supply control unit 21 (see FIG. 1) controls the power supply unit 20 based on the measurement result of the temperature sensor 6. Specifically, when the power supply control unit 21 determines that the temperature of the filter unit 2 has become the first temperature based on the measurement result of the temperature sensor 6, the temperature of the filter unit 2 becomes the second temperature. The power supply unit 20 is controlled. And when it determines with the temperature of the filter part 2 having become 2nd temperature based on the measurement result of the temperature sensor 6, the process which controls the power supply part 20 is performed so that the temperature of the filter part 2 may become 1st temperature . When the power supply control unit 21 repeats these two processes, the atomic oscillator 100 using the filter element 12 shown in FIG. 8 achieves the same operational effects as when the filter element 12 shown in FIG. 5 is used. be able to.

(Second Embodiment)
2. Atomic oscillator 2.1. Configuration Next, an atomic oscillator according to a second embodiment will be described with reference to FIGS. 9 and 10. FIG. 9 is a functional block diagram of the atomic oscillator according to the second embodiment. FIG. 10 is a diagram illustrating a state of reflected light of the filter element. The atomic oscillator 100A according to the second embodiment shown in FIG. 9 is different from the atomic oscillator 100 according to the first embodiment described above in the arrangement configuration of the filter element 12A. Hereinafter, in the description of the second embodiment, the arrangement configuration of the filter element 12A will be mainly described, and the same configurations as those in the first embodiment may be denoted by the same reference numerals and description thereof may be omitted.

  As shown in FIG. 9, the atomic oscillator 100 </ b> A includes a light source 10, a filter element 12 </ b> A, a λ / 4 plate 14, a gas cell 16, a light detection unit 18, a power supply unit 20, a power supply control unit 21, The wavelength variable unit 22, the high frequency generation unit 24, the absorption detection unit 30, the sampling unit 26, the EIT detection unit 28, and the control unit 40 are included. The control unit 40 includes a center wavelength control unit 42 and a high frequency control unit 44. Similar to the first embodiment, the atomic oscillator 100A generates an EIT phenomenon in an alkali metal atom by a resonant light pair (first light and second light) having two different frequency components.

  In the atomic oscillator 100A, the filter element 12A has the same configuration as the filter element 12 described with reference to FIG. 5 in the first embodiment, and includes the filter unit 2 and the filter unit 2 as illustrated in FIG. The first electrode 4a and the second electrode 4b are sandwiched. The filter element 12A includes an incident surface 12f that is a surface located on the incident side of the light L, an emission surface 12b that is a surface located on the emission side of the light pulsed by the filter element 12A (pulse light), It has. In this configuration, the entrance surface 12f and the exit surface 12b are configured to be substantially parallel.

  In the atomic oscillator 100A, the filter element 12A is arranged such that the incident surface 12f or the emission surface 12b is inclined with respect to the virtual surface Q that is a surface having the optical axis of the light L as a normal line. In the example shown in FIG. 9, the light incident surface 12 f of the filter element 12 </ b> A is inclined with respect to the virtual plane Q with an inclination angle θ. In other words, in the filter element 12A, the incident surface 12f or the exit surface 12b is arranged with an inclination of 0 ° <θ <90 ° with respect to the virtual surface Q. Note that the light L exit surface 12 b substantially parallel to the light L incident surface 12 f also has the same inclination angle θ with respect to the virtual surface Q.

  12 A of filter elements have the filter part 2 and the 1st electrode 4a and 2nd electrode 4b which pinch | interpose the filter part 2 similarly to 1st Embodiment shown in FIG. In the filter element 12A, the light L emitted from the light source 10 is pulsed by utilizing the fact that the band gap of the filter unit 2 made of a semiconductor material changes with temperature. Then, as shown in FIG. 10, the filter element 12 </ b> A emits pulsed pulsed light La from the emission surface 12 b to the side opposite to the light source 10.

  According to the atomic oscillator 100A according to the second embodiment, the filter element 12A is arranged with an inclination angle θ with respect to the virtual plane Q, so that the incident surface of the filter element 12A is arranged as shown in FIG. The return light Lb reflected by 12f travels in an axial direction different from the optical axis of the light L emitted from the light source 10. Specifically, the return light Lb is reflected in an axial direction having an angle θ with respect to the normal P direction of the incident surface 12f that has an angle θ with the optical axis of the light L. That is, the return light Lb is reflected at an angle of 2θ with respect to the optical axis of the incident light (light L). Thus, since the return light Lb is directed in a different direction with respect to the optical axis of the incident light (light L), the return light Lb does not return to the light source 10, and the output fluctuation of the light source 10 due to the influence of the return light Lb is suppressed. can do. Thereby, it is possible to provide an atomic oscillator 100A that can suppress a decrease in accuracy due to the return light Lb.

  In addition, this invention is not limited to embodiment mentioned above, A various deformation | transformation implementation is possible within the range of the summary of this invention.

  Further, the above-described embodiments and modifications are examples, and the present invention is not limited to these. For example, each embodiment and each modification can be appropriately combined.

  The present invention includes configurations that are substantially the same as the configurations described in the embodiments (for example, configurations that have the same functions, methods, and results, or configurations that have the same objects and effects). In addition, the invention includes a configuration in which a non-essential part of the configuration described in the embodiment is replaced. In addition, the present invention includes a configuration that exhibits the same operational effects as the configuration described in the embodiment or a configuration that can achieve the same object. Further, the invention includes a configuration in which a known technique is added to the configuration described in the embodiment.

  DESCRIPTION OF SYMBOLS 2 ... Filter part, 2a ... 1st semiconductor layer, 2b ... 2nd semiconductor layer, 3a ... 1st surface, 3b ... 2nd surface, 4a ... 1st electrode, 4b ... 2nd electrode, 6 ... Temperature sensor, 10 ... Light source, 12, 12A ... filter element, 14 ... λ / 4 plate, 16 ... gas cell, 18 ... light detection unit, 20 ... power supply unit, 21 ... power supply control unit, 22 ... center wavelength variable unit, 24 ... high frequency generation unit, 26 ... Sampling unit, 28 ... EIT detection unit, 30 ... Absorption detection unit, 40 ... Control unit, 42 ... Center wavelength control unit, 44 ... High frequency control unit, 100, 100A ... Atomic oscillator.

Claims (5)

A light source;
A filter element for pulsing the light emitted from the light source;
A gas cell in which alkali metal atoms are enclosed and irradiated with light pulsed by the filter element;
A light detection unit for detecting the amount of light transmitted through the gas cell;
A power supply for supplying current to the filter element,
The filter element is
A first electrode and a second electrode electrically connected to the power source;
A filter portion sandwiched between the first electrode and the second electrode,
The atomic oscillator is characterized in that the filter portion is made of a semiconductor material. A power supply control unit for controlling the power supply,
The power control unit
A process of controlling the power supply so that the temperature of the filter unit becomes the first temperature;
2. The atomic oscillator according to claim 1, wherein the process of controlling the power supply is repeatedly performed so that the temperature of the filter unit becomes a second temperature higher than the first temperature.   The atomic oscillator according to claim 1, wherein the first electrode and the second electrode transmit light emitted from the light source.   4. The atomic oscillator according to claim 1, wherein the filter unit includes an n-type first semiconductor layer and a p-type second semiconductor layer. 5.   5. The light incident surface or the light exit surface of the filter element is inclined with respect to a surface having the optical axis of the light as a normal line. 6. 2. An atomic oscillator according to item 1.

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