Atomic oscillator and frequency signal generation system

Abstract

To provide an atomic oscillator having a high extinction ratio of pulsed light irradiated onto an atomic cell, a sufficiently high repetition frequency of the pulsed light, and high stability of the output frequency, and a frequency signal generation system equipped with such an atomic oscillator. [Solution] An atomic oscillator comprising: a frequency oscillation unit that outputs an oscillation signal; a light source unit that emits laser light based on a modulation signal corresponding to the oscillation signal; a pulsation mechanism that emits pulsed light; an atomic cell; a photodetection unit that detects pulsed light that has passed through the atomic cell; and an oscillation control circuit that adjusts the frequency of the oscillation signal based on the pulsed light detection signal, wherein the pulsation mechanism has a light splitting unit; a first mirror; a first mirror drive unit; a first angle adjustment unit that limits the angle range through which the first split light passes; a second mirror; a second mirror drive unit; a second angle adjustment unit that limits the angle range through which the second split light passes; and a photosynthesis unit that combines the pulsed first split light and the pulsed second split light.

Description

[Technical Field]

[0001] This invention relates to an atomic oscillator and a frequency signal generation system. [Background technology]

[0002] As oscillators that exhibit high-precision oscillation characteristics over the long term, atomic oscillators that oscillate based on the energy transitions of alkali metal atoms such as rubidium and cesium are known.

[0003] Patent Document 1 discloses an atomic oscillator that utilizes CPT (Coherent Population Trapping) resonance, which is one of the quantum interference effects.

[0004] The atomic oscillator disclosed in Patent Document 1 comprises an alkali metal cell (atomic cell) containing alkali metals, a light source that irradiates the alkali metal cell with laser light, and a photodetector that detects the light transmitted through the alkali metal cell. Such an atomic oscillator utilizes CPT resonance, which occurs when two different wavelengths of laser light are irradiated onto alkali metal atoms, and the electromagnetically induced transparency (EIT) phenomenon, in which the laser light is transmitted through the alkali metal without being absorbed due to the CPT resonance. In the atomic oscillator, the sharp EIT signal generated in conjunction with the EIT phenomenon is detected by the photodetector and used as a reference signal.

[0005] Furthermore, in the atomic oscillator described in Patent Document 1, the laser light emitted from the light source is pulsed by an AOM (Acousto-Optic Modulator), and by irradiating alkali metal atoms with the laser light at time intervals, Ramsey resonance is generated. By generating Ramsey resonance in this way, the resonance linewidth can be narrowed, and thus the EIT signal can be detected with high accuracy. This improves the stability of the output frequency of the atomic oscillator.

[0006] On the one hand, Non-Patent Document 1 discloses that in an atomic oscillator using CPT resonance, the output of laser light is detected by a photodiode and reflected in the drive of an AOM.

[0007] The atomic oscillator disclosed in Non-Patent Document 1 includes a VCSEL (Vertical Cavity Surface Emitting Laser), an AOM that pulses the laser light emitted from the VCSEL, a photodiode that divides the pulsed light transmitted through the AOM and detects the output of the divided pulsed light, and a Cs-Ne cell (atomic cell). The voltage signal output from the photodiode is compared with a reference voltage and used to correct the RF signal driving the AOM. As a result, appropriate calibration can be performed on the pulsed light output from the AOM, and fluctuations in laser power can be suppressed. Consequently, the output frequency of the atomic oscillator is stabilized.

[0008] When using Ramsey resonance by the methods shown in Patent Document 1 and Non-Patent Document 1, it is necessary to sufficiently increase the extinction ratio of the pulsed light irradiated on the alkali metal atoms. In the methods described in Patent Document 1 and Non-Patent Document 1, the irradiation of the laser light on the alkali metal atoms is switched by an AOM arranged on the optical path of the laser light to achieve pulsing.

[0009] However, in a transmission-type intensity modulation device such as an AOM, even when intensity modulation is performed to block the laser light, the laser light may not be sufficiently blocked, and the extinction ratio may decrease. When the extinction ratio decreases, the stability of the output frequency of the atomic oscillator decreases due to a phenomenon called light shift.

Prior Art Documents

Patent Documents

[0010]

Patent Document 1

Non-Patent Documents

[0012] On the other hand, it is also conceivable to pulse the laser light by switching the reflection optical path of the laser light with a mirror driving device such as a MEMS mirror. In such a MEMS mirror, an improvement in the extinction ratio can be expected compared to a transmission-type intensity modulation device such as an AOM.

[0013] However, the driving frequency of the mirror driving device is generally a low frequency of about 1 kHz and is not sufficiently high. Also, when applying pulsed light to Ramsey resonance, it is desirable to increase the repetition frequency of the pulsed light, but in the pulsing using a MEMS mirror, the driving frequency of the mirror driving device becomes a constraint.

[0014] Then, the repetition frequency of the pulsed light cannot be sufficiently increased, and there is a problem in stabilizing the output frequency of the atomic oscillator.

[0015] Therefore, it has been an issue to realize an atomic oscillator in which the extinction ratio of the pulsed light irradiated to the atomic cell is high, the repetition frequency of the pulsed light is sufficiently high, and the stability of the output frequency is high. [Means for Solving the Problems] <(

[0016] The atomic oscillator according to the application example of the present invention is a frequency oscillation unit that outputs an oscillation signal, a light source unit that emits laser light including first light and second light having different frequencies based on a modulation signal corresponding to the oscillation signal, A pulsing mechanism that pulses the laser light and emits pulsed light, The pulsed light is incident on an atomic cell containing alkali metal atoms, A photodetector that detects the pulsed light transmitted through the atomic cell and outputs a pulsed light detection signal corresponding to the intensity of the pulsed light, An oscillation control circuit adjusts the frequency of the oscillation signal by controlling the operation of the frequency oscillation unit based on the pulse light detection signal, Equipped with, The pulsation mechanism is, A light splitting unit that splits the aforementioned laser light into a first split beam and a second split beam, A first mirror that scans the reflected light path of the first divided light by rotation around a pivot axis, A first mirror drive unit rotates the first mirror at a predetermined period based on a first drive signal, A first angle adjustment unit pulses the first divided light by limiting the angular range through which the first divided light passes within the scanning range of the reflected light path of the first divided light, A second mirror, which scans the reflected light path of the second divided light by rotation around the pivot axis, A second mirror drive unit that rotates the second mirror at a predetermined period based on a second drive signal, A second angle adjustment unit pulses the second divided light by limiting the angular range through which the second divided light passes within the scanning range of the reflected light path of the second divided light, A photosynthesis unit that combines the first segmented light pulsed by the first angle adjustment unit and the second segmented light pulsed by the second angle adjustment unit and emits the pulsed light, It has.

[0017] The frequency signal generation system according to an application example of the present invention is: An atomic oscillator according to an application example of the present invention, A processing unit that processes the output signal output from the atomic oscillator, It is equipped with. [Brief explanation of the drawing]

[0018] [Figure 1] This is a block diagram of an atomic oscillator according to an embodiment. [Figure 2] This diagram shows the energy levels of a cesium atom. [Figure 3] This figure shows an example of an EIT signal. [Figure 4] This figure shows an example of the frequency spectrum of laser light emitted from the light source shown in Figure 1. [Figure 5] This is a conceptual diagram showing the time evolution of the intensity of pulsed light incident on an atomic cell. [Figure 6] This is a timing chart illustrating an example of the operation of the atomic oscillator shown in Figure 1. [Figure 7] A block diagram of an atomic oscillator relating to the first modified example. [Figure 8] This is a timing chart to illustrate an example of operation of the atomic oscillator according to the first modified example. [Figure 9] A block diagram of an atomic oscillator relating to the second modified example. [Figure 10] This is a timing chart illustrating an example of operation of the atomic oscillator according to the second modified example. [Figure 11] This is a block diagram of an atomic oscillator according to the third modified example. [Figure 12] This is a schematic diagram showing a clock transmission system as a frequency signal generation system according to the embodiment. [Modes for carrying out the invention]

[0019] The atomic oscillator and frequency signal generation system of the present invention will be described in detail below based on embodiments shown in the accompanying drawings.

[0020] 1. Atomic oscillator First, the atomic oscillator according to the embodiment will be described.

[0021] 1.1. Overview of Atomic Oscillators Figure 1 is a block diagram showing an atomic oscillator 1 according to an embodiment.

[0022] The atomic oscillator 1 shown in Figure 1 is an atomic oscillator that utilizes the quantum interference effect (CPT: Coherent Population Trapping) when an alkali metal atom is irradiated with laser light containing first and second rays of different frequencies, which reduces the amount of laser light absorbed by the alkali metal atom. This quantum interference effect causes an electromagnetically induced transparency (EIT: Electromagnetically Induced Transparency) phenomenon, in which the amount of laser light transmitted through the alkali metal atom increases. The atomic oscillator 1 utilizes this phenomenon to stabilize the output frequency.

[0023] The atomic oscillator 1 shown in Figure 1 comprises a light source unit 2, an atomic cell 3, a pulsation mechanism 4, a photodetector unit 5, a frequency oscillation unit 6, and an oscillation control circuit 7. The frequency oscillator 6 outputs an oscillation signal S1.

[0024] The light source unit 2 emits laser light L. This laser light L includes a first beam and a second beam, each with a different frequency. The frequencies of these first and second beams are set based on a modulation signal S2 corresponding to an oscillation signal S1 input to the light source unit 2.

[0025] The pulsing mechanism 4 includes a waveform generator 40, a first mirror 410, a first mirror drive unit 412, a first angle adjustment unit 414, a second mirror 420, a second mirror drive unit 422, a second angle adjustment unit 424, a light splitting unit 44, and a photosynthesis unit 45. The pulsing mechanism 4 pulses the incident laser light L by reflecting it using the first mirror 410 and the second mirror 420, respectively, and emits pulsed light PL. At this time, pulsed light PL with a repetition frequency higher than the rotation frequencies of the first mirror 410 and the second mirror 420 is generated by splitting the laser light L, reflecting the split light and limiting the range of its passage angle, and combining the split light.

[0026] Atomic cell 3 encapsulates multiple alkali metal atoms in gaseous form. Examples of alkali metal atoms include cesium atoms, rubidium atoms, sodium atoms, and potassium atoms. Pulsed light PL generated by the pulsation mechanism 4 is incident on atomic cell 3. When pulsed light PL is irradiated onto atomic cell 3, the alkali metal atoms are pulse-excited, and Ramsey resonance occurs. This results in the appearance of a Ramsey fringe, which has a signal shape in which fine vibrations are superimposed on the signal obtained by the EIT phenomenon (EIT signal). By utilizing the peak of the Ramsey fringe, the output frequency of atomic oscillator 1 can be further stabilized.

[0027] The photodetector 5 detects pulsed light PL that has passed through the atomic cell 3. The photodetector 5 outputs a pulsed light detection signal S5 corresponding to the intensity of the pulsed light PL.

[0028] The oscillation control circuit 7 adjusts the frequency of the oscillation signal S1 by controlling the operation of the frequency oscillation unit 6 based on the pulse light detection signal S5. This causes the EIT phenomenon to occur in alkali metal atoms. Controlling the operation of the frequency oscillation unit 6 based on the pulse light detection signal S5 means performing the necessary known processing on the pulse light detection signal S5 and using the processed signal to control the operation of the frequency oscillation unit 6 so that the output frequency stabilizes at a predetermined value.

[0029] With the above configuration, the pulse generation mechanism 4 is used, and the reflection of the laser light L is utilized to create pulses, as described later. This allows for an increase in the extinction ratio of the pulsed light PL irradiated onto the atomic cell 3. Furthermore, the repetition frequency of the pulsed light PL can be sufficiently increased, thereby stabilizing the Ramsey resonance. This enables the realization of an atomic oscillator 1 with high stability of output frequency (frequency of oscillation signal S1). Additionally, since the pulsed light PL is generated by continuous oscillation rather than direct modulation of the light source 20, it is also useful in terms of easily improving the frequency stability of the laser light L.

[0030] 1.2. Electromagnetic Induced Transparency (EIT) Phenomenon Figure 2 shows the energy levels of cesium atoms. As shown in Figure 2, cesium atoms have a ground state of 6S 1 / 2 , an excited state of 6P 1 / 2 , 6P 3 / 2 . The 6S 1 / 2 , 6P 1 / 2 , 6P 3 / 2 each have a hyperfine structure split into multiple energy levels. Also, 6S 1 / 2 has two ground states of F = 3, 4, 6P 1 / 2 has two excited states of F' = 3, 4, and 6P 3 / 2 has four excited states of F' = 2, 3, 4, 5.

[0031] For example, a cesium atom in the ground state of F = 3 of 6S 1 / 2 can transition to an excited state of either F' = 3 or 4 of 6P 1 / 2 by absorbing the D1 line. Also, a cesium atom in the ground state of F = 4 of 6S 1 / 2 can transition to an excited state of either F' = 3 or 4 of 6P 1 / 2 by absorbing the D1 line. Conversely, a cesium atom in an excited state of either F' = 3 or 4 of 6P 1 / 2 can transition to the ground state of F = 3 or F = 4 of 6S 1 / 2 by emitting the D1 line. The three-level system consisting of the two ground states of F = 3, 4 of 6S 1 / 2 and either of the excited states of F' = 3, 4 of 6P 1 / 2 is called a Λ-type three-level system because Λ-type transitions by absorption and emission of the D1 line are possible.

[0032] On the other hand, a cesium atom in the ground state of F = 3 of 6S 1 / 2 can transition to an excited state of either F' = 2, 3, or 4 of 6P 3 / 2 by absorbing the D2 line, but cannot transition to the excited state of F' = 5. A cesium atom in the ground state of F' = 4 of 6S 1 / 2 can transition to an excited state of 6P 3 / 2It can transition to any of the excitation levels F'=3, 4, or 5, but it cannot transition to the excitation level F'=2. These are due to the transition selection rules assuming an electric dipole transition. Conversely, 6P 3 / 2 Cesium atoms in either the F'=3 or F'=4 excited state emit a D2 line and produce 6S 1 / 2 It can transition to a base level of F=3 or F=4. 6S 1 / 2 The two base levels F=3,4 and 6P 3 / 2 The three levels consisting of either the F'=3 or F'=4 excitation levels form a Λ-type three-level configuration because Λ-type transitions are possible via D2 line absorption and emission. In contrast, 6P 3 / 2 A cesium atom in the F'=2 excited state will always emit a D2 line and become 6S. 1 / 2 It transitions to the base level F'=3, and similarly, 6P 3 / 2 A cesium atom in the excited state of F'=5 will always emit a D2 line and become 6S. 1 / 2 It transitions to the F=4 ground level. Therefore, 6S 1 / 2 The two base levels F=3,4 and 6P 3 / 2 The three levels consisting of excited levels F'=2 or F'=5 do not form a Λ-type three-level configuration because Λ-type transitions due to D2 line absorption and emission are impossible. Similarly, alkali metal atoms other than cesium atoms also have two ground levels and excited levels that form a Λ-type three-level configuration.

[0033] When gaseous alkali metal atoms are simultaneously irradiated with a first light and a second light having a predetermined frequency difference, the EIT phenomenon occurs in the alkali metal atoms.

[0034] When the EIT phenomenon occurs, an EIT signal is obtained in the photodetector 5 shown in Figure 1, where the transmittance of the atomic cell 3 increases sharply. An example of the EIT signal is shown in Figure 3. In Figure 3, the horizontal axis is the frequency difference ω1-ω2 between the first and second light, and the vertical axis is the transmittance of the light passing through the atomic cell 3. The difference ω1-ω2 between the frequency ω1 of the first light and the frequency ω2 of the second light is the energy difference ΔE between the two ground levels shown in Figure 2. 12 The frequency corresponding to ω 12When this matches, the EIT signal shows a peak value. For example, when gaseous cesium atoms are 6S 1 / 2 From the base level of F=3 to 6P 1 / 2 The D1 line, which causes a transition to the F'=4 excitation level, is designated as the first light source, and 6S 1 / 2 From the F=4 basis level to 6P 1 / 2 When the D1 line, which causes a transition to the F'=4 excitation level, is simultaneously irradiated as a second light source, the EIT phenomenon occurs. Since the EIT signal has a very steep waveform, it contributes to the stabilization of the output frequency of atomic oscillator 1.

[0035] Figure 4 shows an example of the frequency spectrum of the laser light L emitted from the light source unit 2 shown in Figure 1. In Figure 4, the horizontal axis is frequency and the vertical axis is intensity. As shown in Figure 4, for example, if the laser light L contains at least two first-order sidebands, the frequency difference ω of the two sidebands shown in Figure 4 is... 1-2 The aforementioned energy difference ΔE 12 The frequency corresponding to ω 12 By matching these two bands, one sideband can be used as the first light and the other as the second light, thereby generating the aforementioned EIT phenomenon.

[0036] The laser light L, including the first and second rays as described above, can be emitted by modulating the current supplied to the light source unit 2 shown in Figure 1. For example, as shown in Figure 1, if the light source unit 2 has a light source 20, the bias current corresponding to the center frequency in Figure 4 is modulated by ω 1-2 The drive current obtained by combining the modulated signal S2, which fluctuates at a frequency of 2, should be supplied to the light source 20. Note that the modulation method is not limited to this.

[0037] 1.3. Ramsey Resonance In the atomic oscillator 1 shown in Figure 1, pulsed light PL emitted from the pulsation mechanism 4 is incident on the atomic cell 3.

[0038] When pulsed light (PL) is irradiated, alkali metal atoms are pulse-excited, and Ramsey resonance occurs. This results in the emergence of a Ramsey fringe, which has a signal shape in which fine vibrations are superimposed on the EIT signal. One of the fine vibrations of the Ramsey fringe has a very narrow linewidth and therefore a high Q value. For this reason, the output frequency of atomic oscillator 1 can be further stabilized by utilizing the peak of the Ramsey fringe.

[0039] 1.4.Light source section The light source unit 2 shown in Figure 1 includes a light source 20, a light source drive unit 22, and a frequency multiplier 24.

[0040] The light source 20 is, for example, a vertical cavity surface-emitting laser (VCSEL). Vertical cavity surface-emitting lasers are useful as semiconductor laser elements for the light source 20 because they have a wide modulation bandwidth due to the current.

[0041] The light source drive unit 22 controls the bias current corresponding to the center frequency in Figure 4 to ω 12 A drive current is generated by combining a modulated signal S2 that fluctuates at a frequency of 2. This drive current is then supplied to the light source 20. When such a drive current is supplied to the light source 20, the light source 20 emits laser light L having a center frequency corresponding to the bias current and sidebands with a frequency difference corresponding to the modulated signal S2.

[0042] The frequency multiplier 24 multiplies the oscillation signal S1 output from the frequency oscillator 6 shown in Figure 1, thereby obtaining the energy difference ΔE between the two ground levels shown in Figure 2. 12 The frequency corresponding to ω 12 It generates a signal with half the frequency of the oscillator. Then, it outputs the generated signal as a modulated signal S2. In other words, the frequency multiplier 24 outputs a modulated signal S2 that corresponds to the oscillation signal S1. The frequency multiplier 24 is implemented, for example, by a PLL (Phase Locked Loop) circuit.

[0043] A gain control circuit for amplifying the modulated signal S2 may be provided between the frequency multiplier 24 and the light source drive unit 22.

[0044] Furthermore, the light source unit 2 may have optical elements not shown. Examples of optical elements include filters, lenses, waveplates, etc. These optical elements are arranged, for example, between the light source 20 and the pulsation mechanism 4. Alternatively, optical elements may be arranged between the pulsation mechanism 4 and the atomic cell 3.

[0045] 1.5. Atomic Cells The atomic cell 3 shown in Figure 1 contains multiple alkali metal atoms in gaseous form. The inner wall of the atomic cell 3 may be coated with a hydrocarbon film such as paraffin or OTS (octadecyltrichlorosilane). The atomic cell 3 may also contain a buffer gas along with the alkali metal atoms. Examples of buffer gases include noble gases. A portion of the pulsed light PL incident on the atomic cell 3 passes through the atomic cell 3 and is detected by the photodetector 5.

[0046] A coil (not shown) is provided outside the atomic cell 3. The coil applies a magnetic field in a predetermined direction to the alkali metal atoms housed in the atomic cell 3. This allows for the selection and use of spectra (clock transitions) that are insensitive to changes in the external environment, such as external magnetic fields or temperature.

[0047] The temperature of the atomic cell 3 may be controlled to a desired temperature using a temperature control element such as a Peltier element (not shown).

[0048] 1.6. Pulsation Mechanism First, let's explain the configuration of the pulsation mechanism 4.

[0049] 1.6.1. Configuration of the Pulsation Mechanism The pulsation mechanism 4 shown in Figure 1 includes a waveform generator 40, a first mirror 410, a first mirror drive unit 412, a first angle adjustment unit 414, a second mirror 420, a second mirror drive unit 422, a second angle adjustment unit 424, a light splitting unit 44, and a photosynthesis unit 45.

[0050] The pulsing mechanism 4 divides the incident laser light L in the light splitting unit 44, pulses the resulting first split light L1 and second split light L2 using the rotating first mirror 410 and second mirror 420 and the first angle adjustment unit 414 and second angle adjustment unit 424, respectively, and then synthesizes them in the photosynthesis unit 45 to generate pulsed light PL. This makes it possible to generate pulsed light PL with a repetition frequency higher than the rotation frequencies of the first mirror 410 and the second mirror 420.

[0051] The optical splitting unit 44 splits the incident laser light L into a first split beam L1 and a second split beam L2. Examples of the optical splitting unit 44 include an unpolarized beam splitter and a semi-transparent mirror.

[0052] The waveform generator 40 outputs a first drive signal S41 to the first mirror drive unit 412 and a second drive signal S42 to the second mirror drive unit 422. The first drive signal S41 and the second drive signal S42 are periodic signals with equal frequencies and different phases. Such signals can be generated relatively easily and accurately by the waveform generator 40. The waveforms of the first drive signal S41 and the second drive signal S42 can be set appropriately according to the arrangement of the first mirror 410 and the second mirror 420, and the arrangement of the first angle adjustment unit 414 and the second angle adjustment unit 424, but are not limited to these. Examples of the waveform generator 40 include a signal generator and a function generator.

[0053] The first mirror 410 reflects the first segmented light L1 and rotates around the pivot axis AX1. In Figure 1, the first mirror 410 is configured to oscillate around the pivot axis AX1. This periodically changes the reflection angle of the first segmented light L1. In other words, it scans the reflected light path of the first segmented light L1 within a predetermined angular range. Hereafter, the angular range in which the first segmented light L1 is scanned will also be called the "scanning range".

[0054] The first mirror drive unit 412 rotates the first mirror 410 around the pivot axis AX1 at a predetermined period. The operating modes of the first mirror drive unit 412 include a resonant mode and a non-resonant mode. Of these, the non-resonant mode is preferably used. In the non-resonant mode, the rotation angle of the first mirror 410 can be controlled with greater precision.

[0055] The first mirror 410 and the first mirror drive unit 412 may be composed of a so-called optical scanner. Examples of optical scanners include MEMS (Micro Electro Mechanical Systems) scanners, galvanometer scanners, resonant scanners, and polygon scanners. Of these, MEMS scanners are preferred. MEMS scanners make it easy to miniaturize, lighten, and reduce the power consumption of the first mirror drive unit 412.

[0056] The operating method of the first mirror drive unit 412 is not particularly limited, but examples include electrostatic, piezoelectric, and electromagnetic methods.

[0057] The first angle adjustment unit 414 is located within the scanning range of the first segmented light L1. The first angle adjustment unit 414 pulses the first segmented light L1 intermittently at a predetermined period by limiting the angular range through which the first segmented light L1 reflected by the first mirror 410 passes. In other words, pulsed light is generated that has intensity during the time period when the first segmented light L1, whose reflected light path is being scanned, passes through the first angle adjustment unit 414, and has no intensity at other times. The pulsed first segmented light L1 is emitted toward the photosynthesis unit 45. Examples of the first angle adjustment unit 414 include an optical diaphragm, a slit, a pinhole, etc. Of these, an optical diaphragm is useful because it has high accuracy in the angular range through which the first segmented light L1 passes and the angular range can be easily adjusted. In addition, the generation of stray light can be suppressed by providing the first angle adjustment unit 414.

[0058] The second mirror 420 reflects the second split beam L2 and rotates around the pivot axis AX2 at a predetermined period. In Figure 1, the second mirror 420 is configured to oscillate around the pivot axis AX2. This periodically changes the reflection angle of the second split beam L2. In other words, it scans the reflected light path of the second split beam L2 within a predetermined angular range. Hereafter, the angular range in which the second split beam L2 is scanned will also be called the "scanning range".

[0059] The second mirror drive unit 422 rotates the second mirror 420 around the pivot axis AX2. The operating modes of the second mirror drive unit 422 include a resonant mode and a non-resonant mode. Of these, the non-resonant mode is preferred. In the non-resonant mode, the rotation angle of the second mirror 420 can be controlled with greater precision.

[0060] The second mirror 420 and the second mirror drive unit 422 may be composed of so-called optical scanners. While the aforementioned optical scanners are available, MEMS scanners are preferred. MEMS scanners facilitate miniaturization, weight reduction, and low power consumption of the second mirror drive unit 422.

[0061] The operating method of the second mirror drive unit 422 is not particularly limited, but examples include electrostatic, piezoelectric, and electromagnetic methods.

[0062] The second angle adjustment unit 424 is located within the scanning range of the second segmented light L2. The second angle adjustment unit 424 pulses the second segmented light L2 intermittently at a predetermined period by limiting the angular range through which the second segmented light L2 reflected by the second mirror 420 passes. In other words, pulsed light is generated that has intensity during the time when the second segmented light L2, whose reflected light path is being scanned, passes through the second angle adjustment unit 424, and has no intensity at other times. The pulsed second segmented light L2 is emitted towards the photosynthesis unit 45. Examples of the second angle adjustment unit 424 include an optical diaphragm, a slit, a pinhole, etc. Furthermore, by providing the second angle adjustment unit 424, the generation of stray light can be suppressed.

[0063] The photosynthesis unit 45 synthesizes pulsed first-partition light L1 and pulsed second-partition light L2. This generates pulsed light PL, which the photosynthesis unit 45 emits toward the atomic cell 3. Examples of the photosynthesis unit 45 include an unpolarized beam splitter and a semi-transparent mirror.

[0064] 1.6.2. Pulse width and pulse interval Figure 5 is a conceptual diagram showing the time evolution of the intensity of pulsed light PL incident on atomic cell 3. In Figure 5, the horizontal axis represents time, and the vertical axis represents intensity.

[0065] The intensity of the pulsed light PL incident on the atomic cell 3 changes in a pulse wave pattern, as shown in Figure 5. In the intensity change shown in Figure 5, a first period τ with relatively high intensity and a second period T with relatively low intensity alternate.

[0066] The first period τ is the pulse width, and is the period during which a pulsed light PL with intensity passes through the atomic cell 3. The length of the first period τ can be adjusted, for example, by changing the oscillation speed and oscillation width of the first mirror 410 and the second mirror 420, as well as the angular ranges of the first angle adjustment unit 414 and the second angle adjustment unit 424.

[0067] In the photodetector 5, the time τ is calculated from the start of the first period τ (the rising edge of the pulse). m After a certain period, the intensity of the pulsed light PL is detected. This time is defined as the observation timing OB. After observation timing OB, alkali metal atoms are excited until the end of the first period τ (falling edge of the pulse). The second period T is the pulse interval, which is the free evolution time during which the incidence of the pulsed light PL is paused. By alternately repeating these first period τ and second period T, a Ramsey resonance can be generated.

[0068] The line width of the Ramsey fringe changes according to the length of the second period T shown in Figure 5. Specifically, the full width at half maximum γ of the peaks included in the Ramsey fringe is given by γ = 1 / (2T).

[0069] Based on the above formula, the linewidth of the Ramsey fringe can be narrowed by lengthening the second period T. This further stabilizes the output frequency of the atomic oscillator 1. The length of the second period T can be adjusted, for example, by changing the oscillation speed and oscillation amplitude of the first mirror 410 and the second mirror 420, as well as the angular ranges of the first angle adjustment unit 414 and the second angle adjustment unit 424.

[0070] 1.7. Light detection unit The photodetector 5 shown in Figure 1 detects pulsed light PL transmitted through the atomic cell 3 and outputs a current signal corresponding to the intensity as a pulsed light detection signal S5. The photodetector 5 is implemented, for example, by a photodiode.

[0071] 1.8. Frequency Oscillator The frequency oscillator 6 shown in Figure 1 outputs an oscillation signal S1. The oscillation control circuit 7, described later, can stabilize the output frequency of the oscillation signal S1. As a result, for example, an atomic oscillator 1 capable of outputting a high-quality clock signal CLK can be realized.

[0072] Examples of the frequency oscillation unit 6 include a voltage-controlled oscillator (VCO), a voltage-controlled crystal oscillator (VCXO), and a temperature-compensated crystal oscillator (TCXO). The frequency of the oscillation signal S1 is, for example, several MHz to several tens of MHz.

[0073] The frequency oscillator 6 may also have a frequency conversion circuit (not shown). The frequency conversion circuit converts the frequency of the oscillation signal S1 to an arbitrary frequency and outputs it as a clock signal CLK. The oscillation signal S1 has extremely high frequency accuracy and frequency stability, based on the peak frequency of the high-Q Ramsey fringe that occurs with Ramsey resonance. Therefore, an atomic oscillator 1 capable of outputting a high-quality clock signal CLK can be realized.

[0074] 1.9. Oscillator Control Circuit The oscillation control circuit 7 shown in Figure 1 generates an oscillation control signal S7 to be input to the frequency oscillation unit 6 based on the pulse light detection signal S5, so as to maximize the output of the pulse light detection signal S5. Specifically, the oscillation control signal S44 is, for example, a positive or negative error signal corresponding to the frequency difference from the center frequency. By inputting such an oscillation control signal S7 to the frequency oscillation unit 6, the frequency of the oscillation signal S1 can be finely adjusted so as to maximize the output of the pulse light detection signal S5. As a result, the frequency of the modulation signal S2 is also finely adjusted, and in the light source unit 2 described above, the frequency difference ω1-ω2 between the first light and the second light is equal to the frequency ω 12A laser beam L that matches the specified frequency can be emitted. As a result, the aforementioned EIT phenomenon can be stably generated, and the frequency stability of the oscillation signal S1 and clock signal CLK output from the frequency oscillation unit 6 can be improved.

[0075] The circuit configuration of the oscillation control circuit 7 is not particularly limited, and known circuit configurations can be used. An example of a known circuit configuration is the circuit configuration described in Japanese Patent Application Publication No. 2021-150886.

[0076] 1.10. Example of Atomic Oscillator Operation Figure 6 is a timing chart illustrating an example of the operation of the atomic oscillator 1 shown in Figure 1. Note that the waveforms of each signal shown in Figure 6 are examples only and are not limited to these.

[0077] The first drive signal S41 shown in Figure 6 is an example of a signal waveform input to the first mirror drive unit 412. The waveform of the first drive signal S41 shown in Figure 6 is an example when the operating method of the first mirror drive unit 412 is electromagnetic. In the example shown in Figure 6, the waveform of the first drive signal S41 is a sine wave.

[0078] In the first mirror 410 shown in Figure 1, the first segmented light L1 reflected by the first mirror 410 can pass through the first angle adjustment unit 414 at the timing when the amplitude of the first drive signal S41 becomes zero. In other words, in the pulsation mechanism 4 shown in Figure 1, the arrangement of the first mirror 410 and the first angle adjustment unit 414 is set so that the first segmented light L1 reflected when the deflection angle θ(t) of the first mirror 410 is zero can reach the photosynthesis unit 45. Therefore, the first segmented light L1 reflected by the first mirror 410 is pulsed at the same frequency as the first drive signal S41 and reaches the photosynthesis unit 45. Note that the timing at which the first segmented light L1 reaches the photosynthesis unit 45 is not limited to the timing described above.

[0079] The second drive signal S42 shown in Figure 6 is an example of a signal waveform input to the second mirror drive unit 422. The waveform of the second drive signal S42 shown in Figure 6 is an example when the operating method of the second mirror drive unit 422 is electromagnetic. In the example shown in Figure 6, the waveform of the second drive signal S42 is a sine wave with the same frequency as the first drive signal S41, but its phase is shifted by 90° relative to the first drive signal S41.

[0080] In the second mirror 420 shown in Figure 1, similar to the first mirror 410, the second segmented light L2 reflected by the second mirror 420 can pass through the second angle adjustment unit 424 at the timing when the amplitude of the second drive signal S42 becomes zero. In other words, in the pulsation mechanism 4 shown in Figure 2, the arrangement of the second mirror 420 and the second angle adjustment unit 424 are set so that the second segmented light L2 reflected when the deflection angle θ(t) of the second mirror 420 is zero can reach the photosynthesis unit 45. Therefore, the second segmented light L2 reflected by the second mirror 420 is pulsed at the same frequency as the second drive signal S42 and reaches the photosynthesis unit 45.

[0081] The pulsed first-partitioned light L1 and the pulsed second-partitioned light L2 are synthesized in the photosynthesis unit 45 to form pulsed light PL.

[0082] As described above, the pulsed first split light L1 has a period in which the output rises every 180°. Therefore, the repetition frequency of the pulsed first split light L1 is twice the frequency of the first drive signal S41.

[0083] Furthermore, the pulsed second-division light L2 also has a period in which the output rises every 180°. Therefore, the repetition frequency of the pulsed second-division light L2 is twice the frequency of the second drive signal S42.

[0084] On the other hand, the phase of the pulsed second-partitioned light L2 is shifted by 90° relative to the phase of the pulsed first-partitioned light L1. Therefore, the pulsed light PL, which is formed by the combination of the pulsed first-partitioned light L1 and the pulsed second-partitioned light L2, has a period in which the output rises every 90°.

[0085] Figure 6 shows the time variation of the intensity of the pulsed light PL, which is a pulse wave rising every 90°. In other words, the repetition frequency of the pulsed light PL is four times the frequency of the first drive signal S41 and the second drive signal S42. Therefore, by passing through the pulsation mechanism 4 shown in Figure 1, the laser light L can be pulsed, and the repetition frequency of the pulses can be increased to a high frequency. For example, even if the upper limit of the frequencies of the first drive signal S41 and the second drive signal S42 is 500 Hz, the atomic cell 3 can be irradiated with pulsed light PL with a repetition frequency of 2 kHz. This stabilizes the output frequency of the atomic oscillator 1. In addition, the pulsation mechanism 4 can be fitted with the first mirror 410 and the second mirror 420, which have low drive frequencies. This makes it possible to reduce the cost of the atomic oscillator 1.

[0086] The above-mentioned increase in frequency can be theoretically explained as follows. First, if the operating method of the first mirror drive unit 412 is electromagnetic, then, for example, a current signal is used for the first drive signal S41. The current I(t) of the first drive signal S41 is expressed by the following equation (1).

[0087]

number

[0088] In equation (1) above, I0 is the current amplitude, ω is the frequency, and t is time. The first drive signal S41 represented by equation (1) above is shown in Figure 6.

[0089] Furthermore, if the operating method of the second mirror drive unit 422 is electromagnetic, a current signal, for example, is used for the second drive signal S42. The current I(t) of the second drive signal S42 is expressed by the following equation (2).

[0090]

number

[0091] In equation (2) above, I0 is the current amplitude, ω is the frequency, and t is time. The second drive signal S42, represented by equation (2) above, is shown in Figure 6.

[0092] Furthermore, if the first mirror 410 and the first mirror drive unit 412 are electromagnetic MEMS mirrors, the deflection angle θ(t) of the first mirror 410 when the first drive signal S41 is input to the MEMS mirror is expressed by the following equation (3).

[0093]

number

[0094] In equation (3) above, k is a proportionality constant. The deflection angle θ(t) of the first mirror 410 expressed in equation (3) above is shown in Figure 6.

[0095] Furthermore, if the second mirror 420 and the second mirror drive unit 42 are electromagnetic MEMS mirrors, the deflection angle θ(t) of the second mirror 420 when the second drive signal S42 is input to the MEMS mirror is expressed by the following equation (4).

[0096]

number

[0097] In equation (4) above, k is a proportionality constant. The deflection angle θ(t) of the second mirror 420 expressed in equation (4) above is shown in Figure 6.

[0098] Here, the pulsed first split light L1 reaches the photosynthetic section 45 at the timing θ(t)=0. Similarly, the pulsed second split light L2 reaches the photosynthetic section 45 at the timing θ(t)=0. Then, the time at which the output of the pulsed light PL rises is expressed by the following equation (5).

[0099]

number

[0100] The angle ωt when equation (5) above holds is expressed by the following equation (6).

[0101]

number

[0102] Equation (6) above shows that the repetition frequency of the pulsed light PL is four times the frequency of the first drive signal S41 and the second drive signal S42.

[0103] In this embodiment, the first drive signal S41 and the second drive signal S42 are periodic signals with equal frequencies and different phases, but the phase difference is not limited to 90°.

[0104] Furthermore, the pulsing mechanism 4 allows for reliable switching of the optical path of the first segmented light L1 by utilizing reflection from the first mirror 410. Similarly, the optical path of the second segmented light L2 can be reliably switched by utilizing reflection from the second mirror 420. In other words, it is possible to reliably switch between a state where the optical axes of the first segmented light L1 and the second segmented light L2 overlap with the photosynthesis unit 45 and a state where the optical axes of the first segmented light L1 and the second segmented light L2 are not adjacent to the photosynthesis unit 45. As a result, the probability of stray light entering the atomic cell 3 can be sufficiently reduced during the time when the optical axes of the first segmented light L1 and the second segmented light L2 are not adjacent to the photosynthesis unit 45. Consequently, the extinction ratio of the pulsed light PL irradiated onto the atomic cell 3 can be sufficiently increased. The improvement in the extinction ratio of the pulsed light PL contributes to the stable generation of Ramsey resonance and the stabilization of the output frequency of the atomic oscillator 1.

[0105] 2. Variations Next, an atomic oscillator according to a modified example of the above embodiment will be described.

[0106] 2.1. First Variation Figure 7 is a block diagram showing the atomic oscillator 1 according to the first modified example. Figure 8 is a timing chart illustrating an example of operation of the atomic oscillator 1 according to the first modified example.

[0107] The following describes the first modified example, focusing on the differences from the above embodiment, and omitting explanations of similar items. In Figures 7 and 8, components similar to those in the above embodiment are denoted by the same reference numerals.

[0108] In the pulsation mechanism 4 shown in Figure 7, the deflection angle of the first mirror 410 when the first divided light L1 passes through the first angle adjustment section 414 is different from that of the pulsation mechanism 4 shown in Figure 1. In the pulsation mechanism 4 shown in Figure 7, the deflection angle of the second mirror 420 when the second divided light L2 passes through the second angle adjustment section 424 is different from that of the pulsation mechanism 4 shown in Figure 1.

[0109] Specifically, the pulsing mechanism 4 shown in Figure 7 has reflectors 416 and 418 that reflect the first divided light L1 and change the optical path. The first divided light L1 emitted from the light splitting section 44 is sequentially reflected by the reflectors 416 and 418, then reflected by the first mirror 410, and passes through the first angle adjustment section 414. As mentioned above, in the pulsing mechanism 4 shown in Figure 1, as shown in Figure 6, when the deflection angle θ(t) of the first mirror 410 is zero, the first divided light L1 reflected by the first mirror 410 passes through the first angle adjustment section 414. In contrast, in the pulsation mechanism 4 shown in Figure 7, as shown in Figure 8, the arrangement of the first mirror 410 and the first angle adjustment unit 414 are set such that when the deflection angle θ(t) of the first mirror 410 is an angle θ1 that is neither zero nor the maximum value, the first divided light L1 reflected by the first mirror 410 passes through the first angle adjustment unit 414.

[0110] Furthermore, the pulsing mechanism 4 shown in Figure 7 has reflectors 426 and 428 that reflect the second splitting light L2 and change the optical path. The second splitting light L2 emitted from the light splitting unit 44 is sequentially reflected by the reflectors 426 and 428, then reflected by the second mirror 420, and passes through the second angle adjustment unit 424. As mentioned above, in the pulsing mechanism 4 shown in Figure 1, when the deflection angle θ(t) of the second mirror 420 is zero, the second splitting light L2 reflected by the second mirror 420 passes through the second angle adjustment unit 424. In contrast, in the pulsing mechanism 4 shown in Figure 7, as shown in Figure 8, the arrangement of the second mirror 420 and the second angle adjustment unit 424 are set so that when the deflection angle θ(t) of the second mirror 420 is an angle θ2 that is neither zero nor the maximum value, the second splitting light L2 reflected by the second mirror 420 passes through the second angle adjustment unit 424.

[0111] With the above configuration, by setting the time when the deflection angle θ(t) of the first mirror 410 becomes angle θ1 and the time when the deflection angle θ(t) of the second mirror 420 becomes angle θ2 to be at equal intervals, the photosynthesis unit 45 can synthesize pulsed light PL with a periodic rise in output. This makes it possible to synthesize pulsed light PL with a repetition frequency four times the frequency of the first drive signal S41 and the second drive signal S42.

[0112] Furthermore, in the configuration described above, the same periodic signal can be applied to the first drive signal S41 and the second drive signal S42. In other words, there is no need to use phase-shifted signals as in the above embodiment. For this reason, according to the first modification, the configuration of the waveform generator 40 can be simplified. And even in this case, it is possible to increase the repetition frequency of the pulsed light PL, so the cost and accuracy of the pulsation mechanism 4 can be reduced. In the first modified example described above, the same effects as in the embodiment described above can be obtained.

[0113] 2.2. Second Variation Figure 9 is a block diagram showing the atomic oscillator 1 according to the second modified example.

[0114] The following describes a second modified example, focusing on the differences from the above embodiment, and omitting explanations of similar aspects. In Figure 9, components similar to those in the above embodiment are denoted by the same reference numerals.

[0115] 2.2.1. Configuration of the Pulsation Mechanism The pulsation mechanism 4 shown in Figure 9 is the same as the pulsation mechanism 4 shown in Figure 1, except that it further includes a third mirror 430, a third mirror drive unit 432, and a third angle adjustment unit 434. The light splitting unit 44 shown in Figure 9 has the function of splitting the laser light L into three. Furthermore, the photosynthesis unit 45 shown in Figure 9 has the function of combining the three split lights into one. As a result, it is possible to generate pulsed light PL with a repetition frequency higher than the rotation frequencies of the first mirror 410, the second mirror 420, and the third mirror 430, and even higher than that of the above embodiment.

[0116] The optical splitting unit 44 shown in Figure 9 has the function of splitting the laser light L into a first splitting beam L1, a second splitting beam L2, and a third splitting beam L3. Specifically, the optical splitting unit 44 shown in Figure 9 has a first optical splitter 442 and a second optical splitter 444. The first optical splitter 442 splits the laser light L into a third splitting beam L3 and a fourth splitting beam L4. The second optical splitter 444 further splits the fourth splitting beam L4 into a first splitting beam L1 and a second splitting beam L2.

[0117] The waveform generator 40 shown in Figure 9 further has the function of outputting a third drive signal S43 to the third mirror drive unit 432. The first drive signal S41, the second drive signal S42, and the third drive signal S43 are periodic signals that have the same frequency and different phases. Such signals can be generated relatively easily and accurately by the waveform generator 40. The waveforms of the first drive signal S41, the second drive signal S42, and the third drive signal S43 can be set appropriately according to the arrangement of the first mirror 410, the second mirror 420, and the third mirror 430, as well as the arrangement of the first angle adjustment unit 414, the second angle adjustment unit 424, and the third angle adjustment unit 434, but are not limited to these.

[0118] The third mirror 430 reflects the third segmented light L3 and rotates around the pivot axis AX3. In Figure 9, the third mirror 430 is configured to oscillate around the pivot axis AX3. This periodically changes the reflection angle of the third segmented light L3. In other words, it scans the reflected light path of the third segmented light L3 within a predetermined angular range. Hereafter, the angular range in which the third segmented light L3 is scanned will also be called the "scanning range".

[0119] The third mirror drive unit 432 rotates the third mirror 430 around the pivot axis AX3 at a predetermined period. The operating modes of the third mirror drive unit 432 include a resonant mode and a non-resonant mode. Of these, the non-resonant mode is preferably used. In the non-resonant mode, the rotation angle of the third mirror 430 can be controlled with greater precision.

[0120] The third mirror 430 and the third mirror drive unit 432 may be composed of a so-called optical scanner. Examples of optical scanners include MEMS (Micro Electro Mechanical Systems) scanners, galvanometer scanners, resonant scanners, and polygon scanners. Of these, MEMS scanners are preferred. MEMS scanners allow for easy miniaturization, weight reduction, and low power consumption of the third mirror drive unit 432.

[0121] The operating method of the third mirror drive unit 432 is not particularly limited, but examples include electrostatic, piezoelectric, and electromagnetic methods.

[0122] The third angle adjustment unit 434 is located within the scanning range of the third segmented light L3. The third angle adjustment unit 434 pulses the third segmented light L3 intermittently at a predetermined period by limiting the angular range through which the third segmented light L3 reflected by the third mirror 430 passes. In other words, pulsed light is generated that has intensity during the time period when the third segmented light L3, whose reflected light path is being scanned, passes through the third angle adjustment unit 434, and has no intensity at other times. The third segmented light L3 pulsed by the third angle adjustment unit 434 is emitted toward the photosynthesis unit 45. Examples of the third angle adjustment unit 434 include an optical aperture, a slit, a pinhole, etc. Furthermore, by providing the third angle adjustment unit 434, the generation of stray light can be suppressed.

[0123] The photosynthesis unit 45 shown in Figure 9 has the function of synthesizing pulsed first-partition light L1, pulsed second-partition light L2, and pulsed third-partition light L3. Specifically, the photosynthesis unit 45 in Figure 9 has a first photosynthesizer 452 and a second photosynthesizer 454. The first photosynthesizer 452 synthesizes the first-partition light L1, which is pulsed in the first angle adjustment unit 414, and the second-partition light L2, which is pulsed in the second angle adjustment unit 424. As a result, the first photosynthesizer 452 generates pulsed synthesized light L12. The second photosynthesizer 454 synthesizes pulsed synthesized light L12 and pulsed third-partition light L3. As a result, the second photosynthesizer 454 generates pulsed light PL and emits it toward the atomic cell 3.

[0124] 2.2.2. Example of Atomic Oscillator Operation Figure 10 is a timing chart illustrating an example of operation of the atomic oscillator 1 according to the second modified example. Note that the waveforms of each signal shown in Figure 10 are examples only and are not limited thereto.

[0125] The third drive signal S43 shown in Figure 10 is an example of a signal waveform input to the third mirror drive unit 432. The waveform of the third drive signal S43 shown in Figure 10 is an example when the operating method of the third mirror drive unit 432 is electromagnetic. In the example shown in Figure 10, the waveform of the third drive signal S43 is a sine wave. The first drive signal S41, the second drive signal S42, and the third drive signal S43 are out of phase by 120° from each other.

[0126] In the third mirror 430 shown in Figure 10, the third segmented light L3 reflected by the third mirror 430 can pass through the third angle adjustment unit 434 at the timing when the amplitude of the third drive signal S43 becomes zero. In other words, in the pulsation mechanism 4 shown in Figure 1, the arrangement of the third mirror 430 and the third angle adjustment unit 434 are set so that the third segmented light L3 reflected when the deflection angle θ(t) of the third mirror 430 is zero can reach the photosynthesis unit 45. Therefore, the third segmented light L3 reflected by the third mirror 430 is pulsed at the same frequency as the third drive signal S43 and reaches the photosynthesis unit 45.

[0127] Figure 10 shows the time variation of the intensity of the pulsed light PL. This time variation of intensity is a pulse wave that rises every 60°. In other words, the repetition frequency of the pulsed light PL is six times the frequencies of the first drive signal S41, the second drive signal S42, and the third drive signal S43. Therefore, by passing through the pulsation mechanism 4 shown in Figure 9, the laser light L can be pulsed, and the repetition frequency of the pulses can be made even higher. This makes it possible to stabilize the output frequency of the atomic oscillator 1. In addition, the pulsation mechanism 4 can be fitted with the first mirror 410, the second mirror 420, and the third mirror 430, which have low drive frequencies. Therefore, the cost of the atomic oscillator 1 can be reduced. In the second modified example described above, the same effects as in the embodiment described above can be obtained.

[0128] The second modified example has three mirrors, three mirror drive units, and three angle adjustment units, but the atomic oscillator according to the present invention may have four or more mirrors, four or more mirror drive units, and four or more angle adjustment units. This allows for an even higher repetition frequency of the pulses of the pulsed optical pulser (PL).

[0129] 2.3. Third Variation Figure 11 is a block diagram showing an atomic oscillator 1 according to a third modified example.

[0130] The following describes a third modified example, focusing on the differences from the above embodiment, and omitting explanations of similar items. In Figure 11, components similar to those in the above embodiment are denoted by the same reference numerals.

[0131] In the atomic oscillator 1 shown in Figure 1, when the pulsed first split light L1 and the pulsed second split light L2 are combined in the photosynthesis unit 45, a similar light is emitted in a different direction from the pulsed light PL, along with the pulsed light PL directed toward the atomic cell 3. In the above embodiment, this light is emitted without being used.

[0132] In contrast, the atomic oscillator 1 shown in Figure 11 uses this light as monitor light ML. Specifically, the photosynthesis unit 45 shown in Figure 11 generates pulsed light PL by combining a portion of the first divided light L1 pulsed by the first angle adjustment unit 414 and a portion of the second divided light L2 pulsed by the second angle adjustment unit 424. The photosynthesis unit 45 shown in Figure 11 also generates monitor light ML by combining another portion of the first divided light L1 pulsed by the first angle adjustment unit 414 and another portion of the second divided light L2 pulsed by the second angle adjustment unit 424.

[0133] The atomic oscillator 1 shown in Figure 11 includes a light intensity monitor unit 82 and a light intensity control circuit 84.

[0134] The light intensity monitor unit 82 receives the monitor light ML and outputs a monitor light detection signal S82 corresponding to the intensity of the monitor light ML. Specifically, the light intensity monitor unit 82 outputs a current signal corresponding to the intensity of the monitor light ML as the monitor light detection signal S82. The monitor light detection signal S82 may be converted into a voltage signal by a current-voltage conversion unit (not shown).

[0135] The optical intensity control circuit 84 controls the operation of the light source unit 2 based on the monitor light detection signal S82. This adjusts the intensity of the laser light L. The optical intensity control circuit 84 has a function to control the operation of the light source unit 2 so that the intensity of the laser light L remains constant. Such a function is realized by a known optical output stabilization circuit or the like. By keeping the intensity of the laser light L constant, light shift can be suppressed. Light shift is a phenomenon in which the peak frequency of the EIT signal fluctuates depending on the intensity of the laser light L incident on the atomic cell 3. By suppressing such light shift, the long-term stability of the output frequency of the atomic oscillator 1 can be improved.

[0136] In addition, the light intensity control circuit 84 may have a function to detect the intensity ratio of the pulsed first split light L1 and the pulsed second split light L2. This function contributes to realizing a means to equalize the intensity of the pulsed first split light L1 with the intensity of the pulsed first split light L2. Such a means can be realized by adding an intensity adjustment unit (not shown).

[0137] In the third modified example described above, the same effects as in the above embodiment can be obtained.

[0138] Furthermore, the above configuration prevents the light used as the monitor light ML from becoming stray light.

[0139] 3. Frequency signal generation system Next, a clock transmission system 90 (timing server) will be described as a frequency signal generation system according to the embodiment.

[0140] Figure 12 is a schematic diagram showing a clock transmission system 90 as a frequency signal generation system according to the embodiment.

[0141] The clock transmission system 90 shown in Figure 12 is a system that synchronizes the clocks of each device in a time-division multiplexing network, and has a redundant configuration of N (Normal) and E (Emergency) systems.

[0142] The clock transmission system 90 comprises a higher-level clock supply device 901 and SDH device 902 (Synchronous Digital Hierarchy) belonging to station A, which are of the N system; a higher-level clock supply device 903 and SDH device 904 belonging to station B, which are of the E system; and lower-level clock supply devices 905 and SDH devices 906, 907 belonging to station C. The clock supply device 901 has an atomic oscillator 1 and generates an N system clock signal. The atomic oscillator 1 in the clock supply device 901 generates a clock signal in synchronization with a more accurate clock signal from master clocks 908, 909, which include an atomic oscillator using cesium. The clock supply devices 901 and 903 correspond to processing units that process the frequency signal from the atomic oscillator 1.

[0143] The SDH device 902 transmits and receives the main signal based on the clock signal from the clock supply device 901, and also superimposes the N-system clock signal onto the main signal and transmits it to the lower-level clock supply device 905. The clock supply device 903 has an atomic oscillator 1 and generates an E-system clock signal. The atomic oscillator 1 in the clock supply device 903 generates a clock signal in synchronization with the more accurate clock signals from master clocks 908 and 909, which include atomic oscillators using cesium.

[0144] The SDH device 904 transmits and receives the main signal based on the clock signal from the clock supply device 903, and also superimposes the E-series clock signal onto the main signal and transmits it to the lower-level clock supply device 905. The clock supply device 905 receives the clock signals from the clock supply devices 901 and 903, and generates a clock signal in synchronization with the received clock signal.

[0145] The clock supply device 905 normally generates a clock signal in synchronization with the N-system clock signal from the clock supply device 901. If an abnormality occurs in the N-system, the clock supply device 905 generates a clock signal in synchronization with the E-system clock signal from the clock supply device 903. By switching from the N-system to the E-system in this way, a stable clock supply can be ensured, and the reliability of the clock path network can be improved. The SDH device 906 transmits and receives the main signal based on the clock signal from the clock supply device 905. Similarly, the SDH device 907 transmits and receives the main signal based on the clock signal from the clock supply device 905. This allows the equipment at station C to be synchronized with the equipment at station A or station B.

[0146] The frequency signal generation system according to this embodiment is not limited to the clock transmission system 90. The frequency signal generation system includes a system equipped with an atomic oscillator 1 and consisting of various devices (processing units) that process and utilize the clock signal (output signal) output from the atomic oscillator 1. Such a system has excellent reliability because it is equipped with an atomic oscillator 1 that has excellent frequency stability.

[0147] The frequency signal generation system according to this embodiment may be, for example, a smartphone, tablet terminal, watch, mobile phone, digital still camera, liquid ejection device such as an inkjet printer, personal computer, television, video camera, videotape recorder, car navigation system, pager, electronic organizer, electronic dictionary, calculator, electronic game device, word processor, workstation, videophone, security television monitor, electronic binoculars, POS (point of sales) terminal, medical equipment, fish finder, GNSS (Global Navigation Satellite System) frequency standard, various measuring instruments, instruments, flight simulator, terrestrial digital broadcasting system, mobile phone base station, mobile device, etc. Examples of mobile devices include automobiles, aircraft, ships, etc.

[0148] 4. Effects of the above-described embodiment and the above-described modification The atomic oscillator 1 according to the above embodiment and the above modification comprises a frequency oscillation unit 6, a light source unit 2, a pulsation mechanism 4, an atomic cell 3, a photodetector unit 5, and an oscillation control circuit 7. The frequency oscillation unit 6 outputs an oscillation signal S1. The light source unit 2 emits laser light L, which includes a first light and a second light with different frequencies, based on a modulation signal S2 corresponding to the oscillation signal S1. The pulsation mechanism 4 pulses the laser light L and emits pulsed light PL. The atomic cell 3 is into which the pulsed light PL is incident and contains alkali metal atoms. The photodetector unit 5 detects the pulsed light PL that has passed through the atomic cell 3 and outputs a pulsed light detection signal S5 according to the intensity of the pulsed light PL. The oscillation control circuit 7 adjusts the frequency of the oscillation signal S1 by controlling the operation of the frequency oscillation unit 6 based on the pulsed light detection signal S5.

[0149] The pulsing mechanism 4 also includes a light splitting unit 44, a first mirror 410, a first mirror drive unit 412, a first angle adjustment unit 414, a second mirror 420, a second mirror drive unit 422, a second angle adjustment unit 424, and a photosynthesis unit 45. The light splitting unit 44 splits the laser light L into a first splitting beam L1 and a second splitting beam L2. The first mirror 410 scans the reflected light path of the first splitting beam L1 by rotating around a pivot axis AX1. The first mirror drive unit 412 rotates the first mirror 410 at a predetermined period based on a first drive signal S41. The first angle adjustment unit 414 pulses the first splitting beam L1 by limiting the angle range through which the first splitting beam L1 passes within the scanning range of the reflected light path of the first splitting beam L1. The second mirror 420 scans the reflected light path of the second segmented light L2 by rotating around the pivot axis AX2. The second mirror drive unit 422 rotates the second mirror 420 at a predetermined period based on the second drive signal S42. The second angle adjustment unit 424 pulses the second segmented light L2 by limiting the angle range through which the second segmented light L2 passes within the scanning range of the reflected light path of the second segmented light L2. The photosynthesis unit 45 combines the first segmented light L1 pulsed by the first angle adjustment unit 414 and the second segmented light L2 pulsed by the second angle adjustment unit 424, and emits pulsed light PL.

[0150] This configuration allows for reliable switching between a state where the optical axes of the first and second splitting light L1 and L2 overlap with the photosynthesis unit 45, and a state where the optical axes of the first and second splitting light L1 and L2 are separated from the photosynthesis unit 45. This allows for a sufficiently high extinction ratio of the pulsed light PL irradiated onto the atomic cell 3. The improved extinction ratio contributes to the stable generation of Ramsey resonance and the stabilization of the output frequency of the atomic oscillator 1. Furthermore, even when the drive frequencies of the first mirror 410 and the second mirror 420 are low, a high repetition frequency of the pulse can be achieved. This allows for stabilization of the output frequency of the atomic oscillator 1. In addition, the cost of the atomic oscillator 1 can be reduced.

[0151] In the atomic oscillator 1, the first drive signal S41 and the second drive signal S42 may be periodic signals with equal frequencies and different phases.

[0152] With this configuration, the first drive signal S41 and the second drive signal S42 can be generated relatively easily and accurately.

[0153] In the atomic oscillator 1, the optical splitting unit 44 may split the laser light L into a first splitting beam L1, a second splitting beam L2, and a third splitting beam L3. In this case, the pulsing mechanism 4 further includes a third mirror 430, a third mirror drive unit 432, and a third angle adjustment unit 434. The third mirror 430 scans the reflected light path of the third splitting beam L3 by rotating around the pivot axis AX3. The third mirror drive unit 432 rotates the third mirror 430 at a predetermined period based on the third drive signal S43. The third angle adjustment unit 434 pulses the third splitting beam L3 by limiting the angular range through which the third splitting beam L3 passes within the scanning range of the reflected light path of the third splitting beam L3. The photosynthesis unit 45 then combines the first segmented light L1, which is pulsed by the first angle adjustment unit 414, the second segmented light L2, which is pulsed by the second angle adjustment unit 424, and the third segmented light L3, which is pulsed by the third angle adjustment unit 434, and emits pulsed light PL.

[0154] With this configuration, an atomic oscillator 1 is obtained that can achieve even higher pulse repetition frequencies.

[0155] In atomic oscillator 1, the first drive signal S41, the second drive signal S42, and the third drive signal S43 may be periodic signals with equal frequencies and different phases.

[0156] With this configuration, the first drive signal S41, the second drive signal S42, and the third drive signal S43 can be generated relatively easily and accurately.

[0157] In the atomic oscillator 1, the first drive signal S41 and the second drive signal S42 may be periodic signals with the same frequency and phase. In this case, the arrangement of the first angle adjustment unit 414 relative to the first mirror 410 and the arrangement of the second angle adjustment unit 424 relative to the second mirror 420 are set such that the time at which the first angle adjustment unit 414 passes the first divided light L1 and the time at which the second angle adjustment unit 424 passes the second divided light L2 are different.

[0158] With this configuration, the waveform generator 40 that generates the first drive signal S41 and the second drive signal S42 can be simplified. Furthermore, even in this case, it is possible to increase the repetition frequency of the pulsed optical PL, thereby reducing the cost and improving the precision of the pulsation mechanism 4.

[0159] In the atomic oscillator 1, the first angle adjustment unit 414 may be an optical aperture. With this configuration, a first angle adjustment unit 414 can be realized that has high accuracy in the angle range through which the first divided light L1 passes, and that allows for easy adjustment of the angle range.

[0160] In the atomic oscillator 1, the photosynthesis unit 45 may be configured to generate pulsed light PL by combining a portion of the first split light L1 pulsed by the first angle adjustment unit 414 and a portion of the second split light L2 pulsed by the second angle adjustment unit 424, and to generate monitor light ML by combining another portion of the first split light L1 pulsed by the first angle adjustment unit 414 and another portion of the second split light L2 pulsed by the second angle adjustment unit 424. In this case, the atomic oscillator 1 may further include an optical intensity monitor unit 82 that outputs a monitor light detection signal S82 corresponding to the intensity of the monitor light ML, and an optical intensity control circuit 84 that adjusts the intensity of the laser light L by controlling the operation of the light source unit 2 based on the monitor light detection signal S82.

[0161] With this configuration, the intensity of the laser light L can be kept constant, thereby suppressing the light shift and improving the long-term stability of the output frequency of the atomic oscillator 1.

[0162] The frequency signal generation system according to the above embodiment comprises an atomic oscillator 1 according to the above embodiment and a processing unit that processes the output signal (clock signal CLK) output from the atomic oscillator 1. This configuration provides a frequency signal generation system with excellent reliability.

[0163] Although the atomic oscillator and frequency signal generation system according to the present invention have been described above based on the illustrated embodiments and modified examples, the atomic oscillator and frequency signal generation system according to the present invention is not limited to the above embodiments and modified examples. For example, the atomic oscillator and frequency signal generation system according to the present invention may have the configuration of each part of the above embodiments and modified examples replaced with any other component, or may have any other component added. [Explanation of Symbols]

[0164] 1...Atomic oscillator, 2...Light source unit, 3...Atomic cell, 4...Pulsification mechanism, 5...Photodetector, 6...Frequency oscillator, 7...Oscillation control circuit, 20...Light source, 22...Light source drive unit, 24...Frequency multiplier, 40...Waveform generator, 42...Second mirror drive unit, 44...Light splitting unit, 45...Photosynthesis unit, 82...Light intensity monitor unit, 84...Light intensity control circuit, 90...Clock transmission system, 410...First mirror, 412 ...First mirror drive unit, 414...First angle adjustment unit, 416...Reflector, 418...Reflector, 420...Second mirror, 422...Second mirror drive unit, 424...Second angle adjustment unit, 426...Reflector, 428...Reflector, 430...Third mirror, 432...Third mirror drive unit, 434...Third angle adjustment unit, 442...First light splitter, 444...Second light splitter, 452...First photosynthesizer, 454...Second photosynthesizer ,901...Clock supply device, 902...SDH device, 903...Clock supply device, 904...SDH device, 905...Clock supply device, 906...SDH device, 907...SDH device, 908...Master clock, 909...Master clock, AX1...Rotating axis, AX2...Rotating axis, AX3...Rotating axis, CLK...Clock signal, I...Current, L...Laser light, L1...First division light, L12...Combined light, L2...Second division light, L3...Third division light, L4...Fourth division light, ML...Monitor light, OB...Observation timing, PL...Pulse light, S1...Oscillation signal, S2...Modulation signal, S41...First drive signal, S42...Second drive signal, S43...Third drive signal, S44...Oscillation control signal, S5...Pulse light detection signal, S7...Oscillation control signal, S82...Monitor light detection signal, T...Second period, ΔE 12 ...energy difference, θ1...angle, θ2...angle, θ(t)...angle of deflection, τ...first period, τ m …Time, ω1…Frequency, ω 1-2 …Frequency difference, ω1-ω2…Frequency difference, ω 12 ...frequency, ω2...frequency

Claims

1. A frequency oscillator that outputs an oscillation signal, A light source unit that emits laser light including a first light and a second light having different frequencies based on a modulation signal corresponding to the oscillation signal, A pulsing mechanism that pulses the laser light and emits pulsed light, The pulsed light is incident on an atomic cell containing alkali metal atoms, A photodetector that detects the pulsed light transmitted through the atomic cell and outputs a pulsed light detection signal corresponding to the intensity of the pulsed light, An oscillation control circuit adjusts the frequency of the oscillation signal by controlling the operation of the frequency oscillation unit based on the pulse light detection signal, Equipped with, The pulsation mechanism is, A light splitting unit that splits the laser light into a first split beam and a second split beam, A first mirror that scans the reflected light path of the first divided light by rotation around a pivot axis, A first mirror drive unit rotates the first mirror at a predetermined period based on a first drive signal, A first angle adjustment unit pulses the first divided light by limiting the angular range through which the first divided light passes within the scanning range of the reflected light path of the first divided light, A second mirror, which scans the reflected light path of the second divided light by rotation around the pivot axis, A second mirror drive unit rotates the second mirror at a predetermined period based on a second drive signal, A second angle adjustment unit pulses the second divided light by limiting the angular range through which the second divided light passes within the scanning range of the reflected light path of the second divided light, A photosynthesis unit that combines the first divided light pulsed by the first angle adjustment unit and the second divided light pulsed by the second angle adjustment unit and emits the pulsed light, An atomic oscillator characterized by having the following features.

2. The atomic oscillator according to claim 1, wherein the first drive signal and the second drive signal are periodic signals having equal frequencies and different phases.

3. The optical splitting unit splits the laser light into the first splitting beam, the second splitting beam, and the third splitting beam. The pulsation mechanism further includes: A third mirror, which scans the reflected light path of the third segmented light by rotation around a pivot axis, A third mirror drive unit rotates the third mirror at a predetermined period based on a third drive signal, A third angle adjustment unit pulses the third divided light by limiting the angular range through which the third divided light passes within the scanning range of the reflected light path of the third divided light, It has, The atomic oscillator according to claim 1, wherein the photosynthesis unit combines the first divided light pulsed by the first angle adjustment unit, the second divided light pulsed by the second angle adjustment unit, and the third divided light pulsed by the third angle adjustment unit, and emits the pulsed light.

4. The atomic oscillator according to claim 3, wherein the first drive signal, the second drive signal, and the third drive signal are periodic signals having equal frequencies and different phases.

5. The first drive signal and the second drive signal are periodic signals with the same frequency and phase. The atomic oscillator according to claim 1, wherein the arrangement of the first angle adjustment unit with respect to the first mirror and the arrangement of the second angle adjustment unit with respect to the second mirror are set such that the time at which the first angle adjustment unit passes the first divided light and the time at which the second angle adjustment unit passes the second divided light are different.

6. The atomic oscillator according to claim 1, wherein the first angle adjustment unit is an optical aperture.

7. The photosynthetic section is A portion of the first divided light pulsed by the first angle adjustment unit and a portion of the second divided light pulsed by the second angle adjustment unit are combined to generate the pulsed light, The system is configured to generate monitor light by combining another portion of the first divided light pulsed by the first angle adjustment unit and another portion of the second divided light pulsed by the second angle adjustment unit. A light intensity monitor unit that outputs a monitor light detection signal corresponding to the intensity of the monitor light, A light intensity control circuit adjusts the intensity of the laser light by controlling the operation of the light source based on the monitor light detection signal, The atomic oscillator according to claim 1, further comprising:

8. An atomic oscillator according to any one of claims 1 to 7, A processing unit that processes the output signal output from the atomic oscillator, A frequency signal generation system characterized by comprising the following features.

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