JP6467970B2 - Atomic oscillator, control method therefor, and control program therefor - Google Patents

Description

  The present invention relates to an atomic oscillator, a control method thereof, and a control program thereof.

  As an atomic oscillator using an alkali metal such as cesium or rubidium, a CPT (Coherent Population Trapping) method (also referred to as an electromagnetically induced transmission (EIT) method) using a quantum interference effect is known. In the CPT method, a light absorption phenomenon and a transparency phenomenon due to alkali metal atoms are used. The light absorption phenomenon occurs when a gas cell containing gaseous alkali metal atoms is irradiated with light having a wavelength corresponding to the difference between the ground level and the excited level of the alkali metal atom, and the energy level of the alkali metal atom is reduced. This is a phenomenon in which light is absorbed by transition from the ground level to the excited level. The transparency phenomenon occurs when the frequency difference between the two sidebands that occurs when frequency modulation (FM) is applied to the light matches the energy difference (natural frequency) of the two ground levels of the alkali metal atom. This is a phenomenon in which light absorbed by an alkali metal atom in an excited state is transmitted by the CPT resonance generated in FIG. By controlling the frequency of light so that CPT resonance is maintained, it is possible to generate a very stable frequency signal.

  As a method for detecting the light transmitted through the gas cell, the light transmitted through the gas cell is subjected to photoelectric conversion processing to obtain a DC voltage value, and the wavelength of the light output from the light source is swept to minimize the DC voltage value. In other words, there is a method for specifying a wavelength that maximizes light absorption in the gas cell (Patent Document 1). Further, there is a method of modulating light output from a light source at a low frequency and performing synchronous detection with a lock-in amplifier or the like (Patent Document 2).

  Strictly speaking, there are a plurality of excited levels of alkali metal atoms. The excited level is split by spin-initiated interaction (Fine Structure), and further split by the orbital motion of the electron, the magnetic field by the spin of the electron, the direction of the nuclear magnetic moment, etc. (Hyperfine Structure) ). For this reason, when the energy level of the alkali metal atom is maintained at a certain excitation level and the wavelength of the light irradiated to the alkali metal atom fluctuates due to a disturbance such as a temperature change, the energy level is May be dislocated from the excited level to the adjacent excited level. Such a dislocation of the excited level affects the frequency for realizing the CPT resonance, and thus causes a decrease in the performance of the atomic oscillator.

  This invention is made | formed in view of the above, Comprising: It aims at preventing the performance fall by the rearrangement of the excitation level of an alkali metal atom.

In order to solve the above-described problems and achieve the object, an atomic oscillator of the present invention includes a light emitting unit that outputs light, a sealing unit that encloses gaseous alkali metal atoms irradiated with the light, and the sealing A detection unit that generates a detection signal that changes in accordance with the amount of the light that has passed through the unit, and the light based on the detection signal so that the alkali metal atom maintains an excitation level at which the light is absorbed. A wavelength control unit that generates a wavelength control signal that controls the wavelength of the light, and a frequency that generates a frequency control signal that controls the frequency of the light based on the detection signal so that the alkali metal atom maintains CPT resonance. A comparison result between the control unit, a storage unit storing a target wavelength control signal corresponding to a preset target excitation level, and the wavelength control signal corresponding to the current excitation level and the target wavelength control signal; Base A determination unit for determining whether the current excitation level is the target excitation level, and when the current excitation level is not the target excitation level, based on the comparison result, and a correcting unit for correcting the pre-Symbol wavelength control signal to the excitation level of the said target excitation level, the correction unit, the difference between the current of the wavelength control signal target wavelength control signal the basis value is added to the wavelength control signal, characterized that you correct the wavelength control signal.

  According to the present invention, it is possible to prevent performance degradation due to dislocation of excited levels of alkali metal atoms.

FIG. 1 is a diagram illustrating a functional configuration of the atomic oscillator according to the first embodiment. FIG. 2 is a diagram illustrating energy level transitions of alkali metal atoms in the CPT method. FIG. 3 is a diagram illustrating energy levels split by the fine structure and hyperfine structure of the cesium atom. FIG. 4 is a diagram illustrating a hardware configuration of the atomic oscillator according to the first embodiment. FIG. 5 is a diagram illustrating a global relationship between the wavelength of light output from the laser diode and the voltage output from the photodetector. FIG. 6 is a diagram illustrating the global relationship between the wavelength of light output from the laser diode and the voltage output from the synchronous detection circuit of the wavelength control circuit. FIG. 7 is a diagram illustrating a local relationship between the wavelength of light output from the laser diode and the voltage output from the photodetector. FIG. 8 is a diagram illustrating a local relationship between the wavelength of light output from the laser diode and the voltage output from the synchronous detection circuit of the wavelength control circuit. FIG. 9 is a diagram illustrating the relationship between the laser diode drive current and the voltage output from the photodetector. FIG. 10 is a diagram illustrating the relationship between the drive current of the laser diode and the voltage output from the synchronous detection circuit of the frequency control circuit. FIG. 11 is a diagram exemplifying a change in the drive current of the laser diode, the amount of light output from the laser diode, and the wavelength of the light with respect to time. FIG. 12 is a diagram illustrating the change with time of the voltage output from the photodetector in the regions I and IX shown in FIGS. 9 and 10. FIG. 13 is a diagram illustrating the change with time of the voltage output from the photodetector in the regions II and VI shown in FIGS. 9 and 10. FIG. 14 is a diagram illustrating the change with time of the voltage output from the photodetector in the regions IV and VIII shown in FIGS. 9 and 10. FIG. 15 is a diagram illustrating the change with time of the voltage output from the photodetector in the regions III, V, and VII shown in FIGS. 9 and 10. FIG. 16 is a diagram illustrating information to be stored in the memory in a graph showing the relationship between the drive current of the laser diode and the voltage output from the synchronous detection circuit of the frequency control circuit. FIG. 17 is a flowchart illustrating an excitation level determination process. FIG. 18 is a diagram illustrating the wavelength of light output from a laser diode to which a frequency-modulated drive current is input. FIG. 19 is a diagram illustrating the relationship between the frequency of the high-frequency signal and the voltage output from the photodetector during CPT resonance. FIG. 20 is a diagram illustrating the relationship between the frequency of the high-frequency signal and the voltage output from the synchronous detection circuit of the frequency control unit during CPT resonance. FIG. 21 is a flowchart illustrating a first operation example of the atomic oscillator according to the first embodiment. FIG. 22 is a flowchart illustrating a second operation example of the atomic oscillator according to the first embodiment. FIG. 23 is a diagram illustrating the configuration of the atomic oscillator 111 according to the second embodiment.

  Embodiments of an atomic oscillator will be described below with reference to the accompanying drawings.

(First embodiment)
FIG. 1 is a diagram illustrating a functional configuration of an atomic oscillator 1 according to the first embodiment. The atomic oscillator 1 is a device that generates a stable standard frequency signal by the CPT method. The atomic oscillator 1 includes a light emitting unit 11, an enclosure unit 12, a detection unit 13, a wavelength control unit 14, a frequency control unit 15, a storage unit 16, a determination unit 17, and a correction unit 18.

  The light emitting unit 11 outputs light (electromagnetic wave) irradiated to the enclosing unit 12. The light emitting unit 11 is configured using a semiconductor light emitting element such as a laser diode as a light source, for example. The wavelength and frequency of light output from the light emitting unit 11 are controlled by a wavelength control signal generated by the wavelength control unit 14 and a frequency control signal generated by the frequency control unit 15. Since the wavelength and frequency of light output from the light emitting unit 11 are easily affected by temperature, the temperature of the light emitting unit 11 is controlled to be kept constant.

  The enclosure 12 encloses gaseous alkali metal atoms and buffer gas. The enclosing unit 12 is composed of a unit called a gas cell, for example, and the light output from the light emitting unit 11 is transmitted through the inside of the enclosing unit 12 and output to the outside through a window made of a transmissive material. Has been made. Suitable alkali metal atoms include cesium, rubidium and the like. The temperature of the enclosure part 12 is maintained at a predetermined high temperature so that the alkali metal atoms maintain a stable gas state. In addition, since the light that has entered the enclosure 12 is easily affected by the temperature of the enclosure 12, the temperature of the enclosure 12 is controlled to be kept constant.

  The detection unit 13 generates a detection signal that changes in accordance with the amount of light output from the light emitting unit 11 and transmitted through the enclosing unit 12. The detection unit 13 can be configured using, for example, a photoelectric conversion element, a logic circuit, a processor controlled by a program, and the like. The detection signal may be, for example, a voltage obtained by converting light input to the detection unit 13 into a current and converting the current into a voltage. In this case, the light absorption phenomenon (transition to the excitation level of alkali metal atoms) and the transparency phenomenon (CPT resonance) in the encapsulating part 12 can be detected based on the change in voltage as the detection signal.

  The wavelength control unit 14 generates a wavelength control signal for controlling the wavelength of light output from the light emitting unit 11 based on the detection signal. The wavelength control unit 14 generates a wavelength control signal so that the alkali metal atoms in the enclosing unit 12 maintain the excitation level. The wavelength control signal may include, for example, a drive current that changes the wavelength of light output from the light emitting unit 11. The wavelength control unit 14 can be configured using, for example, a current generation circuit, other logic circuits, a processor controlled by a program, and the like. For example, the wavelength control unit 14 may generate the wavelength control signal so that a detection signal indicating that the light amount is equal to or less than a predetermined value is maintained.

  The frequency control unit 15 generates a frequency control signal for controlling the frequency of light output from the light emitting unit 11 based on the detection signal. The frequency control unit 15 generates a frequency control signal so that the alkali metal atoms in the enclosing unit 12 maintain CPT resonance. The frequency control signal may be, for example, a high-frequency signal superimposed on the drive current as the wavelength control signal. The frequency control unit 15 can be configured using, for example, an oscillation circuit, a PLL (Phase Locked Loop), other logic circuits, a processor controlled by a program, and the like. For example, the frequency control unit 15 may generate the frequency control signal so that the detection signal indicating that the light amount is equal to or greater than a predetermined value is maintained when the excitation level of the alkali metal atom is maintained.

  The storage unit 16 stores a wavelength control signal corresponding to the excitation level of the alkali metal atom. The storage unit 16 can be configured using, for example, a semiconductor memory, and is not limited to a built-in type, but may be an external type. The storage unit 16 stores a target wavelength control signal corresponding to a preset target excitation level. The target excitation level is one or a plurality of excitation levels selected from a plurality of excitation levels based on the fine structure or hyperfine structure of an alkali metal atom. The target excitation level may be, for example, an excitation level achieved in the past, a preset excitation level, or the like. A target wavelength control signal is a wavelength control signal generated when maintaining a target excitation level. Specifically, during operation of the atomic oscillator 1, the value of the wavelength control signal (driving current) generated when the alkali metal atom has reached the excitation level in the past may be stored in the storage unit 16. Further, a wavelength control signal set in advance as a default value may be recorded in the storage unit 16.

  The determination unit 17 determines that the current excitation level is the target excitation level based on the comparison result between the wavelength control signal corresponding to the current excitation level and the target wavelength control signal stored in the storage unit 16. It is determined whether or not there is. The determination unit 17 can be configured using, for example, a processor controlled by a program, a comparison circuit, and the like. For example, when the difference (drive current value difference) between the value indicated by the current wavelength control signal and the value indicated by the target wavelength control signal stored in the storage unit 16 is greater than a predetermined value, the determination unit 17 It may be determined that the excitation level is not the target excitation level.

  The correction unit 18 corrects the current wavelength control signal so that the current excitation level becomes the target excitation level when the determination unit 17 determines that the current excitation level is not the target excitation level. The correction unit 18 can be configured using, for example, an amplifier circuit, other logic circuits, a processor controlled by a program, and the like. For example, the correction unit 18 determines that the current wavelength control signal is a target wavelength control signal based on a difference (a difference in drive current value) between the current wavelength control signal and the target wavelength control signal detected by the comparison process by the determination unit 17. Or the current wavelength control signal may be corrected so that the difference is equal to or smaller than a predetermined value.

  FIG. 2 is a diagram illustrating energy level transitions of alkali metal atoms in the CPT method. When an alkali metal atom is irradiated with first light having a wavelength corresponding to the energy difference between the first ground level (energy level) 101 and the excited level (energy level in the excited state) 103, an alkali metal atom Transition from the first ground level 101 to the excited level 103, and the first light is absorbed. Similarly, when an alkali metal atom is irradiated with a second light having a wavelength corresponding to the energy difference between the second ground level (energy level) 102 and the excitation level 103, the energy level of the alkali metal atom. The level shifts from the second ground level 102 to the excited level 103, and the second light is absorbed.

  When the first light and the second light are irradiated at the same time and their frequency difference exactly matches the energy difference ΔE between the first ground level 101 and the second ground level 102, the two ground levels 101 , 102 are superimposed, that is, a quantum interference state occurs, and a transparency phenomenon (CPT resonance) occurs in which the amount of light transmitted through the encapsulating portion 12 (transmitted light amount) increases. When the wavelength difference between the first light and the second light deviates from ΔE, the CPT resonance disappears and the amount of transmitted light rapidly decreases. Therefore, it is possible to generate a highly accurate standard frequency signal by monitoring a change in the amount of transmitted light and generating a frequency control signal so that CPT resonance is maintained.

  Here, strictly speaking, the excitation level 103 is split by the spin-initiated interaction of the alkali metal atom (fine structure), and further split by the orbital motion of the electron, the magnetic field due to the spin of the electron, the direction of the nuclear magnetic moment, and the like. (Ultra fine structure). The way of splitting depends on the type of atom. FIG. 3 is a diagram illustrating energy levels split by the fine structure and hyperfine structure of the cesium atom. The excitation level 6P is split into two excitation levels 6P1 / 2 and 6P2 / 3 in the fine structure. The cesium atom at the ground level 6S1 / 2 transitions to the excitation level 6P1 / 2 when irradiated with light having a wavelength corresponding to the energy difference indicated by the D1 line, and a wavelength corresponding to the energy difference indicated by the D2 line. Transition to the excitation level 6P2 / 3. The excitation level 6P1 / 2 is further divided into two excitation levels F ′ = 3 and F ′ = 4 in the hyperfine structure. The excitation level 6P2 / 3 is further divided into four excitation levels F ″ = 2, F ″ = 3, F ″ = 4, and F ″ = 5 in the hyperfine structure. The ground level 6S is split into two excited levels F = 3 and F = 4 in the hyperfine structure.

  As described above, since a plurality of excitation levels exist, when a certain target excitation level (for example, F ′ = 4 of 6P1 / 2) is maintained, output from the light emitting unit 11 due to a disturbance such as a temperature change, for example. If the wavelength of the emitted light changes, the energy level may be unexpectedly transferred to another excitation level (for example, F ′ = 3 of 6P2 / 3).

  According to the atomic oscillator 1 shown in FIG. 1, the target wavelength control signal corresponding to the target excitation level stored in the storage unit 16, for example, F ′ = 4 of the excitation level 6P1 / 2 is generated to be maintained. The obtained wavelength control signal (drive current) is compared with the wavelength control signal corresponding to the current excitation level. If it is determined that the current excitation level is not the target excitation level based on the comparison result, the current wavelength control signal (drive current) is set so that the current excitation level becomes the target excitation level. It is corrected. Thereby, even when the excitation level is shifted due to disturbance or the like, the current excitation level can be corrected to the target excitation level. This makes it possible to perform frequency control using the CPT resonance phenomenon with high accuracy.

  FIG. 4 is a diagram illustrating a hardware configuration of the atomic oscillator 1 according to the first embodiment. The atomic oscillator 1 of this example includes an atomic resonance unit 20, a temperature control unit 30, a wavelength control unit 40 (wavelength control unit 14), a frequency control unit 50 (frequency control unit 15), a bias T61, a CPU 65, and a memory 66 (memory). Part 13). As will be described later, the CPU 65 forms part of the wavelength control unit 14, the frequency control unit 15, the determination unit 17, and the correction unit 18 by cooperating with other hardware.

  The atomic resonance unit 20 includes a laser diode 21 (light emitting unit 11), a gas cell 22 (encapsulation unit 12), and a photodetector 23 (detection unit 13). The laser diode 21 outputs light whose wavelength and frequency are controlled according to a frequency-modulated drive current output from a bias T61, which will be described later. The gas cell 22 encloses an alkali metal atom such as gaseous cesium and a buffer gas inside. The photodetector 23 is a semiconductor device that converts light transmitted through the gas cell 22 into current and converts the current into voltage. The laser diode 21 is provided with a temperature sensor 25 and a heater 26. A temperature sensor 27 and a heater 28 are installed in the gas cell 22.

  The temperature control unit 30 includes a first temperature control circuit 31 and a second temperature control circuit 32. The first temperature control circuit 31 controls the heater 26 so that the temperature of the laser diode 21 falls within a predetermined temperature range according to the detection signal of the temperature sensor 25 of the laser diode 21. The second temperature control circuit 32 controls the heater 28 so that the temperature of the gas cell 22 falls within a predetermined temperature range according to the detection signal of the temperature sensor 27 of the gas cell 22. The first temperature control circuit 31 and the second temperature control circuit 32 are controlled according to a control signal from the CPU 65.

  The wavelength control unit 40 includes a first synchronous detection circuit 41, a first low frequency oscillator 42, a first control circuit 43, and a current drive circuit 44. The first synchronous detection circuit 41 processes a signal obtained by multiplying the AC component of the output of the photodetector 23 by the low-frequency signal of the frequency Fm1 output from the first low-frequency oscillator 42 with a low-pass filter. By doing so, a DC voltage is generated. The first control circuit 43 receives the DC voltage generated by the first synchronous detection circuit 41 and outputs a voltage for controlling the current generated by the current drive circuit 44. The first control circuit 43 is controlled in accordance with a control signal from the CPU 65 so that the alkali metal atoms in the gas cell 22 maintain the excitation level. The current driving circuit 44 generates a current that changes according to the voltage output from the first control circuit 43.

  The frequency control unit 50 includes a second synchronous detection circuit 51, a second low frequency oscillator 52, a second control circuit 53, a voltage control crystal oscillator 54, and a PLL 55. The second synchronous detection circuit 51 processes a signal obtained by multiplying the AC component of the output of the photodetector 23 by the low frequency signal of the frequency Fm2 output from the second low frequency oscillator 52 by a low pass filter. By doing so, a DC voltage is generated. The second control circuit 53 receives the DC voltage generated by the second synchronous detection circuit 51 and outputs a voltage for controlling the frequency of the signal generated by the voltage control crystal oscillator 54. The second control circuit 53 is controlled according to a control signal from the CPU 65 so that the CPT resonance of the alkali metal atoms in the gas cell 22 is maintained. The voltage controlled crystal oscillator 54 outputs a standard frequency signal whose frequency is controlled by the voltage output from the second control circuit 53. The PLL 55 multiplies the standard frequency signal output from the voltage controlled crystal oscillator 54 to generate a high frequency signal having the frequency Frf.

  The bias T61 performs frequency modulation on the drive current output from the current drive circuit 44 by the high-frequency signal output from the PLL 55. The frequency-modulated drive current is output to the laser diode 21.

  The CPU 65 outputs control signals to the first temperature control circuit 31, the second temperature control circuit 32, the first control circuit 43, and the second control circuit 53. The CPU 65 performs processing for storing the target wavelength control signal in the memory 66. The target wavelength control signal is, for example, an output current value of the current driving circuit 44 corresponding to the excitation level detected in the past. In addition, a current value set in advance as a default value may be stored in the memory 66.

  The CPU 65 performs an excitation level determination process for determining whether or not the current excitation level is a target excitation level. The first control circuit 43 changes the current output from the current drive circuit 44 after startup once in a general direction, for example, once from a small current side to a large current side. When the current output from the current drive circuit 44 changes from the small current side to the large current side, the wavelength of the light output from the laser diode 21 changes from the small wavelength side to the large wavelength side. The CPU 65 detects a change in the voltage output from the first synchronous detection circuit 41 at this time.

  FIG. 5 is a diagram illustrating a global relationship between the wavelength of light output from the laser diode 21 and the voltage (detection signal) output from the photodetector 23. FIG. 6 is a diagram illustrating the global relationship between the wavelength of light output from the laser diode 21 and the voltage output from the first synchronous detection circuit 41. The voltage shown in FIG. 6 is a direct current voltage and is a differential value of the voltage shown in FIG.

  As shown in FIG. 5, the output voltage from the photodetector 23 in this example greatly decreases in the vicinity of the wavelength A. This decrease in voltage indicates that light has been absorbed by the alkali metal atoms in the gas cell 22, that is, the energy level of the alkali metal atoms has transitioned to the excited level. At this time, the DC voltage output from the first synchronous detection circuit 41 is 0 at the wavelength A, as shown in FIG.

  Next, the first control circuit 43 locally changes the value of the current output from the current drive circuit 44 in the vicinity of the wavelength A where the absorption of light is detected, and the CPU 65 performs the first synchronous detection at this time. A change in the voltage output from the circuit 41 is detected.

  FIG. 7 is a diagram illustrating a local relationship between the wavelength of light output from the laser diode 21 and the voltage output from the photodetector 23. FIG. 8 is a diagram illustrating a local relationship between the wavelength of light output from the laser diode 21 and the voltage output from the first synchronous detection circuit 41. The output voltage from the first synchronous detection circuit 41 shown in FIG. 8 is a differential value of the output voltage from the photodetector 23 shown in FIG.

  As shown in FIG. 7, when the vicinity of the wavelength A is examined in detail, it is detected that light absorption occurs at the two wavelengths A1 and A2. At this time, as shown in FIG. 8, the output voltage from the first synchronous detection circuit 41 becomes 0 at two points of wavelengths A1 and A2. When applied to the example shown in FIG. 3, the energy level of the alkali metal atom is, for example, the excitation level F ′ = 4 at the wavelength A1, and the excitation level F ′ = 3 at the wavelength A2.

  FIG. 9 is a diagram illustrating the relationship between the drive current of the laser diode 21 and the voltage output from the photodetector 23. FIG. 10 is a diagram illustrating the relationship between the drive current of the laser diode 21 and the voltage output from the first synchronous detection circuit 41. The output voltage shown in FIG. 10 is a differential value of the output voltage shown in FIG.

  Since the amount of light output from the laser diode 21 is proportional to the value of the drive current (DC current output from the current drive circuit 44), the output voltage from the photodetector 23 increases as the drive current increases. Therefore, in FIG. 9, when comparing the two regions I and IX in which no light absorption occurs, the voltage of the region IX is larger than the voltage of the region I. In the regions II to VIII, a decrease in voltage indicating light absorption is observed. In regions III and VII, the output voltage is minimum, indicating that the energy level of the alkali metal atom is the excitation level. In regions III and VII, as shown in FIG. 10, the output voltage from the first synchronous detection circuit 41 is zero.

  When applied to the example shown in FIG. 3, the region III corresponds to the excitation level F ′ = 4, and the region VII corresponds to the excitation level F ′ = 3. In this example, the value of the drive current in region III is IF′4, and the value of the drive current in region VII is IF′3. Therefore, it can be specified that the excitation level F '= 3 corresponds to the drive current IF'3, and that the excitation level F' = 4 corresponds to the drive current IF'4. One of the drive currents IF′3 and IF′4 specified in this way is stored in the memory 66 by the CPU 65 as a target wavelength control signal.

  The drive current output from the current drive circuit 44 is superimposed with the low-frequency signal (frequency Fm1 = several Hz to several tens kHz) output from the first low-frequency oscillator 42, and changes periodically. Therefore, the amount of light output from the laser diode 21 and the voltage output from the photodetector 23 change in accordance with the change in the drive current. FIG. 11 is a diagram illustrating changes in drive current of the laser diode 21, the amount of light output from the laser diode 21, and the wavelength of the light with respect to time.

  FIG. 12 is a diagram illustrating a change with time of the voltage output from the photodetector 23 in the regions I and IX shown in FIGS. 9 and 10. When there is no light absorption in the gas cell 22 as in the regions I and IX, the voltage output from the photodetector 23 has the same frequency and phase as the drive current of the laser diode 21 shown in FIG. Change.

  However, when there is light absorption in the gas cell 22 as in the regions II to VIII, the output of the photodetector 23 shows a change different from that in FIG. FIG. 13 is a diagram illustrating the change with time of the voltage output from the photodetector 23 in the regions II and VI shown in FIGS. 9 and 10. In regions II and VI, as the drive current increases, the output voltage of the photodetector 23 decreases at a rate of change greater than the rate of change in regions I and IX. In such regions II and VI, as shown in FIG. 13, the phase of the output voltage is inverted by 180 ° in comparison with the case of FIG. 12, and the amplitude is increased.

  FIG. 14 is a diagram illustrating the change with time of the voltage output from the photodetector 23 in the regions IV and VIII shown in FIGS. 9 and 10. In regions IV and VIII, as the drive current increases, the output voltage of the photodetector 23 increases at a rate of change greater than the rate of change in regions I and IX. In such regions IV and VIII, as shown in FIG. 14, the phase of the output voltage is the same and the amplitude is large in comparison with the case of FIG.

  FIG. 15 is a diagram illustrating a change with time of the voltage output from the photodetector 23 in the regions III, V, and VII shown in FIGS. 9 and 10. In regions III and VII, the light absorption phenomenon due to the transition of the alkali metal atom to the excited level peaks. Even if the drive current is changed across the peak, the output voltage of the photodetector 23 does not change, so the change is zero. On the other hand, in the region V corresponding to the valley between the two peaks of the light absorption phenomenon, even if the drive current is changed across the valley, the output voltage of the photodetector 23 does not change, so the change is zero.

  As described above, the drive current IF′3 or IF′4 specified using the correspondence relationship as shown in FIG. 9 or 10 is stored in the memory 66 as the target wavelength control signal. The information to be stored is not limited to these. FIG. 16 is a diagram illustrating information to be stored in the memory 66 in a graph showing the relationship between the drive current of the laser diode 21 and the voltage output from the first synchronous detection circuit 41. In addition to the driving current IF′3 or IF′4, the driving current IZX corresponding to the zero cross point when the polarity of the output voltage changes from positive to negative between the regions III and VII, the output of the first synchronous detection circuit 41 Drive currents IP1 and IP2 corresponding to the peak point of the voltage, drive currents IB1 and IB2 corresponding to the bottom point of the output voltage of the first synchronous detection circuit 41, and output voltage of the first synchronous detection circuit 41 corresponding to the peak point XP1, XP2, the output voltage XB1, XB2 of the first synchronous detection circuit 41 corresponding to the bottom point, the allowable error range ΔXzero of the output voltage of the first synchronous detection circuit 41 corresponding to the zero cross point, and the first corresponding to the peak point. The allowable error ranges ΔXP1 and ΔXP2 of the output voltage of the first synchronous detection circuit 41, the allowable error ranges ΔXB1 and ΔXB2 of the output voltage of the first synchronous detection circuit 41 corresponding to the bottom point, and the like may be stored in the memory 66.

  In response to a control signal from the CPU 65, the first control circuit 43 changes the output current of the current drive circuit 44 so that the output voltage of the first synchronous detection circuit 41 is maintained at 0 (or within a predetermined error range). Control. When the output voltage of the first synchronous detection circuit 41 is maintained at 0, it can be determined that the energy level of the alkali metal atom is the excitation level. However, only from the phenomenon that the output voltage of the first synchronous detection circuit 41 is 0, it cannot be determined whether or not the currently maintained excitation level is the target excitation level.

  Therefore, the CPU 65 uses the drive current output from the current drive circuit 44 to maintain the current excitation level and the drive current (target drive current) as the target wavelength control signal stored in the memory 66. By comparing, an excitation level determination process for determining whether or not the current excitation level is the target excitation level is performed. When the current drive current does not match the target drive current (or is not within a predetermined error range), the CPU 65 determines that the current excitation level is not the target excitation level, and uses the current drive current as the target drive. The first control circuit 43 is controlled to match the current. For example, when the current drive current is IF′3 and the target drive current stored in the memory 66 is IF′4, the first control circuit 43 corrects the current drive current to IF′4. Thus, the current driving circuit 44 is controlled. Such a correction process can be executed, for example, by calculating a difference between the current drive current and the target drive current. As a result, the current excitation level F ′ = 3 is corrected to the target excitation level F ′ = 4.

  FIG. 17 is a flowchart illustrating an excitation level determination process. First, the current output current of the current drive circuit 44 is changed by adding a value stored in the memory 66 to the current output current (S11), and the output voltage of the first synchronous detection circuit 41 at this time is acquired. (S12). These processing steps S11 and S12 are repeated as many times as the number of output currents to be changed.

  Thereafter, the output current of the current drive circuit 44 is returned to the value before the change (S13), and the output voltage of the synchronous detection circuit 41 acquired in step S12 is compared with the value held in advance in the memory 66 (S14). In step S14, if all the comparison results are coincident (all the comparison results are within the allowable error range of the output voltage in FIG. 16), the return value (ret) is OK (S15), and the comparison result is If they do not match (at least one comparison result does not fall within the allowable error range of the output voltage in FIG. 16), the return value is NG (S16).

  The frequency control unit 50 (see FIG. 4) controls the high-frequency signal Frf output from the PLL 55 based on the output voltage of the photodetector 23 so that the CPT resonance of the alkali metal atoms in the gas cell 22 is maintained. .

  The drive current output from the current drive circuit 44 is frequency-modulated by a high-frequency signal having the frequency Frf at the bias T61 and then input to the laser diode 21. FIG. 18 is a diagram illustrating the wavelength of light output from the laser diode 21 to which the frequency-modulated drive current is input. When the drive current is frequency-modulated by a high-frequency signal having the frequency Frf, side bands 72A and 72B having a frequency difference Frf are generated on both sides of the wavelength 71 of the light output from the laser diode 21. When the frequency difference 2Frf between the side bands 72A and 72B coincides with the energy difference ΔE between the two ground levels of the alkali metal atom, CPT resonance occurs. Therefore, the CPT resonance can be maintained by controlling the voltage controlled crystal oscillator 54 and the PLL 55 so that the frequency Frf becomes a half value of ΔE. CPT resonance occurs in regions III and VII shown in FIG. 9, that is, when the energy level of the alkali metal atom is at the excitation level. When the alkali metal atom is cesium, the frequency Frf is 4.5963 GHz.

  FIG. 19 is a diagram illustrating the relationship between the frequency Frf of the high-frequency signal and the voltage output from the photodetector 23 during CPT resonance. FIG. 20 is a diagram illustrating the relationship between the frequency Frf of the high-frequency signal and the voltage output from the second synchronous detection circuit 51 of the frequency control unit 50 during CPT resonance. In this example, cesium is used as the alkali metal atom.

  The high-frequency signal output from the PLL 55 is a low-frequency signal output from the second low-frequency oscillator 52 (frequency Fm2 = several Hz <Fm2 <several 10 kHz, where Fm2 is preferably at least one digit away from Fm1. ) Is frequency-modulated in advance. Therefore, the high-frequency signal changes with the same phase as the low-frequency signal of Fm2, and the frequency difference between the sidebands of the light output from the laser diode 21 also changes with the same phase as the low-frequency signal of Fm2.

  As shown in FIG. 19, when the frequency Frf of the high-frequency signal output from the PLL 55 is 4.5963 GHz which is a half value of ΔE (see FIG. 2) (region XII), the CPT resonance causes the photodetector 23 to The output voltage (the amount of light transmitted through the gas cell 22) is maximized. Further, since the output voltage of the second synchronous detection circuit 51 shown in FIG. 20 is a differential value of the output voltage of the photodetector 23 shown in FIG. 19 as described above, the polarity changes from positive to negative in the region XII. It becomes a zero-cross point that changes.

  In the regions X and XIV of the frequency Frf where no CPT resonance occurs, the output voltages of the photodetector 23 and the second synchronous detection circuit 51 are constant regardless of the change of the frequency Frf. In the regions XI to XIII of the frequency Frf where the CPT resonance occurs, the output voltages of the photodetector 23 and the second synchronous detection circuit 51 change according to the change of the frequency Frf.

  In response to a control signal from the CPU 65, the second control circuit 53 outputs a standard frequency output from the voltage controlled crystal oscillator 54 so that the output voltage of the second synchronous detection circuit 51 maintains the zero cross point indicated by the region XII. Control the signal.

  The temperature control unit 30 (see FIG. 4) performs strict temperature control so that the temperatures of the laser diode 21 and the gas cell 22 are maintained within predetermined ranges. Since fluctuations in temperature affect the wavelength and frequency of light, the temperature of the laser diode 21 and the gas cell 22 are strictly controlled to prevent disturbance and to perform the wavelength control and frequency control with high accuracy. Become.

  FIG. 21 is a flowchart illustrating a first operation example of the atomic oscillator 1 according to the first embodiment. First, wavelength control is temporarily stopped (S101), and then temperature control and frequency control are temporarily stopped (S102). Thereafter, the excitation level determination process is performed (S103), and the temperature control is resumed (S104).

  Thereafter, it is determined whether or not the return value (ret) from the excitation level determination process is OK (S105). If the return value is OK (Yes), the frequency control is resumed (S106), and the wavelength control is performed. Is resumed (S107). On the other hand, if the return value is NG in step S105 (No), frequency control is initialized in order to redetect the peak of the light transmission phenomenon due to CPT resonance (S108), and the light absorption phenomenon due to the transition to the excitation level. The wavelength control is initialized in order to re-detect the peak (S109).

  FIG. 22 is a flowchart illustrating a second operation example of the atomic oscillator 1 according to the first embodiment. First, wavelength control is temporarily stopped (S201), and then temperature control and frequency control are temporarily stopped (S202). Thereafter, the excitation level determination process is performed (S203).

  Thereafter, it is determined whether or not the return value (ret) from the excitation level determination process is OK (S204). If the return value is OK (Yes), the temperature control is restarted (S205), and the frequency control is performed. (S206) and wavelength control is resumed (S207). On the other hand, if the return value is NG in step S204 (No), the difference added to the output current of the current drive circuit 44 in the excitation level determination process is set to the value at the adjacent excitation level (the current drive current is If IF′3, change to IF′4, IF′4 to IF′3) (S211), and perform excitation level determination processing again (S212).

  Thereafter, it is determined again whether or not the return value from the excitation level determination process is OK (S213). If the return value is OK (Yes), the drive current output from the current drive circuit 204 is changed to step S211. Add the difference from the adjacent excitation level (IF'4 if the current drive current is IF'3, IF'3 if the current drive current is IF'3) (S214), and target the current excitation level After returning to the excitation level, the temperature control is resumed (S205). On the other hand, when the return value is NG in Step S213 (No), after restarting the temperature control (S215), the frequency control is initialized to redetect the peak of the light transmission phenomenon due to CPT resonance (S216), Wavelength control is initialized to redetect the peak of the light absorption phenomenon due to the transition to the excitation level (S217).

  A program for controlling the CPU 65 is a file in an installable or executable format and is recorded on a computer-readable recording medium such as a CD-ROM, a flexible disk (FD), a CD-R, or a DVD (Digital Versatile Disk). To be provided. Further, the program may be provided by being stored on a computer connected to a network such as the Internet and downloaded via the network. The program may be provided or distributed via a network such as the Internet. Further, the program may be provided by being preinstalled in a ROM or the like.

  According to the present embodiment, the current excitation level is based on the comparison result between the wavelength control signal corresponding to the current excitation level and the target wavelength control signal corresponding to the target excitation level stored in the memory 66. It is determined whether or not the level is a target excitation level. When it is determined that the current excitation level is not the target excitation level, the current wavelength control signal is corrected so that the current excitation level becomes the target excitation level. As a result, even when an excitation level dislocation occurs unexpectedly due to a disturbance such as a temperature change, the current excitation level can be corrected to the target excitation level. This makes it possible to perform frequency control using the CPT resonance phenomenon with high accuracy.

  In addition, by providing the temperature control unit 30 that keeps the temperature of the laser diode 21 and the gas cell 22 constant, disturbances due to temperature changes (such as fluctuations in the wavelength and frequency of light) are suppressed, thus realizing more accurate control. It becomes possible to do.

(Second Embodiment)
In the first embodiment, the first synchronous detection circuit 41 is used to detect light absorption due to the excited state of alkali metal atoms, and the second synchronous detection circuit 51 is used to transmit light by CPT resonance. Is detected. However, light absorption may be detected based on the output voltage from the photodetector 23 without using the first synchronous detection circuit 41, or the photodetector 23 without using the second synchronous detection circuit 51. The transmission of light may be detected based on the output voltage from.

  FIG. 23 is a diagram illustrating the configuration of the atomic oscillator 111 according to the second embodiment. Parts that exhibit the same or similar functions and effects as those of the atomic oscillator 1 according to the first embodiment may be denoted by the same reference numerals and description thereof may be omitted.

  The temperature control unit 120 according to the present embodiment includes a first A / D converter 121, a first D / A converter 122, a second A / D converter 123, and a D / A converter 124. Including.

  The first A / D converter 121 outputs an A / D conversion signal as a detection signal of the temperature sensor 25 of the laser diode 21 to the CPU 65. The second A / D converter 123 outputs an A / D conversion signal as a detection signal of the temperature sensor 27 of the gas cell 22 to the CPU 65. The CPU 65 generates a control signal for controlling the heater 26 so as to keep the temperature of the laser diode 21 at a predetermined temperature based on the A / D conversion signal output from the first A / D converter 121. To the first D / A converter 122. The CPU 65 generates a control signal for controlling the heater 28 so as to keep the temperature of the gas cell 22 at a predetermined temperature based on the A / D conversion signal output from the second A / D converter 123. Output to the second D / A converter 124. The first D / A converter 122 outputs the D / A conversion signal of the control signal output from the CPU 65 to the heater 26 of the laser diode 21. The second D / A converter 124 outputs a D / A conversion signal of the control signal output from the CPU 65 to the heater 28 of the gas cell 22. The heater 26 of the laser diode 21 changes the temperature according to the D / A conversion signal output from the first D / A converter 122. The heater 28 of the gas cell 22 changes the temperature according to the D / A conversion signal output from the second D / A converter 124.

  The wavelength control unit 130 according to the present embodiment includes a third A / D converter 131, a third D / A converter 132, a first frequency multiplier 133, a first low frequency oscillator 42, and a current. A drive circuit 44 is included.

  In the present embodiment, the function of the first synchronous detection circuit 41 in the first embodiment is realized by the CPU 65, the third A / D converter 131, and the first frequency multiplier 133. The function of the first control circuit 43 in the first embodiment is realized by the CPU 65 and the third D / A converter 132.

  The output voltage of the photodetector 23 is synchronized with the frequency Fm1 of the first low-frequency oscillator 42 in the third A / D converter 131, and n (n = 2, 3, 3) by the first frequency multiplier 133. 4, ... (however, even number is preferable)) A / D conversion is performed using a signal having a frequency doubled as a trigger signal. This A / D conversion signal is output to the CPU 65 and is synchronously detected by software calculation of the CPU 65. The CPU 65 performs an operation corresponding to the operation of the first control circuit 43 in the first embodiment on the basis of the signal subjected to the synchronous detection, and a current driving circuit via the third D / A converter 132. The output current of 63 is controlled to have a wavelength so that light absorption occurs. Note that the difference added to the output current of the current drive circuit 44 in the excitation level determination process is stored in an area different from the storage area of the program for controlling the CPU 65 in the memory 66.

  The frequency control unit 140 according to the present embodiment includes a fourth A / D converter 141, a fourth D / A converter 142, a second frequency multiplier 143, a second low frequency oscillator 52, and voltage control. A crystal oscillator 54 and a PLL 55 are included.

  In the present embodiment, the function of the second synchronous detection circuit 51 in the first embodiment is realized by the CPU 65, the fourth A / D converter 141, and the second frequency multiplier 143. The function of the second control circuit 53 in the first embodiment is realized by the CPU 65 and the fourth D / A converter 142.

  The output voltage of the photodetector 23 is synchronized with the frequency Fm2 of the second low-frequency oscillator 52 in the fourth A / D converter 141, and n (n = 2, 3, 3) by the second frequency multiplier 143. 4, ... (however, even number is preferable)) A / D conversion is performed using a signal having a frequency doubled as a trigger signal. This A / D conversion signal is output to the CPU 65 and is synchronously detected by software calculation of the CPU 65. The CPU 65 performs an operation corresponding to the operation of the second control circuit 53 in the first embodiment on the basis of the signal subjected to the synchronous detection, and the voltage control crystal via the fourth D / A converter 142. The frequency of the standard frequency signal output from the oscillator 54 is controlled so that CPT resonance occurs.

  Even with the hardware configuration as described above, it is possible to obtain the same functions and effects as those of the first embodiment.

  The present invention is not limited to the above embodiment. For example, in the second embodiment, the configuration including an A / D converter for each control element has been shown. However, a multiplexer is installed before and after the A / D converter, and the multiplexer is switched for a plurality of control elements. May be configured to perform A / D conversion. In addition, an MCU (Micro Control Unit) is used instead of the CPU 65, and some of the components of the memory 66, the temperature control units 30, 120, the wavelength control units 40, 130, and the frequency control units 50, 140 are integrated in the MCU. May be.

DESCRIPTION OF SYMBOLS 1,111 Atomic oscillator 11 Light emission part 12 Inclusion part 13 Detection part 14 Wavelength control part 15 Frequency control part 16 Storage part 17 Determination part 18 Correction part 20 Atomic resonance part 21 Laser diode 22 Gas cell 23 Photo detector 25, 27 Temperature sensor 26 , 28 Heater 30, 120 Temperature control unit 31 First temperature control circuit 32 Second temperature control circuit 40, 130 Wavelength control unit 41 First synchronous detection circuit 42 First low frequency oscillator 43 First control circuit 44 Current drive circuit 50, 140 Frequency control unit 51 Second synchronous detection circuit 52 Second low frequency oscillator 53 Second control circuit 54 Voltage controlled crystal oscillator 55 PLL
61 Bias T
65 CPU
66 Memory 121 First A / D Converter 122 First D / A Converter 123 Second A / D Converter 124 Second D / A Converter 131 Third A / D Converter 132 Third D / A converter 133 First frequency multiplier 141 Fourth A / D converter 142 Fourth D / A converter 143 Second frequency multiplier

JP 2010-161608 A US Pat. No. 6,320,472

Claims (5)

A light emitting unit for outputting light;
An encapsulating part enclosing a gaseous alkali metal atom irradiated with the light;
A detection unit that generates a detection signal that changes according to the amount of the light that has passed through the enclosure;
Based on the detection signal, a wavelength control unit that generates a wavelength control signal that controls the wavelength of the light so that the alkali metal atom maintains an excitation level;
Based on the detection signal, a frequency control unit that generates a frequency control signal for controlling the frequency of the light so that the alkali metal atom maintains CPT resonance;
A storage unit for storing a target wavelength control signal corresponding to a preset target excitation level;
Based on the comparison result of the wavelength control signal corresponding to the current of the excitation level and the target wavelength control signal, a determination section for determining whether or not the current of the excitation level which is the target excitation level ,
A correction unit for correcting the wavelength control signal so that the current excitation level becomes the target excitation level based on the comparison result when the current excitation level is not the target excitation level; Prepared ,
Wherein the correction unit includes a value based on a difference between current of the wavelength control signal and the target wavelength control signal by adding to said wavelength control signal, you and corrects the wavelength control signal atom oscillator. The wavelength control signal includes a drive current input to the light emitting unit,
The correction unit may claim to correct the current of the driving current based on the difference between the value of the driving current corresponding to the value of the driving current corresponding to the current of the excitation level and the target wavelength control signal 1 An atomic oscillator described in 1. A first temperature control unit for maintaining the temperature of the light emitting unit within a first predetermined temperature range;
Temperature second further comprising a second temperature controller to maintain a predetermined temperature range according to claim 1 or 2 atomic oscillator according to the encapsulation. Generating a detection signal that is output from the light emitting unit and changes according to the amount of light that has passed through the enclosing unit that encloses the gaseous alkali metal atoms;
Based on the detection signal, generating a wavelength control signal for controlling the wavelength of the light so that the alkali metal atom maintains an excitation level;
Generating a frequency control signal for controlling the frequency of the light based on the detection signal so that the alkali metal atom maintains CPT resonance;
Based on a comparison result between the wavelength control signal corresponding to the current excitation level and a target wavelength control signal corresponding to a preset target excitation level, the current excitation level is the target excitation level. Determining whether there is,
If the current of the excitation level is not the target excitation level, a step of based on said comparison result, to correct the previous SL wavelength control signal so that the current of the excitation level becomes the target excitation level,
A method for controlling an atomic oscillator , comprising: adding a value based on a difference between the current wavelength control signal and the target wavelength control signal to the wavelength control signal to correct the wavelength control signal . On the computer,
A process of generating a detection signal that is output from the light emitting unit and changes according to the amount of light that has passed through the enclosing unit that encloses the gaseous alkali metal atoms, and
Based on the detection signal, a process of generating a wavelength control signal for controlling the wavelength of the light so that the alkali metal atom maintains an excitation level;
Based on the detection signal, a process of generating a frequency control signal for controlling the frequency of the light so that the alkali metal atom maintains a light transmission state by CPT resonance;
Based on a comparison result between the wavelength control signal corresponding to the current excitation level and a target wavelength control signal corresponding to a preset target excitation level, the current excitation level is the target excitation level. A process for determining whether or not there is,
If the current of the excitation level is not the target excitation level, the processing based on the comparison result, the current of the excitation level to correct the previous SL wavelength control signal so that the target excitation level,
A control program for an atomic oscillator that executes a process of adding a value based on a difference between the current wavelength control signal and the target wavelength control signal to the wavelength control signal to correct the wavelength control signal .

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