JP2015082511A - Optical module and atomic oscillator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical module that can increase stability of an atomic oscillator by controlling a polarization direction of polarized light emitted from a surface emitting laser.SOLUTION: An optical module 100 includes: a surface emitting laser 10 that emits light; a polarization splitting unit 20 that splits the light emitted from the surface emitting laser 10 into a first polarized light L1 polarized in a first direction and a second polarized light L2 polarized in a second direction orthogonal to the first direction; a quarter-wave plate 30 on which the first polarized light L1 is incident; a gas cell 40 that is filled with an alkaline metal gas and is irradiated with light transmitted through the quarter-wave plate 30; a first photodetector 50 that detects intensity of the light transmitted through the gas cell 40; a second photodetector 60 that detects intensity of the second polarized light L2; a drive unit 70 that rotates the surface emitting laser 10 around the optical axis; and a control unit 80 that operates the drive unit 70 in accordance with luminous energy detected by the second photodetector 60.

Description

  The present invention relates to an optical module and an atomic oscillator.

  In recent years, an atomic oscillator using CPT (Coherent Population Trapping), which is one of the quantum interference effects, has been proposed, and downsizing and low power consumption of the apparatus are expected. An atomic oscillator using CPT uses an electromagnetically induced transmission phenomenon (EIT phenomenon: Electromagnetically Induced Transparency) in which absorption of coherent light stops when an alkali metal atom is irradiated with coherent light having two different wavelengths (frequencies). It is an oscillator.

For example, in Patent Document 1, in order to increase the probability of occurrence of the EIT phenomenon, resonant light emitted from a light source is converted into circularly polarized light by a λ / 4 plate, and atoms irradiated to a gas cell in which alkali metal atoms are enclosed are disclosed. An oscillator is disclosed. By irradiating the gas cell with circularly polarized light, an interaction occurs between the alkali metal atom and the circularly polarized light, and the probability that the alkali metal atom exists at the ground level of the magnetic quantum number m _F = 0 is increased. be able to. Thereby, the expression probability of the EIT phenomenon can be increased.

JP 2013-98606 A

  The light generated by the surface emitting laser has coherence and is suitable for obtaining a quantum interference effect. A surface emitting laser generally emits polarized light (polarized light).

  However, the polarization direction of the polarized light emitted by the surface emitting laser changes with time. Therefore, when a surface emitting laser is applied as the light source of the atomic oscillator of Patent Document 1, the polarization direction of the polarized light with respect to the λ / 4 plate changes due to the change in the polarization direction of the polarized light emitted by the surface emitting laser, and λ / 4 The ratio of the circularly polarized component of the light that has passed through the plate changes (for example, it is converted into elliptically polarized light without being converted into circularly polarized light by the λ / 4 plate). Therefore, when the surface emitting laser is applied as the light source of the atomic oscillator of Patent Document 1, the ratio of the circularly polarized component of the light irradiated to the gas cell changes with time, and the stability of the atomic oscillator is lowered. is there.

  One of the objects according to some aspects of the present invention is to provide an optical module capable of controlling the polarization direction of polarized light emitted from a surface emitting laser to increase the stability of an atomic oscillator. . Another object of some aspects of the present invention is to provide an atomic oscillator including the optical module.

The optical module according to the present invention is
An optical module of an atomic oscillator,
A surface emitting laser that emits light;
A polarization separation unit that separates light emitted from the surface emitting laser into first polarized light polarized in a first direction and second polarized light polarized in a second direction orthogonal to the first direction;
A λ / 4 plate on which the first polarized light is incident;
A gas cell filled with an alkali metal gas and irradiated with light transmitted through the λ / 4 plate;
A first light detector for detecting the intensity of light transmitted through the gas cell;
A second light detection unit for detecting the intensity of the second polarized light;
A drive unit for rotating the surface emitting laser around an optical axis;
A control unit that operates the driving unit in accordance with the amount of light detected by the second light detection unit;
including.

  In such an optical module, the light emitted from the surface-emitting laser is incident on the λ / 4 plate as the first polarized light that is separated in the polarization separation unit and polarized in the first direction. Even if the polarization direction changes, the polarization direction of the polarized light incident on the λ / 4 plate can be made constant with respect to the λ / 4 plate. Thereby, it is possible to prevent the ratio of the circularly polarized component of the light irradiated to the gas cell from changing due to the change in the polarization direction of the polarized light with time in the surface emitting laser.

  Furthermore, even if the polarization direction of the polarized light in the surface emitting laser changes, the control unit operates the drive unit to rotate the surface emitting laser around the optical axis, so that the amount of light irradiated to the gas cell is kept constant. can do.

  Therefore, according to such an optical module, the ratio of the circularly polarized component of the light irradiated to the gas cell and the amount of light change due to the change in the polarization direction of the polarized light with time in the surface emitting laser. Therefore, the stability of the atomic oscillator can be improved.

In the optical module according to the present invention,
The control unit operates the driving unit to return the light amount of the second polarized light before the change when the light amount of the second polarized light detected by the second light detection unit is changed. Also good.

  In such an optical module, even if the polarization direction of the polarized light in the surface emitting laser changes, the amount of the first polarized light can be made constant, so that the amount of the light irradiated to the gas cell is made constant. Can do.

In the optical module according to the present invention,
The control unit may operate the driving unit so that a light amount of the second polarized light detected by the second light detection unit becomes a predetermined light amount.

  In such an optical module, even if the polarization direction of the polarized light in the surface emitting laser changes, the amount of the first polarized light can be made constant, so that the amount of the light irradiated to the gas cell is made constant. Can do.

In the optical module according to the present invention,
The polarization separation unit may be a polarization beam splitter that separates light emitted from the surface emitting laser into p-polarized light and s-polarized light.

  In such an optical module, even if the polarization direction of the polarized light in the surface emitting laser changes, the polarization direction of the polarized light incident on the λ / 4 plate can be made constant with respect to the λ / 4 plate. .

In the optical module according to the present invention,
The surface emitting laser may emit polarized light.

The atomic oscillator according to the present invention is
The optical module which concerns on this invention is included.

    Since such an atomic oscillator includes the optical module according to the present invention, the stability of the apparatus can be improved.

The block diagram which shows the atomic oscillator containing the optical module which concerns on this embodiment. The figure which shows the frequency spectrum of resonant light. The figure which shows the relationship of the (LAMBDA) type | mold 3 level model of an alkali metal atom, a 1st sideband, and a 2nd sideband. The top view which shows typically the surface emitting laser and drive part of the optical module which concern on this embodiment. Sectional drawing which shows typically the surface emitting laser and drive part of the optical module which concern on this embodiment.

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

1. Optical Module First, the optical module according to the present embodiment will be described with reference to the drawings. Here, an example in which the optical module according to the present embodiment is applied to an atomic oscillator will be described. FIG. 1 is a block diagram showing an atomic oscillator 1 including an optical module 100 according to this embodiment.

  As shown in FIG. 1, the atomic oscillator 1 includes an optical module 100, a center wavelength control unit 2, and a high frequency control unit 4.

  As shown in FIG. 1, the optical module 100 includes a surface emitting laser 10, a polarization separation unit 20, a λ / 4 plate 30, a gas cell 40, a first light detection unit 50, and a second light detection unit 60. The drive unit 70 and the control unit 80 are included.

  The surface emitting laser 10 is, for example, a vertical cavity surface emitting laser (VCSEL) in which a resonator is formed perpendicular to a semiconductor substrate. The surface emitting laser 10 emits polarized light. Here, the polarized light includes a case of linearly polarized light and a case of elliptically polarized light that can be regarded as substantially linearly polarized light. Linearly polarized light refers to light in which the direction of vibration of the electric field of light is within one plane. In addition, elliptically polarized light that can be regarded as substantially linearly polarized light means that the length of the major axis of the elliptically polarized light is sufficiently longer than the length of the minor axis of the elliptically polarized light. For example, it is elliptically polarized light in which the ratio of the major axis length a to the minor axis length b satisfies the relationship of a / b ≧ 10. Here, the major axis of elliptically polarized light refers to the major axis of the ellipse drawn by the tip of the vibration vector in elliptically polarized light in which the tip of the vibration vector of the electric field of light moves elliptically. The minor axis of elliptically polarized light refers to the minor axis of the ellipse. In FIG. 1, polarized light (linearly polarized light) is indicated by a solid white arrow, and light (circularly polarized light) in which the tip of the vibration vector of the electric field makes a circular motion is indicated by a dashed white arrow. Yes.

  In the surface emitting laser 10, the polarization direction of polarized light (electric field vibration direction in linearly polarized light) changes with time. That is, in the surface emitting laser 10, the polarization plane rotates with time. Here, the polarization plane is a plane including the traveling direction of light and the vibration direction of the electric field. In elliptically polarized light that can be regarded as substantially linearly polarized light, the polarization direction of polarized light can refer to the direction of the major axis of elliptically polarized light.

  The light emitted from the surface emitting laser 10 enters the polarization separation unit 20. Here, in the optical module 100, even if the polarization direction of the polarized light in the surface emitting laser 10 changes, the control unit 80 operates the driving unit 70 to rotate the surface emitting laser 10 around the optical axis as will be described later. By doing so, the polarization direction of the polarized light incident on the polarization separation unit 20 can be set to a fixed direction. Here, the optical axis is an axis passing through the center of the spread of the light emitted from the surface emitting laser 10 (see the optical axis A in FIGS. 4 and 5).

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

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

  The polarization separation unit 20 includes a first polarized light L1 that polarizes light emitted from the surface emitting laser 10 in a first direction, and a second polarized light L2 that polarizes the light in a second direction orthogonal to the first direction. To separate. Here, the first polarized light L1 polarized in the first direction refers to linearly polarized light whose electric field vibration direction is the first direction. Similarly, the second polarized light L2 polarized in the second direction refers to linearly polarized light whose electric field vibration direction is the second direction. Thus, the polarization separation unit 20 separates the polarization component of the incident light.

  The polarization separation unit 20 is, for example, a polarization beam splitter that separates light emitted from the surface emitting laser 10 into p-polarized light and s-polarized light. Here, the p-polarized light is light having a polarization direction parallel to the incident surface of the polarization separation surface 22 of the polarization separation unit 20 (light having a parallel vibration direction of the electric field). Further, the s-polarized light is light having a polarization direction perpendicular to the incident surface of the polarization separation surface 22 of the polarization separation unit 20 (light having a perpendicular vibration direction of the electric field). The incident surface of the deflection separation surface 22 is a plane including the optical axis of light incident on the deflection separation surface 22 and the optical axis of light reflected by the deflection separation surface 22, and is parallel to the paper surface of FIG. Surface. The polarization separation unit 20 separates the p-polarized light and the s-polarized light by transmitting the p-polarized component of the light emitted from the surface emitting laser 10 and reflecting the s-polarized component. At this time, the first direction is a direction parallel to the incident surface of the deflection separation surface 22, and the second direction is a direction perpendicular to the incidence surface of the deflection separation surface 22. The first polarized light L1 corresponds to p-polarized light, and the second polarized light L2 corresponds to s-polarized light.

  The polarization separation unit 20 has a characteristic in which the separation ratio of the first polarized light L1 and the second polarized light L2 differs depending on the polarization direction of the incident polarized light. For example, when the polarization direction of the polarized light incident on the polarization separation unit 20 changes, the ratio between the light amount of the first polarized light L1 and the light amount of the second polarized light L2 also changes. In the optical module 100, since the polarization direction of the polarized light emitted from the surface emitting laser 10 and incident on the polarization separation unit 20 can be set to a fixed direction, as described later, the light amount of the first polarized light L1 and the first light The ratio of the light quantity of the two polarized light L2 can also be made constant.

  In the optical module 100, the light emitted from the surface emitting laser 10 is separated into the first polarized light L1 and the second polarized light L2 by the polarization separation unit 20, thereby two paths (path R1, path R2). Divided into The path R <b> 1 is a light path from being separated by the polarization separation unit 20 to being detected by the first light detection unit 50 through the λ / 4 plate 30 and the gas cell 40. The path R1 is a light path for operating the atomic oscillator 1 as an oscillator using the EIT phenomenon. The path R <b> 2 is a light path from being separated by the polarization separation unit 20 to being detected by the second light detection unit 60. The path R2 is a light path for monitoring the amount of the second polarized light L2. The path R2 can also be said to be a path for indirectly monitoring the light quantity of the first polarized light L1 via the light quantity of the second polarized light L2.

  The first polarized light L1 separated by the polarization separation unit 20 is incident on the λ / 4 plate 30. The λ / 4 plate 30 is a wave plate that gives an optical path difference of ¼ wavelength (90 ° phase difference) between orthogonal linearly polarized light components. The λ / 4 plate 30 converts the first polarized light L1 (linearly polarized light) into circularly polarized light. The λ / 4 plate 30 is arranged such that the fast axis is at an angle of 45 ° with respect to the polarization direction of the first polarized light L1 (the vibration direction of linearly polarized light). As a result, the first polarized light L1 can be converted into circularly polarized light. Here, the fast axis (high-speed axis) means an axis having a small refractive index in the λ / 4 plate, and a slow axis (slow axis, axis having a large refractive index) of the λ / 4 plate. Are orthogonal axes. As the λ / 4 plate 30, for example, a crystal plate, a mica plate, or the like can be used.

  The gas cell 40 is a container in which gaseous alkali metal atoms (sodium atom, rubidium atom, cesium atom, etc.) are sealed. When the gas cell 40 is irradiated with two light waves having a frequency (wavelength) corresponding to the energy difference between the two ground levels of the alkali metal atoms, the alkali metal atoms cause an EIT phenomenon. For example, if the alkali metal atom is a cesium atom, the frequency corresponding to the energy difference between the ground level GL1 and the ground level GL2 in the D1 line is 9.19263... GHz, so the frequency difference is 9.19263. When two light waves of GHz are irradiated, an EIT phenomenon occurs.

  The gas cell 40 is irradiated with light (circularly polarized light) transmitted through the λ / 4 plate 30. In the optical module 100, the light emitted from the surface emitting laser 10 is converted into circularly polarized light by the λ / 4 plate 30 via the polarization separation unit 20 and irradiated to the gas cell 40. Thereby, the expression probability of the EIT phenomenon can be increased.

  The first light detection unit 50 detects the intensity of light transmitted through the alkali metal atoms enclosed in the gas cell 40. The first light detection unit 50 outputs a detection signal corresponding to the intensity of light transmitted through the alkali metal atom. For example, a photodiode is used as the first light detection unit 50.

  The second light detection unit 60 detects the intensity of the second polarized light L <b> 2 separated by the polarization separation unit 20. The second light detection unit 60 outputs a detection signal corresponding to the intensity of the second polarized light L2. For example, a photodiode is used as the second light detection unit 60. The detection signal of the second light detection unit 60 is output to the control unit 80.

  The drive unit 70 rotates the surface emitting laser 10 around the optical axis. Thereby, the polarization direction of the polarized light incident on the polarization separator 20 can be changed. Here, the light quantity of the first polarized light L1 and the light quantity of the second polarized light L2 are determined by the separation ratio of the polarized lights L1 and L2 in the polarization separation unit 20. Further, the separation ratio of the polarized light L1 and L2 is determined by the polarization direction of the polarized light incident on the polarization separation unit 20. Therefore, the light amount of the second polarized light L2 (the light amount of the first polarized light L1) is changed by changing the polarization direction of the polarized light incident on the polarization separation unit 20 by rotating the surface emitting laser 10 by the driving unit 70. Can be made. The drive unit 70 is controlled by the control unit 80. A specific configuration of the drive unit 70 will be described later.

  The control unit 80 operates the driving unit 70 in accordance with the amount of light detected by the second light detection unit 60. Specifically, when the light amount of the second polarized light L2 detected by the second light detection unit 60 changes, the control unit 80 returns the light amount of the second polarized light L2 before the change to the drive unit. 70 is operated. Thereby, since the light quantity of the 1st polarized light L1 can also be returned to the light quantity before changing, the quantity of the light irradiated to the gas cell 40 can be made constant.

  For example, the control unit 80 operates the driving unit 70 so that the light amount of the second polarized light L2 detected by the second light detection unit 60 becomes a predetermined light amount. The predetermined light amount is, for example, the light amount when the light amount of the second polarized light L2 is minimized. That is, the light amount of the second polarized light L2 when the light amount of the first polarized light L1 is maximized. The predetermined light amount is not limited to the light amount when the light amount of the second polarized light L2 is minimized, and can be set as appropriate.

  Specifically, for example, the control unit 80 operates the driving unit 70 to rotate the surface emitting laser 10 about the optical axis and change the polarization direction of the polarized light incident on the polarization separation unit 20 while changing the polarization direction of the second polarized light. The light quantity of the light L2 is monitored, and the operation of the drive unit 70 is stopped when the light quantity of the second polarized light L2 reaches a predetermined light quantity. Thereby, the light quantity of the 2nd polarized light L2 can be made into predetermined light quantity.

The center wavelength control unit 2 generates a drive current having a magnitude corresponding to the detection signal output from the first light detection unit 50, supplies the drive current to the surface emitting laser 10, and the center wavelength λ of light emitted from the surface emitting laser 10 Control ₀ . The center wavelength λ _{0 of the} light emitted from the surface emitting laser 10 is finely adjusted and stabilized by the feedback loop that passes through the surface emitting laser 10, the gas cell 40, the first light detection unit 50, and the center wavelength control unit 2.

Based on the detection result output from the first light detection unit 50, the high-frequency control unit 4 determines that the difference in wavelength (frequency) between the first sideband wave W1 and the second sideband wave W2 is that of alkali metal atoms enclosed in the gas cell 40 Control is made to be equal to the frequency corresponding to the energy difference between the two ground levels. The high frequency control unit 4 generates a modulation signal having a modulation frequency f _m (see FIG. 2) corresponding to the detection result output from the first light detection unit 50.

Due to the feedback loop passing through the surface emitting laser 10, the gas cell 40, the first light detection unit 50, and the high frequency control unit 4, the frequency difference between the first sideband W1 and the second sideband W2 is two ground levels of alkali metal atoms. The feedback control is applied so as to match the frequency corresponding to the energy difference very accurately. As a result, the modulation frequency f _m is very since a stable frequency can be a modulation signal and the atomic oscillator 1 of the output signal (clock output).

2. Configuration of Surface Emitting Laser and Driving Unit Next, an example of the configuration of the surface emitting laser 10 and the driving unit 70 will be described with reference to the drawings. FIG. 4 is a plan view schematically showing the surface emitting laser 10 and the driving unit 70. 5 is a cross-sectional view schematically showing the surface-emitting laser 10 and the drive unit 70, and is a cross-sectional view taken along the line VV of FIG.

  As shown in FIGS. 4 and 5, the surface emitting laser 10 includes a semiconductor stacked body 11, electrodes 12 a and 12 b, and a support substrate 16.

  The semiconductor stacked body 11 includes, for example, a first semiconductor multilayer film mirror, a second semiconductor multilayer film mirror, and an active layer sandwiched between the first and second semiconductor multilayer film mirrors. The first and second semiconductor multilayer mirrors and the active layer constitute a vertical resonator.

  The electrodes 12 a and 12 b are provided on the surface of the semiconductor stacked body 11. When a drive signal is supplied to the electrodes 12a and 12b, light is generated in the active layer. The surface emitting laser 10 emits light from the emission surface 13.

  The support substrate 16 supports the semiconductor stacked body 11. The support substrate 16 is provided with terminals 14a and 14b for supplying drive signals (an output signal of the central wavelength control unit 2 and an output signal of the high frequency control unit 4) to the electrodes 12a and 12b. The terminal 14a and the electrode 12a are connected by a wiring wire 15a. The terminal 14b and the electrode 12b are connected by a wiring wire 15b. The shape of the support substrate 16 is, for example, a disk shape.

  The surface emitting laser 10 is mounted on the stem 17 in the illustrated example.

  The stem 17 supports the support substrate 16. The stem 17 is provided with a groove 18a into which the terminal 14a is inserted and a groove 18b into which the terminal 14b is inserted. As shown in FIG. 4, the grooves 18 a and 18 b are provided concentrically around the optical axis A of the light emitted from the emission surface 13 in plan view. An external electrode 19a is provided on the inner surface of the groove 18a, and an external electrode 19b is provided on the inner surface of the groove 18b. The drive signals generated by the center wavelength control unit 2 and the high frequency control unit 4 are supplied to the electrodes 12a and 12b via the external electrodes 19a and 19b, the terminals 14a and 14b, and the wiring wires 15a and 15b. Since the terminals 14a and 14b are inserted into the grooves 18a and 18b, a drive signal can be supplied to the electrodes 12a and 12b even when the surface emitting laser 10 rotates.

  The stem 17 is made of, for example, Cu, Al, Mo, W, Si, C, Be, Au, a compound thereof (for example, AlN, BeO), an alloy (for example, CuMo), or the like. Moreover, the stem 17 can also be comprised from what combined these illustrations, for example, the multilayered structure of a copper (Cu) layer and a molybdenum (Mo) layer.

  The drive unit 70 includes a motor 71. The motor 71 is, for example, a step motor (stepping motor). The motor 71 is controlled by the control unit 80. The motor 71 rotates the shaft member 71a.

  The shaft member 71 a is connected to the support substrate 16 through a through hole that penetrates the stem 17. The shaft member 71a is disposed so as to overlap the optical axis A in plan view. Therefore, the surface emitting laser 10 rotates around the optical axis A by rotating the shaft member 71 a by the operation of the motor 71. Thereby, the polarization direction of the polarized light emitted from the surface emitting laser 10 can be changed (the polarization plane is rotated).

3. Operation of Optical Module Next, the operation of the optical module 100 will be described with reference to FIG.

  The surface emitting laser 10 emits polarized light. The polarized light emitted from the surface emitting laser 10 enters the polarization separation unit 20. The light incident on the polarization separation unit 20 is separated into the first polarized light L1 and the second polarized light L2 whose directions of polarization are perpendicular to each other. As described above, the light emitted from the surface emitting laser 10 is separated into the first polarized light L1 and the second polarized light L2 by the polarization separation unit 20, thereby being divided into two paths (path R1 and path R2). Divided. Hereinafter, each route R1, R2 will be described.

  First, the route R1 will be described.

  The first polarized light L1 transmitted through the polarization separation unit 20 is incident on the λ / 4 plate 30. The first polarized light L <b> 1 is converted into circularly polarized light by the λ / 4 plate 30 and enters the gas cell 40. Here, the light emitted from the surface emitting laser 10 is two light waves (first sideband wave W1 and second sideband wave W2) having a frequency (wavelength) corresponding to the energy difference between the two ground levels of the alkali metal atom. ), And an alkali metal atom causes an EIT phenomenon. The intensity of the light transmitted through the gas cell 40 is detected by the first light detection unit 50.

The center wavelength control unit 2 and the high frequency control unit 4 match the frequency difference between the first sideband wave W1 and the second sideband wave W2 very accurately with the frequency corresponding to the energy difference between the two ground levels of the alkali metal atom. Thus, feedback control is performed. In atomic oscillator 1, utilizing the EIT phenomenon, the frequency difference _f 1 -f ₂ between the first sideband wave W1 and the second sideband wave W2 corresponds to the energy difference Delta] E ₁₂ between the ground level GL1 and ground level GL2 By detecting and controlling a steep change in light absorption behavior when deviating from the frequency, a highly accurate oscillator can be produced.

  Next, the route R2 will be described.

  The second polarized light L <b> 2 reflected by the polarization separation unit 20 enters the second light detection unit 60. The second light detection unit 60 detects the intensity of the second polarized light L2.

  Here, the polarization separation unit 20 has a characteristic in which the separation ratio of the first polarized light L1 and the second polarized light L2 differs depending on the polarization direction of the incident polarized light. Therefore, for example, when the polarization direction of the polarized light emitted from the surface emitting laser 10 is changed, the separation ratio between the first polarized light L1 and the second polarized light L2 is changed in the polarization separation unit 20. As a result, the amount of light applied to the gas cell 40 changes.

  Therefore, when the light amount of the second polarized light L2 detected by the second light detection unit 60 changes, the control unit 80 operates the drive unit 70 so as to return to the light amount of the second polarized light L2 before the change. Let Thereby, since the light quantity of the 1st polarized light L1 can also be returned to the light quantity before changing, the quantity of the light irradiated to the gas cell 40 can be made constant.

  An example of the processing of the control unit 80 will be specifically described.

  When the intensity of the detection signal output from the second light detection unit 60 changes from the set value, the control unit 80 operates the driving unit 70 to rotate the surface emitting laser 10. Here, the set value is, for example, the intensity of the detection signal of the second light detection unit 60 when the light amount of the second polarized light L2 is minimized. By rotating the surface emitting laser 10, the polarization direction of the polarized light incident on the polarization separation unit 20 changes. Thereby, the separation ratio of the polarized light L1 and L2 of the polarization separation unit 20 changes, and the light amount of the second polarized light L2 changes.

  The control unit 80 monitors the intensity of the detection signal output from the second light detection unit 60 (the amount of light of the second polarized light L2), and drives the driving unit 70 until the intensity of the detection signal reaches a set value (minimum value). Is operated to rotate the surface emitting laser 10. Then, the control unit 80 ends the process when the intensity of the detection signal reaches a set value (minimum value).

  When the surface emitting laser 10 is rotated while the control unit 80 monitors the intensity of the detection signal output from the second light detection unit 60, the control unit 80 is accompanied by rotation of the surface emitting laser 10 (for example, clockwise rotation). When the intensity of the detection signal increases, a process of rotating the surface emitting laser 10 in the reverse direction (for example, counterclockwise rotation) may be performed.

4). Features of Optical Module The optical module 100 according to this embodiment has the following features, for example.

  In the optical module 100, the surface emitting laser 10 and the first polarized light L1 that is polarized in the first direction and the second polarized light that is polarized in the second direction orthogonal to the first direction are emitted from the surface emitting laser 10. The polarized light separating unit 20 that separates into the two polarized light L2, the λ / 4 plate 30 on which the first polarized light L1 is incident, the alkali metal gas is sealed, and the light transmitted through the λ / 4 plate 30 is irradiated. Gas cell 40, first light detection unit 50 for detecting the intensity of light transmitted through gas cell 40, second light detection unit 60 for detecting the intensity of second polarized light L2, and surface emitting laser 10 around the optical axis. And a control unit 80 that operates the drive unit 70 in accordance with the amount of light detected by the second light detection unit 60. As described above, in the optical module 100, the light emitted from the surface emitting laser 10 is incident on the λ / 4 plate 30 as the first polarized light L1 that is separated by the polarization separation unit 20 and polarized in the first direction. Therefore, even if the polarization direction of the polarized light in the surface emitting laser 10 is changed, the polarization direction of the polarized light incident on the λ / 4 plate 30 is set to a fixed direction relative to the λ / 4 plate 30 (the speed of the λ / 4 plate 30). Direction inclined by 45 ° with respect to the axis). Thereby, it is possible to prevent the ratio of the circularly polarized component of the light irradiated to the gas cell 40 from changing due to the polarization direction of the polarized light changing with time in the surface emitting laser 10.

  Further, in the optical module 100, even if the polarization direction of the polarized light in the surface emitting laser 10 changes, the control unit 80 operates the driving unit 70 to rotate the surface emitting laser 10 around the optical axis, whereby the gas cell 40. The amount of light applied to the light can be made constant.

  As described above, according to the optical module 100, the ratio of the circularly polarized component of the light irradiated to the gas cell 40 and the amount of light are changed due to the change in the polarization direction of the polarized light with time in the surface emitting laser 10. Since the change can be prevented, the stability of the atomic oscillator 1 can be improved.

  In the optical module 100, when the light amount of the second polarized light L2 detected by the second light detection unit 60 changes, the control unit 80 returns the light amount of the second polarized light L2 before the change to the drive unit. 70 is operated. Thereby, since the light quantity of the 1st polarized light L1 can be made constant, the quantity of the light irradiated to the gas cell 40 can be made constant.

  In the optical module 100, the control unit 80 operates the drive unit 70 so that the light amount of the second polarized light L2 detected by the second light detection unit 60 becomes a predetermined light amount. Thereby, since the light quantity of the 1st polarized light L1 can be made constant, the quantity of the light irradiated to the gas cell 40 can be made constant.

  In the optical module 100, the polarization separation unit 20 is a polarization beam splitter that separates the light emitted from the surface emitting laser 10 into p-polarized light and s-polarized light. Even if the direction changes, the polarization direction of the polarized light incident on the λ / 4 plate 30 can be made constant with respect to the λ / 4 plate 30.

  The above-described embodiments are examples, and the present invention is not limited to these.

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

DESCRIPTION OF SYMBOLS 1 ... Atomic oscillator, 2 ... Center wavelength control part, 4 ... High frequency control part, 10 ... Surface emitting laser, 11 ... Semiconductor laminated body, 12a, 12b ... Electrode, 13 ... Ejection surface, 14a, 14b ... Terminal, 15a, 15b DESCRIPTION OF SYMBOLS ... Wiring wire, 16 ... Support substrate, 17 ... Stem, 18a, 18b ... Groove, 19a, 19b ... External electrode, 20 ... Polarization separation part, 30 ... λ / 4 plate, 40 ... Gas cell, 50 ... 1st light detection part , 60 ... second light detection unit, 70 ... drive unit, 71 ... motor, 71a ... shaft member, 80 ... control unit, 100 ... optical module

Claims (6)

An optical module of an atomic oscillator,
A surface emitting laser that emits light;
A polarization separation unit that separates light emitted from the surface emitting laser into first polarized light polarized in a first direction and second polarized light polarized in a second direction orthogonal to the first direction;
A λ / 4 plate on which the first polarized light is incident;
A gas cell filled with an alkali metal gas and irradiated with light transmitted through the λ / 4 plate;
A first light detector for detecting the intensity of light transmitted through the gas cell;
A second light detection unit for detecting the intensity of the second polarized light;
A drive unit for rotating the surface emitting laser around an optical axis;
A control unit that operates the driving unit in accordance with the amount of light detected by the second light detection unit;
An optical module comprising:   The control unit operates the driving unit to return the light amount of the second polarized light before the change when the light amount of the second polarized light detected by the second light detection unit is changed. The optical module according to claim 1.   The said control part operates the said drive part so that the light quantity of the said 2nd polarized light detected by the said 2nd light detection part may become predetermined light quantity, The Claim 1 or 2 characterized by the above-mentioned. Optical module.   4. The polarization beam splitter according to claim 1, wherein the polarization separation unit is a polarization beam splitter that separates light emitted from the surface-emitting laser into p-polarized light and s-polarized light. 5. An optical module according to 1.   The optical module according to claim 1, wherein the surface emitting laser emits polarized light.   An atomic oscillator comprising the optical module according to claim 1.

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