阅读说明：本技术 一种光纤式原子磁力仪探头及其调节方法 (Optical fiber type atomic magnetometer probe and adjusting method thereof ) 是由 梁尚清 杨国卿 王琳 于 2021-07-21 设计创作，主要内容包括：本发明公开一种光纤式原子磁力仪探头及其调节方法。由光纤传导出射的激光偏振受光纤影响产生变化时,由侧向位移分光棱镜分解的两束线偏振光的光强会发生变化,但两束线偏振光的偏振稳定且总光强不会发生变化,因此,通过两个四分之一波片转变为偏振相同的圆偏振光后,通过凸透镜的发散作用,两束激光在原子气室处形成了偏振稳定且总光强稳定的激光。本发明光纤式原子磁力仪探头对单模光纤的保偏性能无要求,在降低成本的情况下,保证了进入原子气室的激光功率与偏振稳定,进而保证了原子磁力仪的性能不受光纤传导特性对激光偏振的影响。(The invention discloses an optical fiber type atomic magnetometer probe and an adjusting method thereof. When the laser polarization transmitted by the optical fiber is influenced by the optical fiber to change, the light intensity of two linearly polarized light beams decomposed by the lateral displacement beam splitter prism can change, but the polarization of the two linearly polarized light beams is stable and the total light intensity can not change, therefore, after the two quarter-wave plates are converted into circularly polarized light with the same polarization, the two laser beams form laser with stable polarization and stable total light intensity at an atom air chamber through the divergence effect of the convex lens. The probe of the optical fiber type atomic magnetometer has no requirement on the polarization maintaining performance of the single-mode optical fiber, ensures the power and polarization stability of laser entering an atomic gas chamber under the condition of reducing the cost, and further ensures that the performance of the atomic magnetometer is not influenced by the optical fiber conduction characteristic on the laser polarization.)

1. An optical fiber type atom magnetometer probe is characterized by comprising a laser light source (1), an atom sensing system (2) and a detection system (3); the laser light source (1), the atom sensing system (2) and the detection system (3) are sequentially connected through a laser light path;

the laser light source (1) comprises a semiconductor laser (4), an optical isolator (5), a half wave plate (6), a first optical fiber coupler (7), a single-mode optical fiber (8) and a first collimating lens (9); the semiconductor laser (4) emits laser, and the laser sequentially penetrates through the optical isolator (5) and the half-wave plate (6), enters the single-mode fiber (8) through the first fiber coupler (7) and is emitted out of the first collimating lens (9);

the atom sensing system (2) comprises a lateral displacement beam splitting prism (10), a first quarter wave plate (11), a second quarter wave plate (12), a first convex lens (13), an atom air chamber (14), a second convex lens (15) and a third quarter wave plate (16); the optical axis of the first quarter-wave plate (11) is vertical to that of the second quarter-wave plate (12); laser emitted by the first collimating lens (9) is transmitted by the lateral displacement beam splitter prism (10) and then divided into two linearly polarized light beams which are vertical to each other in polarization and parallel in propagation direction, namely first transmission light (17) and second transmission light (18); the atomic gas cell comprises a first transmission light (17), a second transmission light (18), a first convex lens (13), an atomic gas cell (14), a third convex lens (15), a fourth quarter wave plate (16), a fourth quarter wave plate (11), a fourth quarter wave plate (12), a fourth quarter wave plate (11), a fourth quarter wave plate (18), a fourth quarter wave plate (13), a fourth quarter wave plate (12), a fourth quarter wave plate (16), a fourth quarter wave plate (15), a fourth quarter wave plate (16), a fourth quarter wave plate (13), a fourth quarter wave plate (12), a fourth quarter wave plate, a fourth convex lens (13), a fourth convex lens (15), a fourth convex lens (14), a fourth convex lens (15), an atomic gas cell (14), a fourth convex lens (15), a fourth convex lens (13) and a fourth convex lens (15);

the detection system (3) comprises a second collimating lens (19), a multimode optical fiber (20), a second optical fiber coupler (21) and a photoelectric detector (22); the two linearly polarized light beams which are transmitted by the third quarter-wave plate (16) are transmitted by a second collimating lens (19), enter a multimode fiber (20) and exit from a second fiber coupler (21); the laser light emitted from the second optical fiber coupler (21) is detected by the photoelectric detector (22) to detect the whole light intensity, and the light intensity value is converted into an electric signal.

2. A fiber-optic atomic magnetometer probe according to claim 1 wherein the single mode fiber (8) is connected at one end to the first fiber coupler (7) via an FC/APC interface and at the other end to the first collimating lens (9) via optical cement.

3. A fiber-optic atomic magnetometer probe according to claim 1 wherein the first transmitted light (17) is spaced from the second transmitted light (18) by no more than 2 cm.

4. The probe of claim 1, wherein the atom gas chamber (14) contains therein alkali metal atoms and a buffer gas.

5. The probe of claim 4, wherein the atomic gas cell (14) is a glass bulb containing a saturated vapor of an alkali metal and a buffer gas.

6. A fibre-optic atomic magnetometer probe according to claim 1 characterised in that the multimode fibre (20) is glued at one end to the second collimating lens (19) by optical glue and at the other end to the second fibre coupler (21) by means of an FC/APC interface.

7. A fiber-optic atomic magnetometer probe according to claim 1 wherein the position of the first convex lens (13) is adjusted so that the overlapping portion of the propagation paths of the first transmitted light (17) and the second transmitted light (18) covers the entire atomic gas cell.

8. An adjusting method of an optical fiber type atomic magnetometer probe is characterized by comprising the following steps:

step (1), adjusting a laser light source (1):

1-1, adjusting a semiconductor laser (4), keeping the laser wavelength emitted by the semiconductor laser (4) stable, and keeping the laser wavelength emitted by the semiconductor laser (4) resonant with the basic state energy level of an alkali metal atom in an atom sensing system (2);

1-2, placing an optical isolator (5) in the direction of a laser beam to prevent the occurrence of an optical feedback phenomenon;

1-3, sequentially arranging a half wave plate (6) and a first optical fiber coupler (7) in the direction of a laser beam;

1-4, adjusting the relative position of the first optical fiber coupler (7) and the laser, so that the laser enters a single-mode optical fiber (8) from the first optical fiber coupler (7) and exits from a first collimating lens (9);

1-5, adjusting the direction of the optical axis of the half wave plate (6) to enable the light intensity value of laser emitted by the first collimating lens (9) to be maximum;

step (2), adjusting the atom sensing system (2):

2-1, vertically arranging a lateral displacement light splitting prism (10) in the transmission direction of a laser beam emitted by a first collimating lens (9), and adjusting the position of the lateral displacement light splitting prism (10) to enable the laser beam passing through the lateral displacement light splitting prism (10) to be divided into a first transmission light (17) and a second transmission light (18) which are mutually vertical in polarization direction, wherein the transmission directions of the first transmission light (17) and the second transmission light (18) are parallel;

2-2, vertically placing the first quarter-wave plate (11) in the transmission direction of the first transmission light (17), and adjusting the optical axis direction of the first quarter-wave plate (11) to change the polarization direction of the first transmission light (17) into left-handed circularly polarized light or right-handed circularly polarized light; vertically placing the second quarter-wave plate (12) in the propagation direction of the second transmission light (18), and adjusting the optical axis direction of the second quarter-wave plate (12) to enable the polarization direction of the second transmission light (18) to be the same as that of the first transmission light (17);

2-3, vertically placing a first convex lens (13) in the propagation direction of the first transmitted light (17) and the second transmitted light (18) so that the first transmitted light (17) and the second transmitted light (18) are changed into light from parallel light and the light paths of the first transmitted light and the second transmitted light are overlapped;

2-4, placing the atomic gas chamber (14) at a position where the light paths of the first transmitted light (17) and the second transmitted light (18) are overlapped;

2-5, placing a second convex lens (15) in the propagation direction of the first transmitted light (17) and the second transmitted light (18) after passing through the atomic gas chamber (14), and adjusting the position of the second convex lens (15) to change the first transmitted light (17) and the second transmitted light (18) from divergent light to parallel light;

2-6, vertically placing a third quarter-wave plate (16) in the propagation direction of the first transmitted light (17) and the second transmitted light (18) after passing through the second convex lens (15), and adjusting the optical axis direction of the third quarter-wave plate (16) to ensure that the first transmitted light (17) and the second transmitted light (18) are simultaneously converted into linearly polarized light;

step (3), adjusting the detection system (3):

3-1, adjusting the position of a second collimating lens (19) to enable the first transmitted light (17) and the second transmitted light (18) which pass through a third quarter-wave plate (16) to enter a multimode fiber (20), and enabling the light intensity value of laser emitted by a second fiber coupler (21) to be maximum;

3-2, adjusting the position of the photoelectric detector (22) so that the photoelectric detector (22) receives the laser light emitted by all the second optical fiber couplers (21) and converts the light intensity signal into an electric signal.

9. The method of claim 8, wherein the semiconductor laser (4) emits a laser wavelength within a wavelength range of an optical isolator, a half-wave plate, a lateral shift beam splitter prism, first to third quarter-wave plates, a collimating lens, first to second convex lenses, and first to second fiber couplers.

10. A magnetic field measurement method, which adopts the optical fiber type atomic magnetometer probe of any one of claims 1 to 7 to obtain Larmor precession signals of atoms under a magnetic field to be measured, and further obtains the size of the magnetic field to be measured.

Technical Field

The invention belongs to the field of quantum magnetic sensing, and relates to an optical fiber type atomic magnetometer probe and an adjusting method thereof, which are used for reducing the influence of optical fiber transmission performance on the measurement noise of an atomic magnetometer and further improving the environmental adaptability of the optical fiber type atomic magnetometer.

Background

The atomic magnetometer is a high-precision magnetic sensor based on quantum effect, is widely applied to the field of magnetic field precision measurement, and has important functions in the fields of geological exploration, ocean engineering, biomedicine, target detection and the like. At present, an optical fiber type atomic magnetometer conducts laser through optical fibers, so that electronic devices such as a laser, a signal processing circuit and the like are separated from a sensing probe, and the requirements of the sensing probe on the use environment are greatly reduced. Because the performance of the atomic magnetometer is related to parameters such as laser power and polarization entering the atomic gas chamber, stable laser power and polarization are important factors for ensuring the performance of the atomic magnetometer. At present, a commonly used optical fiber type atomic magnetometer mainly ensures that the power and polarization of laser entering a sensing probe are stable through a high-performance single-mode optical fiber or a single-mode polarization-maintaining optical fiber, so as to ensure that the laser entering an atomic gas chamber has good power stability and polarization stability. However, due to the limitation of the manufacturing process and materials of the optical fiber, most high-performance single-mode optical fibers are relatively expensive, and in an environment with severe vibration, moisture or temperature change, polarization rotation or depolarization during laser transmission can still be caused, so that the polarization stability of laser entering the sensing probe is reduced, and the performance of the optical fiber type atomic magnetometer is further affected. Therefore, a probe structure which does not depend on high-performance optical fibers and can ensure stable laser power and polarization entering an atomic gas chamber is needed.

In a conventional fiber type atomic magnetometer, after laser emitted by a laser light source is conducted through a single-mode fiber and emitted out through a first collimating lens, the laser is generally prepared in a polarization state in two ways. The utility model provides a directly change emergent laser into circular polarization light through quarter wave plate, when the polarization rotation takes place for laser polarization receives single mode fiber influence, because the optical axis of quarter wave plate can't change in real time, this kind of mode can lead to the laser polarization who gets into atom gas chamber to become elliptical polarization even linear polarization to influence atom magnetometer's performance. The other type of the laser polarization purifying device firstly purifies the laser polarization emitted by the first collimating lens through the polarizing element and then converts the laser polarization into circularly polarized light through the quarter-wave plate, although the mode can ensure that the laser polarization entering the atom air chamber is always circularly polarized light, because the laser light intensity passing through the polarizing element is related to the laser polarization direction of the incident polarizing element, when the laser polarization is influenced by the single-mode optical fiber to generate polarization rotation, the laser light intensity passing through the polarizing element is greatly changed, the stability of the laser power entering the atom air chamber cannot be ensured, and therefore the performance of the atom magnetometer is influenced. The invention provides an optical system consisting of a plurality of polarizing optical elements for separating, polarizing and preparing and synthesizing laser transmitted by an optical fiber, thereby reducing the influence of laser power and polarization of laser polarization change entering an atomic gas chamber caused by optical fiber transmission.

Disclosure of Invention

The invention aims to improve the environmental adaptability of the structure of the optical fiber type atomic magnetometer probe on the basis of not increasing excessive device complexity and implementation cost, and provides the optical fiber type atomic magnetometer probe. The invention utilizes an optical system consisting of a plurality of polarized optical elements to separate, polarize, prepare and synthesize the laser transmitted by the optical fiber, thereby reducing the influence of the laser power and polarization of the laser polarization change entering the atomic gas chamber caused by the optical fiber transmission.

The working mechanism of the invention is as follows: laser transmitted and emitted by the optical fiber is decomposed into two linearly polarized lights with mutually vertical polarization by a lateral displacement beam splitter prism (10), and after passing through two quarter-wave plates (11) and (12) with vertical optical axes, the two linearly polarized lights are converted into circularly polarized lights with the same polarization and are subjected to the diverging action of a convex lens (13), so that the propagation paths of the two circularly polarized lights are overlapped when the two circularly polarized lights enter an atom air chamber (14). When the polarization of the laser transmitted and emitted by the optical fiber is influenced by the optical fiber to change, the light intensity of the two linearly polarized light beams decomposed by the lateral displacement beam splitter prism (10) changes, but the polarization of the two linearly polarized light beams is stable and the total light intensity does not change, so that after the two linearly polarized light beams are converted into circularly polarized light with the same polarization through the two quarter-wave plates (11) and (12), the two laser beams form laser with stable polarization and stable total light intensity at the atom air chamber (14) through the divergence effect of the convex lens (13). The device and the method can reduce the requirement of the fiber type atomic magnetometer on the performance of the single-mode fiber (8), ensure the stability of the power and polarization of laser entering the atomic gas chamber (14) under the condition of reducing the cost, and further ensure that the performance of the atomic magnetometer is not influenced by the fiber conduction characteristic on the polarization of the laser.

An optical fiber type atomic magnetometer probe comprises a laser light source (1), an atom sensing system (2) and a detection system (3); the laser light source (1), the atom sensing system (2) and the detection system (3) are sequentially connected through a laser light path;

the laser light source (1) comprises a semiconductor laser (4), an optical isolator (5), a half wave plate (6), a first optical fiber coupler (7), a single-mode optical fiber (8) and a first collimating lens (9); the semiconductor laser (4) emits laser, and the laser sequentially penetrates through the optical isolator (5) and the half-wave plate (6), enters the single-mode fiber (8) through the first fiber coupler (7) and is emitted out of the first collimating lens (9);

preferably, one end of the single-mode fiber (8) is connected with the first fiber coupler (7) through an FC/APC interface, and the other end of the single-mode fiber is glued with the first collimating lens (9) through optical cement;

the atom sensing system (2) comprises a lateral displacement beam splitting prism (10), a first quarter wave plate (11), a second quarter wave plate (12), a first convex lens (13), an atom air chamber (14), a second convex lens (15) and a third quarter wave plate (16); the optical axis of the first quarter-wave plate (11) is vertical to that of the second quarter-wave plate (12); laser emitted by the first collimating lens (9) is transmitted by the lateral displacement beam splitter prism (10) and then divided into two linearly polarized light beams which are vertical to each other in polarization and parallel in propagation direction, namely first transmission light (17) and second transmission light (18); the first transmission light (17) is converted into circularly polarized light after passing through the first quarter-wave plate (11), and the second transmission light (18) is converted into circularly polarized light with the same polarization as the first transmission light (17) after passing through the second quarter-wave plate (12); the first transmitted light (17) and the second transmitted light (18) pass through the first convex lens (13) simultaneously, both of which are converted from parallel light into divergent light, and propagation paths are overlapped, and the propagation directions are the same; the atom gas chamber (14) is positioned at the position where the propagation paths of the first transmitted light (17) and the second transmitted light (18) are overlapped; the first transmission light (17) and the second transmission light (18) passing through the atomic gas chamber (14) simultaneously transmit through the second convex lens (15), the first transmission light and the second transmission light are converted into parallel light from divergent light, and then are converted into two linearly polarized light beams with the same polarization through the third quarter-wave plate (16);

preferably, the distance between the first transmitted light (17) and the second transmitted light (18) is not more than 2 cm;

preferably, alkali metal atoms and buffer gas are arranged in the atom gas chamber (14); more preferably, the atomic gas chamber (14) adopts glass bubbles containing alkali metal saturated steam and buffer gas;

the detection system (3) comprises a second collimating lens (19), a multimode optical fiber (20), a second optical fiber coupler (21) and a photoelectric detector (22); the two linearly polarized light beams which are transmitted by the third quarter-wave plate (16) are transmitted by a second collimating lens (19), enter a multimode fiber (20) and exit from a second fiber coupler (21); the laser emitted from the second optical fiber coupler (21) is detected by a photoelectric detector (22) to detect all light intensity, and the light intensity value is converted into an electric signal;

preferably, one end of the multimode fiber (20) is glued with the second collimating lens (19) through optical cement, and the other end is connected with the second fiber coupler (21) through an FC/APC interface.

The invention also aims to provide an adjusting method of the optical fiber type atomic magnetometer probe, which comprises the following steps:

step (1), adjusting a laser light source (1):

1-1, adjusting a semiconductor laser (4), keeping the laser wavelength emitted by the semiconductor laser (4) stable, and keeping the laser wavelength emitted by the semiconductor laser (4) resonant with the basic state energy level of an alkali metal atom in an atom sensing system (2);

1-2, placing an optical isolator (5) in the direction of a laser beam to prevent the occurrence of an optical feedback phenomenon;

1-3, sequentially arranging a half wave plate (6) and a first optical fiber coupler (7) in the direction of a laser beam;

1-4, adjusting the relative position of the first optical fiber coupler (7) and the laser, so that the laser enters a single-mode optical fiber (8) from the first optical fiber coupler (7) and exits from a first collimating lens (9);

1-5, adjusting the direction of the optical axis of the half wave plate (6) to enable the light intensity value of laser emitted by the first collimating lens (9) to be maximum;

step (2), adjusting the atom sensing system (2):

2-1, vertically arranging a lateral displacement light splitting prism (10) in the transmission direction of a laser beam emitted by a first collimating lens (9), and adjusting the position of the lateral displacement light splitting prism (10) to enable the laser beam passing through the lateral displacement light splitting prism (10) to be divided into a first transmission light (17) and a second transmission light (18) which are mutually vertical in polarization direction, wherein the transmission directions of the first transmission light (17) and the second transmission light (18) are parallel;

2-2, vertically placing the first quarter-wave plate (11) in the transmission direction of the first transmission light (17), and adjusting the optical axis direction of the first quarter-wave plate (11) to change the polarization direction of the first transmission light (17) into left-handed circularly polarized light or right-handed circularly polarized light; vertically placing the second quarter-wave plate (12) in the propagation direction of the second transmission light (18), and adjusting the optical axis direction of the second quarter-wave plate (12) to enable the polarization direction of the second transmission light (18) to be the same as that of the first transmission light (17);

2-3, vertically placing a first convex lens (13) in the propagation direction of the first transmitted light (17) and the second transmitted light (18) so that the first transmitted light (17) and the second transmitted light (18) are changed into light from parallel light and the light paths of the first transmitted light and the second transmitted light partially overlap;

2-4, placing the atomic gas chamber (14) at a position where the light paths of the first transmitted light (17) and the second transmitted light (18) are overlapped;

2-5, placing a second convex lens (15) in the propagation direction of the first transmitted light (17) and the second transmitted light (18) after passing through the atomic gas chamber (14), and adjusting the position of the second convex lens (15) to change the first transmitted light (17) and the second transmitted light (18) from divergent light to parallel light;

2-6, vertically placing a third quarter-wave plate (16) in the propagation direction of the first transmitted light (17) and the second transmitted light (18) after passing through the second convex lens (15), and adjusting the optical axis direction of the third quarter-wave plate (16) to ensure that the first transmitted light (17) and the second transmitted light (18) are simultaneously converted into linearly polarized light;

preferably, the position of the first convex lens (13) is adjusted so that the overlapping portion covers the entire atomic gas cell;

step (3), adjusting the detection system (3):

3-1, adjusting the position of a second collimating lens (19) to enable the first transmitted light (17) and the second transmitted light (18) which pass through a third quarter-wave plate (16) to enter a multimode fiber (20), and enabling the light intensity value of laser emitted by a second fiber coupler (21) to be maximum;

3-2, adjusting the position of the photoelectric detector (22) so that the photoelectric detector (22) receives the laser light emitted by all the second optical fiber couplers (21) and converts the light intensity signal into an electric signal.

Preferably, the laser wavelength emitted by the semiconductor laser (4) is within the wavelength range of an optical isolator, a half-wave plate, a lateral displacement beam splitter prism, a first quarter-wave plate, a third quarter-wave plate, a collimating lens, a first convex lens, a second convex lens and a first optical fiber coupler, a second optical fiber coupler.

In the step (2), the laser emitted by the first collimating lens (9) can use Jones vector in any polarization stateIs shown as

Wherein E is_0xAmplitude of projection of the laser as an electric field component of the electromagnetic wave on the x-axis, δ_xPhase of projection of the electric field component on the x-axis, E_0yAmplitude of projection of the laser as an electric field component of the electromagnetic wave on the y-axis, δ_yThe phase of the projection of the electric field component on the y-axis is shown, e is a natural constant, j represents an imaginary number, and the plane formed by the x-axis and the y-axis is perpendicular to the propagation direction of the laser. Its total light intensity I₀Can be expressed as:

laser emitted by the first collimating lens (9) is divided into first transmission light (17) and second transmission light (18) which are mutually vertical in polarization after passing through the lateral displacement beam splitter prism (10), and the first transmission light (17 Jones vector) after passing through the first quarter-wave plate (11) isAnd the second transmission light (18) Jones vector after passing through the second quarter wave plate (12)Are respectively represented as

Therefore, the light intensity I of the first transmitted light (17) after passing through the first quarter-wave plate (11)₁And the light intensity I of the second transmission light (18) after passing through the second quarter-wave plate (12)₂Can be respectively represented as

When the first transmission light (17) and the second transmission light (18) are overlapped at the atom gas chamber (14) through the first convex lens (13), the total light intensity I of the laser in the atom gas chamber (14)₃Can be expressed as

According to the expressions (3) and (4), since the first transmitted light (17) and the second transmitted light (18) are constantly circularly polarized light in the same polarization state at the atomic gas cell (14), the polarization of the laser light at the atomic gas cell (14) is stable regardless of the polarization state of the laser light emitted from the first collimating lens (9).

From the formulas (2) and (7), the total intensity I of the laser light in the atomic cell (14) can be found₃Identity, etcThe total light intensity I of the laser emitted from the first collimating lens (9)₀Therefore, the laser power at the atomic gas chamber (14) is stable no matter what polarization state the laser emitted by the first collimating lens (9) is.

The invention also aims to provide a magnetic field measuring method, which adopts the optical fiber type atomic magnetometer probe to obtain the larmor precession signal of atoms under a magnetic field to be measured so as to obtain the size of the magnetic field to be measured.

The invention has the beneficial effects that: the method is simple to operate, and only three parts of a laser light source, an atom sensing system and a detection system in a probe structure need to be operated; and secondly, the realization cost is low, the environmental adaptability is strong, and the laser power and polarization stability entering the atomic gas chamber can be realized without a high-performance single-mode optical fiber in a complex environment or a changing environment.

Drawings

FIG. 1 is a schematic flow diagram of the present invention;

FIG. 2 is a detailed flow diagram of the present invention;

FIG. 3 is a graph showing the experimental results of laser polarization under the condition of temperature change of the optical fiber according to the present invention;

FIG. 4 is a graph showing the experimental results of laser polarization under fiber vibration conditions in accordance with the present invention;

FIG. 5 is a graph showing experimental results of laser power and polarization entering an atomic gas cell under the polarization rotation condition of the exiting laser;

FIG. 6 is a graph showing the experimental results of the atomic magnetometer measuring noise under the fiber vibration condition according to the present invention.

Detailed Description

The invention is further analyzed with reference to the following figures.

The laser transmitted and emitted by the optical fiber is decomposed into two linearly polarized lights with mutually vertical polarization by the lateral displacement beam splitter prism, and after passing through the quarter-wave plates with two vertical optical axes, the two linearly polarized lights are converted into circularly polarized lights with the same polarization and are subjected to the diverging action of the convex lens, so that the propagation paths of the two circularly polarized lights are overlapped when the two circularly polarized lights enter the atom air chamber. When the polarization of the laser transmitted and emitted by the optical fiber is influenced by the optical fiber to change, the light intensity of the two linearly polarized light beams decomposed by the lateral displacement beam splitter prism can change, but the polarization of the two linearly polarized light beams is stable and the total light intensity can not change, so that after the two linearly polarized light beams are converted into circularly polarized light with the same polarization through the two quarter-wave plates, the two laser beams form laser with stable polarization and stable total light intensity at the atom air chamber through the divergence effect of the convex lens. The device and the method can reduce the requirement of the fiber type atomic magnetometer on the performance of the single-mode fiber, ensure the power and polarization stability of the laser entering the atomic gas chamber under the condition of reducing the cost, and further ensure that the performance of the atomic magnetometer is not influenced by the conduction characteristic of the fiber on the polarization of the laser.

As shown in fig. 1, the probe structure includes a laser light source 1, an atom sensing system 2, and a detection system 3; the laser light source 1, the atom sensing system 2 and the detection system 3 are connected in sequence through a laser light path;

as shown in fig. 2, the laser light source 1 is composed of a semiconductor laser 4, an optical isolator 5, a half-wave plate 6, a first fiber coupler 7, a single-mode fiber 8 and a first collimating lens 9;

the semiconductor laser 4 emits laser, and the laser enters a single mode fiber 8 from a first fiber coupler 7 after sequentially passing through an optical isolator 5 and a half wave plate 6;

one end of the single mode fiber 8 is connected with the first fiber coupler 7 through an FC/APC interface, the other end of the single mode fiber is glued with the first collimating lens 9 through optical cement, and laser enters the single mode fiber 8 from the first fiber coupler 7 and exits from the first collimating lens 9;

the atom sensing system 2 consists of a lateral displacement beam splitter prism 10, a first quarter wave plate 11, a second quarter wave plate 12, a first convex lens 13, an atom air chamber 14, a second convex lens 15 and a third quarter wave plate 16;

laser emitted by the first collimating lens 9 is divided into first transmitted light 17 and second transmitted light 18 after passing through the lateral displacement beam splitter prism 10, the propagation directions of the first transmitted light 17 and the second transmitted light 18 are parallel, and the distance between the first transmitted light 17 and the second transmitted light 18 is not more than 2 cm;

the first transmission light 17 is converted into circularly polarized light after passing through the first quarter-wave plate 11, and the second transmission light 18 is converted into circularly polarized light with the same polarization as the first transmission light 17 after passing through the second quarter-wave plate 12;

the first transmitted light 17 and the second transmitted light 18 pass through the first convex lens 13 at the same time, both of which are converted from parallel light into divergent light and the propagation paths overlap and the propagation directions are the same;

the atomic gas cell 14 is located at a position where the first transmitted light 17 and the second transmitted light 18 travel paths overlap;

the atomic gas cell 14 is composed of a glass bubble containing an alkali metal saturated vapor and a buffer gas;

the first transmitted light 17 and the second transmitted light 18 passing through the atomic gas cell 14 simultaneously transmit through the second convex lens 15, both of which are converted from divergent light into parallel light, and then both of which are converted into linearly polarized light with the same polarization through the third quarter-wave plate 16;

the detection system 3 is composed of a second collimating lens 19, a multimode optical fiber 20, a second optical fiber coupler 21 and a photoelectric detector 22;

one end of the multimode fiber 20 is glued with the second collimating lens 19 through optical cement, and the other end is connected with the second fiber coupler 21 through an FC/APC interface;

the linearly polarized light transmitted by the third quarter-wave plate 16 enters the multimode fiber 20 through the second collimating lens 19 and exits from the second fiber coupler 21;

the laser light emitted from the second fiber coupler 21 is detected in its entire intensity by the photodetector 22 and converted into an electric signal.

The method for improving the environmental adaptability of the optical fiber type atomic magnetometer by specifically adjusting the probe structure comprises the following steps:

in the embodiment, the semiconductor laser 4 is a DBR laser, the alkali metal atoms in the atomic gas cell 14 are cesium-133 atoms, and the size of the glass bubble of the saturated vapor of cesium atoms is Φ 25 × 25 mm. In the use process, the semiconductor laser 4 is started, and an optical isolator 5 with the applicable wavelength range including 894nm, a half-wave plate 6 and a first optical fiber coupler 7 are sequentially arranged, wherein the optical isolator 5 is a free optical isolator with the model number of IO-5-940-HP manufactured by Thorlab of America, and the first optical fiber coupler 7 is an optical fiber coupler with the model number of PAF2-A4B manufactured by Thorlab of America. One end of the single-mode fiber 8 is connected with the first fiber coupler 7 by adopting an FC/APC interface, and the other end of the single-mode fiber is glued with the first collimating lens 9 to form a nonmagnetic collimating structure. The optical axis angle of the half wave plate 6 is adjusted, so that the laser intensity output by the first collimating lens 9 reaches a maximum value of about 1.7 mW. The lateral displacement beam splitter prism 10 is vertically arranged in the propagation direction of the laser beam emitted by the first collimating lens 9, and the position of the lateral displacement beam splitter prism 10 is adjusted so that the first transmitted light 17 and the second transmitted light 18 are generated in parallel in the propagation direction and are spaced by about 8 mm. The first quarter-wave plate 11 and the second quarter-wave plate 12 with the applicable wavelength range of 894nm are respectively placed in the transmission directions of the first transmission light 17 and the second transmission light 18, the included angle between the optical axis of the first quarter-wave plate 11 and the polarization direction of the first transmission light 17 is adjusted to be 45 degrees, so that the first transmission light 17 is changed into left-handed circularly polarized light after passing through the first quarter-wave plate 11, the included angle between the optical axis of the second quarter-wave plate 12 and the polarization direction of the second transmission light 18 is adjusted to be 45 degrees, so that the second transmission light 18 is also changed into left-handed circularly polarized light after passing through the second quarter-wave plate 12, and the included angle between the optical axis of the first quarter-wave plate 11 and the optical axis of the second quarter-wave plate 12 is 90 degrees. The first convex lens 13 is placed in the propagation direction of the first transmitted light 17 and the second transmitted light 18, the first transmitted light 17 and the second transmitted light 18 are overlapped in the propagation path near the focus through the convergence action of the first convex lens 13, and the glass bubble of cesium atom saturated steam is placed near the focus. The second convex lens 15 is placed on the propagation paths of the first transmitted light 17 and the second transmitted light 18 after passing through the glass bubble of cesium atom saturated vapor, and the position of the second convex lens 15 is adjusted so that the focal point of the second convex lens 15 coincides with the focal point of the first convex lens 13. The third quarter wave plate 16 is placed and the direction of the optical axis thereof is adjusted so that the first transmitted light 17 passing through the third quarter wave plate 16 is converted from left-handed circularly polarized light to linearly polarized light of the same polarization as the second transmitted light 18. One end of the multimode optical fiber 20 is connected with a second optical fiber coupler 21 by adopting an FC/APC interface through a customization mode, and the other end of the multimode optical fiber is glued with a second collimating lens 19 to form a nonmagnetic collimating structure, wherein the second optical fiber coupler 21 is the same type product as the first optical fiber coupler 7. The position of the second collimator lens 19 is adjusted so that the intensity of the laser light emitted from the second fiber coupler 21 is 500uW at maximum. The laser light emitted from the second fiber coupler 21 is detected by a photodetector 22 and converted into an electrical signal, wherein the photodetector 22 is a 2107 photodetector manufactured by Newport corporation of america.

The above-mentioned glass bubbles of cesium atom saturated vapor are atomic gas cells 14.

As shown in fig. 3, the method of the present invention is used to determine the relationship between the fiber temperature (abscissa) and the ellipsometry of the laser entering the atomic gas cell (left ordinate), and the ellipsometry of the laser emitted from the first collimating lens 9 (right ordinate) under the condition of the fiber temperature variation.

The above relationship is that when the temperature of the optical fiber changes from 20 ℃ to 70 ℃, the ellipsometry of the laser emitted from the first collimating lens 9 changes by about 4.5 °, and the ellipsometry of the laser entering the atomic gas cell changes by less than 0.1 °.

The above relationship shows that although the laser ellipsometry emitted from the optical fiber changes with the temperature of the optical fiber after the method of the present invention is performed, the laser ellipsometry entering the atomic gas chamber is not substantially affected by the temperature change of the optical fiber.

As shown in fig. 4, under the condition of fiber vibration (vibration frequency 1Hz), the vibration time (abscissa) is related to the ellipsometry (left ordinate) of the laser entering the atomic gas cell and the ellipsometry (right ordinate) of the laser emitted from the first collimating lens 9 by the method of the present invention.

The above relationship is that under the vibration condition, the ellipsometry change of the laser emitted from the first collimating lens 9 exceeds 4.5 °, but the ellipsometry change of the laser entering the atomic gas cell is less than 1 °.

The above relationship shows that although the laser ellipsometry emitted from the optical fiber changes with the vibration of the optical fiber after the method of the present invention is performed, the laser ellipsometry entering the atomic gas chamber is less affected by the vibration change of the optical fiber.

As shown in fig. 5, by the method of the present invention, under the condition that the polarization angle of the laser emitted from the first collimating lens 9 is changed due to the transmission characteristics of the optical fiber, the relationship between the change of the included angle (abscissa) of the polarization of the laser emitted from the first collimating lens 9, the ellipsometry (left ordinate) of the laser entering the atomic gas cell, and the power (right ordinate) of the laser entering the atomic gas cell is obtained.

The above relationship is that the included angle of the polarization of the laser emitted from the first collimating lens 9 is within the range of 45-135 degrees, the elliptical polarization rate of the laser entering the atomic gas cell changes by less than 0.1 degree, and the power of the laser entering the atomic gas cell changes by less than 1 percent.

The above relationship shows that the ellipsometry and the optical power of the laser entering the atomic gas chamber are less affected by the change of the polarization angle of the laser emitted from the first collimating lens 9 after the method of the present invention.

As shown in fig. 6, the optical fiber type atomic magnetometer realized by the method of the present invention has a noise power spectrum represented by a noise frequency (abscissa) and a noise level (ordinate) under the condition of the vibration of the optical fiber (vibration frequency 1 Hz).

The above results show that the atomic magnetometer noise level before and during vibration is unchanged.

The results show that the measuring noise of the atomic magnetometer is not influenced by the vibration of the optical fiber after the method is adopted.