An atomic sensor optical system based on freeform total internal reflection

Abstract

The application provides an atomic sensor optical system based on free-form surface total reflection, overcomes the defects caused by the fact that a traditional optical path structure is composed of multiple optical elements, designs a free-form surface lens as a single element to complete collimation, beam expansion and reflection of a laser beam, realizes simplification of an optical path structure, improves system stability, and is beneficial to reducing optical power attenuation in the optical path and suppressing fluctuations possibly caused by optical devices.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of optical system design of atomic sensor, and particularly relates to an atomic sensor optical system based on free-form surface total reflection, which is used for laser beam shaping of a miniaturized nuclear magnetic resonance gyro inertial measurement device. BACKGROUND

[0002] As an atomic sensor, a nuclear magnetic resonance gyroscope (NMRG) integrates various core components such as light, electricity, magnetism and heat. With the application demand of chip-based atomic sensors, the NMRG has a development trend of high precision, miniaturization and low cost. In particular, for the key technology of miniaturization of the NMRG, on the one hand, the core device needs to be miniaturized while ensuring performance, and on the other hand, the modules need to be modularized to improve system stability, reduce assembly and adjustment difficulty, and be suitable for small packaging.

[0003] The optical path module is a key component for realizing atomic polarization and laser detection of the miniaturized NMRG. Therefore, the miniaturization and integration of the optical path module are important factors affecting the volume reduction of the atomic sensor, and also put forward higher requirements for the selection of optical devices and the design of optical path structure.

[0004] At present, the optical path of the miniaturized NMRG prototype often includes a laser, a collimating and expanding lens, a mirror, a polarization device and a photodetector.

[0005] Among them, the laser provides the light source for atomic polarization and signal detection. From the mechanism, the optical path module can be divided into pumping light path and detection light path. The pumping light path polarizes alkali metal atoms, and the alkali metal atoms exchange spins with inert atomic nuclei. The detection light path detects the Larmor precession frequency of the inert atomic nuclei in the magnetic field and the carrier rotation angular velocity. Since the unshaped laser has a certain divergence angle, parallel light with a certain spot size needs to be obtained through collimation and expansion to ensure a certain atomic polarization rate and polarization uniformity, so as to suppress the NMRG error and improve the zero bias stability.

[0006] According to the relative position of the laser and the atomic cell, the optical path mainly has two forms, direct introduction and reflection introduction. In the existing optical path, the laser of the pumping light path passes through the collimating and expanding integrated packaging lens, and then passes through the quarter-wave plate to complete the circular polarization of the light beam and then enters the cell to polarize the atoms. The laser of the detection light path passes through the collimating and expanding integrated packaging lens, and then passes through the mirror to turn the light path and then enters the cell for detection.

[0007] In order to realize miniaturization and integration of the optical path module, it is necessary to simplify the optical path structure and integrate the optical path components, which also helps to reduce the optical power attenuation in the optical path and suppress the fluctuation caused by the optical devices.

[0008] The free-form surface has relatively large freedom and flexibility, and using the free-form surface as the surface of the lens or the reflecting surface can greatly improve the system performance, achieve the purposes of reducing the volume of the optical path, folding the optical path, and changing the path of the optical path. Therefore, based on the demand for miniaturization and integration of the optical path module, the free-form surface is used as the surface of the lens or the reflecting surface to design the optical system of the atomic sensor, the laser beam is expanded, collimated and reflected through a single optical component, the difficulty of assembling and adjusting the atomic sensor is reduced, the optical path structure is simplified, and the number of optical devices is reduced to reduce the optical power loss and suppress the optical fluctuation. SUMMARY

[0009] In the application demand of the chip atomic sensor, the present application provides an atomic sensor optical system based on free-form surface total reflection to overcome the defects caused by the traditional optical path structure composed of multiple optical components, realize the simplification of the optical path structure, improve the system stability, and is beneficial to reduce the optical power attenuation in the optical path and suppress the fluctuation caused by the optical devices.

[0010] The technical solution of the present application is as follows:

[0011] An atomic sensor optical system based on free-form surface total reflection, characterized in that it comprises a single device free-form lens for collimating, expanding and reflecting a laser beam, the free-form lens has a first surface with a cylindrical surface type as a laser beam input surface, a second surface with a parabolic surface type as a laser beam reflecting surface, and a third surface with a planar surface type as a laser beam output surface, the third surface forms the upper side of the lens body, the first surface forms the left side of the lens body, and the bottom edge of the left side is connected to the right edge of the upper side through the second surface.

[0012] The laser beam comes from a laser, and the divergence angle of the outgoing light of the laser makes the laser beam form a first spot on the first surface, the first spot forms a second spot with a larger area than the first spot on the second surface, the second spot is reflected to the third surface to form a parallel outgoing light beam reaching the target spot size, and the parallel outgoing light beam is perpendicular to the third surface.

[0013] The first surface and the third surface are both provided with an anti-reflection film, and the anti-reflection film of the third surface is provided with a half-wave plate.

[0014] The third surface is provided with an air chamber above, and the laser beam of the third surface exits through the laser beam incidence surface of the air chamber.

[0015] The light source emission point of the laser beam is located between the cylindrical surface and the symmetry axis of the parabolic surface, and the central axis of the cylindrical surface coincides with the symmetry axis of the parabolic surface.

[0016] Supposing that the focal distance of the parabolic surface is P, the vertical axis Y is the symmetry axis of the parabolic surface, the horizontal axis X is the transverse axis, the longitudinal axis is the Z axis, and the intersection of the symmetry axis and the parabolic surface is the origin O, the parabolic surface satisfies x 2 +z 2 =2Py; the intersection of the optical axis and the Y axis in the XOY plane is (0, P / 2), and the intersection of the optical axis and the parabolic surface is (P, P / 2).

[0017] The optical design method is used to simulate the light path of the laser exit light through the free-form surface lens to determine the parameters of the free-form surface lens.

[0018] The spot radius, beam divergence angle and exit light power decay rate of the light spot after full reflection through the free-form surface lens are set as optimization targets, the distance between the laser and the free-form surface lens is adjusted, and the curvature radii of the first cylindrical surface and the second parabolic surface of the free-form surface lens are optimized, so that the simulated light beam after passing through the three surfaces of the free-form surface lens reaches the target spot size, and a certain collimation and light power size are ensured.

[0019] The technical effects of the present application are as follows: the atomic sensor optical system based on free-form surface full reflection adopts a free-form surface lens as a single optical device to complete the collimation, expansion and reflection of the laser beam, reduces the number of optical elements, reduces the complexity of the optical path, helps to reduce the optical power decay in the optical path and suppress the fluctuations caused by the optical device. At the same time, the use of a single element simplifies the equipment installation difficulty, the free-form surface lens exit surface is glued with a half-wave plate, which helps to construct and adjust the optical path, improves the system stability, and provides a new scheme for simplifying the optical path.

[0020] The present application has the following characteristics: (1) the present application adopts a free-form surface lens as a single optical device to collimate, expand and reflect the laser beam, and the free-form surface lens design has high flexibility, which can complete the shaping of the laser beam on the basis of a single element, and has obvious advantages in reducing the volume and simplifying the structure of the optical path of a small nuclear magnetic resonance gyroscope. (2) The present application effectively reduces the number of optical elements, reduces the difficulty of optical path construction and adjustment, and improves the system stability. (3) The present application can help to reduce the optical power decay in the optical path and suppress the fluctuations caused by the optical device. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 is a schematic diagram of an optical system structure of an atomic sensor based on free-form surface total reflection according to the present application.

[0022] Figure 2 is Figure 1 a schematic diagram of a free-form surface lens structure. Figure 2 In the free-form surface lens structure, the origin O is the intersection of the parabolic axis of symmetry and the parabolic surface, i.e. the y-axis,

[0023] Figure 3 is Figure 1 a schematic diagram of a free-form surface lens model.

[0024] Figure 4 is a schematic diagram of an optical path model based on free-form surface total reflection.

[0025] The reference signs are listed as follows: 1-laser; 2-optical axis; 3-gas chamber; 4-free-form surface lens; 5-anti-reflection coating; 6-second surface (located at the lower right side, the surface type is parabolic, the laser beam reflection surface); 7-first surface (located at the left side, the surface type is cylindrical, the laser beam input surface); 8-third surface (located at the upper side, the surface type is planar, the laser beam output surface); 9-1 / 2 wave plate; (0, P / 2)-parabolic focal point; (P, P / 2)-coordinates of the intersection of the optical axis and the parabola; P-parabolic focal distance. DETAILED DESCRIPTION

[0026] The present application will be described below in conjunction with the accompanying drawings Figures 1-4 and examples.

[0027] Figure 1 is a schematic diagram of an optical system structure of an atomic sensor based on free-form surface total reflection according to the present application. Figure 2 is Figure 1 a schematic diagram of a free-form surface lens structure. Figure 3 is Figure 1 a schematic diagram of a free-form surface lens model. Figure 4 is a schematic diagram of an optical path model based on free-form surface total reflection. Referring to Figures 1 to 4 Fig. 5, an atomic sensor optical system based on free-form surface total reflection includes a single device free-form surface lens 4 for collimating, expanding and reflecting a laser beam, the free-form surface lens 4 having a first surface 7 with a cylindrical surface type as a laser beam input surface, a second surface 6 with a parabolic surface type as a laser beam reflection surface, and a third surface 8 with a planar surface type as a laser beam output surface, the third surface 8 forming the upper side of the lens body, the first surface 7 forming the left side of the lens body, and the bottom edge of the left side being connected to the right edge of the upper side through the second surface 6.

[0028] The laser beam comes from a laser 1, the exit light divergence angle of the laser 1 is such that the laser beam forms a first light spot on the first surface 7, the first light spot forms a second light spot on the second surface 6, the second light spot is larger than the first light spot in area, the second light spot is reflected to the third surface 8 to form a parallel exit light beam reaching a target light spot size, and the parallel exit light beam is perpendicular to the third surface 8. The first surface 7 and the third surface 8 are both provided with an anti-reflection film 5, and the anti-reflection film 5 of the third surface 8 is provided with a half-wave plate 9.

[0029] The third surface 8 is provided with an air chamber 3, and the exit light beam of the third surface 8 enters the air chamber 3 through the laser beam incidence surface of the air chamber 3. The light source emission point of the laser beam is located between the cylindrical surface and the symmetry axis of the parabolic surface, and the central axis of the cylindrical surface coincides with the symmetry axis of the parabolic surface.

[0030] Supposing that the focal length of the parabolic surface is P, the symmetry axis of the parabolic surface is the vertical axis Y axis, the horizontal axis is the X axis, the longitudinal axis is the Z axis, and the intersection of the symmetry axis and the parabolic surface is the origin O, the parabolic surface satisfies x 2 +z 2 =2Py; the intersection of the optical axis and the Y axis in the XOY plane is (0, P / 2), and the intersection of the optical axis and the parabolic surface is (P, P / 2). The optical design method is used to simulate the light path of the laser exit light through the free-form surface lens to determine the parameters of the free-form surface lens. The spot radius, beam divergence angle and exit light power decay rate after total reflection of the free-form surface lens are set as the optimization targets, the distance between the laser and the free-form surface lens is adjusted, and the curvature radii of the first cylindrical surface and the second parabolic surface of the free-form surface lens are optimized, so that the simulated light beam reaches the target spot size after passing through the three surfaces of the free-form surface lens, and a certain collimation and light power size are ensured.

[0031] The application provides an atomic sensor optical system based on free-form surface total reflection, which comprises a laser, a free-form surface lens and a half-wave plate, and forms an atomic chamber detection light path. The free-form surface lens comprises a first surface 7 (or S1) with a cylindrical surface, a second surface 6 (or S2) with a parabolic surface, and a third surface 8 (or S3) with a plane. After a distance of propagation, the laser beam passes through the first surface, the second surface and the third surface of the free-form surface lens in sequence to form a parallel exit light beam reaching a target radius. The first surface and the third surface of the free-form surface lens are both coated with an anti-reflection film. Referring to the attached drawings, Figure 1 .

[0032] The divergence angle of the exit light of the used laser is determined, and the target light spot size and the target light power required by the laser beam reaching the surface of the atomic chamber are determined according to the detection requirements of the sensor.

[0033] The laser is operated at the operating current and temperature required for miniaturized nuclear magnetic resonance gyroscope detection. Assume that the divergence angle of the emitted light is θ and the target spot radius reaching the air chamber surface is r. An off-axis parabola is used as the surface of the free-form lens, the second surface where the laser total internal reflection occurs. The propagation of the laser light in the air-lens material is considered in a plane perpendicular to the optical axis.

[0034] The refractive index of the material used for the free-form surface lens is assumed to be n1, and the refractive index of air is n0. The optical axis of the laser beam is perpendicular to the first surface S1 of the free-form surface lens. The laser beam converges to a certain extent on the first surface of the lens. According to the target spot size, the parabolic focal length P required to obtain the target spot size under the known laser output light divergence angle is designed, and the total reflection surface is designed.

[0035] Assume that the incident angle of the light on the first surface S1 of the free-form surface lens is θ0, and the refraction angle is θ1; the incident angle on the second surface S2 of the lens is θ2, and the refraction angle is θ3.

[0036] The parabola's symmetry axis is the Y axis, and the intersection of the symmetry axis and the parabola is the origin. Figure 2 Establish a coordinate system.

[0037] In the vertical plane including the optical axis, the angle between the edge of the laser beam and the optical axis is half of the divergence angle, that is, According to Snell's law of refraction,

[0038] n0sinθ0=n1sinθ1 (1)

[0039] The exit angle θ1 on the first surface of the lens is calculated as,

[0040]

[0041] The equation of a parabola can be expressed as:

[0042] x 2 +z 2 =2Py (3)

[0043] Assuming that the straight line where the laser optical axis is located passes through the focus of the parabola (0, P / 2) and is perpendicular to the axis of symmetry of the parabola, the coordinates of the intersection of the optical axis light and the parabola are (P, P / 2), and after reflection, the light is emitted parallel to the axis of symmetry of the parabola.

[0044] In the XOY plane, the optical path lengths of the upper and lower edge rays of the beam are:

[0045]

[0046]

[0047] Right now

[0048]

[0049]

[0050] Two straight lines intersect with parabola x 2 = 2Py to find intersection points (x 11 , y 11 ) and (x 22 , y 22 ),

[0051]

[0052]

[0053] The diameter of the exit spot is:

[0054] |x 11 -x 22 | = 2Ptanθ1 (10)

[0055] The diameter of the exit spot is required to reach the target spot size 2r, i.e. |x 11 -x 22 | = 2r, the required parabolic focal distance P is:

[0056]

[0057] At the second surface of the free-form lens, the outgoing light is required to be longitudinally parallel, i.e. the slope of the outgoing light is 0, the slope of the parabolic segment from (x 11 , y 11 ) to (x 22 , y 22 ) ranges from and the slope of the corresponding normal ranges from

[0058] Therefore, the range of the incident angle θ2 at the second surface of the free-form lens is

[0059] According to Snell's law, when light is incident from a denser medium to a rarer medium, total reflection can occur, i.e. θ3 = 90°, at this time the incident critical angle θ c needs to satisfy the following formula:

[0060] n1sinθ c = n0sinθ3 (12)

[0061] Then:

[0062] ​

[0063] That is, the second surface of the free-form lens is required to have an exit light ray with an incident angle θ2≥θ c .

[0064] In order to ensure that all the light rays can satisfy the total reflection condition, the first surface of the free-form lens preferably uses a cylindrical surface type, and the first surface cylinder and the off-axis parabolic surface use the same rotational symmetry axis as an adjustment mode to flexibly ensure that the light rays can be totally reflected.

[0065] The free-form lens model is drawn according to the designed parabolic focal distance. Referring to the attached Figure 3 .

[0066] An optical design method is used to simulate the light path of the laser exit light through the free-form lens. Rectangular detectors are used to monitor the spot quality of the laser before the first surface of the lens, after the second surface of the lens, and after the third surface of the lens. Two rectangular detectors with a certain longitudinal distance are used to monitor the spot quality of the exit light. Referring to the attached Figure 4 .

[0067] The spot radius, beam divergence angle, and power attenuation rate of the light after total reflection and exit through the free-form lens are set as optimization targets, the distance between the laser and the free-form lens is adjusted, and the curvature radii of the first surface cylinder S1 and the second surface parabolic surface S2 of the free-form lens are optimized, so that the simulated light beam after passing through the three surfaces of the free-form lens reaches the target spot size, and a certain collimation and light power size are ensured.

[0068] The divergence angle of the laser exit light is determined, and the required target spot size and target light power of the laser beam reaching the surface of the atomic cell are determined.

[0069] The off-axis parabolic surface is used as the surface type of the second surface of the free-form lens where total reflection of the laser occurs. In the vertical plane containing the optical axis, the surface curvature of the first surface of the free-form lens is initially considered to be 0, the laser beam is focused on the first surface of the lens, and then totally reflected on the second parabolic surface. According to the target spot size, the parabolic focal distance required to obtain the target spot size under the condition of a known laser exit light divergence angle is designed.

[0070] In order to ensure that all the light rays can satisfy the total reflection condition, the first surface of the free-form lens uses a cylindrical surface type, and the first surface cylinder and the off-axis parabolic surface use the same rotational symmetry axis as an adjustment mode to flexibly ensure that the light rays can be totally reflected, and the free-form lens model is drawn according to the designed parabolic focal distance.

[0071] An optical design method is used to simulate the light path of the laser exit light through the free-form lens.

[0072] The spot radius, beam divergence angle and output light power decay rate of the light spot after total reflection and emission of the free-form lens are set as optimization targets, the distance between the laser and the free-form lens is adjusted, and the curvature radii of the first cylindrical surface S1 and the second parabolic surface S2 of the free-form lens are optimized, so that the simulated light beam after passing through the three surfaces of the free-form lens reaches the target spot size, and a certain collimation and light power size are ensured;

[0073] The first surface and the third surface of the free-form lens are optimized to be coated with an antireflection film, and a half-wave plate is glued to the surface of the third surface, and the polarization direction of the laser is adjusted to obtain the required detection light beam.

[0074] The contents not described in detail in the specification of the present application belong to the prior art known to those skilled in the art. It is pointed out that the above description is helpful for those skilled in the art to understand the present application, but does not limit the protection scope of the present application. Any implementation of equivalent replacement, modification, improvement and / or deletion of the above description without departing from the essential content of the present application falls within the protection scope of the present application.

Claims

1. An atomic sensor optical system based on total reflection on a free-form surface, characterized in that: A single-device free-form surface lens for collimating, expanding, and reflecting a laser beam, the free-form surface lens having a first cylindrical surface serving as a laser beam input surface, a second parabolic surface serving as a laser beam reflection surface, and a third planar surface serving as a laser beam output surface, the third surface forming an upper side surface of the lens body, the first surface forming a left side surface of the lens body, and the bottom edge of the left side surface connected to the right side of the upper side surface via the second surface; The laser beam comes from a laser, and the divergence angle of the laser's output light causes the laser beam to form a first light spot on the first surface, the first light spot forms a second light spot with a larger area than the first light spot on the second surface, and the second light spot is reflected to the third surface to form a parallel output light beam reaching a target light spot size, and the parallel output light beam is perpendicular to the third surface.

2. The atomic sensor optical system based on free-form surface total reflection according to claim 1, characterized in that: Both the first surface and the third surface are provided with anti-reflection films, and a half-wave plate is provided on the anti-reflection film of the third surface.

3. The atomic sensor optical system based on free-form surface total reflection according to claim 1, characterized in that: An air chamber is provided above the third surface, and the outgoing light beam from the third surface enters the air chamber through the laser beam incident surface of the air chamber.

4. The atomic sensor optical system based on free-form surface total reflection according to claim 1, characterized in that: The light source emission point of the laser beam is located between the cylinder and the symmetry axis of the parabola, and the central axis of the cylinder coincides with the symmetry axis of the parabola.

5. The atomic sensor optical system based on free-form surface total reflection according to claim 1, characterized in that: Assume that the focal length of the parabola is P, the symmetry axis of the parabola is the vertical axis Y, the horizontal axis is X, the vertical axis is Z, and the intersection of the symmetry axis and the parabola is the origin O. Then the parabola satisfies x 2 +z 2 =2Py; in the XOY plane, the intersection of the optical axis and the Y axis is (0, P / 2), and the intersection of the optical axis and the parabola is (P, P / 2).

6. The atomic sensor optical system based on free-form surface total reflection according to claim 1, characterized in that: An optical design method is used to simulate the optical path of the laser output light passing through the free-form surface lens to determine the parameters of the free-form surface lens.

7. The atomic sensor optical system based on free-form surface total reflection according to claim 1, characterized in that: The spot radius, beam divergence angle, and output light power attenuation rate after total reflection from the free-form surface lens are set as optimization targets. The distance between the laser and the free-form surface lens is adjusted, and the curvature radii of the first cylindrical surface and the second parabolic surface of the free-form surface lens are optimized so that the simulated light beam reaches the target spot size after passing through the three surfaces of the free-form surface lens, and a certain collimation and optical power are guaranteed.

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