IMU (Inertial Measurement Unit) light path structure based on multiple metasurfaces

Abstract

The invention discloses an IMU (Inertial Measurement Unit) light path structure based on a metasurface, which is characterized in that a light beam generated by a laser 1 is divided into three mutually vertical light beams under the action of a beam splitting metasurface 3, and then is converted into circularly polarized light and linearly polarized light through a polarization conversion beam splitting metasurface 4, and the circularly polarized light and the linearly polarized light are respectively used for pumping and detecting a nuclear magnetic resonance gyroscope 6. The beam splitting metasurface 3 is composed of polarization-insensitive cylindrical nanorods, and incident light is split and generates corresponding deflection in combination with the generalized Snell law. The polarization conversion beam splitting metasurface 4 is composed of a polarization-sensitive rectangular nano-column and a polarization-insensitive cylindrical nano-column, the rectangular nano-column is used for converting linearly polarized light into circularly polarized light, and the cylindrical nano-column keeps the linear polarization characteristic and achieves beam splitting and direction adjustment. According to the invention, single laser configuration is adopted, efficient light field regulation and control are realized based on the metasurface, the problem that a traditional IMU light path system depends on a plurality of lasers is avoided, the system size, complexity and energy consumption are reduced, the stability and the integration degree are improved, and the system is suitable for high-precision inertial navigation application.

Description

Technical Field

[0001] The present invention relates to the technical field of inertial measurement units (IMUs), and particularly to an IMU optical path structure based on multiple metasurfaces. Background Art

[0002] In the technology of inertial measurement units (IMUs), nuclear magnetic resonance gyroscopes (NMRGs) play an important role in high-precision inertial navigation fields such as aerospace and marine navigation due to their advantages of high precision and high stability. However, existing NMRG IMU optical path systems usually rely on a large number of discrete optical elements, such as prisms, lenses, mirrors, etc. These optical elements are numerous and large in size, resulting in a large overall size and complex structure of the optical path system, which affects the integration level. At the same time, the assembly and calibration processes of discrete optical elements are prone to introducing errors, thus reducing the stability and reliability of the system. In addition, traditional IMU optical path systems often rely on multiple lasers to work together, which not only increases the system energy consumption but also is not conducive to miniaturized integration.

[0003] In recent years, with the progress of material science and optical technology, metasurface technology provides a new technical path to solve the above problems. A metasurface is a two-dimensional planar material composed of sub-wavelength-scale artificial microstructures, which can precisely control the phase, amplitude, and polarization characteristics of light. Using metasurface technology, high-degree integration of optical functions can be achieved, thereby reducing the use of discrete optical elements and decreasing the system volume and complexity. In addition, the high-efficiency light field control ability of metasurfaces enables the reduction of the number of lasers used in some application scenarios, and even realizes the optical path configuration of a single laser, thus reducing the system power consumption and improving the stability. Therefore, the NMRG IMU optical path structure based on metasurface technology has broad application prospects in miniaturization, integration, and high performance. Summary of the Invention

[0004] Aiming at the problems of existing IMU optical path systems, such as many lasers, low integration level, and many optical elements, the present invention proposes an IMU optical path structure based on multiple metasurfaces.

[0005] The present invention adopts the following technical solution: An NMRG IMU optical path structure based on a metasurface, comprising 1 laser, 1 beam-splitting metasurface, 3 polarization conversion beam-splitting metasurfaces, and 3 nuclear magnetic resonance gyroscopes.

[0006] In the solution, the working wavelength λ0 of the laser is 795 nm.

[0007] In this solution, the beam-splitting metasurface includes a glass substrate and Si nanocolumns, and the Si nanocolumns with beam-splitting effect are placed on the glass substrate, and their heights are all 600 nm.

[0008] In the solution, the splitting metasurface satisfies the generalized Snell's law of refraction: In the formula, θ t and θ i are the refraction angle and the incident angle respectively, n t and n i are the refractive indices of the transmission surface and the incident surface, λ0 is the wavelength in vacuum, is the phase gradient. By adjusting the appropriate phase gradient, the propagation of the light beam in any direction can be achieved. In this solution, the splitting metasurface can split a single incident light beam into three mutually perpendicular light beams.

[0009] In this solution, the polarization conversion splitting metasurface includes a glass substrate, polarization conversion metasurface units, and beam deflection metasurface units. The polarization conversion and beam deflection metasurface units are both placed on the glass substrate.

[0010] In this solution, the polarization conversion metasurface units are composed of rectangular nanocolumns with the same shape and size. Each nanocolumn is equivalent to an independent quarter-wave plate, which is used to convert the incident linearly polarized light into circularly polarized light.

[0011] Furthermore, the beam deflection metasurface units are designed using the phase gradient to deflect the direction of the light beam while maintaining the polarization state of the incident light. The bonding use of the two metasurface unit structures can achieve the multifunctional multiplexing of polarization conversion and beam splitting.

[0012] In this solution, the beam deflection metasurface units in the polarization conversion beam splitting metasurface also satisfy the generalized Snell's law of refraction. Based on the light beam exiting from the splitting metasurface as the incident light perpendicular to the metasurface, the deflection angle of the exiting light beam is 45°.

[0013] In this solution, the polarization conversion beam splitting metasurface can achieve the single-beam pumping of a nuclear magnetic resonance gyroscope.

[0014] Based on the above technical solution, the optical path structure of the present invention can use a single laser to achieve the optical path control of the entire IMU system, significantly reducing the number of lasers and optical elements, and improving the system integration and stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] For a clearer illustration of the embodiments of the present invention, the drawings in the examples of this application are described as follows:

[0016] Figure 1 : Schematic diagram of the IMU optical path structure based on multiple metasurfaces;

[0017] Figure 2 : Schematic diagram of the abnormal deflection of the light beam exiting from the beam splitting metasurface;

[0018] Figure 3 : Schematic diagram of the far field of the spectroscopic metasurface;

[0019] Figure 4 : Phase distribution diagrams of the rectangular nanocolumns in the polarization conversion beam splitting metasurface in the x and y directions;

[0020] Figure 5 : Schematic diagram of the far field of the polarization conversion beam splitting metasurface;

[0021] Figure 6 : Schematic diagram of the polarization state of the outgoing light after the incident light interacts with the rectangular nanocolumn unit and the cylindrical nanocolumn unit in the polarization conversion beam splitting metasurface. Detailed implementation manners

[0022] The present invention will be further described in detail below with reference to the accompanying drawings.

[0023] As Figure 1 shown, the optical path structure of the nuclear magnetic resonance gyro IMU based on the metasurface includes: a laser, a polarization-maintaining fiber, a spectroscopic metasurface, a polarization conversion beam splitting metasurface, a mirror, and a gas chamber.

[0024] Among them, the working wavelength of the laser is set to 795 nm. The polarization-maintaining fiber is used to couple the linearly polarized light output by the laser and vertically incident it on the spectroscopic metasurface. The spectroscopic metasurface divides the incident light beam into three outgoing light beams that are perpendicular to each other and have an angle of 45° with the normal direction through phase gradient design. Subsequently, the three light beams are respectively vertically incident on three polarization conversion beam splitting metasurfaces.

[0025] In the solution, the spectroscopic metasurface substrate is composed of a SiO2 substrate with a thickness of 3 μm, and cylindrical Si nanocolumns with a height of 500 nm and different radii r are placed on the substrate, and a linearly polarized plane wave is vertically incident from below the substrate. The cylindrical nanocolumns are isotropic and thus do not change the polarization state of the light beam. In order to achieve an extraordinary deflection of 45° of the light beam from the normal direction, when r varies in the range of 0 - 125 nm, based on the generalized Snell's law, the radii of the target nanocolumns are screened and arranged in ascending order as 55 μm, 75 μm, 80 μm, 88 μm, and the phase difference between adjacent nanocolumns is π / 2. Periodically arranging them to form the basic unit of the metasurface can achieve an extraordinary deflection of 45° of the light beam as Figure 2 shown.

[0026] Furthermore, to ensure that the pumping lights of the three nuclear magnetic resonance gyros in the IMU system are orthogonal to each other, the present invention adopts the following design: divide the spectroscopic metasurface substrate into three isosceles triangle regions with a vertex angle of 120°, and periodically arrange Si nanocolumns in each region. The far field beam splitting situation of the metasurface is as Figure 3 shown.

[0027] In this solution, the nuclear magnetic resonance gyroscope no longer relies on two lasers with different frequencies to provide pump light and detection light respectively. Instead, a polarization conversion beam splitting metasurface is used to achieve the conversion of linearly polarized light to circularly polarized light and split the light beam, so as to complete the pumping and detection functions of the nuclear magnetic resonance gyroscope under a single-laser configuration.

[0028] Furthermore, the substrate of the polarization conversion beam splitting metasurface is composed of a SiO2 substrate with a thickness of 3 μm, and the entire metasurface is composed of rectangular nanocolumns and cylindrical nanocolumns. The linearly polarized plane wave is incident vertically from below the substrate and exits vertically after passing through the rectangular nanocolumn unit; at the same time, after passing through the cylindrical nanocolumns, it is deflected by 45° relative to the normal direction to achieve beam splitting, and the far-field pattern beam splitting of the metasurface is as Figure 4 shown.

[0029] Furthermore, the rectangular nanocolumns are used to convert linearly polarized light into circularly polarized light as the pump light of the system; the cylindrical nanocolumns are used to maintain the linear polarization characteristics and achieve beam splitting as the detection light of the system. The rectangular nanocolumns are anisotropic and exhibit different optical responses to light beams incident along the x-direction and the y-direction. The rectangular nanocolumns are numerically simulated using FDTD software, Figure 5 showing the phase distributions in the x-direction and the y-direction. The nanocolumns are screened and periodically arranged to form a polarization conversion unit. Since no phase gradient is introduced in this periodic unit, the vertically incident linearly polarized light can be directly converted into vertically outgoing circularly polarized light after passing through the unit, and this polarization conversion unit is equivalent to a quarter-wave plate.

[0030] Furthermore, the cylindrical nanocolumns are isotropic, and the polarization state of the outgoing light is the same as that of the incident light without change. By designing the phase gradient of the cylindrical nanocolumns, the light beam can be deflected to achieve the separation from the circularly polarized light and the beam splitting function. The cylindrical nanocolumns are optimized and simulated using the FDTD method, and the radii of the target nanocolumns are screened to be 75 nm, 80 nm, and 88 nm respectively, and are periodically arranged in the order of increasing radius, so as to achieve the anomalous deflection of the light beam. Figure 6 The outgoing polarization states of the light beam after the action of the rectangular nanocolumns and the cylindrical nanocolumns are shown.

[0031] In this design, in order to enable the deflected linearly polarized detection light to enter the gyroscope system perpendicular to the circularly polarized pump light, a mirror is added in front of the incident end of the detection light to correct the direction of the detection light, so as to ensure the normal operation of the nuclear magnetic resonance gyroscope.

[0032] Without departing from the spirit and protection scope of the invention, the technical solution of the present invention can be appropriately adjusted or deformed, and all similar technical changes should be covered within the protection scope of the present invention.

Claims

1. An optical path structure of a nuclear magnetic resonance gyro IMU based on a metasurface, characterized in that The optical path structure includes: a laser 1 for providing a light source; a polarization-maintaining fiber 2, one end of which is coupled to the laser 1 and the other end is perpendicular to the beam splitting metasurface 3; a beam splitting metasurface 3 for splitting an incident beam into three mutually perpendicular beams; a polarization conversion beam splitting metasurface 4 for converting the polarization state of the beam and splitting the beam; a mirror 5 disposed at the front end of the detection light incident port of the nuclear magnetic resonance gyroscope to adjust the direction of the detection beam; a nuclear magnetic resonance gyroscope 6 mounted perpendicular to the polarization conversion beam splitting metasurface 4; after the incident light emitted by the laser 1 acts on the beam splitting metasurface 3 and the polarization conversion beam splitting metasurface 4, three circularly polarized beams and three linearly polarized beams are generated. Among them, a single incident beam can be split into two beams with different polarization states, namely a circularly polarized beam and a linearly polarized beam, after acting on the polarization conversion beam splitting metasurface 4, which are respectively used for pumping and detection of the nuclear magnetic resonance gyroscope 6.

2. The optical path structure according to claim 1, wherein All the beams in the entire optical path system are generated by the laser 1.

3. The optical path structure according to claim 1, characterized in that The beam splitting metasurface 3 is composed of polarization-insensitive cylindrical nanocolumns, and by reasonably designing and periodically arranging cylindrical nanocolumns of different sizes, the extraordinary deflection of the beam is realized to split a single incident beam into three mutually perpendicular outgoing beams.

4. The optical path structure according to claim 1, wherein The polarization conversion beam splitting metasurface 4 is jointly composed of polarization-sensitive rectangular nanocolumns and polarization-insensitive cylindrical nanocolumns; among them, the rectangular nanocolumn unit is used to convert the linearly polarized light incident on the beam splitting metasurface 3 into circularly polarized light for pumping the nuclear magnetic resonance gyroscope 6; after the action of the beam splitting metasurface 3 and the polarization conversion beam splitting metasurface 4, the three pumping beams in the system remain mutually orthogonal; the cylindrical nanocolumns are used to maintain the linearly polarized characteristics of the beam for detection by the nuclear magnetic resonance gyroscope 6, and at the same time, the propagation direction of the beam undergoes extraordinary deflection.

5. The optical path structure according to claim 1, characterized in that, The output beam after the light generated by the laser 1 acts on the beam splitting metasurface 3 and the polarization conversion beam splitting metasurface 4 can meet the normal working requirements of the nuclear magnetic resonance gyroscope 6 in the entire IMU system. The optical path structure of the present invention realizes the miniaturization, high integration and low power consumption characteristics of the IMU optical path system through the metasurface technology, significantly reduces the number of optical elements used, and is conducive to the miniaturization and integration work of the IMU system.

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