A Blazed Grating MEMS Gyroscope Based on Optical Beat Frequency Detection

Abstract

This invention belongs to the field of MEMS gyroscope technology, specifically relating to a blazed grating MEMS gyroscope based on optical beat frequency detection. A first reflector is positioned along one optical path of a first beam splitter, and a circulator is positioned along the other optical path of the first beam splitter. A collimating lens is positioned along one optical path of the circulator, and the blazed grating gyroscope is positioned along the optical path of the collimating lens. A second beam splitter is positioned along the reflected optical path of the first reflector, and a second reflector is positioned along the other optical path of the circulator. A second beam splitter is positioned along the reflected optical path of the second reflector, and a photodetector is positioned along one optical path of the second beam splitter. This invention measures the angular rate of the MEMS gyroscope by detecting the deflection angle of the blazed grating, reducing manufacturing difficulty and structurally minimizing the impact of crosstalk on the gyroscope's sensitivity.

Description

Technical Field

[0001] This invention belongs to the field of MEMS gyroscope technology, specifically relating to a blazed grating MEMS gyroscope based on optical beat frequency detection. Background Technology

[0002] MEMS gyroscopes, as sensors for measuring angular velocity, are an important component of inertial navigation systems. Due to their advantages such as high integration, low cost, low power consumption, high reliability, and mass production capability, MEMS gyroscopes have been widely used in many fields, including cutting-edge interdisciplinary fields such as aerospace technology, marine engineering, and automotive navigation.

[0003] However, with the increasing demand for higher performance and functionality, the accuracy of mainstream capacitance sensing technology is difficult to improve due to limitations in manufacturing processes and the near-limited resolution of interface circuits. Therefore, to further improve gyroscope accuracy, optical sensing MEMS gyroscopes have become widely used. Compared to traditional MEMS gyroscopes, optical MEMS gyroscopes offer advantages such as higher accuracy, faster response, resistance to electromagnetic interference, and the ability to operate in harsh environments. Therefore, optical MEMS gyroscopes have broad application prospects in fields with high sensitivity requirements, such as inertial navigation, building monitoring, and geophysics.

[0004] Based on their measurement principles, optical MEMS gyroscopes are mainly divided into two categories: those based on geometric optics and those based on wave optics. Geometric optics-based MEMS gyroscopes directly sense changes in angular rate by modulating the intensity of light. They offer advantages such as simple structure and low cost, but their high sensitivity to fluctuations in the incident light source and the external environment often makes it difficult to guarantee accuracy. Wave optics-based grating gyroscopes, on the other hand, work by utilizing the Coriolis force generated when rotation is applied, causing displacement and a change in wavelength (or frequency / phase). Angular rate is detected by sensing this change. This type of optical MEMS gyroscope features a compact optical path and higher accuracy, offering advantages in miniaturization and integration, thus becoming the main direction for the development of wave optics-based MEMS gyroscopes. Currently, the main research area in wave optics involves Fabry-Bragg gratings. These fiber optic sensors offer advantages such as strong anti-interference capabilities, good reproducibility, long lifespan, ease of integration, high thermal stability, and ease of long-distance signal transmission. However, fiber optic sensors suffer from difficulties in fabrication, low resonant frequencies, and high costs associated with lasers and demodulation systems, limiting their application areas. Summary of the Invention

[0005] To address the technical challenges of existing MEMS gyroscopes, such as high fabrication difficulty, low integration, and sensitivity issues caused by crosstalk, this invention provides a blazed grating MEMS gyroscope based on optical beat frequency detection. Under the influence of Coriolis force, the blazed grating in the structure of the blazed grating MEMS gyroscope rotates. The angular rate of the gyroscope is measured by detecting the change in optical frequency caused by the change in the blazing angle. At the same time, a circulator is used to improve the integration of the system.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0007] A blazed grating MEMS gyroscope based on optical beat frequency detection includes a laser, a first beam splitter, a first reflector, a circulator, a collimating lens, a blazed grating gyroscope, a second reflector, a second beam splitter, and a photodetector. The first beam splitter is positioned along the optical path of the laser. A first reflector is positioned along one optical path of the first beam splitter. A circulator is positioned along the other optical path of the first beam splitter. A collimating lens is positioned along one optical path of the circulator. The blazed grating gyroscope is positioned along the optical path of the collimating lens. A second beam splitter is positioned along the reflected optical path of the first reflector. A second reflector is positioned along the other optical path of the circulator. A second beam splitter is positioned along the reflected optical path of the second reflector. A photodetector is positioned along one optical path of the second beam splitter.

[0008] Both the first and second reflectors are 45° reflectors.

[0009] An optical switch is provided between the laser and the first beam splitter.

[0010] The blazed grating gyroscope includes a drive beam, a blazed grating, a detection beam, a substrate, and a mass block. The substrate is connected to the detection beam via the drive beam, and the detection beam is connected to the mass block. The blazed grating is disposed on the mass block.

[0011] A measurement method for a blazed grating MEMS gyroscope based on optical beat frequency detection includes the following steps:

[0012] S1. The laser emits light that passes through the first beam splitter to form two paths of light: reflected light and transmitted light. The reflected light passes through the first reflecting mirror to reach the second beam splitter to form one beam of light in the beat frequency optical path.

[0013] S2. The transmitted light beam passes through the first beam splitter and reaches the circulator. The light output from the lower end of the circulator passes through the collimating lens and acts on the blazed grating gyroscope.

[0014] S3. Due to the Coriolis force generated by the angular rate, the angle of the blazed grating gyroscope incident on the blazed grating changes, causing the frequency of the laser returning to the circulator to shift. This laser beam forms a second beam of light with an optical beat frequency and is output from the right end of the circulator.

[0015] S4. The laser beam then passes through the second reflecting mirror and acts on the second beam splitter, where it is superimposed with the first beam. The optical beat frequency signal is observed on the photodetector, thereby measuring the magnitude of the angular rate of the blazed grating MEMS gyroscope.

[0016] The method for changing the angle of the incident light on the blazed grating in S3 is as follows: a sinusoidal driving force is applied to the driving beam of the blazed grating gyroscope. The sinusoidal driving force is along the y-axis. When the blazed grating gyroscope rotates around the x-axis, the mass block generates a Coriolis force in the z-axis direction, which drives the blazed grating to make an out-of-plane motion, thereby changing the blazed angle of the blazed grating.

[0017] The formula for the blazed grating is:

[0018] 2d sinβ0=mλ0

[0019] β0+θ=β1

[0020] 2dsinβ1=mλ1

[0021] d is the grating constant, β0 is the initial blaze angle of the blazed grating, β1 is the blaze angle of the blazed grating after rotation, m is the diffraction order, λ0 is the blaze wavelength, and θ is the grating rotation angle. One blaze angle of the blazed grating corresponds to a specific blaze wavelength. When the blaze angle changes, the blaze wavelength also changes. When the blazed grating is rotated by the Coriolis force, the blaze angle will change. The deflected blaze angle is the grating rotation angle plus the initial blaze angle.

[0022] The method for measuring the angular velocity of the blazed grating MEMS gyroscope in S4 is as follows: When rotation occurs, the blazed wavelength also changes. The changed optical path is transmitted through the optical path system to the second beam splitter, where it forms an optical beat frequency with the light reflected from the first mirror. The two different interference beams are represented as follows:

[0023]

[0024]

[0025] The ω i The value represents the angular frequency of the laser, where k is the wave vector of the laser. Since the second beam splitter ensures that the two beams propagate in the same direction, the optical beat frequency formed by the superposition of the two beams is:

[0026] ωm =|ω1-ω2|

[0027] The beat frequency is directly detected by a photodetector, the blaze angle after deflection of the blazed grating is obtained, and the angular rate of the MEMS gyroscope is obtained by the change of the blaze angle after deflection.

[0028] Compared with the prior art, the beneficial effects of this invention are:

[0029] This invention improves the integration of the optical system by using an optical circulator in the detection optical path. It measures the angular rate of a MEMS gyroscope by detecting the deflection angle of a blazed grating, reducing manufacturing difficulty and minimizing the impact of crosstalk on gyroscope sensitivity. Furthermore, the detection principle uses optical beat frequency detection, which is more sensitive than diffraction detection methods and enables precise measurement of the gyroscope. Attached Figure Description

[0030] To more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings in the following description are merely exemplary, and those skilled in the art can derive other embodiments based on the provided drawings without creative effort.

[0031] The structures, proportions, sizes, etc. illustrated in this specification are only for the purpose of assisting those skilled in the art in understanding and reading the content disclosed herein, and are not intended to limit the conditions under which the present invention can be implemented. Therefore, they have no substantial technical significance. Any modifications to the structure, changes in the proportions, or adjustments to the size, without affecting the effects and objectives that the present invention can produce, should still fall within the scope of the technical content disclosed in the present invention.

[0032] Figure 1 This is a schematic diagram of the structure of the present invention;

[0033] Figure 2 This is a schematic diagram of the structure of the blazing grating gyroscope of the present invention;

[0034] Figure 3 This is a schematic diagram of the state in which the angular rate blazed grating is not applied according to the present invention;

[0035] Figure 4 This is a schematic diagram showing the state in which the angular rate blazed grating is applied according to the present invention;

[0036] Figure 5 This is a graph showing the relationship between the angular rate and frequency difference of the blazed grating gyroscope of the present invention.

[0037] Wherein: 1 is the laser, 2 is the first beam splitter, 3 is the first reflector, 4 is the circulator, 5 is the collimating lens, 6 is the blazed grating gyroscope, 601 is the driving beam, 602 is the blazed grating, 603 is the detection beam, 604 is the substrate, 605 is the mass block, 7 is the second reflector, 8 is the second beam splitter, 9 is the photodetector, and 10 is the optical switch. Detailed Implementation

[0038] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. These descriptions are only for further illustrating the features and advantages of the present invention, and not for limiting the claims of the present invention. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0039] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples. The following examples are for illustrative purposes only and are not intended to limit the scope of the invention.

[0040] The terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, unless otherwise stated, "a plurality of" means two or more.

[0041] In the description of this application, it should be noted that, unless otherwise expressly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection between two components. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0042] In this embodiment, the detection principle of the blazed grating optical path is as follows: Figure 1As shown, laser 1 emits a laser beam, which is split into two beams by the first beam splitter 2. The first beam is reflected by the first beam splitter 2 and the first reflector 3 to the second beam splitter 8, forming the first beat frequency laser. The second beam is transmitted through the first beam splitter 2, passes through the circulator 4 to change its propagation direction, and after passing through the collimating lens 5, it directly hits the blazed grating gyroscope 6. Due to the external angular velocity, the blazed grating 602 is deflected, causing a change in the frequency of the incident light entering the circulator 4. The laser returns along its original path, passes through the collimating lens 5, and is output from the right end of the circulator 4. It then passes through the second reflector 7 to the second beam splitter 8, forming the second beat frequency signal. The two signals, after passing through the second beam splitter 8, form an optical beat frequency, which is detected by the photodetector 9 and analyzed by the spectrum analyzer to calculate the angular velocity of the gyroscope. The specific scheme is as follows:

[0043] like Figure 2 As shown, the blazed grating gyroscope 6 consists of a drive beam 601, a blazed grating 602, a detection beam 603, a base 604, and a mass block 605. A sinusoidal driving force (along the y-axis) is applied to the drive beam 6 of the blazed grating gyroscope 6. When the blazed grating gyroscope 6 rotates around the x-axis, the mass block 605 generates a Coriolis force in the z-axis direction, causing the blazed grating 602 to perform out-of-plane motion. A schematic diagram of the specific detection principle of the blazed grating 602 is shown below. Figure 3 , Figure 4 As shown, since the light is incident perpendicularly onto the blazed grating 602 through the collimating lens 5, according to the blazed grating formula (1) and Figure 3 It can be seen that a specific blaze angle corresponds to a specific blaze wavelength.

[0044] 2d sinβ0=mλ0 (1)

[0045] β0+θ=β1 (2)

[0046] 2dsinβ1=mλ1 (3)

[0047] When the blazed grating 602 deflects, as Figure 4 It can be seen that when the blazed grating 602 is deflected by the Coriolis force, the blazed angle of the blazed grating 602 will change. According to formula (2), the blazed angle after the blazed grating is rotated is the grating rotation angle plus the blazed angle in the initial state, where β0 is the initial blazed angle of the blazed grating and β1 is the blazed angle after the blazed grating is rotated. According to formula (3), when the rotation occurs, the blazed wavelength also changes. The changed light path is transmitted to the second beam splitter 8 through the optical path system and forms an optical beat frequency with the light reflected from the first mirror 3. The two different interference lights can be expressed as:

[0048]

[0049]

[0050] Where ω i Let represent the angular frequency of the laser, and k be the wave vector of the laser. Since the two beams propagate in the same direction due to the second beam splitter 8, the optical beat frequency formed by the superposition of the two beams is:

[0051] ω m =|ω1-ω2| (6)

[0052] The beat frequency can be directly detected using photodetector 9. The deflection angle of the blazed grating is then calculated using equations (3) and (6). The relationship between the angular velocity and frequency difference of the blazed grating MEMS blazed grating gyroscope is obtained through simulation using Comsol software, as shown below. Figure 5 As shown.

[0053] The above description only illustrates the preferred embodiments of the present invention. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention, and all such changes should be included within the protection scope of the present invention.

Claims

1. A blazed grating MEMS gyroscope based on optical beat frequency detection, characterized in that: The device includes a laser (1), a first beam splitter (2), a first reflector (3), a circulator (4), a collimating lens (5), a blazed grating gyroscope (6), a second reflector (7), a second beam splitter (8), and a photodetector (9). The first beam splitter (2) is arranged in the optical path direction of the laser (1). The first reflector (3) is arranged in one optical path direction of the first beam splitter (2). The circulator (4) is arranged in the other optical path direction of the first beam splitter (2). The collimating lens (5) is arranged in one optical path direction of the circulator (4). The blazed grating gyroscope (6) is arranged in the optical path direction of the collimating lens (5). The second beam splitter (8) is arranged in the reflected optical path of the first reflector (3). The second reflector (7) is arranged in the other optical path direction of the circulator (4). The second beam splitter (8) is arranged in the reflected optical path of the second reflector (7). The photodetector (9) is arranged in one optical path direction of the second beam splitter (8).

2. The blazed grating MEMS gyroscope based on optical beat frequency detection according to claim 1, characterized in that: Both the first reflector (3) and the second reflector (7) are 45° reflectors.

3. A blazed grating MEMS gyroscope based on optical beat frequency detection according to claim 1, characterized in that: An optical switch (10) is provided between the laser (1) and the first beam splitter (2).

4. A blazed grating MEMS gyroscope based on optical beat frequency detection according to claim 1, characterized in that: The blazed grating gyroscope (6) includes a drive beam (601), a blazed grating (602), a detection beam (603), a base (604), and a mass block (605). The base (604) is connected to the detection beam (603) through the drive beam (601), and the detection beam (603) is connected to the mass block (605). The blazed grating (602) is disposed on the mass block (605).

5. A measurement method for a blazed grating MEMS gyroscope based on optical beat frequency detection according to any one of claims 1-4, characterized in that: Includes the following steps: S1. The laser emits light that passes through the first beam splitter to form two paths of light: reflected light and transmitted light. The reflected light passes through the first reflecting mirror to reach the second beam splitter to form a beam of light in the beat frequency optical path. S2. The transmitted light beam passes through the first beam splitter and reaches the circulator. The light output from the lower end of the circulator passes through the collimating lens and acts on the blazed grating gyroscope. S3. Due to the Coriolis force generated by the angular rate, the angle of the blazed grating gyroscope incident on the blazed grating changes, causing the frequency of the laser returning to the circulator to shift. This laser beam forms a second beam of light with an optical beat frequency and is output from the right end of the circulator. S4. The laser beam then passes through the second reflecting mirror and acts on the second beam splitter, where it is superimposed with the first beam. The optical beat frequency signal is observed on the photodetector, thereby measuring the magnitude of the angular rate of the blazed grating MEMS gyroscope.

6. The measurement method for a blazed grating MEMS gyroscope based on optical beat frequency detection according to claim 5, characterized in that: The method for changing the angle of the incident light on the blazed grating in S3 is as follows: a sinusoidal driving force is applied to the driving beam of the blazed grating gyroscope. The sinusoidal driving force is along the y-axis. When the blazed grating gyroscope rotates around the x-axis, the mass block generates a Coriolis force in the z-axis direction, which drives the blazed grating to make an out-of-plane motion, thereby changing the blazed angle of the blazed grating.

7. The measurement method for a blazed grating MEMS gyroscope based on optical beat frequency detection according to claim 6, characterized in that: The formula for the blazed grating is: d is the grating constant, β0 is the initial blaze angle of the blazed grating, β1 is the blaze angle of the blazed grating after rotation, m is the diffraction order, λ0 is the blaze wavelength, and θ is the grating rotation angle. One blaze angle of the blazed grating corresponds to a specific blaze wavelength. When the blaze angle changes, the blaze wavelength also changes. When the blazed grating is rotated by the Coriolis force, the blaze angle will change. The deflected blaze angle is the grating rotation angle plus the initial blaze angle.

8. The measurement method for a blazed grating MEMS gyroscope based on optical beat frequency detection according to claim 6, characterized in that: The method for measuring the angular velocity of the blazed grating MEMS gyroscope in S4 is as follows: When rotation occurs, the blazed wavelength also changes. The changed optical path is transmitted through the optical path system to the second beam splitter, where it forms an optical beat frequency with the light reflected from the first mirror. The two different interference beams are represented as follows: ω1 and ω2 represent the angular frequencies of the two laser beams, respectively, and k is the wave vector of the laser. Since the two beams propagate in the same direction due to the second beam splitter, the optical beat frequency formed by the superposition of the two beams is: The beat frequency is directly detected by a photodetector, the blaze angle after deflection of the blazed grating is obtained, and the angular rate of the MEMS gyroscope is obtained by the change of the blaze angle after deflection.

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