A two-dimensional accelerometer based on nanograting interferometry

Abstract

This invention belongs to the technical field of acceleration sensing devices, specifically relating to a two-dimensional acceleration sensing device based on a nanograting interferometric method. The laser includes a first laser and a second laser. A beam splitter is positioned along the optical path of the first and second lasers. A first metal reflective structure is disposed on the reflected optical path of the first laser through the beam splitter, and a first grating accelerometer structure is disposed on the reflected optical path of the second laser through the beam splitter. A second metal reflective structure is disposed on the transmitted optical path of the first laser through the beam splitter, and a second grating accelerometer structure is disposed on the transmitted optical path of the second laser through the beam splitter. This invention utilizes the change in diffracted light intensity of the nanograting to achieve micro-displacement measurement, thereby detecting the magnitude of acceleration, giving the measurement system higher sensitivity and resolution.

Description

Technical Field

[0001] This invention belongs to the technical field of acceleration sensing devices, specifically relating to a two-dimensional acceleration sensing device based on nanograting interferometry. Background Technology

[0002] As a scale for measuring acceleration, velocity, and position, accelerometers are not only key components of inertial navigation systems, but also play a vital role in a wide range of applications, including automotive safety, earthquake monitoring, gravity detection, heading indication, and attitude measurement. Since the 1980s, with the increasing demand for higher performance, functionality, and miniaturization, MEMS accelerometers, with their advantages of small size, light weight, high integration, high sensitivity, and low noise, have become one of the most popular development directions for accelerometers. They have gradually matured and are widely used in military tactical missiles, inertial navigation systems, as well as in civilian fields such as automobiles, consumer electronics, and medical devices.

[0003] From the current development of MEMS accelerometers, the development can be divided into two main aspects: one is the research and development of accelerometers based on new principles / effects to break through the limitations of existing commercial capacitive accelerometers; the other is the improvement of existing accelerometers towards higher performance and higher precision. It is foreseeable that accelerometers will continue to play an important role in medium- and high-precision inertial navigation and other applications for a considerable period of time, and their future development trend is to further miniaturize them while improving their performance. Common micro-accelerometers can be mainly classified according to their detection principles into: tunneling effect accelerometers, piezoresistive accelerometers, piezoelectric accelerometers, capacitive accelerometers, and resonant accelerometers. Tunneling current accelerometers are highly precise, difficult to manufacture, have low yield, high cost, and poor low-frequency characteristics, making them unsuitable for measuring static acceleration. Piezoresistive accelerometers are simple to manufacture and have low cost, but suffer from low resolution and severe temperature effects. Capacitive accelerometers are highly sensitive, stable, and have relatively small temperature drift. They can also perform self-testing using electrostatic force, offering improved resolution and accuracy compared to piezoresistive accelerometers. However, capacitive accelerometers have a smaller dynamic range, and their capacitance detection principle is susceptible to electromagnetic interference and parasitic capacitance, making noise removal difficult. Summary of the Invention

[0004] To address the technical problems of the relatively small dynamic range of the aforementioned capacitive accelerometers, the susceptibility of capacitance detection to electromagnetic interference and parasitic capacitance, and the difficulty in noise removal, this invention provides a two-dimensional accelerometer based on a nanograting interferometric method. This device combines a biaxial nanograting silicon micro accelerometer structure with a Glan prism structure to achieve the integration of a two-dimensional optical measurement system, featuring high integration, high resolution, and strong anti-electromagnetic interference capability.

[0005] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0006] A two-dimensional accelerometer based on nanograting interferometry includes a laser, a beam splitter, a first metal reflection structure, a second metal reflection structure, a first grating accelerometer structure, and a second grating accelerometer structure. The laser includes a first laser and a second laser. The beam splitter is disposed in the optical path direction of the first laser and the second laser. The first metal reflection structure is disposed in the reflected optical path of the first laser through the beam splitter. The first grating accelerometer structure is disposed in the reflected optical path of the second laser through the beam splitter. The second metal reflection structure is disposed in the transmitted optical path of the first laser through the beam splitter. The second grating accelerometer structure is disposed in the transmitted optical path of the second laser through the beam splitter.

[0007] It includes a first photodetector and a second photodetector. The first photodetector is disposed on the reflected light path of the first metal reflective structure, and the second photodetector is disposed on the reflected light path of the first grating accelerometer structure.

[0008] The beam splitter is disposed between the first metal reflective structure and the first photodetector, and the beam splitter is disposed between the first grating accelerometer structure and the second photodetector.

[0009] The laser, beam splitter, first metal reflector structure, second metal reflector structure, first grating accelerometer structure, second grating accelerometer structure, first photodetector and second photodetector are all housed within a shielded enclosure.

[0010] The beam splitter is a Glan prism.

[0011] Both the first grating accelerometer structure and the second grating accelerometer structure include a grating and a reflector, with the reflector positioned along the optical path of the grating.

[0012] A measurement method based on a nanograting interferometric two-dimensional accelerometer includes the following steps:

[0013] S1. The laser emitted by the first laser is reflected by the beam splitter to the first metal reflective structure on the side, and interferes with the light reflected back from the second grating accelerometer structure transmitted to the bottom of the beam splitter. The light is detected by the first photodetector, and at this time the optical signal is converted into an electrical signal to realize the measurement of the out-of-plane acceleration.

[0014] S2. The laser emitted by the second laser is reflected by the beam splitter to the first grating accelerometer structure on the side. It interferes with the light reflected back from the second metal reflective structure at the bottom of the beam splitter. The light is then converted into an electrical signal by the second photodetector to detect the horizontal acceleration.

[0015] The method for detecting out-of-plane acceleration and horizontal acceleration is as follows:

[0016] A laser beam is incident perpendicularly on a sinusoidal amplitude grating. After diffraction and splitting by the grating, it forms two diffracted beams, one of the +1st order and one of the -1st order. When the grating is introduced with a displacement D... x At that time, the optical paths of the +1st and -1st order diffracted beams remain unchanged.

[0017] Assume the +1st order diffracted light is

[0018]

[0019] The i x The unit direction vector; A1 is the amplitude of the +1st order diffracted light; j is the imaginary unit; z1 is the optical path of the +1st order diffracted light;

[0020] Similarly, the -1st order diffracted light is represented as:

[0021]

[0022] The light field distribution at the interference point is calculated, and the light intensity is expressed as:

[0023]

[0024] The (z1-z2) represents the fixed phase difference between the ±1st order diffracted beams due to the optical path difference, where 4πD is the phase difference between the ±1st order diffracted beams. x / d is the ±1st order diffraction phase difference generated by the horizontal line translation of the grating;

[0025] An incident light beam is incident perpendicularly onto the upper surface of a grating with a period of Λ and a distance of d between the grating and the mirror. Fraunhofer diffraction is used to calculate the relationship between the light intensity and displacement of the grating interference structure.

[0026]

[0027] E(p) is the diffraction complex amplitude, C is the normalization constant, and λ is the incident light wavelength. It is a wave vector, where p = sinθ i -sinθ o The θ o and θ i These are the incident angle and the diffraction angle, respectively; F is a transfer function over a period, and its expression is:

[0028]

[0029] The value of θ in the above formula is determined by the following analytical expression:

[0030]

[0031] The first three orders of light intensity formed after interference between the corresponding orders of the two diffracted beams are expressed as a function of displacement:

[0032]

[0033]

[0034]

[0035] The I in It is the incident light intensity. The relationship between the light intensity of each order and the displacement is a sine or cosine function with the incident light wavelength as the period. The period of each order with the displacement is λ / 2. Therefore, the light intensity change of any order can be used to detect the change of micro displacement, and thus realize the detection of acceleration.

[0036] Compared with the prior art, the beneficial effects of this invention are:

[0037] This invention utilizes the variation in diffraction intensity of light from a nanograting to measure micro-displacement, thereby detecting the magnitude of acceleration and improving the sensitivity and resolution of the measurement system. Furthermore, the nanograting interferometric two-dimensional acceleration measurement system of this invention features a simple and flexible structure with high system integration. Using zero-order light as the detection signal further enhances the system's sensitivity and resolution. The invention employs a Glan prism in the detection optical path, distributing the light source and detector on the same side of the grating, thus improving system integration. The use of a two-dimensional measurement method expands the measurement dimension while maintaining high precision. Attached Figure Description

[0038] 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.

[0039] 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.

[0040] Figure 1 This is a schematic diagram of the structure of the present invention;

[0041] Figure 2 This is a schematic diagram of the equivalent grating interference principle of the present invention;

[0042] Figure 3 This is a simplified optical diagram of the grating accelerometer structure of the present invention during operation;

[0043] Figure 4 This is a graph showing the change in photoelectric detection light intensity as a function of grating displacement in this invention.

[0044] Wherein: 1 is a laser, 101 is a first laser, 102 is a second laser, 2 is a beam splitter, 3 is a first metal reflective structure, 4 is a first grating accelerometer structure, 401 is a grating, 402 is a reflector, 5 is a second metal reflective structure, 6 is a second grating accelerometer structure, 7 is a first photodetector, 8 is a second photodetector, and 9 is a shielding shell. Detailed Implementation

[0045] 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.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] In this embodiment, as Figure 1 As shown, the system comprises a laser 1, a beam splitter 2, a first metal reflective structure 3 and a second metal reflective structure 5, a first grating accelerometer structure 4 and a second grating accelerometer structure 6, a first photodetector 7 and a second photodetector 8, and a shielding shell 9. The laser emitted by the first laser 101 passes through the beam splitter 2. A portion of the light is reflected to the first metal reflective structure 3 on the side, where it interferes with the light reflected back from the second grating accelerometer structure 6 at the bottom of the beam splitter 2. This interference is detected by the first photodetector 7, converting the optical signal into an electrical signal to measure the out-of-plane acceleration. The other laser beam emitted by the second laser 102 is reflected by the beam splitter 2 to the first grating accelerometer structure 4 on the side, where it interferes with the light reflected back from the second metal reflective structure 5 at the bottom. This interference is converted into an electrical signal by the second photodetector 8 to detect the horizontal acceleration. Figure 4 The diagram shows the change in size of the first photodetector 7 and the second photodetector 8 as a function of grating displacement. The specific solution is as follows:

[0050] The principle of grating interference is as follows Figure 2 As shown, when a coherent beam is incident perpendicularly on the upper surface of a sinusoidal amplitude grating, the grating 401 diffracts the incident light. Part of the light is directly reflected, while the other part is diffracted by the grating 401 and then reflected again, producing a diffracted beam containing a series of diffraction orders, such as 0th, ±1st, ±2nd, etc. When the light reflected back from the grating 401 meets the beam reflected by the mirror 402, the corresponding diffraction orders in the two diffracted beams will interfere additively or destructively, forming a series of interference order spots. The positions of these interference spots remain fixed, but their intensity changes with the distance between the grating and the beam splitter 2. In this structure, the grating 401 and the mirror 402 form a phase-sensitive grating interference structure. If the grating is fixed, moving the mirror changes the distance between the grating 401 and the mirror 402, causing the fringes to shift, corresponding to a change in the interference light intensity.

[0051] A laser beam is incident perpendicularly on a sinusoidal amplitude grating, and after diffraction by the grating, it forms two diffracted beams, one for the +1st order and one for the -1st order. When the grating is introduced with a displacement D... xAt that time, the optical paths of the +1st and -1st order diffracted beams remain unchanged.

[0052] Assume the +1st order diffracted light is

[0053]

[0054] In the formula, i x A1 is the unit direction vector; A1 is the amplitude of the +1st order diffracted light; j is the imaginary unit; z1 is the optical path of the +1st order diffracted light.

[0055] Similarly, the -1st order diffracted light can be represented as:

[0056]

[0057] The light field distribution at the interference point can be calculated using formulas (1) and (2), and the light intensity can be expressed as:

[0058]

[0059] In the formula, (z1-z2) represents the fixed phase difference between the ±1st order diffracted beams due to the optical path difference, 4πD x / d is the ±1st order diffraction phase difference generated by the horizontal line translation of the grating.

[0060] Figure 3 This is a simplified optical diagram of a grating interference structure in operation. An incident beam is incident perpendicularly to the upper surface of the grating, the grating period is Λ, and the distance between the grating and the mirror is d. Fraunhofer diffraction is used to calculate the relationship between the light intensity and displacement of the grating interference structure. From Fraunhofer diffraction theory, we know that:

[0061] E(p)=C∫ grating Fe -jkp dx (4)

[0062] In the formula, E(p) is the complex diffraction amplitude, C is the normalization constant, and λ is the incident light wavelength. It is a wave vector, p = sinθ i -sinθ o Where θ o and θ i These are the incident angle and the diffraction angle, respectively. F is a transfer function over a period of time, and its expression is:

[0063]

[0064] The value of θ in the above formula is determined by the following analytical expression:

[0065]

[0066] The first three orders of light intensity formed after interference between the corresponding orders of the two diffracted beams are expressed as a function of displacement:

[0067]

[0068] In the formula I in It is the incident light intensity. Formula (7) shows that the relationship between the light intensity of each order and the displacement is a sine or cosine function with the incident light wavelength as the period, and the period of each order with the displacement is λ / 2. Therefore, the light intensity change of any order can be used to detect the change of micro displacement, and thus realize the detection of acceleration.

[0069] 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 two-dimensional accelerometer based on nanograting interferometry, characterized in that: The system includes a laser (1), a beam splitter (2), a first metal reflection structure (3), a second metal reflection structure (5), a first grating accelerometer structure (4), and a second grating accelerometer structure (6). The laser (1) includes a first laser (101) and a second laser (102). The beam splitter (2) is disposed in the optical path direction of the first laser (101) and the second laser (102). The first laser (101) is provided with the first metal reflection structure (3) in the reflected optical path of the beam splitter (2). The second laser (102) is provided with the first grating accelerometer structure (4) in the reflected optical path of the beam splitter (2). The first laser (101) is provided with the second metal reflection structure (5) in the transmitted optical path of the beam splitter (2). The second laser (102) is provided with the second grating accelerometer structure (6) in the transmitted optical path of the beam splitter (2).

2. The two-dimensional accelerometer based on nanograting interferometry according to claim 1, characterized in that: It includes a first photodetector (7) and a second photodetector (8). The first photodetector (7) is disposed on the reflected light path of the first metal reflective structure (3), and the second photodetector (8) is disposed on the reflected light path of the first grating accelerometer structure (4).

3. The two-dimensional accelerometer based on nanograting interferometry according to claim 2, characterized in that: The beam splitter (2) is disposed between the first metal reflective structure (3) and the first photodetector (7), and the beam splitter (2) is disposed between the first grating accelerometer structure (4) and the second photodetector (8).

4. The two-dimensional accelerometer based on nanograting interferometry according to claim 3, characterized in that: The laser (1), beam splitter (2), first metal reflection structure (3), second metal reflection structure (5), first grating accelerometer structure (4), second grating accelerometer structure (6), first photodetector (7) and second photodetector (8) are all housed inside the shielding shell (9).

5. The two-dimensional accelerometer based on nanograting interferometry according to claim 1, characterized in that: The beam splitter (2) is a Glan prism.

6. The two-dimensional accelerometer based on nanograting interferometry according to claim 1, characterized in that: Both the first grating accelerometer structure (4) and the second grating accelerometer structure (6) include a grating (401) and a reflector (402), with the reflector (402) positioned in the optical path direction of the grating (401).

7. A measurement method based on a nanograting interferometric two-dimensional accelerometer according to any one of claims 1-6, characterized in that: Includes the following steps: S1. The laser emitted by the first laser is reflected by the beam splitter to the first metal reflective structure on the side, and interferes with the light reflected back from the second grating accelerometer structure transmitted to the bottom of the beam splitter. The light is detected by the first photodetector, and at this time the optical signal is converted into an electrical signal to realize the measurement of the out-of-plane acceleration. S2. The laser emitted by the second laser is reflected by the beam splitter to the first grating accelerometer structure on the side. It interferes with the light reflected back from the second metal reflective structure at the bottom of the beam splitter. The light is then converted into an electrical signal by the second photodetector to detect the horizontal acceleration.

8. The measurement method based on a nanograting interferometric two-dimensional accelerometer according to claim 7, characterized in that: The method for detecting out-of-plane acceleration and horizontal acceleration is as follows: A laser beam is incident perpendicularly on a sinusoidal amplitude grating. After diffraction and splitting by the grating, it forms two diffracted beams, one of the +1st order and one of the -1st order. When the grating is introduced with a displacement D... x At that time, the optical paths of the +1st and -1st order diffracted beams remain unchanged; assuming the +1st order diffracted beam is... The The unit direction vector; The amplitude of the +1st order diffracted light; j is the imaginary unit; The optical path length of the +1st order diffracted light; Similarly, the -1st order diffracted light is represented as: The light field distribution at the interference point is calculated, and the light intensity is expressed as: = 2 + 2 +2 cos( ) The = ( - )for The fixed phase difference between the diffracted beams due to the optical path difference, the 4 It is produced by the translation of the horizontal lines of the grating. Phase difference of diffracted light; The incident light beam is incident perpendicularly onto the upper surface of the grating, and the period of the grating is... The distance between the grating and the mirror is d. Fraunhofer diffraction is used to calculate the relationship between the light intensity and displacement of the grating interference structure: The E It is the diffraction complex amplitude, where C is the normalization constant, and the... It is a wave vector. It is the wavelength of the incident light, the stated The and These are the incident angle and the diffraction angle, respectively; F is a transfer function over a period of time, and the expression for F is: In the above formula The value is determined by the following analytical expression: The first three orders of light intensity formed after interference between the corresponding orders of the two diffracted beams are expressed as a function of displacement: The The incident light intensity is the intensity of the incident light. The relationship between the intensity of each order of light and the displacement is a sine or cosine function with a period of the incident light wavelength, and the period of each order of light intensity with displacement is...

2. Therefore, any change in light intensity at any order can be used to detect changes in micro-displacement, thereby enabling the detection of acceleration.

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