CN100340859C - Optical acceleration sensor based on Fresnel diffraction micr-lens - Google Patents

Abstract

The invention discloses an optical acceleration sensor based on a Fresnel diffraction microlens, which is mainly composed of an optical fiber, a glass substrate, a Fresnel diffraction microlens, a microreflective film, a micromass block, a microplane spring, a shell and the like. The micro-reflective film and the Fresnel diffraction micro-lens are placed in parallel, and there is a small gap between them. The side of the micro-reflective film opposite to the Fresnel diffraction micro-lens is coated with a metal reflective film, and a micro-reflective film sensitive to acceleration is processed on the other side. The quality block; the micro-reflective film is connected with the fixed frame through four planar micro-springs. Use an optical fiber to transmit light, and fix the end of the optical fiber at the focal point of the Fresnel diffraction microlens. The external acceleration will cause the micro-mass block to drive the micro-reflective film to produce displacement, so that the light intensity at the focus of the Fresnel diffraction micro-lens changes. By detecting the change of light intensity in the optical fiber, the acceleration can be detected. The sensor can be used in aircraft control systems, and many other fields that require high-precision sensing and high immunity to electromagnetic interference.

Description

Optical Acceleration Sensor Based on Fresnel Diffraction Microlens

Technical field

The invention belongs to the technical field of optical fiber sensing, and in particular relates to an optical acceleration sensor based on the combination of Micro Electro Mechanical System (MEMS—Micro Electro Mechanical System), Fresnel diffraction microlens and optical fiber technology.

Background technique

In the flight control system of the aircraft, inertial navigation is one of the most important navigation methods. Using three orthogonal gyroscopes and three orthogonal acceleration sensors can be integrated into an inertial measurement combination, which can provide information such as the attitude and position of the aircraft. At present, the acceleration sensors actually used in the aviation industry are mostly piezoelectric, electromagnetic and capacitive sensors. These sensors directly obtain electrical signals, and there are problems of weak resistance to electromagnetic interference and electromagnetic shock.

Sensors manufactured using MEMS technology have the advantages of small size, light weight, and low cost. However, the accuracy of the current MEMS acceleration sensor is not high, and it is still difficult to meet the accuracy requirements of some aircraft inertial navigation; in addition, the current MEMS acceleration sensor uses piezoresistive, capacitive, piezoelectric and other principles, which are still electrical signals. category.

The fundamental way to solve the above-mentioned problems is to develop a light transmission control system that uses optics for sensing and information transmission. This will greatly improve the aircraft's ability to resist electromagnetic interference and electromagnetic shock. However, the existing acceleration sensing technology can not meet the needs of the development of the light transmission control system in the flight control system.

It is found through literature search that Chinese patent CN 1588094A (published on March 2, 2005) proposes a microgravity acceleration sensor with a planar optical waveguide. Its principle is that the light emitted by the laser meets the coupling conditions and then is coupled into an optical waveguide structure , when the sensor responds to the acceleration, the displacement of the detection mass causes the change of the thickness of the waveguide layer of the optical waveguide, which leads to the change of the reflected light intensity, and the measurement of the acceleration is realized by measuring the change of the light intensity. This structure has the disadvantages of relatively large volume and mass, and weak anti-environment interference ability.

U.S. Patent 6018390 (Jan.25, 2000) proposes an optical waveguide accelerometer, which symmetrically fixes two helical waveguides on a substrate, and a detection mass sensitive to acceleration is installed on both sides of the substrate, and the external acceleration The function of the detection mass presses the helical waveguide, so that the phase shift of the reflected light in the waveguide occurs, and the acceleration measurement is realized by detecting the change of the light. This kind of sensor structure is greatly affected by temperature changes, and the processing technology is complicated.

The object of the present invention is to provide a new structure of a micro optical accelerator with strong anti-electromagnetic interference and electromagnetic pulse capability, low cost and high precision.

Contents of the invention

For the defects or deficiencies in the prior art, the purpose of the present invention is to propose a kind of optical acceleration sensor based on the combination of microelectromechanical system (MEMS), Fresnel diffraction microlens and optical fiber technology. Acceleration is sensitive to acceleration by changing the new principle of light intensity at the focal point of the Fresnel diffractive microlens.

In order to realize above-mentioned task, the present invention takes following technical solution:

An optical acceleration sensor based on a Fresnel diffraction microlens is characterized in that the sensor includes a glass substrate, an optical fiber for transmitting light is arranged under the glass substrate, and a Fresnel lens is processed on the surface of the glass substrate. There is a microreflective film placed in parallel above the Fresnel diffractive lens. There is a small gap between the microreflective film and the Fresnel diffractive microlens. The reflective surface of the microreflective film faces the Fresnel diffractive lens. The other surface of the film is processed with a micro-mass block sensitive to acceleration. The micro-reflective film is connected to the frame through four planar micro-springs. The ends of the optical fibers are overlapped and placed at the focus of the Fresnel diffraction lens. are fixed on the sensor housing;

The light with a wavelength of λ emitted from the end of the fiber is partially reflected at the Fresnel diffraction microlens, and the other part passes through the Fresnel diffraction microlens and is reflected by the micro-reflective film and then passes through the Fresnel diffraction microlens again. , after the light passes through the Fresnel diffraction microlens, the air gap between the Fresnel diffraction microlens and the microreflective film, and the diffraction of the microreflective film, it will be at the focus of the Fresnel diffraction microlens according to the position of the microreflective film. form different light intensity values. When the sensor responds to the acceleration, the micro-reflective film is displaced relative to the Fresnel diffraction microlens, which causes a change in the light intensity at the focus of the Fresnel diffraction microlens, and the measurement of the acceleration is realized by detecting the light intensity change at the focus.

The Fresnel diffraction microlens mentioned above is processed on the glass substrate by sputtering, photolithography and etching; one side of the reflective surface of the microreflective film is a layer of metal reflective film deposited, and the other side is made of MEMS Technology processes a micro-mass block; place the micro-reflective film and the Fresnel diffraction micro-lens in parallel, and leave a small distance; the end of the optical fiber is both the light-emitting end and the light-receiving end.

Although this sensor is a light intensity sensor, it has the sensitivity of a light interference sensor in theory, so the sensitivity is very high; this sensor is sensitive in the light domain, so it has a good ability to resist electromagnetic interference and electromagnetic shock; at the same time It also has the advantages of small size, light weight, easy mass production, and low cost. This sensor can be used not only in the aviation industry, but also in many high electromagnetic interference environments and fields requiring high-precision sensing, such as ships, generator sets, nuclear power plants and many other occasions.

Description of drawings

Fig. 1 is the structural representation of sensor of the present invention;

Fig. 2 is a schematic diagram of a longitudinal section of the sensor of the present invention;

Fig. 3 is the top view of sensor of the present invention;

Fig. 4 is a schematic diagram of the Fresnel diffraction microlens in the sensor of the present invention.

The technical solution of the present invention will be further described in detail below in conjunction with the accompanying drawings.

Detailed ways

As shown in Fig. 1, Fig. 2, Fig. 3, Fig. 4, the main components of the optical acceleration sensor based on the Fresnel diffraction microlens of the present invention are: optical fiber 1, optical fiber end 2 (the optical fiber end 2 is the optical fiber 1 end), glass substrate 3, Fresnel diffraction micro-lens 4, micro-reflective film 5, micro-mass 6, micro-spring 7, frame 8 for fixing spring, shell (not shown in the figure).

As shown in Figure 1, a Fresnel diffraction microlens 4 is processed on the surface of the glass substrate 3 by sputtering, photolithography, corrosion and other microfabrication techniques, and the odd (or even) half of the Fresnel diffraction microlens 4 The wave bands are coated with a reflective metal film, and the even (or odd) bands keep the transparency of the glass; the micro-reflective film 5 is placed in parallel with the Fresnel diffraction microlens 4 and keeps a small distance (several wavelength orders of magnitude), A metal film is coated on the side adjacent to the micro-reflective film 5 and the Fresnel diffraction micro-lens 4, and a micro-mass 6 for sensitive acceleration is processed on the other side. The micro-reflective film 5 is connected to the fixed frame 8 through four planar micro-springs 7 (in this figure, the frame 8 is not shown). Under the action of acceleration force, the micro-mass 6 will drive the micro-reflective film 5 to generate move. The optical fiber 1 is used to transmit light, and the fiber end 2 is fixed at the focal point of the Fresnel diffraction microlens 4 . In order to ensure the sensitivity of the sensor, the focal point of the optical fiber end 2 and the Fresnel diffraction microlens 4 should have a high degree of coincidence. The optical fiber end 2 is both a light emitting end and a light receiving end, and the light going back and forth is transmitted by the same optical fiber 1 . The optical fiber 1, the glass substrate 3, and the frame 8 are all fixedly connected to a casing (the casing is not shown in the figure, and the casing can be in various forms).

As shown in Figure 2, the light emitted from the fiber end 2 is divided into two parts by the Fresnel diffraction microlens 4, one part is directly reflected back by the Fresnel diffraction microlens 4, and the other part is transmitted through the Fresnel diffraction microlens 4. Diffractive microlenses4. The light passing through the Fresnel diffraction microlens 4 is reflected back through the micro-reflective film 5, and when it reaches the focal point through the Fresnel diffraction microlens 4 again and is directly reflected back by the Fresnel diffraction microlens 4, it reaches the Fresnel. The light at the focal point of the diffractive microlens 4 has a phase difference, and the size of the phase difference is related to the position of the microreflective film 5 . In this way, the light intensity at the focal point is related to the position of the microreflective film 5 . When the sensor responds to the external acceleration, the micro-mass 6 will drive the micro-reflective film 5 to produce a displacement, thereby causing the light intensity at the focus to change, and the measurement of the acceleration is realized by measuring the change of the light intensity at the focus.

Figure 3 shows a top view of the sensor of the present invention. An acceleration-sensitive micro-mass 6 is processed outside the micro-reflective film 5 , and the micro-reflective film 5 is connected to the frame 8 through four planar micro-springs 7 . The frame 8 is fixed together with the shell of the sensor (the shell is not drawn in the figure).

FIG. 4 shows a schematic diagram of the Fresnel diffractive microlens 4 . The Fresnel diffraction microlens 4 is processed on the surface of the glass substrate 3 by methods such as sputtering, photolithography and etching. The radius of the Fresnel diffractive microlens 4 is about 0.2mm-0.6mm, and the corresponding focal length is about 2mm-20mm when the number of half-wave bands is 50. In the picture, a layer of reflective metal film is coated on the even-numbered half-wave bands, and the odd-numbered bands maintain the transparency of the glass. The radius of each half-wave band has special requirements, that is, for the light of the working wavelength λ of the sensor, the round-trip optical path difference from the focal point to the adjacent half-wave band should be λ/2.

Fix this sensor on the object to be measured, when the object has accelerated motion, the micro-mass 6 in the sensor will generate an acceleration force, which will cause the distance between the micro-reflective film 5 and the Fresnel diffraction micro-lens 4 The acceleration can be detected by detecting the change of the light intensity in the optical fiber 1 .

Above is the specific example of an realization that the inventor provides, but the present invention is not limited to this embodiment, the parameter of Fresnel diffractive microlens 4 can change, as long as the simple change done on the structure of technical scheme of the present invention, All should belong to the protection scope of the present invention.

Claims (2)

1. optical acceleration sensor based on Fresnel diffraction micr-lens, this sensor comprises a glass substrate (3), be provided with the optical fiber (1) that is used to transmit light in the below of glass substrate (3), be processed with a Fresnel diffraction micr-lens (4) on the surface of glass substrate (3), the parallel little reflective membrane (5) that is placed with in Fresnel diffraction micr-lens (4) top, between little reflective membrane (5) and the Fresnel diffraction micr-lens (4) a small clearance is arranged, the reflective surface of little reflective membrane (5) is towards Fresnel diffraction micr-lens (4), be processed with little mass (6) of a sensitive acceleration on the another side of little reflective membrane (5), little reflective membrane (5) is connected with framework (8) by four plane Microsprings (7), optical fiber end (2) overlaps the focus place that places Fresnel diffraction micr-lens (4), framework (8), glass substrate (3), optical fiber (1) all is fixed on the sensor outer housing;

It is characterized in that, described fresnel diffraction microlens (4) is as optically focused and sensing element, be coated with one deck reflective membrane on the even number half-wave zone of Fresnel diffraction micr-lens (4), the transparency that keeps glass on the odd number band, and the round optical path difference of light from Fresnel diffraction micr-lens (4) focus to adjacent half-wave zone that the radius of half-wave zone satisfies the operation wavelength λ of sensor is λ/2;

The wavelength that sends from optical fiber end (2) is the light of λ, locate the part that is reflected at Fresnel diffraction micr-lens (4), another part sees through Fresnel diffraction micr-lens (4) back and is reflected once more through Fresnel diffraction micr-lens (4) by little reflective membrane (5), light is through Fresnel diffraction micr-lens (4), air-gap between Fresnel diffraction micr-lens (4) and the little reflective membrane (5), behind the diffraction of little reflective membrane (5), difference according to little reflective membrane (5) position forms different light intensity values at Fresnel diffraction micr-lens (4) focus place in meeting, when the sensor response acceleration, little reflective membrane (5) produces displacement with respect to Fresnel diffraction micr-lens (4), thereby cause Fresnel diffraction micr-lens (4) focus place intensity variations, change the measurement that realizes acceleration by the light intensity of surveying the focus place.

2. the optical acceleration sensor based on Fresnel diffraction micr-lens as claimed in claim 1 is characterized in that, the clearance between described little reflective membrane (5) and the Fresnel diffraction micr-lens (4) is a micron order.

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