A dynamically adjustable performance optical fiber F-P cavity MEMS sensor and a preparation method thereof

Abstract

The application discloses a kind of performance dynamically adjustable optical fiber F-P cavity MEMS sensor and preparation method thereof, belong to optical fiber sensor technical field, include sapphire sensitive structure, sapphire substrate structure, optical fiber sleeve, guided mode resonance grating, F-P cavity and optical fiber, high refractive index dielectric layer, the present application is by introducing guided mode resonance grating on sapphire surface to realize the optimization of sapphire interface reflection spectrum, and then can be designed and controlled F-P interferometer spectrum precision for different demodulation methods, to realize sensor performance regulation and control.Compared with the traditional F-P cavity sensor sensitive structure surface plating with fixed reflectivity metal reflection film and other ways, the present application can realize interface reflectivity adjustment, to realize sensor dynamic performance regulation and control facing different test application scenarios.

Description

Technical Field

[0001] This invention belongs to the field of fiber optic sensor technology, specifically relating to a dynamically adjustable fiber optic FP cavity MEMS sensor and its fabrication method. Background Technology

[0002] Pressure sensing technology in extreme environments has urgent application needs in many important industrial fields such as aerospace engines, oil and gas resource development, and nuclear reactor monitoring. Sensors capable of operating in extreme testing environments are the most critical enabling technology. Intrinsic FP cavity MEMS sensors have outstanding advantages such as high sensitivity, compactness, scalability, and high degree of freedom in sensitive structure design. Sapphire material has excellent optical properties, mechanical properties, and chemical stability, and can operate under harsh conditions with temperatures approaching 2000°C, showing great application potential. Therefore, sapphire-based intrinsic FP sensors are the most effective technical means to achieve sensing in high-temperature extreme environments.

[0003] However, sapphire-based intrinsic FP sensors currently face development bottlenecks, mainly due to: 1. Sapphire's hardness, brittleness, and exceptionally stable physicochemical properties make it difficult to process, resulting in the inability to obtain large and thin sensitive film structures, thus hindering the improvement of sensor mechanical sensitivity; 2. Sapphire is a low-refractive-index material (refractive index below 1.74 in the infrared band), resulting in low interfacial reflectivity. This leads to lower interference spectral precision in sapphire-based FP interferometers, limiting the sensor's optical sensitivity. The paper "A HIGH-TEMPERATURE OPTICAL SAPPHIREPRESSURE SENSOR FOR HARSH ENVIRONMENTS" describes platinum coating on the sapphire surface to improve interfacial reflectivity. However, platinum has a constant interfacial reflectivity, and different application scenarios will require different sensor sensitivity, dynamic response range, and other performance indicators. For example, in high-temperature internal flow field pulsating pressure testing of aero-engines, sensors need to have a large dynamic response range to adapt to pressure fluctuations caused by surge, stall, etc.; while when monitoring minute pulsating pressure and acoustic characteristics caused by oscillating combustion and combustion instability in the engine combustion chamber, sensors need to have high sensitivity to distinguish minute signals. The sensitivity and dynamic range of intriguing FP sensors are related to the fringe fineness of their FP interference spectrum. Due to the low interfacial reflectivity of sapphire material, the FP interference fringe fineness formed is low. Although methods such as coating metal mirrors and Bragg mirrors can improve the interfacial reflectivity, they are difficult to use in high-temperature extreme environments. At the same time, mirrors have constant reflectivity. If reflectivity can be adjusted, it is expected that the sensor performance can be dynamically adjusted according to the application scenario and testing environment, which will greatly broaden the application range of sapphire-based intriguing FP sensors. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a fiber optic FP cavity MEMS sensor and its fabrication method that can realize interface reflectivity adjustment and dynamic performance control of the sensor for different testing application scenarios.

[0005] The technical solution adopted to solve the above technical problems is as follows: A dynamically adjustable fiber optic FP cavity MEMS sensor includes a sapphire sensitive structure, a sapphire substrate structure, an optical fiber sleeve, a guided-mode resonant grating, an FP cavity and optical fiber, and a high-refractive-index dielectric layer. Through holes are processed on the sapphire substrate structure. The through holes of the sapphire substrate structure, the sapphire sensitive structure, and the optical fiber sleeve constitute the FP cavity. The FP cavity is a closed vacuum cavity used to measure the measured pressure. The sapphire sensitive structure is located below the sapphire substrate structure, and the optical fiber sleeve is located above the through holes of the sapphire substrate structure. An optical fiber for measuring spectral changes caused by changes in the measured pressure is set on the optical fiber sleeve. A high-refractive-index dielectric layer is set on the sapphire sensitive structure in the FP cavity and on the sapphire substrate structure around the through holes. A guided-mode resonant grating is set on the sapphire sensitive structure in the FP cavity.

[0006] A method for fabricating a fiber optic FP-cavity MEMS sensor with dynamically tunable performance includes the following steps:

[0007] S1. Two sapphire wafers are selected and cleaned separately. A through hole with a diameter of 2mm is processed on one of the sapphire wafers to obtain a sapphire substrate structure.

[0008] S2, bond the two sapphire wafers from step S1 together;

[0009] S3, polish and thin the other sapphire wafer from step S1 to obtain a sapphire sensitive structure;

[0010] S5, a high refractive index dielectric layer is deposited on the surface of the FP cavity 5 in the sapphire substrate structure around the through hole and on the sapphire sensitive structure by molecular beam epitaxy or atomic layer deposition.

[0011] S4, patterned etching mask on the surface of high refractive index dielectric layer by electron beam lithography or deep ultraviolet lithography, and mode resonant grating structure in FP cavity on sapphire sensitive structure by ICP dry etching or wet etching.

[0012] S6 uses femtosecond or picosecond etching to dice the finished sapphire wafer into small pieces to form sensor chips. The optical fiber and fiber optic sleeve are then fixed into the FP cavity to form the sensor.

[0013] Furthermore, the two sapphire wafers in step S1 have a thickness of 400 μm and a diameter of 10.16 cm.

[0014] Furthermore, the bonding method for the two sapphire wafers in step S2 is as follows: the surfaces of the two sapphire wafers are surface activated by rapid argon ion bombardment, and pressure is applied in the bonding machine to align and bond the two wafers together. The loading temperature is 100℃~400℃ and the loading pressure is 0.25~1MPa.

[0015] Furthermore, the method for polishing and thinning the other sapphire wafer in step S3 is as follows: the other sapphire wafer is thinned and polished with single-crystal diamond polishing slurry and SF1 polishing slurry to reduce its thickness to 5-15 μm.

[0016] This invention optimizes the sapphire interface reflection spectrum by introducing a guided mode resonant grating on the sapphire surface. This allows for the design and control of the spectral precision of the FP interferometer for different demodulation methods, thereby enabling sensor performance regulation. Compared to traditional methods such as depositing a metal reflective film with a fixed reflectivity on the surface of the FP cavity sensor's sensitive structure, this invention enables interface reflectivity adjustment, allowing for dynamic performance regulation of the sensor for different testing application scenarios. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the structure of an embodiment of the fiber optic FP cavity MEMS sensor with dynamically adjustable performance according to the present invention.

[0018] Figure 2 It consists of two perfectly bonded sapphire crystals.

[0019] Figure 3 The sensitive structure of sapphire is formed by thinning and polishing.

[0020] Figure 4 It forms a high refractive index medium layer.

[0021] Figure 5 It constitutes the guided mode resonant grating of the scatterer array.

[0022] Figure 6 These are the reflectance-wavelength curves when the interface reflectance is 30%, 60%, and 90%.

[0023] Figure 7 It is the sensor cavity length-reflected light power formed by the reflectivity corresponding to the interface reflectivity of 30%, 60%, and 90%.

[0024] Figure reference numerals: 1. Sapphire sensitive structure; 2. Sapphire substrate structure; 3. Optical fiber sleeve; 4. Guided mode resonant grating; 5. FP cavity and optical fiber; 6. High refractive index dielectric layer; 7. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0026] like Figure 1 As shown, the dynamically adjustable fiber optic FP cavity MEMS sensor of this embodiment is composed of a sapphire sensitive structure 1, a sapphire substrate structure 2, an optical fiber sleeve 3, a guided mode resonant grating 4, an FP cavity 5, an optical fiber 6, and a high refractive index dielectric layer 7 connected together.

[0027] The dynamically adjustable fiber optic FP cavity MEMS sensor comprises a sapphire sensing structure 1, a sapphire substrate structure 2, an optical fiber sleeve 3, a guided-mode resonant grating 4, an FP cavity 5, an optical fiber 6, and a high-refractive-index dielectric layer 7. A through-hole is fabricated on the sapphire substrate structure 2. The through-hole, the sapphire sensing structure 1, and the optical fiber sleeve 3 together form the FP cavity 5, which is a sealed vacuum cavity used to measure the measured pressure. The sapphire sensing structure 1 is located below the sapphire substrate structure 2, and the optical fiber sleeve 3 is located above the through-hole in the sapphire substrate structure 2. An optical fiber 6, used to measure spectral changes caused by variations in the measured pressure, is mounted on the optical fiber sleeve 3. A high-refractive-index dielectric layer 7 is located on the sapphire sensing structure 1 within the FP cavity 5 and on the sapphire substrate structure 2 around the through-hole. A guided-mode resonant grating 4 is located on the sapphire sensing structure 1 within the FP cavity 5. By introducing a guided-mode resonant grating on the sapphire surface to optimize the sapphire interface reflectance spectrum, the spectral precision of the FP interferometer can be designed and adjusted for different demodulation methods, thereby achieving sensor performance regulation. Compared to traditional methods such as depositing a metal reflective film with a fixed reflectivity on the surface of the FP cavity sensor's sensitive structure, this embodiment can achieve interface reflectivity adjustment, enabling dynamic performance regulation of the sensor for different testing application scenarios.

[0028] like Figure 6 The image shows a typical peak-shaped reflectance spectrum, with reflectance-wavelength curves for interface reflectance of 30%, 60%, and 90%. Figure 7 As shown, the sensor cavity length-reflected light power curves, i.e., optical sensitivity curves, are formed by the reflectivity of the interface at 30%, 60%, and 90%. The higher the interface reflectivity, the sharper the characteristic curve, resulting in increased sensor sensitivity but decreased dynamic range; conversely, decreased interface reflectivity leads to decreased sensor sensitivity and increased dynamic range. Therefore, the interface reflectivity can be adjusted by regulating the center wavelength of the monochromatic DFB light source output, thereby controlling sensor performance. Rapid tuning of the interface reflectivity can be achieved by adjusting the incident monochromatic light wavelength, thereby adjusting the fineness of the FP interferometric spectrum and parameters such as sensor sensitivity and dynamic range.

[0029] A method for fabricating a fiber optic FP-cavity MEMS sensor with dynamically tunable performance includes the following steps:

[0030] S1. Two sapphire wafers are selected and cleaned separately. The thickness of the two sapphire wafers is 400μm and the diameter is 10.16cm. A through hole with a diameter of 2mm is processed on one of the sapphire wafers to obtain sapphire substrate structure 2.

[0031] S2, the two sapphire wafers from step S1 are bonded together. The bonding method for the two sapphire wafers is as follows: the surfaces of the two sapphire wafers are surface-activated by rapid argon ion bombardment; pressure is applied in a bonding machine to align and bond the two wafers together. The loading temperature is 100℃~400℃, and the loading pressure is 0.25~1MPa. Figure 2 As shown.

[0032] S3, the other sapphire wafer from step S1 is polished and thinned to obtain sapphire sensitive structure 1. The method for polishing and thinning the other sapphire wafer is as follows: the other sapphire wafer is thinned and polished using single-crystal diamond polishing slurry and SF1 polishing slurry to reduce its thickness to 5-15 μm. Figure 3 As shown.

[0033] S5, a high-refractive-index dielectric layer 7 is deposited on the surface of the sapphire sensitive structure 1 located in the FP cavity 5 around the through-hole of the sapphire substrate structure 2 using molecular beam epitaxy or atomic layer deposition. Figure 4 As shown.

[0034] S4, an etching mask is patterned on the surface of the high refractive index dielectric layer 7 using electron beam lithography or deep ultraviolet lithography. Then, a mode-guided resonant grating structure 4 is formed on the sapphire sensitive structure 1 within the FP cavity 5 using ICP dry etching or wet etching. Figure 5 As shown.

[0035] S6, using femtosecond or picosecond etching, the processed sapphire wafer is diced into small pieces to form the sensor's sensitive chip. The optical fiber 6 and optical fiber sleeve 3 are then fixedly installed into the FP cavity 5 to form the sensor. Figure 1 As shown.

[0036] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention.

Claims

1. A fiber optic FP-cavity MEMS sensor with dynamically adjustable performance, characterized in that: The structure includes a sapphire sensitive structure (1), a sapphire substrate structure (2), an optical fiber sleeve (3), a guided mode resonant grating (4), an FP cavity (5), an optical fiber (6), and a high refractive index dielectric layer (7). A through hole is processed on the sapphire substrate structure (2). The through hole of the sapphire substrate structure (2), the sapphire sensitive structure (1), and the optical fiber sleeve (3) form an FP cavity (5). The FP cavity (5) is a closed vacuum cavity and is used to measure the pressure to be measured. The sapphire sensitive structure (1) is located below the sapphire substrate structure (2), and the optical fiber sleeve (3) is located above the through hole of the sapphire substrate structure (2). An optical fiber (6) for measuring the spectral changes caused by the change of the pressure to be measured is provided on the optical fiber sleeve (3). A high refractive index dielectric layer (7) is provided on the sapphire sensitive structure (1) in the FP cavity (5) and on the sapphire substrate structure (2) around the through hole. A guided mode resonant grating (4) is provided on the sapphire sensitive structure (1) in the FP cavity (5). The fabrication method of the above-mentioned fiber optic FP-cavity MEMS sensor includes the following steps: S1. Two sapphire wafers are selected and cleaned respectively. A through hole with a diameter of 2mm is processed on one of the sapphire wafers to obtain a sapphire substrate structure (2). S2, bond the two sapphire wafers from step S1 together; The bonding method for the two sapphire wafers in step S2 is as follows: the surfaces of the two sapphire wafers are surface activated by rapid argon ion bombardment, and pressure is applied in the bonding machine to align and bond the two wafers together. The loading temperature is 100℃~400℃ and the loading pressure is 0.25~1MPa. S3, polish and thin the other sapphire wafer from step S1 to obtain a sapphire sensitive structure (1); S4, a high refractive index dielectric layer (7) is deposited on the surface of the FP cavity (5) of the sapphire substrate structure (2) around the through hole and on the sapphire sensitive structure (1) by means of molecular beam epitaxy or atomic layer deposition. S5, patterning an etching mask on the surface of the high refractive index dielectric layer (7) using electron beam lithography or deep ultraviolet lithography, and forming a guided mode resonant grating (4) in the FP cavity (5) on the sapphire sensitive structure (1) using ICP dry etching or wet etching. S6. The sapphire wafer is cut into small pieces by femtosecond or picosecond ablation to form a sensor chip. The optical fiber (6) and the optical fiber sleeve (3) are fixedly installed in the FP cavity (5) to form a sensor.

2. The fiber optic FP-cavity MEMS sensor with dynamically adjustable performance according to claim 1, characterized in that: The two sapphire wafers in step S1 are both 400 μm thick and 10.16 cm in diameter.

3. The fiber optic FP-cavity MEMS sensor with dynamically adjustable performance according to claim 1, characterized in that, The method for polishing and thinning the other sapphire wafer in step S3 is as follows: the other sapphire wafer is thinned and polished with single crystal diamond polishing slurry and SF1 polishing slurry to reduce its thickness to 5-15 μm.

Images