A fiber-optic fabry-perot temperature sensor and method of making the same

Abstract

This invention relates to the field of sensor technology and discloses a fiber optic Fabry-Perot temperature sensor and its fabrication method. The sensor includes a MEMS temperature-sensitive silicon wafer with a first and a second surface; a first quartz sheet, anode-bonded to the first surface, with a through-hole etched thereon; a second quartz sheet, anode-bonded to the second surface, with a first groove etched on the first surface and a second groove etched on the second quartz sheet facing away from the first groove, the first groove communicating with the through-hole; a quartz tube penetrating the through-hole and inserted into the first groove; an optical fiber penetrating the quartz tube and abutting the inner bottom surface of the first groove; a silicon cavity formed between the inner bottom surface of the first groove and the second surface; and a reference cavity formed between the inner bottom surface of the second groove and the side of the second quartz sheet facing away from the second groove. This sensor utilizes fiber optics combined with MEMS technology to achieve precise control over the length of the silicon cavity and the reference cavity, resulting in good product consistency and improved measurement accuracy. By correcting the reference cavity, the temperature sensitivity becomes more accurate.

Description

Technical Field

[0001] This invention relates to the field of sensor technology, and in particular to a fiber optic Fabry-Perot temperature sensor and its fabrication method. Background Technology

[0002] Fiber optic Fabry-Perot temperature sensors are widely used in oil and gas wells, aerospace and other fields due to their inherent resistance to electromagnetic interference, stable operation, fast response speed and high accuracy.

[0003] The vernier effect is a common phenomenon in interferometry that improves measurement accuracy by superimposing the signals from two interferometers with different free spectral ranges (FSRs). In the field of fiber optic sensors, the vernier effect is widely used to enhance sensor sensitivity and resolution. When the signals from two interferometers overlap, their interference frequencies become slightly detuned, resulting in a vernier envelope modulation in the output spectrum. This envelope modulation is amplified relative to the wavelength shift of the individual sensing interferometers constituting the system, thus providing higher sensitivity. This effect is particularly suitable for fiber optic interferometers, such as Fabry-Perot interferometers, which can utilize the vernier effect to enhance performance when measuring physical quantities such as temperature, pressure, and refractive index.

[0004] Traditional fiber optic Fabry-Perot temperature sensors based on the vernier effect mostly rely on processes with poor repeatability, such as welding and cutting, which leads to low production efficiency and poor consistency. When using the vernier effect of the composite cavity reflection spectrum envelope for temperature measurement, measurement errors still exist. Summary of the Invention

[0005] The purpose of this invention is to provide a fiber optic Fabry-Perot temperature sensor and its fabrication method, which can improve the accuracy of temperature measurement.

[0006] To achieve this objective, the present invention adopts the following technical solution:

[0007] The first aspect of this application provides a fiber optic Fabry-Perot temperature sensor, comprising:

[0008] MEMS temperature-sensitive silicon wafers have a first side and a second side arranged opposite to each other along their thickness direction.

[0009] A first quartz sheet, anode-bonded to the first surface, has through holes etched along the thickness direction;

[0010] The second quartz sheet is anode-bonded to the second surface. The first surface is etched with a first groove. The side of the second quartz sheet opposite to the second surface is etched with a second groove facing away from the first groove. The first groove is connected to the through hole.

[0011] A quartz tube, one end of which passes through the through hole and is inserted into the first groove;

[0012] An optical fiber, one end of which passes through the quartz tube and is attached to the inner bottom surface of the first groove;

[0013] The region between the inner bottom surface of the first groove and the second surface forms a silicon cavity, and the region between the inner bottom surface of the second groove and the side of the second quartz sheet opposite to the second groove forms a reference cavity.

[0014] In some embodiments, the length of the silicon cavity and the length of the reference cavity satisfy the following relationship in the thickness direction:

[0015]

[0016] in, l 1 represents the length of the silicon cavity. l 2 is the length of the reference cavity, n s Let n be the refractive index of the silicon cavity. y denoted as the refractive index of the reference cavity, B as the monitoring wavelength bandwidth, k as the number of periods displaying the complete envelope within the monitoring wavelength bandwidth, and λ as the operating wavelength of the fiber optic Fabry-Perot temperature sensor.

[0017] In some embodiments, the monitoring wavelength bandwidth B, the number of periods k displaying the complete envelope within the monitoring wavelength bandwidth, and the operating wavelength λ of the fiber optic Fabry-Perot temperature sensor satisfy the following conditions:

[0018] 2≤k≤3; 1500nm≤λ≤1600nm; B=100nm.

[0019] In some embodiments, the inner diameter of the through hole is 320 μm to 380 μm.

[0020] In some embodiments, the inner diameter of the second groove is larger than the inner diameter of the first groove; and / or, the thickness of the MEMS temperature-sensitive silicon wafer is 100 μm to 180 μm.

[0021] In some embodiments, the thickness of the first quartz sheet is 130 μm to 200 μm; and / or, the thickness of the second quartz sheet is 200 μm to 300 μm.

[0022] In some embodiments, the fiber optic Fabry-Perot temperature sensor further includes a demodulation module configured to perform the following steps during temperature demodulation at the actual temperature:

[0023] Based on the optical path difference change caused by the reference cavity at the actual temperature, the original composite cavity reflection spectrum formula constructed based on the actual sampling data is corrected to obtain the corrected composite cavity reflection spectrum formula.

[0024] The modified reflection spectrum envelope was obtained by using the modified composite cavity reflection spectrum formula. Temperature was then calculated using the vernier effect to obtain the measurement results. The modified composite cavity reflection spectrum formula is as follows:

[0025] .

[0026] Where A represents the DC component of the reflection spectrum, B is the amplitude of the reflection spectrum of the silicon cavity, C is the amplitude of the reflection spectrum of the reference cavity, and D is the amplitude of the reflection spectrum of the silicon-quartz composite cavity. l 1 represents the length of the silicon cavity. l 2 is the length of the reference cavity, n s Let n be the refractive index of the silicon cavity. y α is the refractive index of the reference cavity, β is the thermal expansion coefficient of quartz, β is the thermo-optical coefficient of quartz, λ is the operating wavelength of the fiber optic Fabry-Perot temperature sensor, and I is the refractive index of the reference cavity. re This represents the light intensity of the corrected composite cavity reflection spectrum. This indicates the actual temperature change relative to the reference temperature, calculated based on a pre-calibrated silicon cavity temperature.

[0027] In some embodiments, before the demodulation module performs temperature demodulation, the calibration of the monitored temperature of the fiber optic Fabry-Perot temperature sensor is further included, wherein the calibration of the monitored temperature of the fiber optic Fabry-Perot temperature sensor includes:

[0028] Determine the temperature T measured by the standard thermometer 温度计 The temperature calibration of the silicon cavity was completed by analyzing the relationship between the peak wavelength of the silicon cavity spectral waveform and the change in the wavelength of the silicon cavity spectral waveform.

[0029] Based on the temperature T measured using the corresponding standard thermometer 温度计 Based on the sampled data obtained, a formula for the uncorrected composite cavity reflectance spectrum at any temperature is constructed, where the standard thermometer measures temperature T. 温度计 Including reference temperature;

[0030] Temperature T is measured using a standard thermometer based on a reference temperature and at any given temperature. 温度计 Determine the amount of temperature change ;

[0031] Based on the temperature change at any given temperature The thermal expansion coefficient α and the thermo-optical coefficient β of quartz are used to find the quartz refractive index-temperature relationship table and the original composite cavity reflection spectrum formula. The original composite cavity reflection spectrum formula at the corresponding temperature is then corrected to obtain the corrected composite cavity reflection spectrum formula at the corresponding temperature.

[0032] Based on the formula for the corrected composite cavity reflection spectrum at any temperature, determine the envelope wavelength shift of the corrected reflection spectrum envelope at that temperature compared to the corrected reflection spectrum envelope at the reference temperature.

[0033] Determine the amount of temperature change The relationship between the envelope wavelength shift and the corrected reflection spectrum envelope was used to complete the temperature calibration of the corrected reflection spectrum envelope.

[0034] In some embodiments, the temperature demodulation process of the fiber optic Fabry-Perot temperature sensor includes:

[0035] Based on actual sampling data obtained at real temperatures, the corresponding silicon cavity spectrum is obtained through FFT transformation and peak selection filtering. Using this spectrum, the pre-completed silicon cavity temperature calibration is located to determine the current peak wavelength shift of the silicon cavity spectrum waveform. Finally, based on this peak wavelength shift, the current temperature change is determined. ;

[0036] Based on the actual sampling data obtained at the actual temperature, the corresponding formula for the pre-corrected composite cavity reflection spectrum is constructed.

[0037] Based on the current temperature change The thermal expansion coefficient α and the thermo-optical coefficient β of quartz are used. Combined with the quartz refractive index-temperature relationship table, the original composite cavity reflection spectrum formula is corrected to obtain the corresponding corrected composite cavity reflection spectrum formula at this temperature.

[0038] Based on the formula for the corrected composite cavity reflection spectrum at this temperature, determine the envelope wavelength shift of the corrected reflection spectrum envelope at this temperature compared to the corresponding corrected reflection spectrum envelope at the reference temperature.

[0039] Based on the envelope wavelength shift, the temperature calibration of the pre-completed corrected reflection spectrum envelope is found, the relationship between the envelope shift of the corrected reflection spectrum envelope and temperature change is determined, and temperature demodulation is completed.

[0040] A second aspect of this application provides a method for fabricating a fiber optic Fabry-Perot temperature sensor, comprising:

[0041] The lower surface of the MEMS temperature-sensitive silicon wafer is anodized to the upper surface of the first quartz wafer;

[0042] A first circular hole is formed on the lower surface of the first quartz sheet by photolithography, and photoresist is uniformly coated on the other areas of the lower surface of the first quartz sheet except for the first circular hole.

[0043] By etching the first circular hole to form a through hole, the lower surface of the MEMS temperature-sensitive silicon wafer is brought into contact with the outside world.

[0044] The area of ​​the lower surface of the MEMS temperature-sensitive silicon wafer facing the through hole is etched to form a first groove, and the area between the inner bottom surface of the first groove and the upper surface of the MEMS temperature-sensitive silicon wafer away from the first groove forms a silicon cavity.

[0045] Remove the photoresist from the area outside the first circular hole, and anodize and bond a second quartz sheet to the upper surface of the MEMS temperature-sensitive silicon wafer;

[0046] A second circular hole is formed on the upper surface of the second quartz sheet by photolithography. The upper surface of the second quartz sheet, except for the second circular hole, is uniformly coated with photoresist. The inner diameter of the second circular hole is larger than the inner diameter of the first circular hole.

[0047] A second groove is formed by etching the second circular hole area, and a reference cavity is formed in the area between the inner bottom surface of the second groove and the side of the second quartz sheet opposite to the second groove.

[0048] Remove the photoresist from the area outside the second circular hole;

[0049] The optical fiber is welded and fixed to the quartz tube, and the quartz tube with the optical fiber is welded and fixed inside the through hole.

[0050] The beneficial effects of this invention are as follows:

[0051] By combining optical fiber with MEMS technology, precise control of the silicon cavity length and reference cavity length can be achieved, which is beneficial for mass production, ensures good product consistency, and improves measurement accuracy.

[0052] In the calibration and demodulation process of the fiber optic Fabry-Perot temperature sensor, an algorithm for optical path correction of the reference cavity is introduced to correct the optical path difference caused by the reference cavity at different temperatures. Then, the temperature is calculated, which greatly improves the accuracy of temperature measurement and enables precise measurement of cavity length changes. Attached Figure Description

[0053] Figure 1 This is a schematic diagram of the fiber optic Fabry-Perot temperature sensor of the present invention.

[0054] Figure 2 This is a flowchart illustrating the calibration process of the fiber optic Fabry-Perot temperature sensor of this invention.

[0055] Figure 3 This is a block diagram of the demodulation process of the fiber optic Fabry-Perot temperature sensor of the present invention.

[0056] Figure 4 The composite cavity reflection spectrum of the fiber optic Fabry-Perot temperature sensor was obtained through simulation calculations.

[0057] Figure 5 This is the reflection spectrum of the composite cavity without optical path correction for the reference cavity.

[0058] Figure 6 This is the reflection spectrum of the quartz cavity (reference cavity) without optical path correction.

[0059] Figure 7 This is the reflection spectrum of the silicon cavity without optical path correction for the reference cavity.

[0060] Figure 8 This is the reflection spectrum of the quartz cavity (reference cavity) after optical path correction.

[0061] Figure 9 This is the composite cavity reflection spectrum after optical path correction of the reference cavity.

[0062] Figure 10 This is a schematic diagram of the fabrication process of the fiber optic Fabry-Perot temperature sensor of the present invention. Detailed Implementation

[0063] The embodiments of the technical solution of this application will now be described in detail with reference to the accompanying drawings. These embodiments are only used to more clearly illustrate the technical solution of this application and are therefore merely examples, and should not be used to limit the scope of protection of this application.

[0064] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit this application.

[0065] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.

[0066] Traditional fiber optic Fabry-Perot temperature sensors based on the vernier effect mostly rely on processes with poor repeatability, such as welding and cutting, which leads to low production efficiency and poor consistency. When using the vernier effect of the composite cavity reflection spectrum envelope for temperature measurement, measurement errors still exist.

[0067] Based on the above issues, such as Figure 1 As shown, some embodiments of this application provide a fiber optic Fabry-Perot temperature sensor, which includes an optical fiber 1, a quartz tube 2, a first quartz plate 3, a MEMS temperature-sensitive silicon wafer 4, and a second quartz plate 5. The MEMS temperature-sensitive silicon wafer 4 has a first surface and a second surface arranged opposite to each other along its thickness direction. A first quartz plate 3 is anoly bonded to the first surface of the MEMS temperature-sensitive silicon wafer 4, and a through hole 31 is etched on the first quartz plate 3 along its thickness direction. A second quartz plate 5 is anoly bonded to the second surface of the MEMS temperature-sensitive silicon wafer 4. A first groove 41 is etched on the first surface of the MEMS temperature-sensitive silicon wafer 4. A second groove 51 opposite to the second surface of the second quartz plate 5 is etched on one side facing away from the second surface, and the first groove 41 communicates with the through hole 31. One end of a quartz tube 2 passes through the through hole 31 and is inserted into the first groove 41. One end of an optical fiber 1 passes through the quartz tube 2 and is attached to the inner bottom surface of the first groove 41. The area between the inner bottom surface of the first groove 41 and the second surface of the MEMS temperature-sensitive silicon wafer 4 forms a silicon cavity, which can also be called a sensing cavity. The area between the inner bottom surface of the second groove 51 and the side of the second quartz plate 5 facing away from the second groove 51 forms a reference cavity.

[0068] In the embodiments of this application, a quartz material is used to construct the reference cavity, and a silicon material is used to construct the sensing cavity. The temperature sensitivity of the silicon cavity is amplified by constructing an envelope of the composite cavity and measuring temperature based on the vernier effect, thus achieving accurate temperature measurement. Furthermore, with the continuous development of microelectromechanical systems (MEMS) technology, fiber optic combined with MEMS processes has been widely studied due to its advantages such as high consistency, mass production, and low cost. Since MEMS-based etching processes can precisely and effectively control the wafer etching depth to fabricate a specific FP cavity length, the vernier effect can be precisely controlled. In the embodiments of this application, the first quartz wafer 3, the MEMS temperature-sensitive silicon wafer 4, and the second quartz wafer 5 are manufactured and assembled using MEMS processing technology, which facilitates precise control of the silicon cavity length and the reference cavity length, promotes mass production, and improves product consistency.

[0069] In some implementations, reference Figure 1 In the thickness direction of the MEMS temperature-sensitive silicon wafer 4, the silicon cavity length l 1 and reference cavity length l The relationship between the two is (1):

[0070] (1)

[0071] in, l 1 represents the length of the silicon cavity. l 2 represents the length of the reference cavity, and n s Let n be the refractive index of the silicon cavity. y λ is the refractive index of the reference cavity, B is the monitoring wavelength bandwidth, k is the number of cycles displaying the complete envelope within the monitoring wavelength bandwidth, and λ is the operating wavelength of the fiber optic Fabry-Perot temperature sensor.

[0072] In some implementations, B = 100 nm; k is 2 or 3; 1500 nm ≤ λ ≤ 1600 nm; preferably, k is set to 3.

[0073] In some embodiments, the thickness of the first quartz plate 3 is 130 μm to 200 μm.

[0074] In some embodiments, the inner diameter of the second groove 51 is larger than the inner diameter of the first groove 41.

[0075] In some implementations, the thickness of the MEMS temperature-sensitive silicon wafer 4 is 100 μm to 180 μm.

[0076] In some embodiments, the thickness of the second quartz plate 5 is 200 μm to 300 μm.

[0077] In some embodiments, the inner diameter of the through hole 31 is 320 μm to 380 μm.

[0078] In some implementations, the fiber optic Fabry-Perot temperature sensor also includes a demodulation module configured to perform the following steps during temperature demodulation at the actual temperature:

[0079] Based on the optical path difference change caused by the reference cavity at the actual temperature, the original composite cavity reflection spectrum formula constructed based on the actual sampling data is corrected to obtain the corrected composite cavity reflection spectrum formula.

[0080] The modified reflection spectrum envelope is obtained by using the modified composite cavity reflection spectrum formula. Temperature is then calculated using the vernier effect to obtain the measurement result. The modified composite cavity reflection spectrum formula (2) is as follows:

[0081] (2)

[0082] Where A represents the DC component of the reflection spectrum, B is the amplitude of the reflection spectrum of the silicon cavity, C is the amplitude of the reflection spectrum of the reference cavity, and D is the amplitude of the reflection spectrum of the silicon-quartz composite cavity. l 1 represents the length of the silicon cavity. l2 represents the length of the reference cavity, and n s Let n be the refractive index of the silicon cavity. y α is the refractive index of the reference cavity, α is the thermal expansion coefficient of quartz, β is the thermo-optical coefficient of quartz, λ is the operating wavelength of the fiber optic Fabry-Perot temperature sensor, and I is the refractive index of the reference cavity. re This represents the light intensity of the corrected composite cavity reflection spectrum. This indicates the actual temperature change relative to the reference temperature, calculated based on a pre-calibrated silicon cavity temperature.

[0083] When the ambient temperature changes, the envelope of the composite cavity reflection spectrum, and the characteristic spectral wavelengths of the silicon cavity and the reference cavity all experience drift; for example... Figure 2 As shown, the temperature calibration process of the fiber optic Fabry-Perot temperature sensor in this application mainly includes:

[0084] Step 110: Determine the standard thermometer measurement temperature T. 温度计 By relating the temperature of the silicon cavity to the peak wavelength of its spectral waveform, the silicon cavity temperature can be calibrated. Interpretatively, this calibration can be used to represent different temperature values ​​(T). 温度计 The corresponding peak wavelength shift of the silicon cavity spectral waveform. For example, T 温度计 Temperatures included 0, 5, 10, 15, 20, and 25 degrees Celsius. Using 0 degrees Celsius as the reference temperature, the peak wavelength shift of the silicon cavity spectral waveform at other temperatures was determined, thus establishing the correlation between temperature change and the peak wavelength shift of the silicon cavity spectral waveform. The peak wavelength of the silicon cavity spectral waveform refers to the wavelength corresponding to the peak value of the waveform formed in the silicon cavity spectrum. With changes in temperature, this peak wavelength shifts.

[0085] Step 120: Measure the temperature T using the corresponding standard thermometer. 温度计 Based on the sampled data obtained, a formula for the uncorrected composite cavity reflectance spectrum at any temperature is constructed, where the standard thermometer measures temperature T. 温度计 Including reference temperature;

[0086] For explanatory purposes, the reference temperature can be 25 degrees Celsius or 0 degrees Celsius, etc.; the formula for the pre-correction composite cavity reflection spectrum at any temperature can be expressed as the following formula (3).

[0087] Step 130: Measure temperature T based on the reference temperature and a standard thermometer measured at any given temperature. 温度计 Determine the amount of temperature change ;

[0088] Explanatory, temperature change The corresponding formula for the uncorrected composite cavity reflection spectrum can be expressed as:

[0089] .

[0090] Step 140: Based on the temperature change at any given temperature Find the thermal expansion coefficient α and the thermo-optical coefficient β of quartz, look up the quartz refractive index-temperature relationship table and the original composite cavity reflection spectrum formula, modify the original composite cavity reflection spectrum formula at this temperature, and obtain the modified composite cavity reflection spectrum formula at this temperature.

[0091] Explanatoryly, the corrected formula for the composite cavity reflectance spectrum at this temperature can be expressed as:

[0092] .

[0093] It should be noted that, This represents the parameter value at any given temperature, determined by combining the quartz refractive index-temperature relationship table and the original formula for the composite cavity reflection spectrum. Among these, For the optical path difference correction process of the reference cavity, here and The formula for the composite cavity reflection spectrum was obtained before the correction was determined.

[0094] Step 150: Based on the formula for the corrected composite cavity reflection spectrum at any temperature, determine the envelope wavelength shift of the corrected reflection spectrum envelope at that temperature compared to the corrected reflection spectrum envelope at the reference temperature.

[0095] Interpretive, the corresponding corrected reflectance spectrum envelope can be constructed at the reference temperature and at any temperature. It is assumed that the corrected reflectance spectrum envelope constructed at the reference temperature is the same as the original reflectance spectrum envelope at that temperature. Thus, the amount of envelope wavelength shift of the corrected reflectance spectrum envelope constructed at any temperature compared to the corrected reflectance spectrum envelope at the reference temperature can be determined.

[0096] Step 160: Determine the temperature change. The relationship between the envelope wavelength shift and the corrected reflection spectrum envelope was used to complete the temperature calibration of the corrected reflection spectrum envelope.

[0097] Since the envelope wavelength shift of the corrected reflectance spectrum envelope constructed at any temperature is obtained compared to the corrected reflectance spectrum envelope at the reference temperature, the corresponding standard thermometer measurement temperature T is obtained. 温度计 and the corresponding temperature change at any given temperature This has also been obtained, which allows us to construct the envelope wavelength shift and temperature change. The relationship is as follows. For example, the monitoring temperature at any given temperature = reference temperature + envelope wavelength drift * sensitivity; sensitivity represents the temperature change corresponding to every 1nm shift in the envelope wavelength.

[0098] In summary, once the temperature monitoring calibration is completed, the temperature can be demodulated during subsequent actual temperature monitoring.

[0099] like Figure 3 As shown, the demodulation process of the embodiments of this application mainly includes:

[0100] Step 210: Based on the actual sampling data obtained at the actual temperature, the corresponding silicon cavity spectrum is obtained through FFT (Fast Fourier Transform) and peak selection filtering. Based on this silicon cavity spectrum, the pre-completed silicon cavity temperature calibration is located to determine the current peak wavelength shift of the silicon cavity spectrum waveform. Based on the current peak wavelength shift of the silicon cavity spectrum waveform, the current temperature change is determined. ;

[0101] At this point, the silicon cavity temperature coefficient can be determined based on the silicon cavity temperature calibration, and thus the temperature change required for subsequent corrections can be obtained. The silicon cavity temperature coefficient is used to characterize the relationship between temperature change and silicon cavity spectral shift.

[0102] Step 220: Based on the actual sampling data obtained at the actual temperature, construct the corresponding formula for the pre-correction composite cavity reflection spectrum;

[0103] The explanatory, pre-corrected composite cavity reflectance spectrum formula, constructed through fitting based on actual sampled data, can be expressed in the following form:

[0104] .

[0105] Step 230: Based on the current temperature change The thermal expansion coefficient α and the thermo-optical coefficient β of quartz are used. Combined with the quartz refractive index-temperature relationship table, the original composite cavity reflection spectrum formula is corrected to obtain the corresponding corrected composite cavity reflection spectrum formula at this temperature.

[0106] Explanatory, combined with the current temperature change The current temperature can be roughly determined. Based on this roughly determined current temperature and the quartz refractive index-temperature relationship table, the corresponding... The value of α, combined with the thermal expansion coefficient α and the thermo-optical coefficient β of quartz, can be used to correct the original composite cavity reflection spectrum formula. The corrected composite cavity reflection spectrum formula at this temperature can be expressed in the following form:

[0107] .

[0108] Step 240: Based on the formula for the corrected composite cavity reflection spectrum at this temperature, determine the envelope wavelength shift of the corrected reflection spectrum envelope at this temperature compared to the corresponding corrected reflection spectrum envelope at the reference temperature.

[0109] Step 250: Based on the envelope wavelength drift, find the pre-completed temperature calibration of the corrected reflection spectrum envelope, determine the relationship between the envelope drift of the corrected reflection spectrum envelope and the temperature change, and complete the temperature demodulation.

[0110] Interpretive sensitivity can be determined by finding the temperature calibration of the pre-completed corrected reflectance spectrum envelope, and then the corresponding actual temperature can be calculated to complete temperature demodulation.

[0111] Furthermore, the above embodiments provide implementation methods for temperature calibration of the fiber optic Fabry-Perot temperature sensor and temperature demodulation involving the correction process. In some embodiments, the fiber optic Fabry-Perot temperature sensor can be corrected using the above-described correction method before demodulation in each temperature demodulation process; in other embodiments, the fiber optic Fabry-Perot temperature sensor may further include the following before each temperature demodulation process:

[0112] Set a correction time list, which lists the time points that need to be corrected using the correction method described above; for example, 6 PM, midnight, etc., or every half hour as a correction time point;

[0113] Determine whether the current time point is the time point recorded in the correction time list. If so, use the correction method described above to correct and then demodulate. Otherwise, use the correction formula of the composite cavity reflection spectrum determined after the previous correction using the above correction method to determine the envelope wavelength shift of the correction reflection spectrum envelope at this temperature compared to the corresponding correction reflection spectrum envelope at the reference temperature, and complete the temperature demodulation.

[0114] Under normal monitoring conditions, short-term temperature changes are not too large, so repeated correction operations are unnecessary in a short period of time. The above steps can reduce the number of corrections and reduce the demodulation workload. For explanation, when performing the first temperature measurement in the initial state, the composite cavity reflectance spectrum formula corresponding to the reference temperature can be set to the corrected composite cavity reflectance spectrum formula determined after the first correction using the above correction method, as described above.

[0115] Furthermore, this application has been verified through specific experiments as follows:

[0116] First, the uncorrected reflection spectrum formula for the composite cavity consisting of the silicon cavity and the reference cavity is:

[0117] .

[0118] Where R1, R2, and R3 are the reflectivities of the three reflective interfaces, R1 = R2 = (n s -n y ) 2 / (n s +n y ) 2 n s With n y R3 represents the refractive index of the silicon cavity and the reference cavity, respectively, with values ​​of 3.42 and 1.45 at the base temperature; R3 = (n s -n a ) 2 / (n s +n a ) 2 n a is the refractive index of air, with a value of 1; l 1 and l 2 represents the silicon cavity length and the reference cavity length, respectively.

[0119] The above formula can be simplified to the following formula (3):

[0120] (3)

[0121] It should be noted that the reflection spectrum formula for this silicon-quartz composite cavity neglects the transmission loss coefficients of each reflection interface and the two FP cavities, representing an ideal situation. As can be seen from the formula, the reflection spectrum contains three frequency components, representing the silicon cavity, the reference cavity, and the silicon-reference cavity, respectively.

[0122] The relationship between the silicon cavity and the reference cavity can be determined by the free spectral range (FSR) of the reflection spectral envelope. env The decision was made based on the fact that single-mode fiber experiences very little transmission attenuation (≤0.3dB / km) in the 1550nm communication band. Therefore, the monitoring band of a typical fiber optic sensor analyzer (1500nm~1600nm) was selected as the simulation band for this sensor.

[0123] The applicant found that, within this wavelength range (1500nm~1600nm), to ensure complete real-time monitoring of the wavelength shift of the reflectance spectral envelope, it is reasonable to display 2~3 envelope periods within the 1500nm~1600nm range. env At 32nm, it is possible to display three cycles completely within this wavelength range.

[0124] Assuming silicon cavity length l 1 is 100μm, FSR env With silicon cavity length l Substituting into formula (1) yields the reference cavity length. l2 is 210 μm. This is determined by the length of the silicon cavity. l 1 and reference cavity length l 2. The optical path length n of the silicon cavity can be obtained. s l 1. Optical path n with reference cavity y l The values ​​are 342 μm and 304.5 μm, respectively.

[0125] The reflection spectrum of the fiber optic Fabry-Perot temperature sensor was obtained through simulation calculation using formula (3) as follows: Figure 4 As shown, an envelope signal is superimposed on the high-frequency signal, which is a typical characteristic of the vernier effect. The vernier effect produces the free spectral range (FSR) of the reflectance spectral envelope. env ) can be determined by the free spectral range (FSR) of the silicon cavity. s ) and the reference cavity free spectral range (FSR) y The calculation is performed using formulas (4) to (6).

[0126] (4)

[0127] (5)

[0128] (6)

[0129] As can be seen from the composite cavity reflection spectrum, the FSR of the composite cavity reflection spectrum envelope is... env The FSR is 31.7 nm, calculated using formula (5). env The value is 32.0 nm, which is consistent with the simulation value. Therefore, it is determined that a vernier effect occurs.

[0130] Due to the thermal expansion coefficient of silicon (α) s ) and thermo-optic coefficient (β) s The values ​​are 2.5 × 10⁻⁶ respectively. -6 With 1.84×10 -4 The coefficient of thermal expansion of quartz (α) y ) and thermo-optic coefficient (β) y The values ​​are 5.5 × 10⁻⁶ respectively. -7 With 1×10 -5 The temperature sensitivity of the silicon cavity and the reference cavity is calculated by formula (7).

[0131] (7)

[0132] Since the coefficients of thermal expansion of silicon and quartz are much smaller than their thermo-optical coefficients, the thermo-optical coefficient plays a dominant role in influencing the optical path difference when the temperature changes. In an ideal vernier effect, the optical path of the reference cavity should ideally be unaffected by the external environment to achieve accurate measurement of external physical quantities. However, in reality, although the thermo-optical coefficient of quartz is an order of magnitude smaller than that of silicon, the optical path of the reference cavity still changes during temperature variations, thus affecting the amplification factor of the vernier effect and causing measurement errors.

[0133] Experimental analysis shows that, under actual conditions, without correction for the optical path difference of the reference cavity, assuming an increase in ambient temperature of 20°C, due to the thermo-optical effect and thermal expansion effect of silicon and quartz, the characteristic reflection spectra of both the silicon cavity and the reference cavity exhibit a redshift. Although the thermo-optical coefficient of quartz is an order of magnitude smaller than that of silicon, a slight redshift still occurs, with the silicon cavity and reference cavity redshifting by 1.63 nm and 0.23 nm respectively. The temperature sensitivity of the silicon cavity is 0.08 nm / °C. This redshift in both the silicon and reference cavities leads to a redshift in the sensor's reflection spectrum, and the envelope of the reflection spectrum also exhibits a redshift, with a wavelength shift of 12.86 nm and a temperature sensitivity of 0.63 nm / °C. Figures 5-7 As shown.

[0134] In the vernier effect, the sensitivity of the reflectance spectrum envelope is related to the sensitivity of the silicon cavity by formula (8), where the envelope sensitivity is M times the silicon cavity sensitivity. Formula (8) is:

[0135] (8)

[0136] The amplification factor of 9.045 can be calculated from formula (8), and the wavelength shift of the envelope can be calculated to be 14.74 nm. The simulation result is 1.88 nm smaller than the calculated result. This error is caused by the drift of the wavelength of the reference cavity reflection spectrum with temperature change. It can be seen that the temperature sensitivity of the fiber Fabry-Perot temperature sensor without optical path correction (i.e. before correction) will be less than the theoretical calculated value.

[0137] Now, the optical path of the reference cavity is corrected using formula (2). Similarly, assuming the ambient temperature increases by 20℃, after correcting the optical path of the reference cavity using formula (2), the characteristic wavelength shift of the reference cavity's characteristic spectrum after the temperature rise is 0 nm, and the characteristic spectra before and after the temperature rise completely overlap, as shown below. Figure 8 As shown. The wavelength shift of the sensor's reflection spectrum at a temperature rise of 20°C is as follows. Figure 9 As shown, the envelope wavelength shift of the reflection spectrum is 14.70 nm, which differs from the calculated theoretical value by only 0.04 nm. The temperature sensitivity is 0.74 nm / ℃, which is an improvement compared to before the optical path correction.

[0138] Therefore, the implementation method of this application, by introducing an optical path correction algorithm for the reference cavity, corrects the changes in optical path difference caused by the reference cavity at different temperatures, amplifies the enhancement characteristics, and makes the temperature sensitivity more accurate.

[0139] Explanatory Figure 4 The composite cavity reflection spectrum of the fiber optic Fabry-Perot temperature sensor was obtained through simulation calculations. Figure 4 The solid lines represent the composite cavity reflection spectrum lines, and the dashed lines represent the composite cavity reflection spectrum envelope obtained from the composite cavity reflection spectrum lines. Figure 5 This is the reflection spectrum of the composite cavity without optical path correction for the reference cavity. Figure 5 The solid blue line represents the composite cavity reflection spectrum before drift; the dashed yellow line represents the composite cavity reflection spectrum envelope corresponding to the composite cavity reflection spectrum before drift; the solid orange-yellow line represents the composite cavity reflection spectrum after drift; the dashed purple line represents the composite cavity reflection spectrum envelope corresponding to the composite cavity reflection spectrum after drift; the wavelength shift of the envelope is 12.86 nm. Figure 6 This is the reflection spectrum of the quartz cavity (reference cavity) without optical path correction. Figure 6 The solid blue line represents the quartz cavity reflection spectrum before drift; the solid yellow line represents the quartz cavity reflection spectrum after drift; the drift of the quartz cavity reflection spectrum is 0.23 nm. Figure 7 This is the reflection spectrum of the silicon cavity without optical path correction for the reference cavity. Figure 7 The solid blue line represents the silicon cavity reflection spectrum before drift; the solid yellow line represents the silicon cavity reflection spectrum after drift; the drift of the silicon cavity reflection spectrum is 1.63 nm. Figure 8 This is the reflection spectrum of the quartz cavity (reference cavity) after optical path correction. Figure 9 This is the composite cavity reflection spectrum after optical path correction of the reference cavity. Figure 9 The solid orange-yellow line represents the composite cavity reflection spectrum line before drift; the purple dashed line represents the composite cavity reflection spectrum envelope corresponding to the composite cavity reflection spectrum line before drift; the solid yellow line represents the composite cavity reflection spectrum line after drift; the green dashed line represents the composite cavity reflection spectrum envelope corresponding to the composite cavity reflection spectrum line after drift; the wavelength shift of the envelope is 14.70 nm. Figure 4-9 In optics, dB refers to decibels, a unit used to describe the intensity of light signals; composite cavity refers to a composite cavity; and wavelength refers to the wavelength.

[0140] In some embodiments, this application also provides a method for fabricating a fiber optic Fabry-Perot temperature sensor, used to fabricate the fiber optic Fabry-Perot temperature sensor provided in the above embodiments. The method for fabricating the fiber optic Fabry-Perot temperature sensor includes the following steps:

[0141] The lower surface of the MEMS temperature-sensitive silicon wafer 4 is anoly bonded to the upper surface of the first quartz wafer 3, such as... Figure 10 (a);

[0142] A first circular hole is formed on the lower surface of the first quartz plate 3 through photolithography. The remaining areas on the lower surface of the first quartz plate 3, excluding the first circular hole, are uniformly coated with photoresist. Figure 10 (b);

[0143] By etching the first circular hole area to form a through hole (31), the lower surface of the MEMS temperature-sensitive silicon wafer 4 is brought into contact with the outside world, such as... Figure 10 (c);

[0144] The area on the lower surface of the MEMS temperature-sensitive silicon wafer 4 opposite to the via 31 is etched to form a first groove 41. A silicon cavity is formed between the inner bottom surface of the first groove 41 and the upper surface of the MEMS temperature-sensitive silicon wafer 4 opposite to the first groove 41. Figure 10 (d); where the etching method can be reactive ion etching or plasma etching; by controlling the etching time or etching rate, the etching depth can be precisely controlled, thereby controlling the silicon cavity length. l 1.

[0145] Remove the photoresist from the area outside the first circular hole, and anodize and bond the second quartz sheet 5 to the upper surface of the MEMS temperature-sensitive silicon wafer 4, as shown below. Figure 10 (e) and Figure 10 (f);

[0146] A second circular hole is formed on the upper surface of the second quartz wafer 5 through photolithography. The remaining areas of the upper surface of the second quartz wafer 5, excluding the second circular hole, are uniformly coated with photoresist. In some embodiments, the inner diameter of the second circular hole is larger than the inner diameter of the first circular hole, such as... Figure 10 (g);

[0147] A second groove 51 is formed by etching the area of ​​the second circular hole; a reference cavity is formed in the area between the inner bottom surface of the second groove 51 and the side of the second quartz plate 5 facing away from the second groove 51. Figure 10 (h); wherein, the etching method can be reactive ion etching or plasma etching; by controlling the etching time or etching rate, the etching depth can be precisely controlled, thereby controlling the reference cavity length. l 2; The reference cavity amplifies and corrects the temperature sensitivity of the silicon cavity;

[0148] Remove the photoresist from areas other than the second circular hole, such as... Figure 10 (i);

[0149] The optical fiber 1 is welded and fixed to the quartz tube 2, and the quartz tube 2 with the optical fiber 1 is welded and fixed inside the through hole 31.

[0150] Explanatoryly, a fiber optic Fabry-Perot temperature sensor generally includes a probe and a demodulation device connected to the probe. The above process describes the probe fabrication process, and then the temperature calibration and demodulation method provided in the above embodiments of this application can be used for debugging.

[0151] The fiber optic Fabry-Perot temperature sensor fabrication method provided in this application utilizes fiber optics combined with MEMS technology to achieve precise control over the length of the silicon cavity and the reference cavity, facilitating mass production and ensuring good product consistency. Furthermore, an algorithm for optical path correction of the reference cavity is introduced during the calibration and demodulation process of the fiber optic Fabry-Perot temperature sensor. This corrects for changes in the optical path difference caused by different temperatures in the reference cavity, followed by temperature calculation, significantly improving the accuracy of temperature measurement and enabling precise measurement of cavity length changes.

[0152] The technical principles of the present invention have been described above with reference to specific embodiments. These descriptions are merely for explaining the principles of the invention and should not be construed as limiting the scope of protection of the invention in any way. Based on this explanation, those skilled in the art can readily conceive of other specific embodiments of the invention without inventive effort, and these embodiments will all fall within the scope of protection of the present invention.

[0153] It should be understood that the disclosed apparatus and methods can also be implemented in other ways, given the several embodiments provided in this application. The apparatus embodiments described above are merely illustrative. For example, the flowcharts and block diagrams in the accompanying drawings illustrate the architecture, functionality, and operation of possible implementations of apparatus, methods, and computer program products according to various embodiments of this application. In this regard, each block in a flowchart or block diagram may represent a module, segment, or portion of code, which contains one or more executable instructions for implementing a specified logical function. It should also be noted that in some alternative implementations, the functions marked in the blocks may occur in a different order than those marked in the drawings. For example, two consecutive blocks may actually be executed substantially in parallel, or they may sometimes be executed in reverse order, depending on the functions involved. It should also be noted that each block in a block diagram and / or flowchart, and combinations of blocks in block diagrams and / or flowcharts, can be implemented using a dedicated hardware-based system that performs the specified function or action, or using a combination of dedicated hardware and computer instructions.

[0154] In addition, the functional modules in the various embodiments of this application can be integrated together to form an independent part, or each module can exist independently, or two or more modules can be integrated to form an independent part.

[0155] The above description is only an optional implementation of the embodiments of this application, but the protection scope of the embodiments of this application is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the embodiments of this application should be covered within the protection scope of the embodiments of this application.

Claims

1. A fiber-optic Fabry-Perot temperature sensor, characterized by, include: MEMS temperature-sensitive silicon wafers have a first side and a second side arranged opposite to each other along their thickness direction. A first quartz sheet, anode-bonded to the first surface, has through holes etched along the thickness direction; The second quartz sheet is anode-bonded to the second surface. The first surface is etched with a first groove. The side of the second quartz sheet opposite to the second surface is etched with a second groove facing away from the first groove. The first groove is connected to the through hole. A quartz tube, one end of which passes through the through hole and is inserted into the first groove; An optical fiber, one end of which passes through the quartz tube and is attached to the inner bottom surface of the first groove; The region between the inner bottom surface of the first groove and the second surface forms a silicon cavity, and the region between the inner bottom surface of the second groove and the side of the second quartz sheet opposite to the second groove forms a reference cavity. The fiber optic Fabry-Perot temperature sensor also includes a demodulation module configured to perform the following steps during temperature demodulation at the actual temperature: Based on the optical path difference change caused by the reference cavity at the actual temperature, the original composite cavity reflection spectrum formula constructed based on the actual sampling data is corrected to obtain the corrected composite cavity reflection spectrum formula. The modified reflection spectrum envelope was obtained by using the modified composite cavity reflection spectrum formula. Temperature was then calculated using the vernier effect to obtain the measurement results. The modified composite cavity reflection spectrum formula is as follows: Where A represents the DC component of the reflection spectrum, B is the amplitude of the reflection spectrum of the silicon cavity, C is the amplitude of the reflection spectrum of the reference cavity, and D is the amplitude of the reflection spectrum of the silicon-quartz composite cavity. l 1 represents the length of the silicon cavity. l 2 is the length of the reference cavity, n s Let n be the refractive index of the silicon cavity. y α is the refractive index of the reference cavity, β is the thermal expansion coefficient of quartz, β is the thermo-optical coefficient of quartz, λ is the operating wavelength of the fiber optic Fabry-Perot temperature sensor, and I is the refractive index of the reference cavity. re This represents the light intensity of the corrected composite cavity reflection spectrum. This indicates the actual temperature change relative to the reference temperature, calculated based on the pre-calibrated silicon cavity temperature. The formula for the original composite cavity reflection spectrum is expressed as follows: 。 2. The fiber optic Fabry-Perot temperature sensor according to claim 1, characterized in that, In the thickness direction, the length of the silicon cavity and the length of the reference cavity satisfy the following relationship: in, l 1 represents the length of the silicon cavity. l 2 is the length of the reference cavity, n s Let n be the refractive index of the silicon cavity. y denoted as the refractive index of the reference cavity, B as the monitoring wavelength bandwidth, k as the number of periods displaying the complete envelope within the monitoring wavelength bandwidth, and λ as the operating wavelength of the fiber optic Fabry-Perot temperature sensor.

3. The fiber optic Fabry-Perot temperature sensor according to claim 2, characterized in that, The monitoring wavelength bandwidth B, the number of periods k that display the complete envelope within the monitoring wavelength bandwidth, and the operating wavelength λ of the fiber optic Fabry-Perot temperature sensor satisfy the following conditions: 2≤k≤3; 1500nm≤λ≤1600nm; B=100nm.

4. The fiber optic Fabry-Perot temperature sensor according to claim 1, characterized in that, The inner diameter of the through hole is 320μm to 380μm.

5. The fiber optic Fabry-Perot temperature sensor according to claim 1, characterized in that, The inner diameter of the second groove is larger than the inner diameter of the first groove; and / or, the thickness of the MEMS temperature-sensitive silicon wafer is 100μm to 180μm.

6. The fiber optic Fabry-Perot temperature sensor according to claim 1, characterized in that, The thickness of the first quartz sheet is 130 μm to 200 μm; and / or the thickness of the second quartz sheet is 200 μm to 300 μm.

7. The fiber optic Fabry-Perot temperature sensor according to claim 1, characterized in that, Before the demodulation module performs temperature demodulation, the calibration of the monitored temperature of the fiber optic Fabry-Perot temperature sensor is also included. This calibration includes: Determine the standard thermometer measured temperature T 温度计 With the change of the peak wavelength of the silicon cavity spectrum waveform, the temperature calibration of the silicon cavity is completed. According to the temperature T measured by the corresponding standard thermometer 温度计 The sampling data obtained below, construct any temperature before the correction of the complex cavity reflection spectrum formula, the standard thermometer measures temperature T 温度计 Including the reference temperature; Temperature T is measured using a standard thermometer based on a reference temperature and at any given temperature. 温度计 Determine the amount of temperature change ; Based on the temperature change at any given temperature The thermal expansion coefficient α and the thermo-optical coefficient β of quartz are used to find the quartz refractive index-temperature relationship table and the original composite cavity reflection spectrum formula. The original composite cavity reflection spectrum formula corresponding to any temperature is then modified to obtain the modified composite cavity reflection spectrum formula corresponding to any temperature. Based on the formula for the corrected composite cavity reflection spectrum at any temperature, determine the envelope wavelength shift of the corrected reflection spectrum envelope at that temperature compared to the corrected reflection spectrum envelope at the reference temperature. Determine the amount of temperature change The relationship between the envelope wavelength shift and the corrected reflection spectrum envelope was used to complete the temperature calibration of the corrected reflection spectrum envelope.

8. The fiber optic Fabry-Perot temperature sensor according to claim 1, characterized in that, The temperature demodulation process of the fiber optic Fabry-Perot temperature sensor includes: Based on actual sampling data obtained at real temperatures, the corresponding silicon cavity spectrum is obtained through FFT transformation and peak selection filtering. Using this spectrum, the pre-completed silicon cavity temperature calibration is located to determine the current peak wavelength shift of the silicon cavity spectrum waveform. Finally, based on this peak wavelength shift, the current temperature change is determined. ; Based on the actual sampling data obtained at the actual temperature, the corresponding formula for the pre-corrected composite cavity reflection spectrum is constructed. Based on the current temperature change The thermal expansion coefficient α and the thermo-optical coefficient β of quartz are used, along with the quartz refractive index-temperature relationship table, to correct the original composite cavity reflection spectrum formula and obtain the corrected composite cavity reflection spectrum formula at the current temperature. Based on the formula for the corrected composite cavity reflection spectrum at the current temperature, determine the envelope wavelength shift of the corrected reflection spectrum envelope at the current temperature compared to the corresponding corrected reflection spectrum envelope at the reference temperature. Based on the envelope wavelength shift, the temperature calibration of the pre-completed corrected reflection spectrum envelope is found, the relationship between the envelope shift of the corrected reflection spectrum envelope and temperature change is determined, and temperature demodulation is completed.

9. A method for fabricating a fiber optic Fabry-Perot temperature sensor, used to fabricate the fiber optic Fabry-Perot temperature sensor of claim 1, characterized in that, include: The lower surface of the MEMS temperature-sensitive silicon wafer is anodized to the upper surface of the first quartz wafer; A first circular hole is formed on the lower surface of the first quartz sheet by photolithography, and photoresist is uniformly coated on the other areas of the lower surface of the first quartz sheet except for the first circular hole. By etching the first circular hole to form a through hole, the lower surface of the MEMS temperature-sensitive silicon wafer is brought into contact with the outside world. The area of ​​the lower surface of the MEMS temperature-sensitive silicon wafer facing the through hole is etched to form a first groove, and the area between the inner bottom surface of the first groove and the upper surface of the MEMS temperature-sensitive silicon wafer away from the first groove forms a silicon cavity. Remove the photoresist from the area outside the first circular hole, and anodize and bond a second quartz sheet to the upper surface of the MEMS temperature-sensitive silicon wafer; A second circular hole is formed on the upper surface of the second quartz sheet by photolithography, and photoresist is uniformly coated on the other areas of the upper surface of the second quartz sheet except for the second circular hole. A second groove is formed by etching the second circular hole area, and a reference cavity is formed in the area between the inner bottom surface of the second groove and the side of the second quartz sheet opposite to the second groove. Remove the photoresist from the area outside the second circular hole; The optical fiber is welded and fixed to the quartz tube, and the quartz tube with the optical fiber is welded and fixed inside the through hole.

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