Dual-band MOEMS optical fiber grating sensing system capable of self-encoding and self-calibrating

Abstract

The invention discloses a self-encoding and self-calibrating dual-band MOEMS optical fiber grating-like sensing system, which is characterized by comprising a sensing mechanism based on ultraviolet modulation band and visible light sensing band detection, the sensing mechanism comprises a dual-band optical fiber and a grating-like arranged on the outer side of the dual-band optical fiber, and the grating-like is arranged on the outer side of the dual-band optical fiber. The grating-like structure is formed by filling a plurality of groups of MOEMS periodic grooves and ZnO grooves, and self-adjustment of the grating-like structure is realized through ultraviolet light intensity coding. According to the sensing mechanism, the barrier that the sensing characteristics cannot be changed after a traditional grating is processed is broken through, the existence and the strength of the grating can be realized through optical band coding, so that a coding self-adjusting function on an ultraviolet spectrum according to the characteristics of data to be collected is realized; secondly, time domain demodulation calculation can be utilized, interference of interference variables such as temperature and pressure on a traditional grating is removed, and the method has good practicability.

Description

Technical Field

[0001] The present invention belongs to the technical field of fiber grating sensing devices, and particularly relates to a dual-band MOEMS fiber grating sensing system capable of self-encoding and self-calibration. Background Art

[0002] Characteristic parameters such as liquid density, concentration, and pollution degree are all important bases for evaluating liquid quality. Liquid sensing technology is not only of great significance in the field of basic research, but also very important in important application industries related to the national economy and people's livelihood, such as food safety, environmental governance, and aerospace. At present, with the development of high-precision all-optical sensing systems, traditional electronic liquid measurement systems are gradually unable to meet the application requirements. Therefore, how to achieve non-destructive measurement of liquid parameters with high precision and high sensitivity has become the research focus of academia and industry.

[0003] Due to advantages such as intrinsic safety, simple structure, small size, passivity, and electromagnetic interference resistance, fiber optic sensing structures are widely used in modern industrial production, especially in extreme and complex environments, where they can achieve sensing safely and stably, which makes fiber optic sensing systems have great application potential. As an important branch of fiber optic sensing structures, fiber Bragg gratings are widely used in temperature sensing and stress sensing due to their advantages such as high sensitivity and high precision. However, in existing fiber Bragg grating liquid density sensing schemes, traditional fiber Bragg gratings are usually used. Once fabricated, their structural characteristics are fixed, with poor flexibility, unable to be adjusted according to usage requirements, and having cross-sensitivity interference of pressure and temperature, which can no longer meet the development needs of miniaturized, integrated, and intelligent high-precision sensing systems.

[0004] For example, the existing patent CN116839655A discloses a solar intelligent building fiber optic sensing intelligent perception system, which includes a fiber optic gas concentration sensing module, a fiber optic temperature / humidity sensing module, a fiber optic vibration sensing module, a signal processing module, a communication bus, and an input / output module; the fiber Bragg grating gas sensing module, the fiber Bragg grating temperature / humidity sensing module, and the fiber Bragg grating vibration sensing module are respectively connected to the signal processing unit through a fiber optic junction box, and the signal processing unit is connected to the input / output module through the communication bus. This technology uses ZnO composite materials coated on the grating surface. It utilizes the material to absorb CO, generate heat, cause the grating to thermally expand and contract, and the central wavelength to change, thereby realizing the gas sensing function. The reaction between ZnO and CO utilizes a chemical reaction. Secondly, the thermal expansion and contraction of the grating cause the grating period to change, thereby causing the central wavelength to change.

[0005] For example, existing patent CN110672135A discloses a temperature-compensated fiber Bragg grating (FBG) ultraviolet sensing method and device, comprising a sequentially connected light source, a UV sensor head, and an optical signal processor. The UV sensor head comprises a single-mode optical fiber, a multimode optical fiber, a plastic fiber Bragg grating (PBG), and a ZnO-composite graphene oxide (GO). Each component is connected via fiber fusion splicing. The ZnO-composite GO, prepared using a sol-gel-assisted hydrothermal method, is coated on the PBG. Changes in UV intensity are indirectly determined by measuring changes in the interference spectrum. However, this technology utilizes changes in the interference pattern caused by changes in the propagation constant of ZnO under UV irradiation. Its sensing principle is based on a five-segment fiber coupling structure between the FBG and the multimode optical fiber, and its sensing principle is multimode interference. Moreover, its sensing optical fiber material is plastic optical fiber, and its sensing loss, sensing characteristics, sensing stability, and reliability are quite different from those of quartz optical fiber. It can hardly be reused and has no application value. Moreover, its grating structure does not have a substantial impact on the sensing structure. It only utilizes sensitivity enhancement, which is the same effect as punching sensitivity enhancement points on the optical fiber, and does not utilize the sensing characteristics of the grating. Summary of the invention

[0006] The purpose of the present invention is to provide a dual-band MOEMS fiber grating sensing system that can self-encode and self-calibrate, aiming to solve the above-mentioned problems.

[0007] The present invention is mainly achieved through the following technical solutions:

[0008] A self-encoding and self-calibrating dual-band MOEMS fiber-optic grating-like sensing system includes a sensing mechanism based on detection of the ultraviolet modulation band and the visible light sensing band. The sensing mechanism includes a dual-band optical fiber and a grating-like sensor arranged outside the dual-band optical fiber. The grating-like sensor is composed of several groups of MOEMS periodic grooves and ZnO groove fillings. The grating-like sensor is self-adjusted by encoding the ultraviolet light intensity. The maximum reflectivity R max and the corresponding peak wavelength λ max for:

[0009] R max =tanh 2 (kL)(19)

[0010]

[0011] Where: k is the mode coupling coefficient;

[0012] L is the grating-like length;

[0013] Λ is the grating-like period;

[0014] Δn max is the effective refractive index n effThe maximum modulation range.

[0015] To better implement the present invention, further, the system further includes a signal modulation generator, a light source, a circulator, and a signal demodulator arranged in sequence from front to back. The circulator is respectively connected to the sensing mechanism and the signal demodulator, and the sensing mechanism is connected to the signal demodulator; the light source is used to provide ultraviolet light and visible light; the signal modulation generator is used to act on the light source through encoding to make the light source generate encoded pulsed light, and the pulsed light enters the sensing mechanism as a signal through the circulator.

[0016] To better implement the present invention, further, the encoded pulsed light includes a zero-point calibration area and a calibration area; in the zero-point calibration area, only ultraviolet light is output; in the calibration area, both visible light and ultraviolet light are output, and the effective refractive index n of the pseudo-grating eff The change amount is:

[0017]

[0018] Wherein: Represents the modulation of the average effective refractive index of the optical fiber;

[0019] υ represents the visibility of the refractive index change fringes of the pseudo-grating;

[0020] Λ represents the period of the pseudo-grating;

[0021] z is the coordinate in the transmission direction;

[0022] Represents the grating phase shift of the pseudo-grating under the influence of ultraviolet light modulation.

[0023] To better implement the present invention, further, the calibration of the sensing mechanism is as follows: when the effective refractive index n of the pseudo-grating eff Changes, the center wavelength of the reflection peak becomes λ B2 , this signal enters the signal demodulator through the reflection optical path for demodulation to obtain the wavelength drift amount Δλ B =λ B2 -λ B1 ; on the other hand, the liquid also absorbs ultraviolet light, and the ultraviolet transmitted light enters the signal demodulator through the incident optical path to obtain the ultraviolet transmitted light intensity I UV And the transmission spectrum to complete the calibration. At this time, the wavelength drift amount Δλ B And the ultraviolet transmitted light intensity I UV Are all initial sampling values, and the accuracy of the data is judged by mutual reference.

[0024] To better implement the present invention, further, several zero-point calibration areas and calibration areas are sequentially arranged for the encoded pulsed light to perform calibration several times.

[0025] To better implement the present invention, further, the ultraviolet modulation band is 200 nm to 380 nm; the visible light sensing band is 380 nm to 670 nm, which is used to shield unnecessary signals.

[0026] To better implement the present invention, further, the ultraviolet modulation band is 200 nm to 360 nm, which is used for sensitivity modulation of the sensing mechanism; the visible light sensing band includes 380 nm to 450 nm and 550 nm to 670 nm, which are respectively used for oil quality detection and density sensing.

[0027] To better implement the present invention, further, it is applied to realize the measurement of liquid density, concentration, and contamination degree.

[0028] The beneficial effects of the present invention are as follows:

[0029] (1) The sensing mechanism of the present invention breaks through the barrier of the sensing characteristics that cannot be changed after traditional grating processing. The presence, absence, and intensity of the grating can be realized through optical band coding, so as to realize the self-adjustment function of encoding the ultraviolet spectrum according to the characteristics of the data to be collected. Secondly, the present invention can use time-domain demodulation calculation to remove the interference of interference quantities such as temperature and pressure on the traditional grating, and has good practicability.

[0030] (2) The present invention can be adapted to the measurement of liquid density, concentration, and contamination degree. The ultraviolet light intensity of the present invention can adaptively adjust the sensitivity and measurement range of the sensing mechanism to meet the measurement application requirements of different liquid densities; the ultraviolet band sensing of the sensing mechanism of the present invention is based on the absorption of liquids. Therefore, not only can the density change of the liquid be judged by the ultraviolet light intensity, but also the quantitative analysis of liquid molecules can be carried out through the absorption spectrum, which can be used for liquid contamination sensing; the structure of the sensing mechanism of the present invention is simple and compact, easy to install, and a single sensor can complete multiple functions such as density measurement, contamination measurement, self-calibration, elimination of temperature and stress interference, improvement of sensing accuracy, and adjustable sensitivity. The measurement system has a clear structure and simple operation. Description of the Drawings

[0031] Figure 1 It is a schematic structural diagram of the sensing mechanism;

[0032] Figure 2 It is a principle block diagram of the self-encoding and self-calibrating dual-band MOEMS fiber grating sensing system of the present invention;

[0033] Figure 3 It is a timing diagram of the ultraviolet light and visible light of the light source of the encoded pulsed light in Example 2;

[0034] Figure 4 It is an absorption spectrum diagram of RP-3 aviation kerosene in Example 3;

[0035] Figure 5 It is the principle block diagram of the RP-3 oil quality sensor in Example 4.

[0036] Where: 1 - sensing mechanism, 2 - dual-band optical fiber, 3 - MOEMS periodic groove, 4 - ZnO groove filling, 5 - light source, 6 - signal modulation generator, 7 - circulator, 8 - signal demodulator. Specific implementation mode

[0037] Example 1:

[0038] A dual-band MOEMS fiber grating sensing system that can perform self-encoding and self-calibration. When ZnO is irradiated by ultraviolet light, the carriers change, resulting in a change in the effective refractive index n eff which changes, and ultimately causes a change in the center wavelength λ of the fiber grating B This change is controllable. Through this characteristic, ultraviolet pulse coding is used to achieve the self-adjustment function of the fiber grating. At the backend, time-domain demodulation calculation is used to shield interference quantities such as temperature and pressure. And the presence, absence, and strength of the fiber grating can be achieved through optical band coding, so as to perform autonomous adjustment according to the characteristics of the data to be collected.

[0039] The dual band includes an ultraviolet modulation band and a visible light sensing band, where 200nm - 380nm is the ultraviolet modulation band and 380nm - 670nm is the visible light sensing band. When only the light in the 380nm - 670nm band is used for sensing, the sensing structure can be approximated as an ordinary optical fiber structure and does not have an obvious sensing function. This state can be used to shield unnecessary signals. When light in the 200nm - 380nm band is injected, the carriers in the ZnO in the sensing structure change, and the effective refractive index changes with the ultraviolet light intensity, showing a "fiber grating-like" effect. At this time, when light in the 380nm - 670nm band is injected into the sensing structure, liquid density sensing can be achieved. The present invention can achieve modulation and sensing simultaneously through the ultraviolet light and visible light bands, and the two sensing principles of ultraviolet based on absorption and visible light based on interference are more reliable when carried out simultaneously. And functional self-check, fiber grating sensing characteristic adjustment, and temperature interference elimination can also be carried out through coding.

[0040] Preferably, the 380nm - 670nm band can be replaced by other infrared bands, such as 1500 - 1600nm / 1300nm - 1400nm. From an engineering perspective, using this band can reduce the volume of the light source, facilitate observation, and greatly reduce the use cost and system complexity.

[0041] Preferably, the key points of the present invention lie in the mode theory derivation of light transmission in the fiber grating-like, the time-domain spectrum of ultraviolet light modulation of the fiber grating-like, and the modulation process.

[0042] Assume that the ultraviolet light (200nm - 380nm) intensity I at a certain momentUVC is:

[0043] I UVC = I0 + i UVC (t) (1)

[0044] where: I0 is the initial light intensity,

[0045] i UVC (t) is the function of the light intensity varying with time t.

[0046] In addition, in the theory of fiber grating-like coupling, the adjustment of the fiber grating-like structure to the optical fiber is regarded as a perturbation treatment. The effective refractive index modulation δn of the fiber grating-like eff can be expressed as:

[0047]

[0048] where: represents the average effective refractive index modulation of the optical fiber;

[0049] υ represents the visibility of the refractive index change fringes of the fiber grating-like;

[0050] Λ represents the period of the fiber grating-like;

[0051] z is the coordinate in the transmission direction;

[0052] represents the grating phase shift or chirp function of the fiber grating-like under the influence of ultraviolet light modulation.

[0053] Analyzing the transverse mode field E of the fiber grating-like from the analysis method of the linearly polarized mode T :

[0054]

[0055] where: and respectively represent the amplitudes of the p-th ideal mode propagating forward and backward along the fiber axis, and the propagation constant β = 2πn eff / λ, where λ is the central wavelength of the fiber grating-like.

[0056] The influence of the ultraviolet light i UVC (t) on the mode field can be reflected in the time variable t, and there is no coupling between the ideal modes of each order, but the refractive index modulation of the fiber grating-like can cause coupling between the modes of each order, and respectively taking partial derivatives with respect to z, can be expressed as:

[0057]

[0058] where A q (z, i UVC (t)) and Bq (z, i UVC (r)) represent the amplitudes of the q-th ideal mode propagating forward and backward along the fiber axis, respectively, and i UVC (t) is the ultraviolet light intensity, t is the time, ω is the angular frequency, Δε(x, y, z) represents the perturbation of the dielectric constant of the grating-like medium, e(x, y) represents the distribution of the mode field in the propagation cross-section, the superscript T represents the transverse mode field, the subscript p represents the p-th mode, i is the imaginary unit, and z is the coordinate in the propagation direction, which can be regarded as the propagation distance.

[0059]

[0060] In the formula, Δε(x, y, z) represents the perturbation of the dielectric constant of the grating-like medium. When the refractive index modulation depth is much smaller than the refractive index, the transverse coupling in the fiber is much larger than the longitudinal coupling. Therefore, the longitudinal coupling is ignored, and only the transverse coupling is shown in the formula. Define the self-coupling coefficient ξ qp (z) and the cross-coupling coefficient k qp to describe the change in the refractive index of the grating:

[0061]

[0062] Substitute into formulas (4) and (5), and factor out the coefficient related to i UVC (t) as the correlation correction coefficient σ(i UVC (t)), and simplify to:

[0063]

[0064]

[0065] In the grating-like medium, the forward and backward propagating lights with the same wavelength near the central wavelength are coupled, and the amplitudes are A p (z, t) and B P (z, t), respectively. To simplify the calculation, define the physical quantities A + (z, i UVC (t)), B + (z, i UVC (t)), ξ + , and δ d as:

[0066]

[0067] where

[0068] where λ B = 2n eff Λ, and calculate the effective refractive index of n eff (z, i UVC ) according to the axial position division of the grating-like medium, which can be expressed as:

[0069]

[0070] where f(z) and g(z) are the fiber distribution function of the grating-like and the distribution function of the ZnO groove filling in the grating-like, respectively. Assuming that the ZnO filling is uniform and in an ideal state, L d is the size of the sensing structure.

[0071] For the sake of convenience of representation, let:

[0072]

[0073] The coupled-mode equations are obtained according to the boundary conditions. Then the normalized amplitude C is:

[0074]

[0075] The reflectivity R is the square of the normalized amplitude, expressed as:

[0076]

[0077] When ξ + = 0, the grating reflectivity is the maximum. At this time, substituting n eff into the formula:

[0078]

[0079] where n eff (z, t) = n eff,0 + δn eff (z, i UVC ), and given Equation (2), it can be known that the maximum reflectivity R max corresponding to the peak wavelength λ max is:

[0080] R max = tanh 2 (kL)(19)

[0081]

[0082] Based on this, the sensing structure is designed. The MOEMS groove period Λ and the initial effective refractive index n eff.0 of the sensing structure are both constants. The relationship between the maximum refractive index modulation depth and the maximum sensing center wavelength can be modulated by ultraviolet light.

[0083] Example 2:

[0084] A dual-band MOEMS fiber grating-like sensing system that can self-encode and self-calibrate can achieve high-precision measurement and has no interference from fiber grating cross-sensitivity. As Figure 1 andFigure 2 As shown, it includes a light source, a signal modulation generator, a circulator, a sensing mechanism, and a signal demodulator. The light source is respectively connected to the signal modulation generator and the circulator. The circulator is respectively connected to the sensing mechanism and the signal demodulator, and the sensing mechanism is connected to the signal demodulator. The light source is used to provide ultraviolet light and visible light. The signal modulation generator is used to act on the light source through encoding, so that the light source generates Figure 3 the encoded pulsed light as shown, and the pulsed light enters the sensing mechanism as a signal through the circulator.

[0085] Preferably, the sensing mechanism includes a dual-band optical fiber and a grating-like structure. The grating-like structure is composed of several groups of MOEMS periodic grooves filled with ZnO grooves. The MOEMS periodic grooves and the ZnO groove filling can form a grating-like structure. The sensing mechanism is a left-right symmetric structure. Therefore, any port can be selected as the input port, and the other end is the output port. Here, the left side is selected as the incident port.

[0086] As Figure 3 shown, where area ① is the zero-point calibration area. At this time, the visible light output is 1, and the ultraviolet light output is 0 (here, 0 and 1 represent logical values, 0 means no output, and 1 means there is output). At this time, the center wavelength of the reflection peak is λ B1 (which can be regarded as a very small quantity).

[0087] Among them, area ② is the calibration area. At this time, the visible light output is 1, and the ultraviolet light output is also 1. At this time: on the one hand, the ZnO groove filling in the MOEMS periodic grooves absorbs the ultraviolet light in the band, and the effective refractive index n eff of the grating-like structure changes, and the change amount is:

[0088] The specific calibration steps are as follows:

[0089] First, at a certain moment, the functional relationship between the center wavelength λ B of the grating-like structure and the effective refractive index n eff can satisfy the ordinary grating relationship:

[0090] λ B = 2n eff Λ(21)

[0091] On this basis, when n eff changes, the center wavelength of the reflection peak becomes λ B2 , and this signal enters the signal demodulator through the reflection optical path for demodulation to obtain the wavelength drift amount Δλ B = λ B2 - λ B1 ; on the other hand, the liquid also absorbs ultraviolet light, and the ultraviolet transmitted light enters the signal demodulator through the incident optical path to obtain the ultraviolet transmitted light intensity I UVand the transmission spectrum to complete the calibration. At this time, the wavelength drift amount Δλ B and the ultraviolet transmission light intensity I UV are both sampling values of the initial liquid density, and can be used with reference to each other to judge the accuracy of the data, realizing the self-check of the sensor function, which is more reliable and safe than single-parameter measurement.

[0092] Repeat the calibration process of ① and ② above. Calibration can be carried out once or multiple times. Multiple calibrations can improve the calibration accuracy.

[0093] When the external liquid density changes, the central wavelength of the grating-like changes accordingly, and the ultraviolet light intensity changes with the liquid density. By simultaneously solving ΔI and Δλ B =λ B -λ B2 to measure the liquid density and contamination degree, and the transmission spectrum of the ultraviolet light can quantitatively analyze the liquid components. In addition, the sensitivity and measurement range of the sensor can be adjusted by modulating the intensity of the ultraviolet light band. As the ultraviolet light power increases, the sensitivity of the sensor increases, but n eff The maximum adjustable range Δn max is limited. Considering the sensing central wavelength Δλ B According to the above function relation (20), parameter balance design is carried out.

[0094] In addition, aiming at the problem that the grating-like is cross-sensitive to temperature and stress, before the ultraviolet light is incident, λ B The wavelength is insensitive to the external liquid density. The central wavelength at this time can be marked as the initial central wavelength. The Δλ B calculated later is not affected by temperature and stress. Assuming that the temperature and stress environment of the test environment remain unchanged within Δt time, self-calibration is carried out by encoding and modulating the waveform of the ultraviolet pulsed light, and Δλ B can also be verified for abnormality through the changes in ultraviolet light intensity and ultraviolet absorption spectrum. This sensor can be used alone or in multiple groups for reference. Multiple groups are used as reference groups for each other, and the effect is better.

[0095] The sensing mechanism of the present invention has a simple and compact structure, is easy to manufacture and install, and can be used alone or in multiple groups according to application requirements. A single-group sensor can complete multiple functions such as density measurement, contamination degree measurement, self-calibration, elimination of temperature and stress interference, improvement of sensing accuracy, and adjustable sensitivity. The measurement system has a clear structure and simple operation.

[0096] Embodiment 3:

[0097] A self-coding and self-calibrating dual-band MOEMS fiber grating-like sensing system is applied to an RP-3 oil quality sensor, which can measure the density and oil quality of RP-3 aviation kerosene and realize the measurement of the contamination degree of aviation kerosene RP-3.

[0098] like Figure 4 As shown, the three groups of data are a blank group, clean RP-3, and contaminated RP-3 (pollution level is about 8); by comparison, it can be seen that the absorption spectrum of RP-3 kerosene is 215nm to 310nm (RP-3 absorptivity is 100%, absorptivity = 100% - transmittance), and this band can be used as the characteristic absorption band of RP-3 kerosene; in the range of 380nm to 450nm, the absorptivity of clean kerosene is 0%, while the absorptivity of contaminated kerosene is 50% to 87%, and this band can be used as the RP-3 pollution-sensitive band for pollution level measurement; the bands of 310nm to 380nm and 450nm to 550nm are transitional regions and do not participate in the measurement, and above 550nm is the saturation region with an absorptivity of 0%.

[0099] Based on the RP-3 kerosene absorption spectrum, the sensitive band of pollution sensing can be accurately located at 380nm to 450nm. Purple LED lamp beads can be used to replace the laser light source, and photodetectors can be used to replace the demodulation system. This can not only reduce the volume and weight of the measurement system by 99%, facilitating miniaturization and engineering implementation, but also reduce costs by more than 99%.

[0100] like Figure 5 , the light source is divided into three bands: 200nm~360nm is used for sensitivity modulation of the sensing mechanism;

[0101] The wavelength range of 550nm to 670nm is used for density sensing, while the wavelength range of 380nm to 450nm is used for oil quality detection. The central wavelength of the grating-like sensor is set to 620nm to avoid interference from kerosene absorption. This example can simultaneously monitor the density and quality of RP-3 kerosene, which has important engineering significance in the aviation field.

[0102] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Any simple modification or equivalent change made to the above embodiment based on the technical essence of the present invention shall fall within the scope of protection of the present invention.

Claims

1. A dual-band MOEMS fiber grating sensing system capable of self-encoding and self-calibration, characterized in that, It includes a sensing mechanism based on the detection of the ultraviolet modulation band and the visible light sensing band. The sensing mechanism includes a dual-band optical fiber and a grating-like structure arranged outside the dual-band optical fiber. The grating-like structure is composed of several groups of MOEMS periodic grooves and ZnO groove fillings. The self-adjustment of the grating-like structure is realized by encoding the ultraviolet light intensity, where the maximum reflectivity R max and the corresponding peak wavelength λ max are as follows: R max =tanh 2 (kL)(19) Where: k is the mode coupling coefficient; L is the length of the grating-like structure; Λ is the period of the grating-like structure; Δn max is the effective refractive index n eff of the maximum modifiable range.

2. The dual-band MOEMS fiber grating sensing system capable of self-encoding and self-calibration according to claim 1, wherein The system further includes a signal modulation generator, a light source, a circulator, and a signal demodulator arranged in sequence from front to back. The circulator is respectively connected to the sensing mechanism and the signal demodulator, and the sensing mechanism is connected to the signal demodulator; the light source is used to provide ultraviolet light and visible light; the signal modulation generator is used to act on the light source through coding to make the light source generate coded pulsed light, and the pulsed light enters the sensing mechanism as a signal through the circulator.

3. A self - encoding and self - calibrating dual - band MOEMS fiber - type grating sensing system according to claim 2, characterized in that, The encoded pulsed light includes a zero-point calibration region and a calibration region; in the zero-point calibration region, only ultraviolet light is output; in the calibration region, both visible light and ultraviolet light are output, and the change amount of the effective refractive index n of the grating-like eff is: Wherein: represents the modulation of the average effective refractive index of the optical fiber; υ represents the visibility of the refractive index change fringes of the grating-like structure; Λ represents the period of the grating-like structure; z is the coordinate in the transmission direction; Indicates the grating phase shift of the grating-like under the influence of ultraviolet light modulation.

4. A self - encoding and self - calibrating dual - band MOEMS fiber - like grating sensing system according to claim 3, characterized in that, The calibration of the sensing mechanism is as follows: when the effective refractive index n of the grating-like object eff changes and the center wavelength of the reflection peak becomes λ B2 , this signal enters the signal demodulator through the reflection optical path for demodulation to obtain the wavelength drift Δλ B = λ B2 - λ B1 ; on the other hand, the liquid also absorbs ultraviolet light, and the ultraviolet transmitted light enters the signal demodulator through the incident optical path to obtain the ultraviolet transmitted light intensity I UV and the transmission spectrum to complete the calibration. At this time, both the wavelength drift Δλ B and the ultraviolet transmitted light intensity I UV are the initial sampling values, and they are mutually referenced to judge the accuracy of the data.

5. A self - encoding and self - calibrating dual - band MOEMS fiber - type grating sensing system according to claim 3, characterized in that, The coded pulsed light is sequentially provided with a number of zero-point calibration areas and calibration areas for calibration a number of times.

6. A self - encoding and self - calibrating dual - band MOEMS fiber - type grating sensing system according to any one of claims 1 - 5, characterized in that, The ultraviolet modulation band is 200nm - 380nm; the visible light sensing band is 380nm - 670nm, which is used to shield unnecessary signals.

7. A self - encoding and self - calibrating dual - band MOEMS fiber - type grating sensing system according to claim 6, characterized in that, The ultraviolet modulation band is 200nm - 360nm, which is used for sensitivity modulation of the sensing mechanism; the visible light sensing band includes 380nm - 450nm and 550nm - 670nm, which are respectively used for oil quality detection and density sensing.

8. A self - encoding and self - calibrating dual - band MOEMS fiber - type grating sensing system according to claim 6, characterized in that, It is applied to realize the measurement of liquid density, concentration, and pollution degree.

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