A flexible cascaded fiber optic sensing-based multi-parameter non-invasive pathological monitoring device and method

Abstract

Invention Title: A Flexible Cascaded Fiber Optic Sensing-Based Non-invasive Pathological Multi-parameter Monitoring Device and Method Abstract: This invention relates to the fields of fiber optic sensing and biomedical technology, and discloses a flexible cascaded fiber optic sensing-based non-invasive multi-parameter monitoring device and method. Targeting the screening needs of diabetic foot, this device employs two tilted fiber Bragg gratings (TFBGs) with different tilt angles and cascaded micro-nano fiber couplers to achieve simultaneous measurement of temperature, humidity, and deformation. The system incorporates an optical switch structure to adapt to different lesion detection scenarios. Through spectral characteristic peak position drift analysis and multi-parameter decoupling algorithms, cross-interference is effectively separated, enabling independent real-time acquisition of the three types of parameters. Simultaneously, it integrates intelligent demodulation and pathological threshold comparison functions, enabling early identification and warning of the risk of diabetic foot neuropathy. This invention features a simple structure, flexible layout, and strong anti-electromagnetic interference capability. Relying on flexible wearable packaging adapted for foot monitoring, it can be used for dynamic monitoring of human physiological parameters and pathological tissues, providing an efficient and reliable solution for multi-parameter non-invasive detection.

Description

Technical Field

[0001] This invention relates to the fields of fiber optic sensing and biomedicine, specifically to a dual tilted fiber Bragg grating (TFBG) combination using cascaded micro-nano fiber couplers to achieve simultaneous measurement of temperature, humidity, and deformation. Background Technology

[0002] Diabetes mellitus is a prevalent chronic metabolic disease, and diabetic foot neuropathy is a highly insidious and serious complication that can easily lead to foot ulcers, infections, and even amputation. Early diabetic foot neuropathy may not present with substantial visible lesions, but it will initially manifest with three major physiological characteristics: abnormal foot temperature, disordered sweat gland secretion, and uneven foot deformation distribution. These abnormal parameters precede abnormal blood glucose levels and physical foot injuries, serving as a core basis for early risk warning of diabetes. Therefore, achieving multi-parameter, non-invasive, and accurate monitoring of the foot is crucial for the early prevention and control of diabetic foot neuropathy.

[0003] Current venous blood glucose screening can only reflect instantaneous overall blood glucose levels and cannot detect early local lesions in the foot, resulting in low efficiency and delayed warnings. Secondly, existing conventional foot sensor monitoring and ordinary fiber optic detection solutions mostly adopt single-parameter detection modes, which cannot simultaneously collect the three core pathological parameters of foot temperature, moisture content, and deformation, and cannot match the multidimensional disordered lesion characteristics of early diabetic foot. At the same time, the traditional fiber optic sensing path is fixed and cannot match the corresponding detection accuracy according to the severity of the patient's lesions. It has limited ability to capture weak early pathological signals, and there is coupling interference between multi-parameter signals, making it impossible to complete accurate decoupling calculation and risk quantification. In addition, poor wearability and insufficient dynamic monitoring stability make it difficult to meet the needs of clinical practice.

[0004] Based on the aforementioned technological gaps in the industry, this invention innovatively designs a coupled cascaded two-channel TFBG sensor structure, paired with an optical path switcher to achieve adaptive switching of the sensing path, which can match the corresponding detection accuracy according to the severity of symptoms; at the same time, it is equipped with a flexible foot wearable structure to achieve real-time synchronous non-invasive acquisition of three major pathological parameters of the foot, and completes automatic decoupling analysis of multiple parameters and pathological threshold comparison through the background, realizing non-invasive early warning of diabetes risk, which is suitable for clinical outpatient screening and routine risk screening of sub-healthy people, making up for the core shortcomings of existing technologies. Summary of the Invention

[0005] A flexible cascaded fiber optic sensing-based non-invasive multi-parameter pathological monitoring device and method, characterized in that: the monitoring device includes a broadband light source (1), an input fiber optic cable (2), a flexible fiber optic sensing unit (3), an optical path switcher (4), an output fiber optic cable (5), a spectrometer (6), and a computer (7).

[0006] The flexible fiber optic sensing unit (3) is a coupled cascaded structure, specifically including: an input end (3-1), a micro-nano fiber coupling waist region (3-2), a coupler output port one (3-3), a 5° TFBG (3-4), a humidity-sensitive film (3-5), a first output port (3-6), a coupler output port two (3-7), a 65° TFBG (3-8), a second output port (3-9), and a flexible encapsulation film (3-10).

[0007] The output wavelength range of the light source (1) is 1520 nm to 1620 nm; the input fiber (2) and the output fiber (5) are single-mode fiber (SMF-28e) with a numerical aperture of 0.14.

[0008] The monitoring method is as follows: a stable broadband optical signal is emitted by a light source (1). The optical signal passes through an input optical fiber (2), enters the input end (3-1), passes through the waist area (3-2) of a micro-nano fiber coupler, and then the converter (4) selects different output paths. The output paths are: the light passes through a 5° TFBG (3-4) and outputs the optical signal from the first output end (3-6); the light passes through a 65° TFBG (3-8) and outputs the optical signal from the second output end (3-9). The 5° TFBG (3-4) and 65° TFBG (3-8) are also coated with a humidity-sensitive film (3-5). Finally, the collected composite spectral data is transmitted from the spectrometer (6) to the computer (7) for processing via the output optical fiber (5). Since the design parameters of the two TFBGs are different, there are differences in the response sensitivity to temperature, humidity and deformation. By constructing a multi-parameter response matrix, the independent calculation of the three physical quantities can be realized, and the real-time synchronous monitoring results of each physical quantity can be output.

[0009] The drift of three characteristic wavelengths in the composite spectrum—the loss peak of micro / nano fiber, the core mode resonance peak of TFBG, and the cladding mode resonance peak of TFBG—is analyzed. Based on the wavelength drift of the spectral characteristics, temperature, humidity, and deformation parameters are calculated respectively. Finally, the three parameters are measured simultaneously through calibration curves and decoupling algorithms.

[0010] A flexible cascaded fiber optic sensing-based multi-parameter non-invasive pathological monitoring device and method is characterized in that: the flexible fiber optic sensing unit (3) in the monitoring method adopts a flexible encapsulation film (3-10), which is integrated into the foot for sensing, precisely fitting the main pressure-bearing and nerve-dense areas of the human foot, providing a hardware basis for the accurate acquisition of early diabetic foot lesion signals. The three parameters collected by this device—temperature, humidity, and deformation—correspond to the specific pathological characteristics of early diabetic foot. The foot temperature parameter corresponds to foot microcirculatory nerve lesions; the foot humidity parameter corresponds to foot sweat gland nerve function damage; and the foot deformation parameter corresponds to foot microedema and peripheral nerve perception abnormalities.

[0011] This monitoring method also possesses two core pathological monitoring functions: intelligent threshold diagnosis and light-switching, making it suitable for the needs of stratified diabetes screening.

[0012] First, the device's backend stores standard pathological threshold ranges for foot temperature, moisture content, and deformation of healthy individuals. During testing, the three parameters obtained through real-time decoupling are compared with the standard thresholds in real time. When any single parameter or combination of multiple parameters exceeds the healthy threshold range, the system automatically determines that the subject has an early risk of diabetic foot neuropathy and quickly outputs abnormal diagnostic results, achieving non-invasive and rapid pathological screening.

[0013] Second, the optical path is adaptively switched based on the severity of symptoms. This device relies on a coupled cascaded dual TFBG sensing path. Based on the results of the computer (7), the results are fed back to the optical switch (4) to realize intelligent gear switching, which is adapted to different screening groups and lesion degrees: For screening groups with high blood sugar and sub-health, and no obvious symptoms, it automatically switches to the 65° TFBG sensing path. This path has rich cladding modes and higher sensitivity, and can capture weak early pathological parameter fluctuations in the foot; For groups with mild parameter abnormalities and mild early lesions, it automatically switches to the 5° TFBG sensing path; It can identify the early risk of diabetes before the appearance of significant diabetic lesions in the foot, realize effective early warning, and thus replace the traditional single blood glucose screening, realizing non-invasive and rapid screening.

[0014] A flexible cascaded fiber optic sensing-based multi-parameter non-invasive pathological monitoring device and method, characterized in that: the waist region diameter of the MFC in the flexible fiber optic sensing unit (3) is 8.5 μm, 5°TFBG (3-4) and 65°TFBG (3-8) have a grating period of 538 nm, a grating length of 15 mm, and a modulation depth of 0.1%. The humidity-sensitive film (3-5) is prepared by the following steps: MXene-titanium carbide (Ti3C2) and polyvinyl alcohol (PVA) are mixed in a 1:3 ratio, and water is added for ultrasonic dispersion to obtain a sensing solution. The solution is then uniformly coated onto the surface of 5°TFBG (3-4) and 65°TFBG (3-8) to form a humidity-sensitive film (3-5). Finally, the film is dried at room temperature to complete the curing process, and the thickness of the humidity-sensitive film is controlled to be in the range of 100 nm to 500 nm.

[0015] A pathological multi-parameter monitoring device and method based on a cascaded fiber structure is characterized in that: the temperature measurement is mainly obtained by linearly shifting the wavelength of the MFC loss peak with temperature through the composite spectrum output by the spectrometer (5), the moisture content measurement is mainly obtained by linearly shifting the wavelength of the TFBG cladding film with moisture content, the deformation measurement is mainly achieved by changing the bandwidth of the MFC reflection spectrum or splitting the peak, and finally the changes of the three parameters are obtained by the parameter decoupling equation.

[0016] A flexible cascaded fiber optic sensing-based non-invasive multi-parameter pathological monitoring device and method is characterized by the following: the monitoring method has a precise monitoring and measurement range of temperature 20~40 ℃, moisture content 4%~18%, and deformation 0~1000 με, which can completely cover the range of foot parameter changes in healthy people, sub-healthy people with high blood sugar, and people with early-stage mild diabetes. Attached Figure Description

[0017] Figure 1 A schematic diagram of a flexible cascaded fiber optic sensing-based multi-parameter non-invasive pathological monitoring device and method provided by the present invention.

[0018] Figure 2 This is a structural diagram of the flexible fiber optic sensing unit according to an embodiment of the present invention.

[0019] Figure 3 This is a schematic diagram of the composite spectral wavelength change for temperature measurement in an embodiment of the present invention.

[0020] Figure 4 This is a schematic diagram of linear fitting of the composite spectral wavelength change for temperature measurement in an embodiment of the present invention.

[0021] Figure 5 This is a schematic diagram of the composite spectral wavelength variation for measuring moisture content in an embodiment of the present invention.

[0022] Figure 6 This is a schematic diagram of linear fitting of the composite spectral wavelength change for measuring moisture content in an embodiment of the present invention.

[0023] Figure 7 This is a schematic diagram of the composite spectral wavelength change for measuring deformation according to an embodiment of the present invention.

[0024] Figure 8 This is a schematic diagram of linear fitting of composite spectral wavelength changes for deformation measurement in an embodiment of the present invention.

[0025] In the diagram: 1—Broadband light source, 2—Input fiber, 3—Flexible fiber optic sensing unit, 4—Optical path switcher, 5—Input fiber, 6—Spectrometer, 7—Computer, 3-1—Incident end one, 3-2—Coupled waist region, 3-3—Coupler output port one, 3-4—5°TFBG, 3-5—Humidity-sensitive film, 3-6—First output port, 3-7—Coupler output port two, 3-8—65°TFBG, 3-9—Second output port, 3-10—Encapsulation protective film. Detailed Implementation

[0026] according to Figure 1Connect the various modules. The fabrication process of the micro-nano fiber coupler is as follows: melt and taper the single-mode fiber to form a micro-nano fiber coupling waist region (3-2) with a diameter of 8.5 μm. Construct a dual-output port coupling structure to obtain coupler output port one (3-3) and coupler output port two (3-7) to realize the power distribution of incident light.

[0027] Dual-path TFBG fabrication and cascading: A TFBG (3-4) with a tilt angle of 5° is fabricated on the first output port (3-3) of the coupler, with a grating period of 538 nm, a grating length of 15 mm, and a modulation depth of 0.1% to 0.2%; A TFBG (3-8) with a tilt angle of 65° is fabricated on the second output port (3-7) of the coupler, with grating parameters consistent with the 5° TFBG; The two TFBGs are cascaded with the coupler output ports to form a coupled cascaded dual-path sensing structure, finally obtaining the first output port (3-6) and the second output port (3-9).

[0028] Preparation and coating of the humidity-sensitive film: MXene-titanium carbide (Ti3C2) powder and polyvinyl alcohol (PVA) were mixed at a mass ratio of 1:3, and a mixture with a solid content of 1–3 wt% was prepared using deionized water as the medium. The mixture was stirred in an 80 ℃ water bath until the PVA was partially dissolved, and then ultrasonically dispersed in an ice bath for 40 minutes to obtain a uniformly dispersed coating solution. Subsequently, the TFBG fiber grating region was wiped with anhydrous ethanol, dried with nitrogen, and then vertically immersed in the coating solution and allowed to stand for 10 seconds. It was then uniformly pulled at a speed of 7 mm / s to form a film. It was first pre-dried naturally at room temperature for 1 hour, and then dried in a 40 ℃ environment for 3 hours to fully cure it, forming a uniform humidity-sensitive film with a thickness of 100–300 nm on the grating surface. In addition, the bonding strength between the film and the optical fiber and the long-term stability can be improved by modification with KH550 silane coupling agent or argon plasma treatment.

[0029] In the sensing system, the TFBG core mode, cladding mode, and cascaded MFC structure all experience wavelength shifts in their respective resonant spectra when affected by external temperature, deformation, and ambient humidity. Since the three types of sensing units exhibit significant differences in wavelength response sensitivity to the three measured parameters, this response difference can be used as a decoupling basis to separate cross-sensitive interference, thereby accurately and synchronously acquiring real-time values ​​of temperature, deformation, and humidity. These three physical quantities act on the spectrum through different mechanisms, forming cross-sensitive but distinguishable response signals. The responses of these three parameters are illustrated below using a 5° TFBG as an example:

[0030] Deformation response: Deformation (stretching / compression) will simultaneously change the geometry and refractive index of the optical fiber, resulting in different effects on MFC and TFBG. The deformation measurement range that this device can measure is 0~1000 με. During the deformation measurement process, the device uses the different wavelength shift sensitivity characteristics of TFBG core mode, cladding mode and cascaded micro-nano fiber coupler (MFC) to achieve deformation demodulation. When the object under test undergoes axial deformation, the optical fiber is stretched or compressed, and its physical length and refractive index distribution change. As can be seen from Figure (3), it will cause the resonant wavelength of TFBG core mode, the resonant wavelength of cladding mode and the transmission peak wavelength of MFC to shift simultaneously. Since the response coefficients of the three to deformation have inherent differences, the response matrix can be established by calibration and solved by combining the response data corresponding to temperature and humidity, thereby separating the deformation contribution and realizing high-precision, cross-interference-free measurement of deformation. The device utilizes the different wavelength response sensitivity of the three to deformation.

[0031] Temperature Response: This device can measure temperatures ranging from 20 to 40 °C. It utilizes the sensitivity characteristics of the TFBG core mode, cladding mode, and cascaded micro / nano fiber coupler (MFC) to different wavelength shifts in response to temperature to achieve temperature demodulation. When the ambient temperature changes, the refractive index and physical dimensions of the fiber material change due to thermo-optical and thermal expansion effects, causing simultaneous shifts in the resonant wavelengths of the TFBG core mode, cladding mode, and MFC transmission peak. Since the response coefficients of these three components to temperature have inherent differences, a response matrix can be established through calibration. This matrix, combined with response data corresponding to deformation and moisture content, can then be used to solve for the temperature contribution, achieving high-precision, cross-interference-free temperature measurement.

[0032] Moisture Content Response: The titanium carbide (Ti3C2) / PVA humidity-sensitive film coated on the TFBG cladding surface is the core of the humidity response. During moisture content measurement, this device utilizes the different wavelength shift sensitivity characteristics of the TFBG cladding mode, the fiber core mode, and the cascaded micro / nano fiber coupler (MFC) to achieve moisture content demodulation. When the ambient humidity changes, the humidity-sensitive film coated on the TFBG surface undergoes refractive index and volume changes due to water absorption or dehydration, causing a significant drift in the resonant wavelength of the TFBG cladding mode. The fiber core mode, with its optical field confined within the fiber core, shows almost no response to changes in moisture content. The cascaded MFC, due to the interaction between the evanescent field and the humidity-sensitive film, exhibits different humidity response characteristics than the cladding mode. By establishing the response matrices of the three modes through calibration and combining them with the response data corresponding to temperature and deformation, the contribution of moisture content can be separated, achieving high-precision, cross-interference-free measurement of moisture content. Selection and Fitting Instructions for Two-Way 5°TFBG and 65°TFBG for Different Stages of Diabetic Foot Disease

[0033] This invention employs a cascaded dual-path structure of 5° low-tilt TFBG and 65° high-tilt TFBG. Leveraging the inherent differences in the number of envelope modes, spectral sensitivity, and resistance to cross-interference between the two, and combined with the classification of diabetic foot lesions, it achieves precise stratified matching and selection. The specific adaptation rules are as follows:

[0034] 65° high tilt angle TFBG applicable scenarios and users: The 65° TFBG grating has a larger tilt angle, which excites a richer number of cladding modes, more spectral resonance peaks, and higher sensitivity to weak parameters. It has a strong ability to capture small fluctuations in foot temperature, slight changes in epidermal moisture content, and slight soft tissue deformation.

[0035] Suitable for: people undergoing health checkups, people with high blood sugar and sub-health conditions, and people at high risk of diabetic foot grade 0 (no visible foot ulcers, no obvious edema or inflammation, only potential damage to nerve function). The early pathological features of this group are hidden and the parameter changes are small. Switching to the 65° TFBG sensing path can capture trace spectral drift with high sensitivity, identify the risk of subclinical lesions in advance, and achieve early warning and early intervention.

[0036] 5° low tilt angle TFBG applicable scenarios and users: The 5° TFBG grating has a small tilt angle, which makes the core mode resonance peak more stable, the cladding mode interference less, the spectrum has strong resistance to environmental interference, and the parametric decoupling stability is excellent. It is not easily affected by stray signals caused by human foot posture and wearing pressure.

[0037] Suitable for: Individuals with mild foot parameter abnormalities and those with early stage 1 diabetic foot (mild microcirculatory inflammation, sweat gland secretion disorder, foot microedema and deformation, and early signs of neuropathy). This population has a larger parameter deviation range, so ultra-high sensitivity is not required, but higher measurement stability and decoupling accuracy are needed. Switching to the 5° TFBG path can suppress multi-parameter cross-interference, stably output pathological parameter values, and accurately determine the degree of lesion.

[0038] The optical path adaptive switching logic device uses a computer to analyze the drift of spectral characteristic peaks in real time and automatically determines the population level of the subject: if no parameter exceeds the limit and only blood glucose is high, the default is to lock the 65° TFBG high-sensitivity detection mode; if any parameter such as temperature, humidity, or deformation shows a continuous shift, the system automatically switches to the 5° TFBG high-stability detection mode and combines it with the background pathological threshold range for risk rating. Through differentiated selection and adaptation of two TFBG paths, non-invasive monitoring of diabetic foot is achieved across all levels from health screening to high-risk early warning to mild case diagnosis, solving the technical shortcomings of traditional single-path fiber optic sensing that cannot simultaneously capture weak signals and provide stable and accurate measurement.

Claims

1. A flexible cascaded fiber optic sensing-based non-invasive multi-parameter pathological monitoring device and method, characterized in that: The monitoring device includes a broadband light source (1), an input optical fiber (2), a flexible optical fiber sensing unit (3), an optical switch (4), an output optical fiber (5), a spectrometer (6), and a computer (7). The output wavelength range of the light source (1) is 1520 - 1620 nm; the input fiber (2) and the output fiber (5) are standard single-mode fiber (SMF-28e) with a numerical aperture of 0.

14. The flexible fiber optic sensing unit (3) is a coupled cascaded structure, specifically including: an input end (3-1), a micro-nano fiber coupling waist region (3-2), a coupler output port one (3-3), a 5° TFBG (3-4), a humidity-sensitive film (3-5), a first output port (3-6), a coupler output port two (3-7), a 65° TFBG (3-8), a second output port (3-9), and a flexible encapsulation film (3-10). In the monitoring method, the broadband optical signal output by the broadband light source (1) is modulated by the input optical fiber (2) and then the transmission optical path is selectively controlled by the optical switch (4) so ​​that the optical signal is switched between 5°TFBG (3-4) and 65°TFBG (3-8). The modulated optical signal is transmitted to the spectrometer (6) for spectral acquisition via the output optical fiber (5) and then demodulated by the computer (7). The computer (7) performs feedback control on the optical switch (4) according to the demodulation result to realize the switching of the dual TFBG sensing channels. The aforementioned spectral demodulation involves analyzing the drift of three characteristic wavelengths in the composite spectrum: interference loss peak, core mode resonance peak, and cladding mode resonance peak. Based on the wavelength drift of the spectral characteristics, temperature, humidity, and deformation parameters are calculated respectively. Finally, through calibration curves and decoupling algorithms, the three parameters are measured simultaneously.

2. The flexible cascaded fiber optic sensing-based non-invasive multi-parameter pathological monitoring device and method according to claim 1, characterized in that: The flexible fiber sensing unit (3) has a micro-nano fiber coupling waist region (3-2) with a diameter of 8.5 μm; the grating period of 5°TFBG (3-4) and 65°TFBG (3-8) is 538 nm, the grating length is 15 mm, and the modulation depth is 0.1%; the humidity-sensitive film (3-5) is prepared by the following steps: titanium carbide and polyvinyl alcohol are mixed in a 1:3 ratio, water is added and ultrasonically dispersed to obtain a sensing solution, and the solution is dipped and uniformly coated on the surface of 5°TFBG (3-4) and 65°TFBG (3-8) to form a dense humidity-sensitive film (3-5) with a thickness of 100 nm to 500 nm.

3. The flexible cascaded fiber optic sensing-based non-invasive multi-parameter pathological monitoring device and method according to claim 1, characterized in that: The flexible fiber optic sensing unit (3) adopts an integrated structure of flexible encapsulation film (3-10) to fit the pressure-bearing and nerve-dense areas of the foot, realizing non-invasive acquisition of temperature, moisture content and deformation, respectively corresponding to the pathological characteristics of inflammation or ulcer, sweat gland nerve function damage and microedema.

4. The optical switch (4) according to claim 1 selectively controls the transmission optical path, characterized in that: The computer (7) pre-stores the standard threshold range of three parameters for healthy people and compares the real-time decoupled data. When any or more parameters exceed the threshold range, it outputs a risk warning of early diabetic foot neuropathy, realizing non-invasive and rapid screening. Furthermore, the light switch (4) is graded and controlled according to the detection results: when the subject is in a sub-healthy state, it switches to the 65° TFBG sensing channel to improve the sensitivity of weak signal detection; when there is a mild abnormality, it switches to the 5° TFBG sensing channel for fine monitoring, thereby realizing graded screening and dynamic monitoring based on the degree of lesion.

5. The flexible cascaded fiber optic sensing-based non-invasive multi-parameter pathological monitoring device and method according to claim 1, characterized in that: This monitoring method has a precise monitoring range of temperature 20~40 ℃, humidity 4%~18%, and deformation 0~1000 με, which can fully cover the range of foot parameter changes in healthy people, sub-healthy people with high blood sugar, and people with early-stage diabetes.

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