CN118078240B - Optical fiber Michelson interference type heart rate sensor and heart rate monitoring system - Google Patents

Abstract

The invention provides an optical fiber Michelson interference type heart rate sensor and a heart rate monitoring system, wherein the optical fiber Michelson interference type heart rate sensor comprises a first transmission section, a coupling section, a second transmission section and an optical fiber ball which are sequentially connected, and an optical fiber of the second transmission section comprises a central fiber core and a side core; the optical fiber is characterized in that one end of the optical fiber ball is used as a contact section for contacting with a part to be detected, signal light is output from one end of the first transmission section and is transmitted to the optical fiber ball through the first transmission section, the coupling section and the second transmission section, an optical signal is fed back to the first transmission section from the optical fiber ball, modulation interference intensity is realized based on phase difference generated by the central fiber core and the side core in the transmission process of the optical signal in the second transmission section, and heart rate monitoring is carried out. When the sensor is fixed at the monitoring position, the heartbeat effect can cause the bending of the optical fiber ball, so that the optical path of Michelson interference is changed, the interference intensity is finally modulated, and the heart rate can be detected by monitoring the change of the interference spectrum intensity.

Description

Optical fiber Michelson interferometer heart rate sensor and heart rate monitoring system

Technical Field

The present invention relates to the field of optical fiber sensing technology, and in particular to an optical fiber Michelson interference heart rate sensor and a heart rate monitoring system.

Background technique

With the rapid development of science and the improvement of living standards, people's attention to physical health has increased significantly. Human heart rate is one of the most important indicators of human physiological activities. Heart rate is related to the health status of the human body. It can not only be used as an auxiliary diagnosis of heart system diseases, but also as an important physiological parameter for monitoring. The normal heart rate range can help maintain the health of the cardiovascular system, improve physical endurance and exercise effects, and serve as an indicator of physical stress response and health of the elderly. In clinical medical research, some premature infants and special populations with chronic diseases are prone to heart rate pauses, so heart rate monitoring is of great significance, which can identify diseases in time and take appropriate treatment measures to avoid adverse events. In addition, heart rate monitoring can analyze the emotional state of humans to prevent occupational diseases. Therefore, high-precision and fast heart rate monitoring is of great significance in clinical applications and health fields. Traditional heart rate monitoring sensors are mainly electrophysiological sensors that measure electrocardiogram (ECG) signals, that is, electrical signals generated by heart electrical activity are measured by electrodes attached to the body. ECG sensors give accurate heart rate data and can detect other parameters of the heart, such as arrhythmias. However, these sensors are easily affected by electromagnetic interference, which affects the accuracy of monitoring.

In recent years, optical sensors have been widely developed due to their advantages of anti-electromagnetic interference, wide range of applicable environments and high precision. Existing fiber optic heart rate sensors all monitor heart rate using a Mach-Zehnder interferometer transmission structure. This structure requires both ends to be fixed to the body part being tested at the same time, which means that precise control and careful fixation are required during the test, and the robustness is poor.

Summary of the invention

In view of this, an embodiment of the present invention provides a fiber optic Michelson interferometer heart rate sensor and a heart rate monitoring system to eliminate or improve one or more defects existing in the prior art.

One aspect of the present invention provides an optical fiber Michelson interferometer heart rate sensor, the optical fiber Michelson interferometer heart rate sensor comprises a first transmission segment, a coupling segment, a second transmission segment and an optical fiber ball connected in sequence, the optical fiber of the second transmission segment comprises a central core and a side core;

One end of the optical fiber ball is used as a contact segment for contacting the part to be measured. The signal light is output from the end where the first transmission segment is located, and is transmitted to the optical fiber ball through the first transmission segment, the coupling segment, and the second transmission segment. The optical signal is then fed back from the optical fiber ball to the first transmission segment. During the transmission of the optical signal in the second transmission segment, the interference intensity is modulated based on the phase difference generated by the central core and the side core to monitor the heart rate.

With the above scheme, when light is transmitted from the coupling section to the second transmission section, part of the light is coupled into the central core of the second transmission section, and the other part is coupled into the side core of the second transmission section and excites the side core fundamental mode and a small amount of cladding mode. However, the cladding mode in the second transmission section is relatively weak and does not participate in the interference process and can be ignored. Therefore, the core fundamental mode and the side core fundamental mode are reflected on the optical fiber ball of the second transmission section, propagate in the reverse direction along the second transmission section, enter the coupling section again, interfere in it, and then couple into the core of the first transmission section and output. In the second transmission section, the side core is equivalent to the sensing arm of the traditional Michelson interferometer, the central core is equivalent to the reference arm, and the optical fiber ball acts as a reflector to reflect the central core mode and the side core mode back to the second transmission section for reverse transmission. The coupling section acts as a coupler. When the optical fiber ball is bent, the optical path difference of the Michelson interference changes, resulting in a change in the interference intensity. When the sensor is fixed at the monitoring position, the heartbeat will cause the optical fiber ball to bend, resulting in a change in the optical path of the Michelson interference, and finally modulate the interference intensity. The detection of heart rate can be achieved by monitoring the change in the intensity of the interference spectrum.

In some embodiments of the present invention, the second transmission segment uses a seven-core optical fiber, a twelve-core optical fiber, or a photonic crystal fiber.

In some embodiments of the present invention, the optical fiber ball is an optical fiber ball formed by multiple discharges at one end of the optical fiber of the second transmission segment.

In some embodiments of the present invention, the coupling section is made of polydimethylsiloxane material or multimode optical fiber.

In some embodiments of the present invention, the first transmission segment uses a single-mode optical fiber.

In some embodiments of the present invention, the interference light intensity of the reflected light signal output by the optical fiber Michelson interferometer heart rate sensor is expressed as:

;

in, and Respectively represent the light intensity of the central core fundamental mode and the side core fundamental mode of the second transmission segment, It represents the phase difference between the center core fundamental mode and the side core fundamental mode. is the reflectivity of the optical fiber ball, m represents the number of side cores, and I represents the interference light intensity of the reflected light signal output by the optical fiber Michelson interferometer heart rate sensor.

In some embodiments of the present invention, the reflectivity of the optical fiber ball is expressed as:

;

in, and They represent the refractive index of the optical fiber core and the medium wrapping the optical fiber core, and R represents the reflectivity of the optical fiber ball.

In some embodiments of the present invention, the phase difference between the center core fundamental mode and the side core fundamental mode is expressed as:

;

in, It represents the phase difference between the center core fundamental mode and the edge core fundamental mode; represents the effective refractive index difference between the central core fundamental mode and the side core fundamental mode; L represents the length of the optical fiber ball in the length direction of the optical fiber Michelson interferometer heart rate sensor; Represents the wavelength of incident light.

In some embodiments of the present invention, when the phase difference between the center core fundamental mode and the side core fundamental mode satisfies When , the interference light intensity reaches the minimum value, and the wavelength corresponding to the interference valley in the transmission spectrum of the output light signal is expressed as:

;

in, represents the wavelength corresponding to the interference valley in the transmission spectrum of the output light signal constituted by the output light signal of the optical fiber Michelson interferometer heart rate sensor; represents the effective refractive index difference between the central core fundamental mode and the side core fundamental mode; L represents the length of the optical fiber ball in the length direction of the optical fiber Michelson interferometer heart rate sensor; is an integer.

Another aspect of the present invention provides a heart rate monitoring system, which includes an adjustable laser resonator, an optical fiber circulator, a wavelength division multiplexer, a photocell, a data acquisition card, a computer and the above-mentioned optical fiber Michelson interferometer heart rate sensor, wherein the adjustable laser resonator, the wavelength division multiplexer and the photocell are connected by an optical path through the optical fiber circulator, the computer, the data acquisition card and the photocell are connected by an electric circuit, and the optical fiber Michelson interferometer heart rate sensor is connected to the wavelength division multiplexer by an optical path.

Additional advantages, purposes, and features of the present invention will be described in part in the following description, and will become apparent to those skilled in the art after studying the following, or may be learned from the practice of the present invention. The purposes and other advantages of the present invention may be specifically pointed out and obtained in the specification and the accompanying drawings.

Those skilled in the art will appreciate that the objectives and advantages that can be achieved with the present invention are not limited to the above specific description, and the above and other objectives that can be achieved by the present invention will be more clearly understood from the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings described herein are used to provide a further understanding of the present invention, constitute a part of this application, and do not constitute a limitation of the present invention.

FIG1 is a schematic diagram of an embodiment of an optical fiber Michelson interferometer heart rate sensor of the present invention;

FIG2 is a schematic cross-sectional view of a seven-core optical fiber in the present invention;

FIG3 is a schematic diagram of another embodiment of the optical fiber Michelson interferometer heart rate sensor of the present invention;

FIG. 4 is a schematic diagram of an embodiment of a heart rate monitoring system of the present invention.

Detailed ways

In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments and the accompanying drawings. Here, the illustrative embodiments of the present invention and their descriptions are used to explain the present invention, but are not intended to limit the present invention.

It should also be noted that, in order to avoid obscuring the present invention due to unnecessary details, only structures and/or processing steps closely related to the solutions according to the present invention are shown in the accompanying drawings, while other details that are not closely related to the present invention are omitted.

Introduction to existing technology

Some existing optical sensors use LED light sources to illuminate the skin and monitor the light signals reflected by the skin through photodetectors. These sensors are usually used in devices such as wrist smart watches, sports bracelets and smartphones, and can estimate heart rate by measuring the absorption and reflection of light. However, this measurement method is sensitive to factors such as external light and skin color. Strong or weak light environments, dark or bright skin, and dynamic changes in muscles during exercise may affect the accuracy of optical sensors. Therefore, in some special environments, the accuracy of optical sensors may be affected to a certain extent.

As shown in FIGS. 1 to 3 , the present invention provides an optical fiber Michelson interferometer heart rate sensor, wherein the optical fiber Michelson interferometer heart rate sensor comprises a first transmission segment, a coupling segment, a second transmission segment and an optical fiber ball connected in sequence, wherein the optical fiber of the second transmission segment comprises a central core and a side core;

One end of the optical fiber ball is used as a contact segment for contacting the part to be measured. The signal light is output from the end where the first transmission segment is located, and is transmitted to the optical fiber ball through the first transmission segment, the coupling segment, and the second transmission segment. The optical signal is then fed back from the optical fiber ball to the first transmission segment. During the transmission of the optical signal in the second transmission segment, the interference intensity is modulated based on the phase difference generated by the central core and the side core to monitor the heart rate.

In the specific implementation process, in this scheme, when the heart beats, the micro-nano deformation of the monitoring part will cause the change of the optical fiber curvature, the interference light path will change, and finally modulate the intensity of the interference spectrum. Therefore, the heart rate detection can be achieved by monitoring the change of the intensity of the sensor interference spectrum.

With the above scheme, when light is transmitted from the coupling section to the second transmission section, part of the light is coupled into the central core of the second transmission section, and the other part is coupled into the side core of the second transmission section and excites the side core fundamental mode and a small amount of cladding mode. However, the cladding mode in the second transmission section is relatively weak and does not participate in the interference process and can be ignored. Therefore, the core fundamental mode and the side core fundamental mode are reflected on the optical fiber ball of the second transmission section, propagate in the reverse direction along the second transmission section, enter the coupling section again, interfere in it, and then couple into the core of the first transmission section and output. In the second transmission section, the side core is equivalent to the sensing arm of the traditional Michelson interferometer, the central core is equivalent to the reference arm, and the optical fiber ball acts as a reflector to reflect the central core mode and the side core mode back to the second transmission section for reverse transmission. The coupling section acts as a coupler. When the optical fiber ball is bent, the optical path difference of the Michelson interference changes, resulting in a change in the interference intensity. When the sensor is fixed at the monitoring position, the heartbeat will cause the optical fiber ball to bend, resulting in a change in the optical path of the Michelson interference, and finally modulate the interference intensity. The detection of heart rate can be achieved by monitoring the change in the intensity of the interference spectrum.

In some embodiments of the present invention, the second transmission segment uses a seven-core optical fiber, a twelve-core optical fiber, or a photonic crystal fiber.

In some embodiments of the present invention, the optical fiber ball is an optical fiber ball formed by multiple discharges at one end of the optical fiber of the second transmission segment.

In some embodiments of the present invention, the coupling section is made of polydimethylsiloxane material or multimode optical fiber.

In some embodiments of the present invention, the first transmission segment uses a single-mode optical fiber.

In some embodiments of the present invention, the interference light intensity of the reflected light signal output by the optical fiber Michelson interferometer heart rate sensor is expressed as:

;

in, and Respectively represent the light intensity of the central core fundamental mode and the side core fundamental mode of the second transmission segment, It represents the phase difference between the center core fundamental mode and the side core fundamental mode. is the reflectivity of the optical fiber ball, m represents the number of side cores, and I represents the interference light intensity of the reflected light signal output by the optical fiber Michelson interferometer heart rate sensor.

In some embodiments of the present invention, the reflectivity of the optical fiber ball is expressed as:

;

in, and They represent the refractive index of the optical fiber core and the medium wrapping the optical fiber core, and R represents the reflectivity of the optical fiber ball.

In some embodiments of the present invention, the phase difference between the center core fundamental mode and the side core fundamental mode is expressed as:

;

in, It represents the phase difference between the center core fundamental mode and the edge core fundamental mode; represents the effective refractive index difference between the central core fundamental mode and the side core fundamental mode; L represents the length of the optical fiber ball in the length direction of the optical fiber Michelson interferometer heart rate sensor; Represents the wavelength of incident light.

In some embodiments of the present invention, when the phase difference between the center core fundamental mode and the side core fundamental mode satisfies When , the interference light intensity reaches the minimum value, and the wavelength corresponding to the interference valley in the transmission spectrum of the output light signal is expressed as:

;

in, represents the wavelength corresponding to the interference valley in the transmission spectrum of the output light signal constituted by the output light signal of the optical fiber Michelson interferometer heart rate sensor; represents the effective refractive index difference between the central core fundamental mode and the side core fundamental mode; L represents the length of the optical fiber ball in the length direction of the optical fiber Michelson interferometer heart rate sensor; is an integer.

Embodiment 1

As shown in FIG3 , in some embodiments of the present invention, the first transmission segment uses a single-mode fiber (SMF), the second transmission segment uses a seven-core fiber (SCF), and the coupling segment uses a multi-mode fiber (MMF), and the end faces of the seven-core fiber are discharged and fused into a fiber ball. When the light emitted by the light source enters the MMF along the core of the SMF, the core mismatch between the two optical fibers causes multiple modes to be excited, and the mode field diameter is expanded. Since the core radius of the MMF and the distance between the cores of the SCF are close in value, when the light is transmitted from the multi-mode fiber to the SCF, a part of the light is coupled into the central core of the SCF, and the other part is coupled into the side core of the SCF and excites the side core fundamental mode and a small amount of cladding mode. However, the cladding mode in the SCF is relatively weak and does not participate in the interference process and can be ignored. Therefore, the core fundamental mode and the side core fundamental mode are reflected on the fiber ball of the SCF, propagate in the opposite direction along the SCF for a distance, and then enter the MMF again, where interference occurs and then they are re-coupled into the core of the single-mode fiber and output. In the seven-core fiber, the side core is equivalent to the sensing arm of the traditional Michelson interferometer, the center core is equivalent to the reference arm, and the fiber ball acts as a reflector to reflect the center core mode and the side core mode back to the seven-core fiber for reverse transmission. The MMF acts as a coupler to form a Michelson interferometer.

In some embodiments of the present invention, specifically, the core diameter of SMF is 9 μm, the refractive index is 1.4682, the cladding diameter is 125 μm, and the refractive index is 1.4628; the core diameter of MMF is 105 μm, the refractive index is 1.4666, the cladding diameter is 125 μm, and the refractive index is 1.447; the seven germanium-doped cores in SCF are composed of three layers of materials with different refractive indices, the refractive indices of the inner layer, the middle layer and the outermost layer are 1.448, 1.442 and 1.442 respectively, the diameters are 8.2 μm, 19 μm and 30 μm respectively, and the distance between the seven cores arranged in a regular hexagon is 41.5 μm; the refractive index of the SCF cladding is 1.444, and the cladding diameter is 150 μm, which is larger than the cladding diameter of MMF. The end faces of SMF, MMF and SCF are cut flat and cleaned with alcohol, and SMF, MMF and SCF are fused to the cores in sequence using a commercial fusion splicer. Finally, the end face of the SCF is discharged multiple times to form an optical fiber ball. The length of the MMF is 1-3 mm, preferably 2 mm.

As shown in FIG4 , another aspect of the present invention provides a heart rate monitoring system, which includes an adjustable laser resonator, an optical fiber circulator, a wavelength division multiplexer, a photocell, a data acquisition card, a computer, and the above-mentioned optical fiber Michelson interferometer heart rate sensor, wherein the adjustable laser resonator, the wavelength division multiplexer, and the photocell are connected by an optical path through the optical fiber circulator, the computer, the data acquisition card, and the photocell are connected by an electric circuit, and the optical fiber Michelson interferometer heart rate sensor is connected to the wavelength division multiplexer by an optical path.

In some embodiments of the present invention, the scheme of the heart rate monitoring system is shown in Figure 4, including the proposed sensor, tunable laser, fiber circulator, wavelength division multiplexer, photocell, data acquisition card and computer. In the heart rate test, the sensor is worn on the chest wall and wrist pulse of the tester, and the light emitted by the tunable laser enters the sensor through the fiber circulator and wavelength division multiplexer. When the heart beats and contracts, blood is pumped into the blood vessels with force. This movement can be conducted through the chest wall, especially in the part where the heart is located near the surface of the chest wall. The periodic fluctuations of the chest wall or pulse cause changes in the interference intensity of the sensor. Then, the optical signal is converted into an electrical signal by the photocell, and displayed on the computer after passing through the data acquisition card to detect the human heart rate in real time.

In the specific implementation process, this solution uses a laser to emit multiple lights of different wavelengths, which are then used through a wavelength division multiplexer to perform multi-point measurements of human body parts.

The beneficial effects of this program include:

1. This scheme proposes a reflective optical fiber heart rate sensor, which is easy to package, has good robustness, can measure at multiple points, and is easier to integrate into wearable devices;

2. The fiber optic ball area of this solution can achieve a larger contact area between light and the human body, which improves the sensitivity of the sensor to subtle changes in the chest wall and solves the key problem of monitoring tiny displacements;

3. The presence of the fiber optic ball helps to buffer the impact of external environmental changes and improve the stability and reliability of the measurement;

4. The fiber optic heart rate sensor is composed of all optical fibers, and the length of the sensor can be adjusted according to the actual heart rate monitoring environment. Therefore, it not only has a high spatial resolution, but also meets the measurement requirements of a small space;

5. The fiber optic heart rate sensor is a passive device, so it overcomes the disadvantage that traditional heart rate sensors cannot work under strong electromagnetic interference. Compared with traditional heart rate sensors, it also has the advantages of small size and light weight.

In the specific implementation process, according to previous work experience, optical fiber sensors for measuring parameters such as breathing, pulse and heart rate are all transmission structures (the interference principle is Mach-Zehnder interference), and the present invention proposes a reflection structure (the interference principle is Michelson interference).

It should be understood by those skilled in the art that the exemplary components, systems and methods described in conjunction with the embodiments disclosed herein can be implemented in hardware, software or a combination of the two. Whether it is performed in hardware or software depends on the specific application and design constraints of the technical solution. Professional and technical personnel can use different methods to implement the described functions for each specific application, but such implementation should not be considered to be beyond the scope of the present invention. When implemented in hardware, it can be, for example, an electronic circuit, an application-specific integrated circuit (ASIC), appropriate firmware, a plug-in, a function card, etc. When implemented in software, the elements of the present invention are programs or code segments used to perform the required tasks. The program or code segment can be stored in a machine-readable medium, or transmitted on a transmission medium or a communication link via a data signal carried in a carrier.

It should be clear that the present invention is not limited to the specific configuration and processing described above and shown in the figures. For the sake of simplicity, a detailed description of the known method is omitted here. In the above embodiments, several specific steps are described and shown as examples. However, the method process of the present invention is not limited to the specific steps described and shown, and those skilled in the art can make various changes, modifications and additions, or change the order between the steps after understanding the spirit of the present invention.

In the present invention, features described and/or illustrated for one embodiment may be used in the same or similar manner in one or more other embodiments, and/or combined with features of other embodiments or replace features of other embodiments.

The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the embodiments of the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims (7)

1. An optical fiber Michelson interferometer heart rate sensor, characterized in that the optical fiber Michelson interferometer heart rate sensor comprises a first transmission segment, a coupling segment, a second transmission segment and an optical fiber ball connected in sequence, and the optical fiber of the second transmission segment comprises a central core and a side core; One end of the optical fiber ball is used as a contact section for contacting the part to be measured. The signal light is output from the end where the first transmission section is located, and is transmitted to the optical fiber ball through the first transmission section, the coupling section, and the second transmission section. The optical signal is then fed back from the optical fiber ball to the first transmission section. During the transmission of the optical signal in the second transmission section, the phase difference generated by the central fiber core and the side core is used to realize the modulation interference intensity, so as to monitor the heart rate. The interference light intensity of the reflected light signal output by the optical fiber Michelson interferometer heart rate sensor is expressed as: ; in, and Respectively represent the light intensity of the central core fundamental mode and the side core fundamental mode of the second transmission segment, It represents the phase difference between the center core fundamental mode and the side core fundamental mode. is the reflectivity of the optical fiber ball, m is the number of side cores, I is the interference light intensity of the reflected light signal output by the optical fiber Michelson interferometer heart rate sensor, The reflectivity of the fiber optic ball is expressed as: ; in, and They represent the refractive index of the optical fiber core and the medium wrapping the optical fiber core, respectively, and R represents the reflectivity of the optical fiber ball; The phase difference between the center core fundamental mode and the side core fundamental mode is expressed as: ; in, It represents the phase difference between the center core fundamental mode and the edge core fundamental mode; represents the effective refractive index difference between the central core fundamental mode and the side core fundamental mode; L represents the length of the optical fiber ball in the length direction of the optical fiber Michelson interferometer heart rate sensor, Represents the wavelength of incident light. 2. The optical fiber Michelson interferometer heart rate sensor according to claim 1 is characterized in that the second transmission segment adopts seven-core optical fiber, twelve-core optical fiber or photonic crystal fiber. 3. The optical fiber Michelson interferometer heart rate sensor according to claim 1 is characterized in that the optical fiber ball is an optical fiber ball formed by multiple discharges at one end of the optical fiber of the second transmission segment. 4. The optical fiber Michelson interferometer heart rate sensor according to claim 1, characterized in that the coupling section is made of polydimethylsiloxane material or multimode optical fiber. 5. The optical fiber Michelson interferometer heart rate sensor according to claim 1 is characterized in that the first transmission segment adopts single-mode optical fiber. 6. The optical fiber Michelson interferometer heart rate sensor according to claim 1, characterized in that when the phase difference between the center core fundamental mode and the side core fundamental mode satisfies When , the interference light intensity reaches the minimum value, and the wavelength corresponding to the interference valley in the transmission spectrum of the output light signal is expressed as: ; in, represents the wavelength corresponding to the interference valley in the transmission spectrum of the output light signal constituted by the output light signal of the optical fiber Michelson interferometer heart rate sensor; represents the effective refractive index difference between the central core fundamental mode and the side core fundamental mode; L represents the length of the optical fiber ball in the length direction of the optical fiber Michelson interferometer heart rate sensor; is an integer. 7. A heart rate monitoring system, characterized in that the heart rate monitoring system comprises an adjustable laser resonator, an optical fiber circulator, a wavelength division multiplexer, a photocell, a data acquisition card, a computer and the optical fiber Michelson interferometer heart rate sensor according to any one of claims 1 to 6, wherein the adjustable laser resonator, the wavelength division multiplexer and the photocell are connected by an optical path through the optical fiber circulator, the computer, the data acquisition card and the photocell are connected by an electric circuit, and the optical fiber Michelson interferometer heart rate sensor is connected to the wavelength division multiplexer by an optical path.