Detection system of micro optical fiber coupler based on bidirectional optical frequency comb vernier effect

Abstract

The invention provides a detection system of a micro optical fiber coupler based on a bidirectional optical frequency comb vernier effect, which can be applied to the technical field of photoelectric detection. The system comprises: an optical frequency comb light source configured to emit detection light; the beam splitter is arranged to split the detection light into first sub-detection light and second sub-detection light; the reference sensing unit is arranged to guide the first sub detection light to interact with a reference solution through an evanescent field of the first micro optical fiber coupler so as to output first transmission light; the detection sensing unit is arranged to guide the second sub detection light to interact with the solution to be detected through an evanescent field of the second micro optical fiber coupler so as to output second transmission light; the beam combiner is set to combine the first transmission light and the second transmission light to obtain a combined light spectrum; the spectrum analyzer is set to collect the combined light and generate a vernier spectrum; and the processor is set to determine the concentration of the liquid to be detected according to the vernier spectrum.

Description

Technical Field

[0001] The present disclosure relates to the field of optoelectronic detection technologies, and more particularly, to a detection system for a microfiber coupler based on a bidirectional optical frequency comb vernier effect and a method for detecting solution concentration. Background Art

[0002] Industrial waste gases, waste liquids, and heavy metal pollution pose threats to the environment and human health. These pollutants widely exist in natural water bodies and soil, and their concentration changes directly affect the stability of the ecosystem and the quality of human life. Since the concentration change causes the refractive index of the liquid to change, monitoring the refractive index of the liquid or the solute concentration is of great significance in environmental pollution control. In addition, in the field of biomedicine, the refractive index change of a solution is also closely related to the concentration of biomolecules such as proteins, antibiotics, viruses, and bacteria, providing key data support for disease diagnosis, drug development, and food safety monitoring. For example, abnormal changes in blood glucose levels, antibody content, and biomarkers can all be monitored and analyzed through accurate determination of the refractive index of the solution. Therefore, developing highly sensitive sensors based on the refractive index of liquids is of great value for promoting environmental, medical, and industrial monitoring. Summary of the Invention

[0003] In view of this, the present disclosure provides a detection system for a microfiber coupler based on a bidirectional optical frequency comb vernier effect and a method for detecting solution concentration.

[0004] One aspect of the present disclosure provides a detection system for a microfiber coupler based on a bidirectional optical frequency comb vernier effect, including:

[0005] An optical frequency comb light source configured to emit detection light;

[0006] A beam splitter connected to the optical frequency comb light source and configured to divide the detection light into a first sub-detection light and a second sub-detection light;

[0007] A reference sensing unit connected to the beam splitter, including a first microfiber coupler. The first microfiber coupler is configured to transmit the first sub-detection light, and the reference sensing unit is configured to guide the first sub-detection light to interact with a reference solution located outside the first microfiber coupler through the evanescent field of the first microfiber coupler to output a first transmitted light;

[0008] A detection sensing unit connected to the beam splitter, including a second microfiber coupler. The second microfiber coupler is configured to transmit the second sub-detection light, and the detection sensing unit is configured to guide the second sub-detection light to interact with a solution to be measured located outside the second microfiber coupler through the evanescent field of the second microfiber coupler to output a second transmitted light;

[0009] A beam combiner, connected to the first microfiber coupler and the second microfiber coupler described above, is configured to combine the first transmitted light and the second transmitted light to obtain combined light;

[0010] A spectral analyzer, connected to the beam combiner, is configured to collect the combined light and convert the combined light into a cursor spectrum with bidirectional cursor spectral characteristics;

[0011] A processor, connected to the spectral analyzer, is configured to determine the concentration of the solution to be measured according to the cursor spectrum.

[0012] According to an embodiment of the present disclosure, the first microfiber coupler includes: a first multimode fiber arm, a second multimode fiber arm, a first multimode fiber through-arm, a first multimode fiber coupling arm, a first fused taper region, a second fused taper region, and a first micro-nano waist region;

[0013] According to an embodiment of the present disclosure, the second microfiber coupler includes: a third multimode fiber arm, a fourth multimode fiber arm, a second multimode fiber through-arm, a second multimode fiber coupling arm, a third fused taper region, a fourth fused taper region, and a second micro-nano waist region.

[0014] According to an embodiment of the present disclosure, the first microfiber coupler is configured to control the first sub-detection light to input from the first multimode fiber arm, and realize energy transfer between the first multimode fiber arm and the second multimode fiber arm through mode matching coupling in the first fused taper region; when the first sub-detection light is transmitted to the first micro-nano waist region, the optical fields between the first multimode fiber arm and the second multimode fiber arm interact with the reference solution located outside the first microfiber coupler through the evanescent field of the first microfiber coupler, and the combined optical field after interaction is subjected to power redistribution through the second fused taper region, and the modulated first transmitted light is output from the first multimode fiber through-arm or the first multimode fiber coupling arm;

[0015] Wherein, the second microfiber coupler is configured to control the second sub-detection light to input from the third multimode fiber arm, and realize energy transfer between the third multimode fiber arm and the fourth multimode fiber arm through mode matching coupling in the third fused taper region; when the second sub-detection light is transmitted to the second micro-nano waist region, the optical fields between the third multimode fiber arm and the fourth multimode fiber arm interact with the solution to be measured located outside the second microfiber coupler through the evanescent field of the second microfiber coupler, and the combined optical field after interaction is subjected to power redistribution through the fourth fused taper region, and the modulated second transmitted light is output from the second multimode fiber through-arm or the second multimode fiber coupling arm.

[0016] According to an embodiment of the present disclosure, the part of the first microfiber coupler that interacts with the first sub-detection light is the first optical sensitive part. When the first sub-detection light is transmitted through the first microfiber coupler, inter-mode interference is generated in the first optical sensitive part. The part of the second microfiber coupler that interacts with the second sub-detection light is the second optical sensitive part. When the second sub-detection light is transmitted through the second microfiber coupler, inter-mode interference is generated in the second optical sensitive part.

[0017] According to an embodiment of the present disclosure, the reference sensing unit further includes a first substrate and a first microfluidic chip disposed on the first substrate. The first microfluidic chip includes a first sample injection area, a first sample discharge area, a first sample detection area, a first drainage channel, and a first discharge channel;

[0018] Wherein, the first microfluidic chip is configured to control the reference solution to enter the first sample detection area through the first drainage channel when the reference solution is injected through the first sample injection area, be detected by the first microfiber coupler in the first sample detection area, reach the first sample discharge area through the first discharge channel, and be discharged from the first sample discharge area;

[0019] The detection sensing unit further includes a second substrate and a second microfluidic chip disposed on the second substrate. The second microfluidic chip includes a second sample injection area, a second sample discharge area, a second sample detection area, a second drainage channel, and a second discharge channel;

[0020] Wherein, the second microfluidic chip is configured to control the test solution to enter the second sample detection area through the second drainage channel when the test solution is injected through the second sample injection area, be detected by the second microfiber coupler in the second sample detection area, reach the second sample discharge area through the second discharge channel, and be discharged from the second sample discharge area.

[0021] According to an embodiment of the present disclosure, the detection sensing unit is further configured to guide the second sub-detection light to interact with the reference solution located outside the second microfiber coupler through the evanescent field of the second microfiber coupler to output a third transmitted light;

[0022] The beam combiner is further configured to combine the first transmitted light and the third transmitted light to obtain an initial combined light with bidirectional vernier spectral characteristics;

[0023] The spectral analyzer is further configured to collect the initial combined light and convert the initial combined light into the initial vernier spectrum;

[0024] The above-mentioned processor is also configured to determine the concentration of the solution to be measured according to the above-mentioned initial cursor spectrum and the above-mentioned combined cursor spectrum.

[0025] According to an embodiment of the present disclosure, the difference between the free spectral range of the above-mentioned first microfiber coupler and the free spectral range of the above-mentioned second microfiber coupler is less than 10%.

[0026] According to an embodiment of the present disclosure, both the above-mentioned first substrate and the above-mentioned second substrate are made of magnesium fluoride, and both the above-mentioned first microfluidic chip and the above-mentioned second microfluidic chip are made of polydimethylsiloxane.

[0027] Another aspect of the present disclosure provides a method for detecting the concentration of a solution, which is applied to the detection system as described above. The method for detecting the concentration of the solution includes:

[0028] An initial cursor spectrum is obtained according to the first transmitted light obtained by the reference sensing unit based on the reference solution and the third transmitted light obtained by the detection sensing unit based on the above-mentioned reference solution;

[0029] A cursor spectrum is obtained according to the above-mentioned first transmitted light and the second transmitted light obtained by the detection sensing unit based on the solution to be measured;

[0030] The concentration of the solution to be measured is determined according to the envelope offset between the above-mentioned initial cursor spectrum and the above-mentioned cursor spectrum.

[0031] According to an embodiment of the present disclosure, the above-mentioned initial cursor spectrum includes a first transmission spectrum corresponding to the above-mentioned first transmitted light and a third transmission spectrum corresponding to the above-mentioned third transmitted light, and the above-mentioned cursor spectrum includes the above-mentioned first transmission spectrum and a second transmission spectrum corresponding to the above-mentioned second transmitted light;

[0032] The step of determining the concentration of the solution to be measured according to the envelope offset between the above-mentioned initial cursor spectrum and the above-mentioned cursor spectrum includes:

[0033] The concentration of the solution to be measured is determined according to the offset of the above-mentioned cursor spectrum in the above-mentioned initial cursor spectrum.

[0034] According to an embodiment of the present disclosure, through a first microfiber coupler and a second microfiber coupler connected in parallel, the first transmitted light (reference light) and the second transmitted light (carrying information of the solution to be measured) undergo dual optical frequency comb interference to generate a detection vernier spectrum with a periodically enveloped modulation. The concentration of the solution to be measured changes its refractive index, causing a phase change in the second transmitted light, resulting in a periodic shift of the characteristic peak of the vernier spectrum envelope. The concentration can be determined by measuring this shift. The design of the micro-nano waist regions of the first microfiber coupler and the second microfiber coupler can enhance the interaction depth between the evanescent field and the environment. For example, an asymmetric fused taper structure can selectively amplify the coupling efficiency of specific modes, converting a small change in refractive index into a significant shift of interference fringes, thereby improving the system sensitivity. By adjusting the stretching length and waist diameter of the two couplers, the ratio of the free spectral range (FSR) of the first transmitted light to the second transmitted light can be independently controlled to achieve dynamic optimization of the vernier envelope period and the offset sensitivity. Description of the Drawings

[0035] Through the following description of the embodiments of the present disclosure with reference to the drawings, the above and other objects, features, and advantages of the present disclosure will become clearer. In the drawings:

[0036] Figure 1 Schematically shows a connection diagram of a detection system of a microfiber coupler based on the bidirectional optical frequency comb vernier effect according to an embodiment of the present disclosure;

[0037] Figure 2 Schematically shows a connection diagram of a first microfiber coupler according to an embodiment of the present disclosure;

[0038] Figure 3 Schematically shows a connection diagram of a first microfiber coupler according to an embodiment of the present disclosure;

[0039] Figure 4 Schematically shows a connection diagram of a reference sensing unit according to an embodiment of the present disclosure;

[0040] Figure 5 Schematically shows a three-dimensional structure diagram of a reference sensing unit according to an embodiment of the present disclosure;

[0041] Figure 6 Schematically shows a flowchart of a preparation method of a sensing unit according to an embodiment of the present disclosure;

[0042] Figure 7 Schematically shows a flowchart of an application method of a detection system of a microfiber coupler based on the bidirectional optical frequency comb vernier effect according to an embodiment of the present disclosure. Detailed Embodiments

[0043] Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings. However, it should be understood that these descriptions are merely exemplary and are not intended to limit the scope of the present disclosure. In the following detailed description, for the sake of explanation, numerous specific details are set forth in order to provide a comprehensive understanding of the embodiments of the present disclosure. However, it is obvious that one or more embodiments can also be implemented without these specific details. In addition, in the following description, descriptions of well-known structures and technologies are omitted to avoid unnecessarily confusing the concepts of the present disclosure.

[0044] The terms used herein are merely for describing specific embodiments and are not intended to limit the present disclosure. The terms "including", "comprising", etc. used herein indicate the presence of the described features, steps, operations, and / or components, but do not exclude the presence or addition of one or more other features, steps, operations, or components.

[0045] All terms used herein (including technical and scientific terms) have the meanings commonly understood by those of ordinary skill in the art, unless otherwise defined. It should be noted that the terms used herein should be interpreted as having a meaning consistent with the context of this specification and should not be interpreted in an idealized or overly rigid manner.

[0046] In cases where expressions similar to "at least one of A, B, and C, etc." are used, generally, it should be interpreted according to the meaning commonly understood by those of ordinary skill in the art (for example, "a system having at least one of A, B, and C" should include, but is not limited to, a system having only A, only B, only C, having A and B, having A and C, having B and C, and / or having A, B, and C, etc.).

[0047] In the embodiments of the present disclosure, in terms of the collection, update, analysis, processing, use, transmission, provision, disclosure, storage, etc. of the data involved (for example, including but not limited to user personal information), they all comply with the provisions of relevant laws and regulations, are used for legal purposes, and do not violate public order and good customs. In particular, necessary measures are taken for user personal information to prevent illegal access to user personal information data and to maintain the security of user personal information and network security.

[0048] In the embodiments of the present disclosure, before obtaining or collecting user personal information, the authorization or consent of the user has been obtained.

[0049] Refractive index sensors, as key analytical tools, are widely used in the measurement of substance concentration and the monitoring of physical and chemical properties. Common refractive index sensors can be classified into two types, electrical and optical, according to the detection method. Among them, electrical sensors indirectly characterize the refractive index through changes in physical quantities such as resistance, capacitance, piezoelectricity, and triboelectricity. Although they have a lower cost, they are usually vulnerable to environmental interference and have limited sensitivity. Optical sensors, based on the changes in the propagation characteristics of light waves, have the advantages of high sensitivity, wide dynamic range, and non-contact measurement, and perform particularly well in refractive index detection. Among optical sensors, fiber optic sensors have become a research hotspot due to their small size, strong anti-electromagnetic interference ability, and adaptability to various environments. According to different detection principles, fiber optic sensors can be further divided into sensing technologies based on fiber Bragg gratings (FBGs), fiber interferometers, surface plasmon resonance (SPR), and micro-nano fiber structures. Among them, micro-nano fibers have obvious advantages in liquid refractive index sensing due to their ultra-high light field confinement and flexible geometric design. However, in related technologies, the mode interference-based fiber optic sensors using micro-nano fibers utilize the interference between different modes in the same fiber to sense changes in the surrounding environment, which have high structural requirements for parameters such as the taper angle and waist region size, and poor repeatability.

[0050] In view of this, embodiments of the present disclosure provide a detection system based on a bidirectional optical frequency comb vernier effect of a microfiber coupler, including: an optical frequency comb light source configured to emit detection light; a beam splitter connected to the optical frequency comb light source and configured to divide the detection light into a first sub-detection light and a second sub-detection light; a reference sensing unit connected to the beam splitter, including a first microfiber coupler configured to transmit the first sub-detection light, and the reference sensing unit configured to guide the first sub-detection light to interact with a reference solution located outside the first microfiber coupler through the evanescent field of the first microfiber coupler to output a first transmitted light; a detection sensing unit connected to the beam splitter, including a second microfiber coupler configured to transmit the second sub-detection light, and the detection sensing unit configured to guide the second sub-detection light to interact with a solution to be measured located outside the second microfiber coupler through the evanescent field of the second microfiber coupler to output a second transmitted light; a combiner connected to the first microfiber coupler and the second microfiber coupler and configured to combine the first transmitted light and the second transmitted light to obtain a combined light with bidirectional vernier spectral characteristics; a spectral analyzer connected to the combiner and configured to collect the combined light and convert the combined light into a vernier spectrum; and a processor connected to the spectral analyzer and configured to determine the concentration of the solution to be measured according to the vernier spectrum.

[0051] Figure 1 Schematically shows a connection diagram of a detection system based on a bidirectional optical frequency comb vernier effect of a microfiber coupler according to an embodiment of the present disclosure.

[0052] As Figure 1As shown, the detection system 100 of the microfiber coupler based on the two-way optical frequency comb vernier effect includes an optical frequency comb light source 110, a beam splitter 120, a reference sensing unit 130, a detection sensing unit 140, a beam combiner 150, a spectrum analyzer 160, and a processor 170.

[0053] Among them, the optical frequency comb light source 110 is configured to emit detection light.

[0054] The beam splitter 120 is connected to the optical frequency comb light source 110 and is configured to divide the detection light into a first sub-detection light and a second sub-detection light.

[0055] The reference sensing unit 130 is connected to the beam splitter 120 and includes a first microfiber coupler. The first microfiber coupler is configured to transmit the first sub-detection light. The reference sensing unit is configured to guide the first sub-detection light to interact with a reference solution located outside the first microfiber coupler through the evanescent field of the first microfiber coupler, so as to output a first transmitted light.

[0056] The detection sensing unit 140 is connected to the beam splitter 120 and includes a second microfiber coupler. The second microfiber coupler is configured to transmit the second sub-detection light. The detection sensing unit is configured to guide the second sub-detection light to interact with a solution to be measured located outside the second microfiber coupler through the evanescent field of the second microfiber coupler, so as to output a second transmitted light.

[0057] The beam combiner 150 is connected to the first microfiber coupler and the second microfiber coupler and is configured to combine the first transmitted light and the second transmitted light to obtain a combined light.

[0058] The spectrum analyzer 160 is connected to the beam combiner 150 and is configured to collect the combined light and convert the combined light into a vernier spectrum with two-way vernier spectral characteristics.

[0059] The processor 170 is connected to the spectrum analyzer 160 and is configured to determine the concentration of the solution to be measured according to the vernier spectrum.

[0060] According to an embodiment of the present disclosure, the detection light emitted by the optical frequency comb light source 110 may be broadband light with multiple equally spaced frequency components, which is used to provide an optical frequency comb signal with high precision and a wide spectral range.

[0061] According to an embodiment of the present disclosure, the beam splitter 120 and the beam combiner 150 may be 3dB couplers.

[0062] According to an embodiment of the present disclosure, the first microfiber coupler in the reference sensing unit 130 can transmit the first sub-detection light, and the outside of the first microfiber coupler can be a reference solution. During the process of controlling the transmission of the first sub-detection light from the first microfiber coupler, the first sub-detection light can interact with the reference solution through the evanescent field of the first microfiber coupler, and the first transmitted light is output. The reference solution can be deionized water.

[0063] According to an embodiment of the present disclosure, the second microfiber coupler in the detection sensing unit 140 can transmit the second sub-detection light, and the outside of the second microfiber coupler can be a solution to be measured. During the process of controlling the transmission of the second sub-detection light from the second microfiber coupler, the second sub-detection light interacts with the external solution to be measured through the evanescent field of the second microfiber coupler, and the second transmitted light carrying the refractive index change of the solution to be measured is output.

[0064] According to an embodiment of the present disclosure, after the first transmitted light and the second transmitted light are combined and passed through the optical spectrum analyzer 160, a Vernier spectrum can be obtained. The Vernier spectrum can be a spectrum with bidirectional Vernier spectrum characteristics. Among them, the refractive index of the solution to be measured can affect the coupling structure of the second sub-detection light. The characteristic wavelengths shown by the second transmitted light obtained according to the solutions to be measured with different refractive indexes are different in the Vernier spectrum, and there is a mapping relationship between the concentration and the refractive index of the solution to be measured. Therefore, according to the wavelength corresponding to the characteristic peak in the Vernier spectrum, the concentration of the solution to be measured can be finally calculated. The concentration of the solution to be measured proposed in the present disclosure refers to the content of the solute per unit volume or unit mass in the solution.

[0065] According to an embodiment of the present disclosure, the optical frequency comb Vernier effect means that the spectral part corresponding to the first transmitted light in the detected Vernier spectrum is regarded as the main scale part of the Vernier caliper, and the spectral part corresponding to the second transmitted light is regarded as the vernier scale part of the Vernier caliper. Since the concentration of the solution to be measured will affect the refractive index of the solution to be measured, the second transmitted light changes accordingly, and then the spectral part corresponding to the second transmitted light changes in the Vernier spectrum. The concentration of the solution to be measured is determined according to the change amount. The bidirectional optical frequency comb Vernier characteristic means that on the basis of the optical frequency comb Vernier effect, the spectrum changing with the external environment in the Vernier spectrum is centrosymmetrically distributed.

[0066] According to an embodiment of the present disclosure, the first transmitted light and the second transmitted light are combined and interfered, and then a Vernier spectrum is formed by a spectrum analyzer. The envelope characteristic thereof is determined by the free spectral range of the two optical frequency combs. In the Vernier spectrum, it is the superposition of the first transmitted spectrum corresponding to the first transmitted light and the second transmitted spectrum corresponding to the second transmitted light. Since the concentration of the solution to be measured affects the phase of the second transmitted light by changing the refractive index, it causes a periodic shift of the Vernier envelope in the Vernier spectrum. By measuring the shift amount of the envelope characteristic peak, the concentration value of the solution to be measured can be reflected. Calculating the concentration of the solution to be measured based on the optical frequency comb Vernier effect has relatively low structural requirements for the reference sensing unit and the detection sensing unit. Moreover, the first microfiber coupler in the reference sensing unit and the second microfiber coupler in the detection sensing unit can amplify the influence of the external environment change on the mode coupling, so that the response of the external environment change to the optical signal coupling modulation is more significant, and the sensitivity of the detection system is improved. Furthermore, the interference fringes of the first microfiber coupler and the second microfiber coupler can be flexibly regulated, which can not only obtain higher sensitivity, but also enhance the dynamic adjustment ability of the optical frequency comb Vernier effect spectrum.

[0067] Figure 2 Schematically shows a connection schematic diagram of a first microfiber coupler according to an embodiment of the present disclosure.

[0068] As Figure 2 shown, the first microfiber coupler 200 includes: a first multimode fiber arm 201, a second multimode fiber arm 202, a first multimode fiber straight-through arm 203, a first multimode fiber coupling arm 204, a first fused taper region 205, a second fused taper region 206, and a first micro-nano waist region 207.

[0069] One end of the first multimode fiber arm 201 and the second multimode fiber arm 202 is connected to the first fused taper region 205, the first multimode fiber straight-through arm 203 and the first multimode fiber coupling arm 204 are connected to the second fused taper region 206, and the first fused taper region 205 and the second fused taper region 206 are connected through the first micro-nano waist region 207.

[0070] The first microfiber coupler 200 is configured to control the first sub-detection light to be input from the first multimode fiber arm 201, and realize the energy transfer between the first multimode fiber arm 201 and the second multimode fiber arm 202 through mode matching coupling in the first fused taper region 205; when the first sub-detection light is transmitted to the first micro-nano waist region 207, the optical fields between the first multimode fiber arm 201 and the second multimode fiber arm 202 interact with the reference solution located outside the first microfiber coupler 200 through the evanescent field of the first microfiber coupler 200. The composite optical field after the interaction is subjected to power re-distribution through the second fused taper region 206, and the modulated first transmitted light is output from the first multimode fiber straight-through arm 203 or the first multimode fiber coupling arm 204.

[0071] The first micro fiber coupler 200 may include four ports, port 1 , port 2 , port 3 and port 4 . Port 1 may be a port connected to the beam splitter 120 , and port 3 may be a port connected to the beam combiner 150 .

[0072] According to an embodiment of the present disclosure, the portion of the first micro-fiber coupler that interacts with the first sub-detection light is the first optically sensitive portion. When the first micro-fiber coupler transmits the first sub-detection light, the first optically sensitive portion generates inter-mode interference, and ultimately, the first transmitted light is output from the first multimode fiber straight-through arm 203 and the first multimode fiber coupling arm 204 in a certain splitting ratio.

[0073] Figure 3 The figure schematically shows a connection diagram of the first and second micro-fiber couplers according to an embodiment of the present disclosure.

[0074] like Figure 3 As shown, the second micro-fiber coupler 300 includes: a third multimode fiber arm 301, a fourth multimode fiber arm 302, a second multimode fiber straight-through arm 303, a second multimode fiber coupling arm 304, a third melt cone region 305, a fourth melt cone region 306 and a second micro-nano waist region 307.

[0075] Among them, one end of the third multimode optical fiber arm 301 and the fourth multimode optical fiber arm 302 are connected to the third melt cone zone 305, the second multimode optical fiber straight-through arm 303 and the second multimode optical fiber coupling arm 304 are connected to the fourth melt cone zone 306, and the third melt cone zone 305 and the fourth melt cone zone 306 are connected through the second micro-nano waist zone 307.

[0076] The second micro-fiber coupler 300 is configured to control the second sub-detection light to be input from the third multimode fiber arm 301, and realize the energy transfer between the third multimode fiber arm 301 and the fourth multimode fiber arm 302 through mode matching coupling in the third melt cone area; when the second sub-detection light is transmitted to the second micro-nano waist area 307, the light field between the third multimode fiber arm 301 and the fourth multimode fiber arm 302 interacts with the solution to be tested located outside the second micro-fiber coupler 300 through the evanescent field of the second micro-fiber coupler 300, and the composite light field after the interaction is redistributed in power through the fourth melt cone area 306, and the modulated second transmitted light is output from the second multimode fiber straight-through arm 303 or the second multimode fiber coupling arm 304.

[0077] The second micro-fiber coupler 300 may include four ports, namely, port 5 , port 6 , port 7 and port 8 . Port 5 may be a port connected to the beam splitter 120 , and port 7 may be a port connected to the beam combiner 150 .

[0078] According to an embodiment of the present disclosure, the part of the second microfiber coupler that interacts with the second sub-detection light is the second optical sensitive part. When the second microfiber coupler transmits the second sub-detection light, the second optical sensitive part generates inter-mode interference. Finally, the second transmitted light is output from the second multimode fiber direct-through arm 303 and the second multimode fiber coupling arm 304 respectively with a certain splitting ratio.

[0079] It can be seen from Figure 2 and Figure 3 that the first microfiber coupler 200 and the second microfiber coupler 300 are identical in structure.

[0080] According to an embodiment of the present disclosure, in the detection system of the present disclosure, the reference sensing unit is responsible for providing a functional transmission spectrum as a reference to ensure the generation of the Vernier effect of the detection system and does not participate in the sensing of the information to be measured; while the detection sensing unit is responsible for the response sensing of environmental parameters.

[0081] According to an embodiment of the present disclosure, the free spectral range of the first microfiber coupler and the free spectral range of the second microfiber coupler have a difference of less than 10%. That is .

[0082] As an example, the diameter of the first micro-nano waist region of the first microfiber coupler can be 3.33 μm; the diameter of the second micro-nano waist region of the second microfiber coupler can be 2.95 μm.

[0083] The free spectral range of the microfiber coupler is jointly determined by the effective refractive indices of the odd and even modes in the microfiber and the coupling length. When the interference periods of the first microfiber coupler and the second microfiber coupler are approximately the same, that is, their free spectral ranges are slightly detuned, a Vernier effect characteristic output spectrum will be formed after the two sets of transmission spectra are superimposed. Once the transmission spectrum corresponding to the coupled light output by the detection sensing unit changes, the Vernier effect will show a spectral shift. By tracking the envelope shift of the Vernier output spectrum, the sensing sensitivity can be amplified by several orders of magnitude. Therefore, by optimizing the matching of the free spectral ranges of the first microfiber coupler and the second microfiber coupler, the output spectrum generates uniformly distributed optical frequency comb interference fringes. When the refractive index of the external environment of the detection sensing unit changes, the interference fringes in space show a significant spectral shift, and the characteristic value is the change in the fringe spacing at the co-directional or anti-directional matching points, thereby realizing high-sensitivity detection of the external refractive index or environmental parameters.

[0084] According to an embodiment of the present disclosure, the bidirectional optical frequency comb vernier effect proposed by the present disclosure is driven by the detection light with a wide spectrum provided by an optical frequency comb light source, and is based on two parallel first microfiber couplers or second microfiber couplers. It should be noted here that it can be easily extended to other types of fiber optic sensors with different configurations, such as Fabry - Perot interferometers, Sagnac interferometers, or some fiber optic resonators. When the free spectral ranges of the first microfiber coupler or the second microfiber coupler are slightly detuned, their transmitted spectra will form an envelope spectrum with a vernier effect after superposition. The envelope spectrum is centrosymmetrically distributed, and its symmetry center is the turning point when the phase differences of the first microfiber coupler or the second microfiber coupler are equal; the spectral envelopes on both sides of the symmetry center shift in the same / opposite directions with the change of the external solution concentration.

[0085] When the detection light travels in a microfiber coupler (e.g., the first microfiber coupler or the second microfiber coupler), the interference effect for inter - mode transmission generates a phase difference. Specifically, the phase difference is determined by the effective refractive index difference between the odd and even modes and the optical transmission path length (i.e., the coupling length) in the microfiber coupler.

[0086] The phase difference ( ) can be expressed as:

[0087] (1)

[0088] where, is the coupling length, is the effective refractive index difference between the odd and even modes, is the wavelength of the detection light.

[0089] The phase difference change rate is the derivative of the phase difference with respect to the wavelength , that is:

[0090] (2)

[0091] By taking the derivative, the expression of the phase difference change rate can be obtained:

[0092] (3)

[0093] This formula shows that the phase difference change rate consists of two parts: (1) , representing the contribution of the change of the effective refractive index with respect to the wavelength to the phase difference change rate; (2) , representing the contribution of the change of the wavelength itself to the phase difference change rate.

[0094] Specifically, the parallel first microfiber coupler is named MFC - a, and the second microfiber coupler is named MFC - b.

[0095] Then the phase difference of the first microfiber coupler MFC-a is:

[0096] (4)

[0097] where is the coupling length in the first microfiber coupler MFC-a; is the effective refractive index difference between the odd and even modes of the first microfiber coupler MFC-a.

[0098] The phase difference of the second microfiber coupler named MFC-b is:

[0099] (5)

[0100] where is the coupling length in the second microfiber coupler MFC-b; is the effective refractive index difference between the odd and even modes of the second microfiber coupler MFC-b.

[0101] Then the rate of change of the phase difference of the first microfiber coupler MFC-a and the rate of change of the phase difference of the second microfiber coupler MFC-b are respectively:

[0102] (6)

[0103] (7)

[0104] The position where the rate of change of the phase difference (rate of change of phase difference) of two parallel MFCs with respect to wavelength is equal at a certain wavelength is called the turning point of the rate of change of phase difference. When the rates of change of the phase differences of the two MFCs are equal at this wavelength, their free spectral ranges (FSRs) are also equal, and at this time, the envelope of the output spectrum is symmetrically distributed centered at this point.

[0105] The wavelength corresponding to the turning point of the rate of change of phase difference can be expressed as:

[0106] (8)

[0107] The present disclosure realizes the optical frequency comb vernier effect by connecting two groups of microfiber couplers with similar free spectral ranges in parallel. This structure can significantly improve the sensitivity of the detection system. By utilizing the adjustable characteristics of the microfiber couplers, the interference fringes of the two spectra can be flexibly regulated, not only obtaining higher sensitivity but also enhancing the dynamic adjustment ability of the optical frequency comb vernier effect spectrum. In addition, by optimizing the geometric structures and mode matching conditions of the two couplers, the envelope characteristics of the optical frequency comb can be further adjusted, enabling the system to have stronger adaptability and precision under different external environmental changes.

[0108] Figure 4 Schematically shows a connection schematic diagram of a reference sensing unit according to an embodiment of the present disclosure.

[0109] Figure 5 Schematically shows a three-dimensional structure schematic diagram of a reference sensing unit according to an embodiment of the present disclosure.

[0110] As Figure 4 and Figure 5 shown, the reference sensing unit 130 further includes a first substrate 131 and a first microfluidic chip 132 disposed on the first substrate 131. The first microfluidic chip 132 includes a first sample injection area 1321, a first sample discharge area 1322, a first sample detection area 1323, a first drainage channel 1324, and a first discharge channel 1325.

[0111] Among them, the first microfluidic chip 132 is configured to control the reference solution to enter the first sample detection area 1323 through the first drainage channel 1324 when the reference solution is injected through the first sample injection area 1321, be detected by the first microfiber coupler 200 in the first sample detection area 1323, reach the first sample discharge area 1322 through the first discharge channel 1325, and be discharged from the first sample discharge area 1322. The first microfluidic chip and the first substrate can be connected by bonding, chemical bonding, thermocompression bonding, or other means to complete the fabrication of the integrated structure.

[0112] According to an embodiment of the present disclosure, in order to reduce the difficulty of the package design, the structure of the detection sensing unit can refer to the reference sensing unit shown in Figure 4 and Figure 5 .

[0113] According to an embodiment of the present disclosure, the detection sensing unit further includes a second substrate and a second microfluidic chip disposed on the second substrate. The second microfluidic chip includes a second sample injection area, a second sample discharge area, a second sample detection area, a second drainage channel, and a second discharge channel.

[0114] Among them, the second microfluidic chip is configured to control the solution to be measured to enter the second sample detection area through the second discharge channel when the solution to be measured is injected through the second sample injection area, and is detected by the second microfiber coupler in the second sample detection area, and then reaches the second sample discharge area through the second discharge channel and is discharged from the second sample discharge area. The second microfluidic chip and the second substrate can be connected by bonding, chemical bonding, thermal compression bonding or other means to complete the fabrication of the integrated structure.

[0115] According to an embodiment of the present disclosure, both the first substrate and the second substrate are made of magnesium fluoride (MgF2), and both the first microfluidic chip and the second microfluidic chip are made of polydimethylsiloxane (PDMS).

[0116] According to an embodiment of the present disclosure, the key reason for using MgF2 as the substrate is that its refractive index is about 1.38, which is lower than the refractive index of optical fiber silica (SiO2) (about 1.45). This property avoids the possibility of light energy leakage to the substrate when the optical signal is transmitted in the microfiber coupler, effectively reducing the dissipation loss. In addition, MgF2 has excellent optical transparency and can maintain a high light transmittance in a wide spectral range, thus ensuring the high-quality output of the optical signal. At the same time, the excellent mechanical and chemical stability of MgF2 enables it to maintain long-term reliability in harsh environments.

[0117] The PDMS microfluidic chip plays an important role in the encapsulation unit. It not only has excellent biocompatibility and is suitable for the detection of biological samples, but also has flexibility and easy processability. PDMS can closely adhere to the surface of the microfiber coupler to form a stable encapsulation interface, and at the same time its low refractive index and high transparency have minimal interference with the optical signal. In addition, the processing convenience of PDMS supports the design of complex microfluidic channels, enabling the cyclic flow of the sample liquid and optimizing the fluid distribution, providing guarantee for high-sensitivity sensing in a dynamic environment.

[0118] The present disclosure combines the functional sensor device with a micro-nano fiber structure and microfluidic technology, which can achieve high-precision detection of ultra-trace environmental parameters and significantly improve the sensitivity and adaptability of the system. With the adaptability of this composite structure to harsh environments (such as dangerous, high-intensity, high-precision, ultra-trace conditions), its related technologies can be widely applied to precision sensing fields such as biochemical analysis, electric field detection, pesticide residues, and soil heavy metals to meet the multi-functional sensing requirements in complex environments.

[0119] According to an embodiment of the present disclosure, the detection sensing unit is further configured to guide the second sub-detection light to interact with a solution to be measured located outside the second microfiber coupler through the evanescent field of the second microfiber coupler, so as to output a third transmitted light; the beam combiner is further configured to combine the first transmitted light and the third transmitted light to obtain an initial combined light; the spectral analyzer is further configured to acquire the initial combined light and convert the initial combined light into an initial cursor spectrum; the processor is further configured to determine the concentration of the solution to be measured according to the initial cursor spectrum and the cursor spectrum.

[0120] According to an embodiment of the present disclosure, the detection sensing unit can also couple a reference solution to output a third transmitted light. The initial combined light formed by the first transmitted light and the third transmitted light can generate an initial cursor spectrum in the spectral analyzer. The initial cursor spectrum can be a reference spectrum. By comparing the difference between the cursor spectrum and the initial cursor spectrum, the refractive index change between the solution to be measured and the reference solution can be determined, and then the concentration of the solution to be measured can be determined.

[0121] As Figures 1 - 5 shown, the detection light output by the optical frequency comb light source is split into two beams, namely the first sub-detection light and the second sub-detection light, by a 3dB beam splitter. Among them, the first sub-detection light enters the first multimode fiber arm of the first microfiber coupler, passes through the first fused taper region, and enters the first micro-nano waist region. In the first micro-nano waist region, the evanescent field of the first microfiber coupler enhances the mode field coupling, forming significant inter-mode interference. Since the mode field energy is distributed in the cladding and the external environment, the phase characteristics of the spectrum of the output first transmitted light are highly sensitive to the change of the environmental refractive index.

[0122] The second sub-detection light enters the third multimode fiber arm of the second microfiber coupler, passes through the third fused taper region, and enters the second micro-nano waist region.

[0123] The reference sensing unit where the first microfiber coupler is located and the detection sensing unit where the second microfiber coupler is located are in a parallel beam splitting structure. The respective micro-nano coupling regions generate characteristic spectra through different responses to the external environment, and finally generate optical frequency comb interference fringes with a cursor effect through the spectral analyzer.

[0124] According to an embodiment of the present disclosure, the present disclosure also proposes a preparation method of a sensing unit. The preparation method of the sensing unit can be used to prepare the reference sensing unit and the detection sensing unit in a detection system based on a microfiber coupler with a two-way optical frequency comb cursor effect.

[0125] Figure 6 Schematically shows a flowchart of the preparation method of the sensing unit according to an embodiment of the present disclosure.

[0126] As Figure 6 shown, the preparation method of the sensing unit includes operation S610 to operation S630.

[0127] In operation S610, two multimode optical fibers are formed into a microfiber coupler through a fused biconical taper process. The microfiber coupler includes a fifth multimode optical fiber arm, a sixth multimode optical fiber arm, a third multimode optical fiber straight-through arm, a third multimode optical fiber coupling arm, a fifth fused taper region, a sixth fused taper region, and a third micro-nano waist region. One end of the fifth multimode optical fiber arm and the sixth multimode optical fiber arm is connected to the fifth fused taper region, the third multimode optical fiber straight-through arm and the third multimode optical fiber coupling arm are connected to the sixth fused taper region, the fifth fused taper region and the sixth fused taper region are connected through the third micro-nano waist region, and both the fifth fused taper region and the sixth fused taper region are conical.

[0128] In operation S620, the microfiber coupler is fixed on a substrate.

[0129] In operation S630, a microfluidic chip is formed on the substrate.

[0130] According to an embodiment of the present disclosure, the core diameter / cladding diameter of the multimode optical fiber can be 62.5 / 125 μm, and the core refractive index / cladding refractive index can be 1.4504 / 1.4447.

[0131] According to an embodiment of the present disclosure, fused biconical taper can be performed by a flame of a biconical taper machine. The specific operation can be as follows:

[0132] S1, Select two multimode optical fibers of appropriate length, and use a Miller clamp to strip the coating layer of a middle section of the multimode optical fibers. The length can be 3 cm. The part without the coating layer should not be too long to avoid causing the multimode optical fibers to break during the biconical taper process. Repeatedly wipe the bare fiber part without the coating layer with alcohol or acetone to keep the fiber surface clean and avoid contamination of the multimode optical fibers by residual debris and dust during the biconical taper process.

[0133] S2, After wiping, wind the bare fiber parts of the two multimode optical fibers together in parallel to ensure there is no gap between the fibers, and then fix the prepared multimode optical fibers on the biconical taper platform through a multimode optical fiber clamping tool.

[0134] S3, Turn on the hydrogen generator and ignite it until the flame is stable.

[0135] S4, Adjust the ceramic flame outlet to be directly above the middle of the optical fiber, and adjust the height so that the multimode optical fiber just touches the outer flame of the hydrogen-oxygen flame.

[0136] S5, Turn on the stepping motor controller, control the horizontal scanning speed and range of the flame head, and scan and preheat the pre-stretched winding part for 1 minute.

[0137] S6, Turn on two motors to melt and biconical taper the optical fibers in opposite directions. After the biconical taper of the microfiber coupler is completed, turn off the motors and withdraw the heater.

[0138] According to an embodiment of the present disclosure, the stop condition for fused tapering can be that when the optical power of the input waveguide drops sharply, the optical power of the coupled waveguide rises rapidly, and the optical power begins to frequently alternate between the optical fibers, according to the change of the transmission spectrum, the tapering is stopped in time when the spectral characteristics meet the experimental requirements, and the heater is exited.

[0139] According to an embodiment of the present disclosure, after the fused tapering of the microfiber coupler is completed, a low refractive index ultraviolet glue can be used to fix the microfiber coupler. A small amount of ultraviolet glue is dropped at the positions of the tapered transition regions at both ends of the optical fiber and the non-tapered regions at both ends. Then, the magnesium fluoride substrate is placed on the microfiber coupler. After it is in full contact with the ultraviolet glue, the ultraviolet lamp is used to irradiate the glue-dropped part for several seconds. After the ultraviolet glue is cured, the magnesium fluoride substrate is carefully removed and placed on the table with the optical fiber facing up. Then, a microchannel made of PDMS with an inlet pipe, an outlet pipe, and an intermediate detection area is placed above.

[0140] According to an embodiment of the present disclosure, in order to ensure the stability of the sensor and avoid the influence brought by external disturbances, both ends of the microfiber coupler are fixed on the magnesium fluoride substrate, and then the side of the substrate adhering to the sensor faces up, and the layer structure shown in Figure 5 is covered and fixed with the PDMS microfluidic chip, and it is ensured that the sensing area of the microfiber coupler is located in the central detection area of the flow channel pool, so that the tapered area of the microfiber coupler can be in full contact with the solution. The design of the encapsulation is to ensure the tightness of the flow channel pool, avoid the leakage of the solution to be measured, and ensure that the sensing detection process is stable and not interfered by other external factors.

[0141] According to an embodiment of the present disclosure, since the parallel microfiber coupler composite structure has strict requirements on the transmission spectrum of each coupler, in order to obtain an effective Vernier effect and a high sensitivity gain effect, the difference in the free spectral ranges of the two groups of microfiber couplers should be controlled within 10%. Therefore, during the preparation process, the input and output ports of the microfiber coupler should always be connected to the broadband light source and the spectral analyzer to monitor the change of the transmission spectrum in real time.

[0142] According to an embodiment of the present disclosure, a sensing unit designed and fabricated based on multimode optical fiber has the characteristics of simple manufacturing process and excellent performance. On the one hand, there are naturally multiple modes in multimode optical fiber. Compared with single-mode optical fiber, the core-cladding ratio is small, and the waist region of micro-nano optical fiber is more likely to excite mode coupling and energy exchange, thereby enhancing the coupling efficiency between modes. This characteristic helps to form a denser interference fringe distribution. Even a small change in environmental refractive index or temperature can cause a significant spectral frequency shift, enabling high-sensitivity detection. On the other hand, the micro-nano waist region of the microfiber coupler significantly enhances the spatial confinement force and evanescent field characteristics of the optical field, while expanding the extension range of the mode field into the cladding and the surrounding environment, significantly improving the action depth of the evanescent field. This structure amplifies the influence of external environmental changes on mode coupling, and at the same time, the frequent energy exchange between modes introduces a higher non-linearity, thus making the response of external environmental parameters to the modulation of optical signals more significant. And the mode stability and coupling uniformity of multimode optical fiber during the tapering process are controllable, which helps to cope with different detection environments and mass production.

[0143] Figure 7 FIG. schematically shows a flowchart of an application method of a detection system of a microfiber coupler based on the two-way optical frequency comb vernier effect according to an embodiment of the present disclosure.

[0144] As Figure 7 shown, the application method includes operation S710 to operation S730.

[0145] In operation S710, an initial vernier spectrum is obtained based on the first transmitted light obtained from the reference solution by the reference sensing unit and the third transmitted light obtained from the reference solution by the detection sensing unit.

[0146] In operation S720, a vernier spectrum is obtained based on the first transmitted light and the second transmitted light obtained from the test solution by the detection sensing unit.

[0147] In operation S730, the concentration of the test solution is determined based on the initial vernier spectrum and the envelope offset of the vernier spectrum.

[0148] According to an embodiment of the present disclosure, the initial vernier spectrum is formed by the interference and superposition of the first transmitted light and the third transmitted light, where the first transmitted light is output by the first microfiber coupler and carries the information of the reference solution, and the third transmitted light is output by the second microfiber coupler and also carries the information of the reference solution.

[0149] According to an embodiment of the present disclosure, the vernier spectrum is formed by the interference and superposition of the first transmitted light and the second transmitted light, and the second transmitted light is output by the second microfiber coupler and carries the information of the test solution.

[0150] According to an embodiment of the present disclosure, the initial vernier spectrum can be a spectrum used as a reference. By comparing the difference between the vernier spectrum and the initial vernier spectrum, the refractive index change between the test solution and the reference solution can be determined. There is a certain mapping relationship between the refractive index and the liquid concentration, so the concentration of the test solution can be determined based on the refractive index.

[0151] According to an embodiment of the present disclosure, the initial vernier spectrum includes a first transmission spectrum corresponding to the first transmission light and a third transmission spectrum corresponding to the third transmission light, and the vernier spectrum includes the first transmission spectrum and a second transmission spectrum corresponding to the second transmission light.

[0152] Determining the concentration of the solution to be tested according to the initial vernier spectrum and the envelope offset of the vernier spectrum includes: determining the concentration of the solution to be tested according to the offset of the vernier spectrum in the initial vernier spectrum.

[0153] According to an embodiment of the present disclosure, the process of determining the concentration of the solution to be tested according to the initial vernier spectrum and the vernier spectrum is as follows:

[0154] The initial vernier spectrum is generated by the interference of the detection light and the reference solution light, and its envelope presents a periodic spectral structure; the vernier spectrum is generated by the interference of the detection light and the test solution light, and the overall envelope shifts due to the difference in the refractive index of the test solution. By comparing the position difference of the corresponding envelope characteristic peaks in the two spectra, the characteristic peak shift caused by the test solution is calculated to obtain the concentration value of the test solution.

[0155] According to the embodiments of the present disclosure, the envelope offset of the vernier spectrum presents central symmetry, that is, with the phase matching point as the symmetry center, the envelope peaks on both sides expand or shrink synchronously. This symmetrical offset mode can effectively suppress common mode interference such as temperature drift and improve detection reliability. The system sensitivity is determined by the ratio of the free spectral ranges of the two optical frequency combs. The closer the ratio is to 1, the more significant the amplification effect. The core of the vernier effect is to convert tiny refractive index changes into measurable spectral displacements through periodic modulation of the interference envelope, thereby achieving high-precision concentration detection.

[0156] The flowcharts and block diagrams in the accompanying drawings illustrate the architecture, functionality, and operation of possible implementations of systems, methods, and computer program products according to various embodiments of the present disclosure. In this regard, each block in the flowchart or block diagram may represent a module, a segment of a program, or a portion of code, which contains one or more executable instructions for implementing the specified logical function. It should also be noted that in some alternative implementations, the functions noted in the blocks may occur in a different order than noted in the accompanying drawings. For example, two consecutive blocks shown may actually be executed substantially in parallel, or they may sometimes be executed in the reverse order, depending on the functions involved. It should also be noted that each block in the block diagram or flowchart, and combinations of blocks in the block diagram or flowchart, can be implemented by a dedicated hardware-based system that performs the specified functions or operations, or by a combination of dedicated hardware and computer instructions. Those skilled in the art will appreciate that the features described in the various embodiments of the present disclosure can be combined and / or combined in various ways, even if such combinations or combinations are not explicitly described in the present disclosure. In particular, without departing from the spirit and teachings of the present disclosure, the features described in the various embodiments of the present disclosure can be combined and / or combined in various ways. All such combinations and / or combinations fall within the scope of the present disclosure.

[0157] The embodiments of the present disclosure have been described above. However, these embodiments are for illustrative purposes only and are not intended to limit the scope of the present disclosure. Although the embodiments have been described separately above, this does not mean that the measures in each embodiment cannot be used advantageously in combination. Without departing from the scope of the present disclosure, those skilled in the art can make various substitutions and modifications, and all such substitutions and modifications should fall within the scope of the present disclosure.

Claims

1. A detection system for a micro-fiber coupler based on a bidirectional optical frequency comb vernier effect, comprising: An optical frequency comb light source configured to emit detection light; A beam splitter connected to the optical frequency comb light source, configured to split the detection light into a first sub-detection light and a second sub-detection light; a reference sensing unit connected to the beam splitter, comprising a first micro-fiber coupler, wherein the first micro-fiber coupler is configured to transmit the first sub-detection light, and the reference sensing unit is configured to guide the first sub-detection light to interact with a reference solution located outside the first micro-fiber coupler through an evanescent field of the first micro-fiber coupler to output a first transmitted light; a detection sensing unit connected to the beam splitter, comprising a second micro-fiber coupler, wherein the second micro-fiber coupler is configured to transmit the second sub-detection light, and the detection sensing unit is configured to guide the second sub-detection light to interact with a solution to be detected outside the second micro-fiber coupler through an evanescent field of the second micro-fiber coupler, so as to output a second transmitted light; a beam combiner connected to the first micro-fiber coupler and the second micro-fiber coupler, and configured to combine the first transmitted light and the second transmitted light to obtain a combined light; A spectrum analyzer connected to the beam combiner, configured to collect the combined light beam and convert the combined light beam into a vernier spectrum having a bidirectional vernier spectrum characteristic; A processor is connected to the spectrum analyzer and is configured to determine the concentration of the solution to be tested according to the vernier spectrum.

2. The detection system according to claim 1, wherein: The first micro-fiber coupler comprises: a first multimode fiber arm, a second multimode fiber arm, a first multimode fiber straight-through arm, a first multimode fiber coupling arm, a first melt cone region, a second melt cone region and a first micro-nano waist region; The second micro-fiber coupler includes: a third multimode fiber arm, a fourth multimode fiber arm, a second multimode fiber straight-through arm, a second multimode fiber coupling arm, a third fused cone region, a fourth fused cone region and a second micro-nano waist region.

3. The detection system according to claim 2, wherein: The first micro-fiber coupler is configured to control the first sub-detection light to be input from the first multi-mode optical fiber arm, and to realize energy transfer between the first multi-mode optical fiber arm and the second multi-mode optical fiber arm through mode matching coupling in the first melt cone region; When the first sub-detection light is transmitted to the first micro-nano waist region, the light field between the first multimode optical fiber arm and the second multimode optical fiber arm interacts with the reference solution located outside the first micro-optical fiber coupler through the evanescent field of the first micro-optical fiber coupler, and the composite light field after the interaction is subjected to power redistribution through the second melting cone region, and the modulated first transmitted light is output from the first multimode optical fiber straight-through arm or the first multimode optical fiber coupling arm; Among them, the second micro-fiber coupler is configured to control the second sub-detection light to be input from the third multi-mode fiber arm, and realize the energy transfer between the third multi-mode fiber arm and the fourth multi-mode fiber arm through mode matching coupling in the third melt cone region; when the second sub-detection light is transmitted to the second micro-nano waist region, the light field between the third multi-mode fiber arm and the fourth multi-mode fiber arm interacts with the solution to be tested located outside the second micro-fiber coupler through the evanescent field of the second micro-fiber coupler, and the composite light field after the interaction is subjected to power redistribution through the fourth melt cone region, and the modulated second transmitted light is output from the second multi-mode fiber straight-through arm or the second multi-mode fiber coupling arm.

4. The detection system according to claim 3, wherein: The portion of the first micro-fiber coupler that interacts with the first sub-detection light is a first optically sensitive portion. When the first micro-fiber coupler transmits the first sub-detection light, the first optically sensitive portion generates inter-mode interference. The portion of the second micro-fiber coupler that interacts with the second sub-detection light is a second optically sensitive portion. When the second micro-fiber coupler transmits the second sub-detection light, the second optically sensitive portion generates inter-mode interference.

5. The detection system according to claim 1, wherein: The reference sensing unit further comprises a first substrate and a first microfluidic chip disposed on the first substrate, wherein the first microfluidic chip comprises a first sample injection area, a first sample discharge area, a first sample detection area, a first discharge channel and a first discharge channel; Wherein, the first microfluidic chip is configured to control the reference solution to enter the first sample detection area through the first discharge channel when the reference solution is injected through the first sample injection area, to be detected by the first micro-fiber coupler in the first sample detection area, to reach the first sample discharge area through the first discharge channel, and to be discharged from the first sample discharge area; Wherein, the detection sensing unit further includes a second substrate and a second microfluidic chip disposed on the second substrate, and the second microfluidic chip includes a second sample injection area, a second sample discharge area, a second sample detection area, a second discharge channel and a second discharge channel; Wherein, the second microfluidic chip is configured to control the test solution to enter the second sample detection area through the second discharge channel when the test solution is injected through the second sample injection area, be detected by the second micro-fiber coupler in the second sample detection area, reach the second sample discharge area through the second discharge channel, and be discharged from the second sample discharge area.

6. The detection system according to claim 5, wherein: The detection sensing unit is further configured to guide the second detection sub-light to interact with the reference solution located outside the second micro-fiber coupler through the evanescent field of the second micro-fiber coupler to output a third transmission light; The beam combiner is further configured to combine the first transmitted light and the third transmitted light to obtain an initial combined light with a bidirectional vernier spectral characteristic; The spectrum analyzer is further configured to collect the initial combined light beam and convert the initial combined light beam into an initial vernier spectrum; The processor is further configured to determine the concentration of the solution to be tested according to the initial vernier spectrum and the vernier spectrum.

7. The detection system according to claim 6, wherein: A difference between a free spectral range of the first micro-fiber coupler and a free spectral range of the second micro-fiber coupler is less than 10%.

8. The detection system according to claim 6, wherein: The first substrate and the second substrate are both made of magnesium fluoride, and the first microfluidic chip and the second microfluidic chip are both made of polydimethylsiloxane.

9. A method for detecting solution concentration, applied to the detection system according to any one of claims 1 to 8, the method comprising: Obtaining an initial vernier spectrum according to a first transmitted light obtained by the reference sensing unit based on the reference solution and a third transmitted light obtained by the detection sensing unit based on the reference solution; Obtaining a vernier spectrum according to the first transmitted light and the second transmitted light obtained by the detection sensor unit based on the solution to be tested; The concentration of the solution to be tested is determined according to the initial vernier spectrum and the envelope offset of the vernier spectrum.

10. The method according to claim 9, wherein: The initial vernier spectrum includes a first transmission spectrum corresponding to the first transmission light and a third transmission spectrum corresponding to the third transmission light, and the vernier spectrum includes the first transmission spectrum and a second transmission spectrum corresponding to the second transmission light; The step of determining the concentration of the solution to be tested according to the initial vernier spectrum and the envelope offset of the vernier spectrum comprises: The concentration of the solution to be tested is determined according to the offset of the vernier spectrum in the initial vernier spectrum.

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