Visual micro-nano optical waveguide refractive index sensing system

Abstract

The application provides a visual micro-nano optical waveguide refractive index sensing system, and a hardware part comprises a nano fiber taper coupled fluorescent doped polymer microwire; the nano fiber taper coupled fluorescent doped polymer microwire is coupled by a nano fiber taper and a fluorescent doped polymer microwaveguide; the nano fiber taper is obtained by adopting a flame tapering method from a standard single-mode optical fiber; the fluorescent doped polymer microwaveguide is directly prepared by wire drawing from a mixed solution doped with a fluorescent dye; the nano fiber taper and the fluorescent doped polymer microwaveguide placed in a channel of an optical substrate jointly form an evanescent wave coupling structure; a signal analysis part enhances, edge extracts, smoothes and peak extracts a fluorescent image of the microwire through an image analysis algorithm, obtains an oscillation period of a fluorescent light path in the microwire under a current environment, establishes a response relationship between the light path period and the environmental refractive index, realizes direct real-time obtaining of environmental change conditions from optical images of a sensing unit shot by a camera, and thus obtains the change of the refractive index.

Description

TECHNICAL FIELD

[0001] The present application relates to a micro-nano sensing system applied to the field of environmental sensing, and in particular to a micro-polymer waveguide sensor based on direct visualization of fluorescence indication and signal analysis thereof. BACKGROUND

[0002] At present, optical sensing is used to analyze the changes in the environment, which has become a fast and sensitive monitoring method. With the gradual increase of the integration and sensitivity requirements of chip systems, various fine micro-nano structures with small size and light weight greatly improve the integration of optical sensors. Among them, the micro-nano optical waveguide as a sensing unit, by using the characteristics of its strong evanescent field, can enhance the interaction between the optical signal and the external environment, and is very sensitive to the change of environmental refractive index, so it has the advantages of high sensitivity and fast response, and has become a research hotspot of the new generation of micro sensors.

[0003] The environmental refractive index sensor based on micro-nano optical fiber has a small structure, and due to the limitation of the processing and preparation precision, the output light signal characteristics often fluctuate greatly, resulting in large individual differences of the device and low repeatability of the device, which cannot meet the industrial requirements. The output signal of the optical sensor based on micro-nano optical fiber is weak (in the order of nW), so in the conventional micro-nano optical fiber sensing system taking light intensity and spectrum as the analysis object, the stability of the light source and environmental noise directly affect the stability of the light signal, thereby causing poor stability of the micro-nano optical fiber sensor. At the same time, when recording the weak signal output by the micro-nano optical fiber sensor, professional detection equipment with high resolution and high sensitivity is needed, which not only increases the economic cost of the sensing system, but also increases the cost of data analysis. As can be seen, the optical refractive index sensor taking micro-nano optical waveguide as a sensitive unit has many problems such as large individual difference, poor stability, high system cost, etc., which greatly limits the large-scale industrial production of such devices. Therefore, how to design a simple and stable structure and use a convenient and fast analysis method to obtain a micro-nano optical waveguide refractive index sensing system with stable performance and low cost has become a bottleneck problem to be solved in the practical process of micro-nano optical waveguide sensor.

[0004] Researches in micro-nano photonics show that the polymer micro optical waveguide doped with fluorescent dye can excite fluorescence in the micro waveguide through evanescent wave coupling with nano optical fiber. A sinusoidal oscillation fluorescent light path is formed in the doped polymer micro optical waveguide, and the oscillation period is related to the environmental refractive index and can be directly observed and recorded by a camera under the far field of an optical microscope. By using this characteristic, the fluorescence light path of a single optical waveguide is directly used to feedback the change of environmental refractive index by displaying the period, which becomes a new idea for sensor design. SUMMARY

[0005] The present application aims at the problems of poor performance stability of micro-nano optical waveguide sensors and high system cost, and provides a visual micro-nano optical waveguide refractive index sensing system which is simple in structure, high in stability and convenient and fast in analysis.

[0006] The present application solves the problem by the technical scheme that the visual micro-nano optical waveguide refractive index sensing system comprises a hardware part and a signal analysis part.

[0007] The hardware part comprises a nano optical fiber taper coupled fluorescent doped polymer microwire.

[0008] The nano optical fiber taper coupled fluorescent doped polymer microwire is coupled by a nano optical fiber taper and a fluorescent doped polymer microwaveguide; the nano optical fiber taper is obtained by flame tapering of a standard single-mode optical fiber; the fluorescent doped polymer microwaveguide is directly prepared by wire drawing from a mixed solution doped with fluorescent dye; and the nano optical fiber taper and the fluorescent doped polymer microwaveguide placed on the optical substrate jointly constitute an evanescent wave coupling structure.

[0009] The signal analysis part enhances, edge extracts, smooths and peak extracts the fluorescent image of the microwire by an image analysis algorithm, obtains the oscillation period of the fluorescent light path in the microwire under the current environment, establishes a response relationship between the light path period and the environmental refractive index, realizes direct real-time obtaining of the environmental change from the optical image of the sensing unit shot by the camera, and thus obtains the change of the refractive index.

[0010] In a preferred embodiment, the optical substrate is provided with a channel for supporting the fluorescent doped polymer microwaveguide and the nano optical fiber taper.

[0011] In a preferred embodiment, the fluorescent dye is a dye substance capable of emitting fluorescence in the visible light band.

[0012] In a preferred embodiment, the diameter of the fluorescent doped polymer microwaveguide is 1-2 microns, and the length is 100-200 microns.

[0013] In a preferred embodiment, the optical substrate is an optical material with a material refractive index lower than 1.40, the substrate area is 1mm 2 , the width of the channel is 100 microns, and the length of the channel is greater than 250 microns.

[0014] In a preferred embodiment, the external optical signal is input through the standard optical fiber end of the nano optical fiber taper, and the input light wavelength matches the optimal excitation wavelength of the doped fluorescent dye.

[0015] Compared with the prior art, the technical scheme of the present application has the following beneficial effects:

[0016] The application provides a visual micro-nano optical waveguide refractive index sensing system, which takes a fluorescent dye doped polymer microwire as a basic structural unit, adopts waveguide excitation to couple input light into the microwire, excites fluorescence in the microwire while the light propagates, and obtains a fluorescent microimage of the doped microwire. The light path period in the fluorescent image is extracted through an image analysis algorithm, and a response relationship between the light path period and the environmental refractive index is established. The fluorescence in the microwire is used to present the light field energy distribution in the waveguide, the influence of the environmental refractive index on the energy distribution period is analyzed, a response relationship between the environmental refractive index and the energy period is established, and a visual sensing system based on the microwire fluorescent image is obtained. The micro-nano optical fiber sensing system using fluorescence indication can directly display the change of the environmental refractive index, the sensitive unit structure is simple, the optical response stability is high, and the economic cost is low, and it is an intuitive, stable and economical and efficient optical sensing system based on micro-nano optical fiber. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 Structure diagram of a nano optical fiber taper;

[0018] Figure 2 Structure diagram of a fluorescent doped polymer microwire optical waveguide;

[0019] Figure 3 Schematic diagram of evanescent wave coupling between a nano optical fiber taper and a fluorescent doped polymer microwire optical waveguide placed in a channel of an optical substrate;

[0020] Figure 4 Schematic diagram of an industrial camera recording fluorescent light path information of a microwire optical waveguide in a coupling structure;

[0021] Figure 5 Flowchart of image processing of an optical image of fluorescent light path information. DETAILED DESCRIPTION

[0022] The technical solutions in the embodiments of the application will be clearly and completely described below with reference to the drawings in the embodiments of the application; obviously, the described embodiments are only part of the embodiments of the application, rather than all the embodiments of the application, and all other embodiments obtained by a person of ordinary skill in the art without creative labor on the basis of the embodiments in the application belong to the protection scope of the application.

[0023] In the description of the present application, it should be noted that the terms "upper", "lower", "inner", "outer", "top / bottom end" and the like indicate the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application. In addition, the terms "first", "second" are only for descriptive purposes and cannot be understood as indicating or implying relative importance.

[0024] In the description of the present application, it should be noted that unless otherwise explicitly specified and limited, the terms "mounting", "provided with", "sleeved / connected", "connected" and the like should be broadly understood, for example, "connected" can be wall-mounted connection, can also be detachable connection, or integrally connected, can be mechanical connection, can also be electrical connection, can be directly connected, can also be indirectly connected through an intermediate medium, can be the communication between two elements, and those skilled in the art can understand the specific meaning of the above terms in the present application according to the specific circumstances.

[0025] The structure of the nanometer optical fiber taper drawn from the standard single-mode optical fiber by the flame tapering method is shown in Figure 1 .

[0026] The tip diameter of the nanometer optical fiber taper prepared by this method is 20-50 nm, and the taper angle is 10-15°. The excitation light is input from the standard optical fiber port of the nanometer optical fiber taper, transmitted through the optical waveguide, and output at one end of the nanometer optical fiber taper.

[0027] The structure of the polymer micrometer optical waveguide doped with fluorescent dye drawn by the mixed solution tapering method is shown in Figure 2 .

[0028] The mixed solution is a mixture of polymethyl methacrylate (PMMA) and chloroform, and is further doped with fluorescent dye. Taking rhodamine B as an example, a fluorescent doped polymer micrometer optical waveguide with a diameter of 1.5 μm is drawn by doping 3.0 mg / g of rhodamine B in the mixed solution.

[0029] Under an optical microscope, the coupling of the nanometer optical fiber taper and the fluorescent doped polymer micrometer optical waveguide on the optical substrate is completed by precise control of the three-dimensional fine adjustment frame.

[0030] The coupling of the nanometer optical fiber taper and the polymer nanometer optical waveguide is shown in Figure 3 .

[0031] When the excitation light is introduced into the standard single-mode optical fiber, the optical signal enters the fluorescent doped polymer micrometer optical waveguide through the evanescent wave of the nanometer fiber taper tip, and is transmitted in the doped polymer micrometer optical waveguide in a multimode oscillation mode according to the evanescent wave transmission principle. In the transmission process, the optical signal excites the fluorescence in the doped polymer micrometer optical waveguide, and the fluorescence path in the doped polymer micrometer optical waveguide is recorded in real time by an industrial camera placed on an optical microscope.

[0032] The fluorescence path in the dark-field micrometer optical waveguide recorded by the camera is shown in FIG. 2. Figure 4

[0033] The micrograph of the original fluorescence path is subjected to dark-field optical image and then subjected to image enhancement by an algorithm, such as a contrast enhancement method after Fourier transform. The enhanced image is subjected to contour recognition. The image after edge contour extraction is subjected to burr smoothing by an interpolation method. After smoothing, the curve maximum value position (corresponding to the pixel point order of the picture) is extracted. The length (L) of 5 consecutive fluorescence periods is read, and the average oscillation period Δ in the micrometer optical fiber (Δ = L / 5) is further calculated.

[0034] The flowchart of the image analysis algorithm is shown in FIG. 3. Figure 5

[0035] The above-mentioned visualized micro-nano optical waveguide refractive index sensing system takes a fluorescent dye doped polymer micrometer wire as a basic structural unit, uses waveguide excitation to couple the input light into the micrometer wire, excites the fluorescence in the micrometer wire while the light beam propagates, and obtains a fluorescence micrograph of the doped micrometer wire. The light path period in the fluorescence image is extracted by an image analysis algorithm, and a response relationship between the light path period and the environmental refractive index is established. The fluorescence in the micrometer wire is used to present the light field energy distribution in the waveguide, the influence of the environmental refractive index on the energy distribution period is analyzed, a response relationship between the environmental refractive index and the energy period is established, and a visualized sensing system based on the fluorescence image of the micrometer wire is obtained. This micro-nano optical fiber sensing system using fluorescence indication can directly display the change of the environmental refractive index, and has simple sensitive unit structure, high optical response stability and low economic cost, and is an intuitive, stable and economical and efficient optical sensing system based on micro-nano optical fiber.

[0036] The above-mentioned, only for the preferred embodiment of the present application, but the design concept of the present application is not limited to this, any skilled in the art of the technical range disclosed by the present application, using this concept to make non-essential changes to the present application, all belong to the act of infringing the protection scope of the present application.​​

Claims

1. A visualized micro / nano optical waveguide refractive index sensing system, characterized in that... Includes hardware and signal analysis components; The hardware component includes fluorescent doped polymer microwires coupled with nanofiber tapers. The fluorescent-doped polymer microwire coupled with the nanofiber taper is formed by coupling a nanofiber taper and a fluorescent-doped polymer microwaveguide. The nanofiber taper is obtained from a standard single-mode fiber using a flame taper method. The fluorescent-doped polymer microwaveguide is prepared by directly drawing fibers from a mixed solution of doped fluorescent dyes. The nanofiber taper and the fluorescent-doped polymer microwaveguide placed on an optical substrate together constitute an evanescent wave coupling structure. An external optical signal is input through one end of the standard fiber of the nanofiber taper, and the input light wavelength matches the optimal excitation wavelength of the doped fluorescent dye. The signal analysis section enhances, extracts edges, smooths, and extracts peaks from the micron-line fluorescence image using image analysis algorithms. This yields the oscillation period of the fluorescence optical path in the micron-line under the current environment. The response relationship between the optical path period and the refractive index of the environment is established, enabling the sensor unit optical image captured by the camera to directly obtain the environmental changes in real time, thereby obtaining the change in refractive index. The mixed solution is a mixture of polymethyl methacrylate and chloroform, further doped with a fluorescent dye; specifically, Rhodamine B is doped into the mixed solution at a doping concentration of 3.0 mg / g, and drawn into a fluorescent doped polymer micron-sized optical waveguide with a diameter of 1.5 μm; the optical substrate is an optical material with a refractive index lower than 1.

40.

2. The visualized micro / nano waveguide refractive index sensing system according to claim 1, characterized in that: The optical substrate has channels for supporting the fluorescent doped polymer micron-sized optical waveguide and the nanofiber taper.

3. The visualized micro / nano waveguide refractive index sensing system according to claim 1, characterized in that: The length of the fluorescent doped polymer micron waveguide is 100~200 μm.

4. The visualized micro / nano waveguide refractive index sensing system according to claim 2, characterized in that: The area of ​​the optical substrate is 1 mm. 2 The width of the channel is 100 μm, and the length of the channel is greater than 250 μm.

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