A carbon dioxide sensing structure and system based on a fiber end-face integrated metasurface

Abstract

The application discloses a carbon dioxide sensing structure and system based on a fiber end face integrated metasurface. The carbon dioxide sensing structure is characterized in that a gold film with a subwavelength thickness is evaporated on a fiber end face, a plurality of micro-nano structures are etched on the gold film, each micro-nano structure is composed of a plurality of circular holes, and a specific adsorption material layer is covered on the gold film to convert carbon dioxide gas concentration changes into spectral changes. The system comprises the carbon dioxide sensing structure, an ultra-continuous laser light source, a fiber coupler and a spectrum analyzer. The application proposes a gas sensing idea, combines micro-nano structures with a fiber end face, realizes reflective measurement, and can be used for gas sensing in a narrow environment or an extreme environment, such as medical invasive detection or gas detection in an explosive environment.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of micro-nano sensing, and particularly relates to a carbon dioxide sensing structure and system based on a fiber end face integrated metasurface. BACKGROUND

[0002] Carbon dioxide is a colorless and odorless gas, and it is one of the important components of the atmosphere. Accurate sensing and measurement of carbon dioxide gas plays a vital role in many fields such as industry, agriculture, national defense, medical health, environmental protection, aerospace, etc.

[0003] The two most commonly used methods at present are electrochemical sensing using gas-selective ceramics and non-dispersive infrared (NDIR) sensing using optical elements. Although electrochemical sensors are widely used in the market, and can be further reduced in size for portable electronic applications in ideal cases, electrochemical sensors for carbon dioxide sensing have a long response time, which is not conducive to real-time monitoring. NDIR sensors have low hysteresis, but in a mixed sensing environment, various pollutant gases including water vapor coexist and interfere at the same working wavelength, and the selectivity is limited. More importantly, NDIR sensors require a centimeter-long optical interaction length and low-roughness sidewalls to achieve a high signal-to-noise ratio detection limit, so the sensor device is bulky and not conducive to system integration.

[0004] A metasurface is an artificial ultrathin planar material composed of subwavelength units, which can flexibly and effectively control the polarization, amplitude, phase, polarization mode, and propagation mode of electromagnetic waves, and has wide applications in sensing, communication, filtering, and many other fields. Currently, micro-nano gas sensors based on metasurfaces (for example, a hydrogen sensing micro-nano structure composed of a gold thin film as a bottom layer, MgF2 as an electrolyte layer, and periodically arranged palladium nanodisks on the MgF2 electrolyte layer), can greatly reduce the size of the sensor, but generally require oblique incidence of the light source, and then receive the reflected light signal of the micro-nano structure. Therefore, the designed sensor needs to work at a specific light source incidence angle, and the oblique incidence structure is not conducive to shortening the lateral size of the sensor. At the same time, whether the sensing system is free-space light incidence or input through a fiber light source, a gas channel needs to be left between the micro-nano structure gas-sensitive unit and the emission and reception units of the light source, so these components must be physically separated, which is also not conducive to the integration of the sensing system and the remote real-time detection application in special scenarios.

[0005] Therefore, it is of great significance to invent a micro gas sensor with good safety, high integration, and small size. SUMMARY

[0006] The present application is directed to the deficiencies of the prior art, and provides a carbon dioxide sensing structure and system based on a fiber end face integrated metasurface.

[0007] The object of the present application is achieved by the following technical solutions:

[0008] A carbon dioxide sensing structure based on fiber end face integrated metasurface, a subwavelength thickness gold film is evaporated on the fiber end face, a plurality of micro-nano structures are etched on the gold film, each micro-nano structure is composed of a plurality of circular holes; a specific adsorption material layer is covered on the gold film for converting carbon dioxide gas concentration change into spectral change.

[0009] Further, the plurality of micro-nano structures are arrayed.

[0010] Further, the circular holes in each micro-nano structure are four, uniformly distributed.

[0011] Further, the specific adsorption material is polyhexamethylene biguanide hydrochloride.

[0012] A carbon dioxide sensing system based on fiber end face integrated metasurface, comprising the carbon dioxide sensing structure, and a supercontinuum laser light source, a fiber coupler and a spectrum analyzer;

[0013] The laser light output by the supercontinuum laser light source is incident to the micro-nano structure of the fiber end face from the fiber substrate after passing through the fiber coupler, the micro-nano structure and the surface plasmon resonance of the specific adsorption material layer are excited, the light reflected from the end face is received by the spectrum analyzer, and the spectrum of the light is characterized by a resonant reflection peak trough;

[0014] When the carbon dioxide concentration change in the environment causes the refractive index change of the specific adsorption material layer, the wavelength of the reflection peak moves, the refractive index change of the specific adsorption material layer and the gas concentration change are converted from the wavelength drift, and the accurate measurement of the carbon dioxide gas concentration in the environment is realized.

[0015] The present application has the following advantages:

[0016] 1. The present application proposes a gas sensing idea, combines micro-nano structures with fiber end faces, realizes reflective measurement, and can perform gas sensing in narrow or extreme environments, such as medical invasive detection or gas detection in explosive environments.

[0017] 2. The sensing method proposed by the present application uses specific adsorption material to convert gas concentration change into spectral change, the detection process does not need to be heated, and is safer and can realize real-time and rapid sensing.

[0018] 3. The carbon dioxide sensor structure provided by the present application is simple to prepare, compatible with the preparation process of semiconductor CMOS devices, and can be prepared in batches on different fiber end faces of a plurality of fiber bundles to achieve a highly integrated fiber bundle for simultaneously detecting a plurality of gas concentrations. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 Schematic diagram of an optical fiber end face integrated metasurface;

[0020] Figure 2 Schematic diagram of a metasurface structure for an implementation example;

[0021] Figure 3 Schematic diagram of a gas sensing system of an optical fiber end face integrated metasurface;

[0022] Figure 4 Calculation curve diagram of the change in the refractive index of PHMB material causing the change in the reflection resonance peak;

[0023] Figure 5 Sensitivity curve. DETAILED DESCRIPTION

[0024] The preferred embodiments of the present application are described in detail below with reference to the accompanying drawings. In the description of the drawings, the same symbols are used for the same or equivalent parts, and repeated descriptions are omitted. In addition, the dimensional proportions of the respective drawings may not be consistent with the actual proportions.

[0025] As shown in Figure 1 , the present embodiment provides a sensing structure based on an optical fiber end face integrated metasurface, which includes an optical fiber, a metal thin film layer 2 sputtered on the end face of the fiber core 1, a periodic etching of the same micro-nano structure on the metal thin film layer, and incident light and reflected light in the fiber core 1, as indicated by arrows in Figure 1 .

[0026] As shown in Figure 2 , four gold holes 7 with equal aperture sizes are etched on the gold thin film layer 2 to form a periodic micro-nano structure, and a PHMB layer 8 (polyhexamethylene biguanide hydrochloride) is covered on the gold thin film layer; the thickness of the gold thin film layer is 60 nm, the radius of the gold hole is 140 nm, and the distribution period of the entire structure is 1000 nm. The polyhexamethylene biguanide hydrochloride (PHMB) material in the present embodiment is a polymer material that reversibly and specifically absorbs carbon dioxide molecules, and the material refractive index changes with the change in the external carbon dioxide concentration. When the carbon dioxide concentration changes, the different material electron densities caused by the combination with PHMB molecules cause the material refractive index to change, and thus the material can be used for carbon dioxide sensing. According to literature reports, the refractive index change corresponding to the change in the gas concentration is about 2.03 x 10 -4RIU / ppm (RIU refers to refractive index unit).

[0027] As shown in Figure 3 ; the system comprises a supercontinuum laser light source 3, a fiber coupler 6, a metasurface sensing probe 5, and a spectrum analyzer 4. The laser output by the supercontinuum laser light source is incident on the micro-nano structure of the fiber end face from the fiber substrate after passing through the fiber coupler, excites the surface plasmon resonance of the interface between the micro-nano structure and the surface PHMB material, and the spectrum of the light reflected back to the fiber by the spectrometer shows a resonant reflection peak trough. When the concentration of carbon dioxide in the environment changes, the refractive index of PHMB changes, the wavelength of the reflection peak moves, and thus the change of the refractive index of PHMB and the change of the gas concentration can be calculated from the wavelength drift, and the accurate measurement of the concentration of carbon dioxide gas in the environment is realized.

[0028] Further, after etching, a PHMB layer with a thickness of 500 nm is spin-coated on the gold thin film layer, and the refractive index and the carbon dioxide concentration change rate of the material are S n =2.03×10 -4 RIU / ppm.

[0029] Further, the software simulation of the structure as shown in Figure 4 is performed by using the finite difference time domain software, and the corresponding reflected light spectrum diagram is calculated when the refractive index of the PHMB material changes (the refractive index range of the PHMB for carbon dioxide concentration sensing is 1.48 to 1.54); the relationship between the resonant peak center wavelength and the change of the refractive index of the PHMB material is as shown in Figure 5 , and the calculated refractive index sensitivity is S ’ =564.07 nm / RIU, according to the relationship between the refractive index of the PHMB material and the carbon dioxide concentration, it is calculated that the sensitivity of the resonant peak generated by the gold film four-hole micro-nano structure of the present application for carbon dioxide gas sensing is S=S n ×S ’ =114.5pm / ppm.

[0030] According to the above specific implementation case, compared with the traditional carbon dioxide gas sensor, the carbon dioxide gas sensor based on the gold film hole super surface of the fiber end face of the present application has smaller volume, higher flexibility, higher sensing sensitivity, wider application range, and safer use.

[0031] Although the present application has been described with reference to certain aspects and embodiments, those skilled in the art will appreciate that modifications in form and detail can be made without departing from the spirit and scope of the application.

Claims

1.A carbon dioxide sensing structure based on a fiber end-face integrated metasurface, characterized in that, A layer of gold film with sub-wavelength thickness is evaporated on the end face of an optical fiber, the thickness of the gold film is 60 nm, a plurality of micro-nano structures are etched on the gold film, each micro-nano structure is composed of a plurality of circular holes, and the radius of the gold hole is 140 nm; a layer of specific adsorption material is covered on the gold film, which is used for converting the change of carbon dioxide gas concentration into spectral change; The circular holes in each micro-nano structure are four, uniformly distributed, and constitute a periodic micro-nano structure, and the distribution period of the whole structure is 1000 nm; the specific adsorption material is polyhexamethylene biguanide hydrochloride, and the thickness is 500 nm. 2.The carbon dioxide sensing structure based on fiber end-face integrated metasurface of claim 1, wherein, The plurality of micro-nano structures are arrayed. 3.A carbon dioxide sensing system based on fiber end-face integrated metasurface, characterized in that: The carbon dioxide sensing structure of claim 1 or 2, a super-continuous laser light source, a fiber coupler and a spectrum analyzer are included; The laser output by the super-continuous laser light source is incident on the micro-nano structure of the end face of the optical fiber after passing through the fiber coupler, the micro-nano structure and the surface plasmon resonance of the specific adsorption material layer are excited, the reflected light from the end face is received by the spectrum analyzer, and the spectrum of the received light shows a resonant reflection peak trough; When the change of the carbon dioxide concentration in the environment causes the change of the refractive index of the specific adsorption material layer, the wavelength of the reflection peak moves, the change of the refractive index of the specific adsorption material layer and the change of the gas concentration are converted from the wavelength drift, and the accurate measurement of the carbon dioxide concentration in the environment is realized.

Images