A fiber-optic sensor based on magneto-optic surface plasmon resonance

Abstract

The application belongs to the technical field of optical fiber sensing, and particularly relates to a kind of optical fiber sensors based on magneto-optical surface plasmon resonance. The optical fiber sensor is formed by removing the cladding of a single-mode optical fiber through polishing and grinding to form a D-shaped optical fiber region; a metal film and a magneto-optical film are sequentially coated on the plane of the D-shaped optical fiber region to form a D-shaped optical fiber sensing region; a magnetic field is applied in the vertical direction of the optical fiber sensing region; probe light from a broadband light source is input from one end of the single-mode optical fiber, passes through the optical fiber sensing region, is output from the other end of the single-mode optical fiber, and is detected by a spectrometer; when the refractive index of the external environment in contact with the magneto-optical material film changes, the change in the resonance peak wavelength in the MOKE spectrum of the sensor will be caused, and the sensing of the refractive index of the external environment is realized by detecting the resonance wavelength. Compared with the optical fiber SPR sensor, the application greatly improves the quality factor while maintaining high sensitivity, thereby improving the actual detection accuracy of the sensor.

Description

Technical Field

[0001] This invention belongs to the field of fiber optic sensing technology, and specifically relates to a fiber optic sensor. Background Technology

[0002] Currently, fiber optic surface plasmon resonance (SPR) sensing technology, which combines surface plasmon resonance (SPR) with fiber optic structures, is well-developed. Due to its advantages such as miniaturization, non-destructive measurement, high sensitivity, and real-time detection, fiber optic SPR sensors are widely used in gas detection, biochemical sensing, and environmental monitoring. With the development of modern technology, the requirements for sensor detection performance in related fields and technologies are becoming increasingly demanding. Traditional sensors based solely on SPR technology are finding it increasingly difficult to meet practical needs. By introducing magnetic materials with magneto-optical effects into the sensor structure, magneto-optical surface plasmon resonance (MOSPR) technology, which combines magneto-optical effects with surface plasmon resonance, can further improve the detection accuracy of sensors. Compared to the resonance peaks in SPR spectra, the resonance peaks in MOKE spectra obtained using MOSPR technology have much narrower peak widths, thus greatly improving the sensor's quality factor and enabling higher detection accuracy. However, to date, sensors using MOSPR technology are still limited to planar structures, and there are no sensors based on fiber optic structures. If MOSPR technology can be implemented in fiber optic structures, the performance of fiber optic sensors will be further enhanced.

[0003] This invention designs a high-performance fiber optic sensor based on MOSPR technology. A metal thin film (gold, silver, etc.) and a magneto-optical material (e.g., Ce:YIG) thin film are sequentially deposited on the surface of a single-mode fiber polished into a D-shape using various coating techniques (such as ion beam sputtering). The transmission spectrum of the fiber optic sensor is measured under forward, reverse, and no magnetic field conditions perpendicular to the film. The change in the wavelength of the resonance peak in the MOKE spectrum is used to sense the refractive index of the external medium of the fiber. Compared with fiber optic SPR sensors, this invention significantly improves the quality factor while maintaining high sensitivity, thereby enhancing the actual detection accuracy of the sensor. Summary of the Invention

[0004] The purpose of this invention is to provide a fiber optic sensor based on magneto-optical surface plasmon resonance with high detection accuracy.

[0005] The fiber optic sensor based on magneto-optical surface plasmon resonance provided by this invention has the following structure: Figure 1 , Figure 2As shown; on a single-mode fiber, the cladding 2 is removed by polishing to form a D-shaped fiber region (its cross-section is D-shaped); let d be the distance between the plane (i.e., polished surface) of the D-shaped fiber region and the core 1 of the single-mode fiber, and control d to be 100 nanometers to 3 micrometers; metal thin film 3 and magneto-optical material thin film 4 are sequentially deposited on the plane of the D-shaped fiber region to form a sensing region of the D-shaped fiber.

[0006] An external magnetic field 5 is applied to the D-type fiber sensing region in a direction perpendicular to the thin film plane. Probe light from a broadband light source enters from one end of a single-mode fiber, passes through the D-type fiber sensing region, and then exits from the other end of the single-mode fiber, where it is detected by a spectrometer. When the refractive index of the external environment outside the D-type sensor region, which is in contact with the magneto-optical material thin film 4, changes, it will cause a change in the wavelength of the resonance peak in the sensor's MOKE spectrum. Sensing the external refractive index can be achieved by detecting the resonance wavelength.

[0007] In this invention, the length L of the D-type optical fiber region is 1-10 mm.

[0008] In this invention, the metal thin film 3 has a thickness of t. m The thickness of the magneto-optical material film is 40–70 nanometers, and the thickness is 4 t. d It is 50-100 nanometers.

[0009] In this invention, the metal thin film 3 is made of gold, silver, aluminum, or copper, preferably silver.

[0010] In this invention, the magneto-optical material thin film 4 is made of Ce:YIG, Bi:YIG, or an iron-cobalt alloy, preferably Ce:YIG.

[0011] In this invention, the plating method can utilize ion beam sputtering or electron beam deposition.

[0012] Traditional fiber optic SPR sensors have a low quality factor (typically only tens of RIU) due to the large peak width of the SPR resonance peak. -1 Traditional D-type fiber optic SPR sensors, while maintaining comparable sensitivity, significantly improve the quality factor, thereby greatly enhancing the detection accuracy of fiber optic sensors. This invention utilizes MOSPR technology to design an optical fiber sensor that, while achieving a sensitivity comparable to traditional D-type fiber optic SPR sensors, substantially improves the quality factor. Attached Figure Description

[0013] Figure 1 This is a schematic diagram of the fiber optic sensor.

[0014] Figure 2 This is a schematic diagram of the cross-section of the D-type region of the fiber optic sensor.

[0015] Figure 3The transmission loss of the fiber optic sensor is measured when positive and negative magnetic fields are applied and when no magnetic field is applied.

[0016] Figure 4 To detect the MOKE spectrum of the fiber optic sensor when the refractive index of the medium is 1.330 and 1.332. Detailed Implementation

[0017] The present invention will be further described below with reference to specific embodiments and accompanying drawings.

[0018] Fabrication of fiber optic sensors based on magneto-optical surface plasmon resonance.

[0019] In a standard single-mode fiber (such as Coning SMF-28, core diameter 8.3 μm, cladding diameter 125 μm), the cladding 2 is removed by polishing to form a D-shaped fiber region. The polished region is then sequentially deposited with a silver thin film 3 and a magneto-optical material Ce:YIG thin film 4 using ion beam sputtering or electron beam deposition, with d = 500 nm, L = 2 mm, and t... m =50nm, t d =60nm.

[0020] An external magnetic field 5 is applied to the D-shaped optical fiber region in a direction perpendicular to the thin film plane. Probe light from a broadband light source enters from one end of the fiber, passes through the D-shaped sensing region, and is then output from the other end to the spectrometer for detection. When the refractive index of the external environment outside the D-shaped sensor region, which is in contact with the magneto-optical material thin film 4, changes, it will cause a change in the wavelength of the resonance peak in the sensor's MOKE spectrum. Sensing the external refractive index can be achieved by detecting the resonance wavelength.

[0021] Figure 3 The diagram shows the transmission loss spectra of the fiber optic sensor when a silver film thickness of 50 nm and a magneto-optical material film thickness of 60 nm are applied, with the external sensing medium being an aqueous solution (refractive index 1.330). These spectra are denoted by Loss(+), Loss(-), and Loss(0) respectively, applied vertically to the D-type sensing region under positive, negative, and no magnetic field conditions. The loss spectra are then processed using the formula... Calculate the MOKE spectrum of the sensor to obtain, for example... Figure 4 The MOKE spectrum is shown below. The MOKE spectrum is also shown when the refractive index of the external detection medium changes to 1.332. Figure 4 As can be seen, as the refractive index of the detection medium changes from 1.330 to 1.332, the wavelength of the resonance peak in the MOKE spectrum shifts from 1501.4 nm to 1511.4 nm. The sensor sensitivity is 5000 nm / RIU, and the quality factor is approximately 8333 RIU. -1 It has a quality factor that is far greater than that of fiber optic SPR sensors, which are typically only in the tens.

Claims

1. A fiber optic sensor based on magneto-optical surface plasmon resonance, characterized in that, On a single-mode fiber, the cladding is removed by polishing to form a D-type fiber region; the distance d between the plane of the D-type fiber region, i.e. the polished surface, and the fiber core (1) of the single-mode fiber is 100 nanometers to 3 micrometers; a metal thin film and a magneto-optical material thin film are sequentially deposited on the plane of the D-type fiber region to form a D-type fiber sensing region. An external magnetic field is applied in the direction perpendicular to the thin film plane in the D-type fiber sensing region (5); the probe light from the broadband light source is input from one end of the single-mode fiber, passes through the D-type fiber sensing region, and is output from the other end of the single-mode fiber and detected by the spectrometer; when the refractive index of the external environment in contact with the magneto-optical material thin film outside the D-type sensor region changes, it will cause a change in the wavelength of the resonance peak in the MOKE spectrum of the sensor, and the sensing of the external refractive index is achieved by detecting the resonance wavelength. The length of the D-type optical fiber region is 1-10 mm; the thickness of the metal thin film is 40-70 nanometers, and the thickness of the magneto-optical material thin film is 50-100 nanometers.

2. The fiber optic sensor according to claim 1, characterized in that, The metal thin film material is gold, silver, aluminum, or copper.

3. The fiber optic sensor according to claim 1, characterized in that, The magneto-optical thin film material is Ce:YIG, Bi:YIG, or an iron-cobalt alloy.

Images