CN105092535B - Distributed surface plasma resonance optical fiber sensor - Google Patents

Abstract

The invention provides a distributed surface plasmon resonance optical fiber sensor. Pairs of V-shaped grooves are processed on a section of dual-core optical fiber. The depth of the V-shaped grooves exceeds the fiber core. Sensitive layer; in each pair of V-shaped grooves, the broad-spectrum light incident from the first fiber core excites the SPR at the slope of the first V-shaped groove and undergoes total reflection, and when reflected to the slope of the second V-shaped groove, it also excites the SPR and reflects to the second fiber core; the light is sequentially transmitted in each pair of V-shaped grooves to realize distributed sensing. The sensor of the invention can be well connected with an all-fiber system with low loss, and has outstanding advantages such as small size and simple structure. In the distributed SPR optical fiber sensor of the present invention, multiple sets of sensing areas are made on the side of the optical fiber, and the special structure of the optical fiber is used to connect the plurality of sensing areas in series to realize real-time multi-channel distributed measurement.

Description

Distributed surface plasmon resonance fiber optic sensor

technical field

The invention relates to an optical fiber sensor, in particular to a distributed SPR optical fiber sensor mainly used for sensing and measuring external environment refractive index, air concentration and the like.

Background technique

The Surface Plasmon Resonance (SPR) effect is a physical optical phenomenon that is very sensitive to changes in the external environment and occurs at the interface between a metal and a dielectric. The total internal reflection of the light wave at the interface between the metal and the dielectric produces an evanescent wave. When the wave vector of the incident light along the direction of the interface is equal to the wave vector of the surface plasmon wave, the evanescent wave causes surface plasmon resonance, resulting in a light wave An energy loss occurs during the transmission, i.e. a distinct resonant trough appears in the spectrum. Changes in the refractive index or gas concentration of the external environment can cause a shift in the position of the resonance trough, so the sensing of the refractive index or gas concentration of the external environment can be realized by real-time monitoring of the resonance trough.

SPR sensing technology has the advantages of high sensitivity, easy implementation, and no labeling, and has been widely used in various detection fields. The earliest realized SPR sensor is a prism-type SPR sensor, but its application is limited due to its disadvantages such as high cost, complex system, large volume, and inconvenient portability. In 1993, Dr. R.C.Jorgenson of the United States proposed the fiber optic SPR sensor (Ralph Corleissen Jorgenson. Fiber-optic chemical sensor based on surface plasmon resonance. Sensors and Actuator[J]s, B: Chemical, v B12, n 3, Apr 151993, p 213 -220), which has since opened a new chapter in fiber optic SPR sensors. Because the optical fiber SPR sensor has the advantages of small size, easy integration, and no interference from mechanical vibration and light source fluctuation, it has become the mainstream direction of SPR sensor research.

In 2003, Cao Zhenxin and others successfully developed a longitudinally distributed SPR fiber optic sensor, and applied for an invention patent named "Longitudinal Distributed Surface Plasmon Wave Sensor" (patent application number: 03113077.1), this longitudinally distributed SPR fiber optic sensor The production principle is the same as that of the traditional single-channel SPR sensor. Since the sensing area on the side of the optical fiber is fixed, the sensor can only adjust the resonance wavelength by changing the film thickness. The corresponding detection spectrum is the superposition of the effects of multiple incident angles. As a result, the half-bandwidth and intensity of the measurement signal are not ideal; in 2005, Peng Wei et al. developed a multi-channel SPR fiber sensor using a multi-mode fiber with a core diameter of 600 μm, and applied for a patent called "angle-tuned multi-channel fiber surface plasmon Body Resonance Sensing Probe" patent (patent application number: 201110089650.4), this SPR fiber optic sensor integrates multiple sensing channels at one fiber end, but it can only perform real-time detection of a single channel, for multiple parameters Time-sharing testing is required.

Contents of the invention

The purpose of the present invention is to provide a distributed surface plasmon resonance optical fiber sensor with simple structure, high sensitivity and the ability to realize multi-channel real-time measurement.

The object of the present invention is to realize like this:

Pairs of V-shaped grooves are processed on a section of dual-core optical fiber. The depth of the V-shaped grooves exceeds the fiber core. Sensitive layer; in each pair of V-shaped grooves, the broad-spectrum light incident from the first fiber core excites the SPR at the slope of the first V-shaped groove and undergoes total reflection, and when reflected to the slope of the second V-shaped groove, it also excites the SPR and reflects to the second fiber core; the light is sequentially transmitted in each pair of V-shaped grooves to realize distributed sensing.

The present invention may also include:

1. The misalignment L of the two V-shaped grooves in each pair of V-shaped grooves satisfies L=d*cotΦ, where d is the distance between two fiber cores, and Φ is the apex angle of the V-shaped grooves.

2. The thickness of the sensing layer is 35-65 nanometers, and the material of the sensing layer is gold, silver, aluminum or copper.

The invention provides a distributed SPR optical fiber sensor with simple structure, high sensitivity and the ability to realize multi-channel real-time measurement. A section of dual-core optical fiber 1 is processed with multiple sets of V-groove pairs 2 on the side. The slopes of the V-groove pairs 2 are coated with a sensing layer 3 . The SPR is excited at the position and total reflection occurs. Since the angles of the two V-shaped grooves opposite to each other are the same, the light will be reflected to the slope 6 of the second V-shaped groove, and the SPR will also be excited and reflected to the second core 7, and so on. distributed sensing. The distance between two cores of the dual-core optical fiber 1 is d. Each V-shaped groove pair 2 is composed of two V-shaped grooves with the same angle Φ and a displacement L of d*cotΦ, and the depth of the V-shaped groove exceeds the fiber core. The V-groove pair 2 may have the same angle or different angles, but the angle condition for exciting the SPR should be met. The sensing layer) can have the same thickness or different thicknesses on different V-shaped groove pairs 2, but the V-shaped groove pairs 2 with the same angle should be plated with sensing layers 3 of different thicknesses. The sensing layer 3 can be gold, silver, aluminum or copper with a thickness of 35-65 nanometers, or other materials capable of stimulating SPR.

Its working principle is:

As shown in Figure 3, the principle of SPR sensing is that the incident light field uses metal/optical medium as the excitation structure, total reflection occurs at the interface between the medium and the metal film, and evanescent waves are generated. The wave vector K _EW of the evanescent wave and the metal surface plasmon When the wave vector K _spz of the bulk wave matches, the two electromagnetic wave modes will be strongly coupled, causing a part of the energy of the incident light to be absorbed by the surface plasmon wave, resulting in a significant decrease in the intensity of the reflected light. SPR sensor is based on this phenomenon to realize the detection of external environmental parameters.

The SPR wave vector matching formula is:

In the formula, ω is the light frequency, c is the speed of light, θ is the incident angle, ε ₀ , ε ₁ , ε ₂ are the dielectric constants of the waveguide medium, the metal film, and the medium to be measured, respectively, and Δk is the wave vector loss caused by the material. Dosing.

In the optical fiber SPR sensor, the optical fiber is used as the optical medium and the metal film is combined to form the excitation surface of the SPR effect. In the distributed SPR optical fiber sensor, the inclined surface of the V-shaped groove coated with the sensing layer is the excitation surface of the SPR effect. Broad-spectrum light is irradiated on the slope of the V-groove. When the incident angle of the light (V-groove slope angle), the thickness of the sensing layer and the refractive index of the ambient medium are appropriate, the light will undergo total internal reflection on the slope and evanescent Field, and make K _EW and K _spz match, produce SPR effect, the surface plasmon wave will absorb part of the energy of the incident light, resulting in a significant decrease in the light intensity of a certain wavelength. The light passes through multiple V-groove pairs, and the light propagates alternately in the two cores. Since different V-groove pairs have different angles of slope or different thickness of the sensing layer, there will be multiple absorption valleys in the outgoing spectrum. When changing When the refractive index of a certain medium in the outside world, the corresponding spectral absorption valley will move obviously, and the change of the refractive index of the medium can be judged according to the change of the spectrum. Multiple sets of V-groove pairs on the same sensor can realize multi-channel real-time monitoring, namely distributed sensing.

Compared with prior art, the advantage of the present invention is:

1. The present invention provides a novel distributed SPR optical fiber sensor based on dual-core optical fiber. The sensor can be well connected with an all-fiber system with low loss, and has outstanding advantages such as small size and simple structure.

2. Distributed SPR optical fiber sensor makes multiple sets of sensing areas on the side of the optical fiber, and uses the special structure of the optical fiber to connect multiple sensing areas in series to realize real-time multi-channel distributed measurement.

Description of drawings

Figure 1 is a schematic diagram of a three-dimensional structure of a distributed SPR fiber optic sensor.

Figure 2 is a schematic diagram of the optical path of the distributed SPR fiber optic sensor.

Figure 3 is a KretschnLann three-layer dielectric waveguide model diagram.

detailed description

The following examples describe the present invention in more detail.

As shown in Figure 1, a kind of distributed SPR optical fiber sensor comprises a section of dual-core optical fiber 1, and the cladding diameter of dual-core optical fiber 1 is 125 microns, has two symmetrically distributed cores in the cladding, and the diameters of the two cores are 6-10 microns, and the distance d between centers of the fiber cores is 30-100 microns. There are two or more V-groove pairs 2 on the side of the dual-core optical fiber 1, the V-groove angle in each V-groove pair is Φ, the misalignment L is d*cotΦ, and the slope angle of the V-groove should be able to To meet the actual needs and meet the conditions of total internal reflection of light, the V-groove slope should be plated with a sensing layer 3 with a thickness of 35-65 nanometers; the depth of the V-groove should be 1-10 microns deeper than the corresponding fiber core. The SPR optical fiber sensor in the present invention can also use other multi-core optical fibers with symmetrically distributed optical fiber cores, and the two symmetrically distributed cores should meet the basic distribution conditions of the above-mentioned dual-core optical fiber 1 core.

The specific manufacturing method of the distributed SPR optical fiber sensor of the present invention is: using a femtosecond laser to manufacture a distributed SPR optical fiber sensor. Proceed as follows:

1. Optical fiber pretreatment: Take a section of dual-core optical fiber 1 with a diameter of 125 microns, use Miller pliers to strip 25 mm of the optical fiber coating at a certain position of the optical fiber, and clean the exposed optical fiber cladding with alcohol.

2. Place the dual-core optical fiber 1 on the fixed frame of the femtosecond laser, so that the exposed part of the optical fiber is in the working area of the laser, and ensure that the plane where the two cores of the optical fiber are located is perpendicular to the horizontal plane.

3. Use a femtosecond laser to write the first V-groove at the bare fiber on the side of the dual-core fiber 1. Since the core spacing of the dual-core fiber 1 is 35 microns and the V-groove angle is 150°, the first group will be The V-groove misalignment L is controlled at about 60 microns, and the V-groove crosses the fiber core by about 10 microns. In order to make the surface plasmon resonance wavelength about 650 nanometers, it is 40 microns away from the first V-groove and closer to the light incident end. position to program the second V-groove.

4. Repeat steps 1, 2, and 3 according to the same principle, and complete the programming of other V-groove pairs 2.

5. Use deionized water and an ultrasonic cleaner to clean the V-groove area on the fiber.

6. Make the V-shaped groove upward, fix the optical fiber on the glass slide, and use the sputtering coating technology to coat the film for 3.5 minutes, so that the slope of the V-shaped groove is plated with a 50 nm thick gold film.

7. Repeat step 6 to plate gold film on each V-shaped groove.

8. Place the V-shaped groove pair 2 of the dual-core optical fiber 1 in the U-shaped quartz groove and fix it with epoxy resin to form a distributed SPR optical fiber sensor.

The measurement of liquid refractive index is realized by distributed SPR optical fiber sensor. Proceed as follows:

1. Take a standard single-mode optical fiber and a finished distributed SPR optical fiber sensor, use Miller pliers to remove about 30mm of the coating at both ends of the optical fiber and clean the exposed optical fiber cladding with alcohol, use a fiber cutter The two ends are cut so that the end faces of the two ends of the optical fiber form a flat section perpendicular to the axis of the optical fiber.

2. Use an optical fiber fusion splicer to make the core of the single-mode optical fiber face the first core of the dual-core optical fiber 1, and weld the two optical fibers together with a suitable welding current.

3. Place the welding points of the two optical fibers in a thermoplastic sealing tube, and heat the thermoplastic sealing tube to ensure that the soldering points can be well protected.

4. Using a supercontinuum light source with a spectral range of 400-1200 nanometers, injecting light output by the light source into a single-mode optical fiber.

5. Connect the unwelded end of the dual-core optical fiber 1 to the OSA spectrometer, and adjust the detection wavelength range of the spectrometer to 400-1200 nanometers.

6. Put the sensing part of the sensor (V-groove pair (2)) into the liquid to be tested with a refractive index of about 1.333 (distilled water).

7. Turn on the light source and observe the transmission spectrum of the sensor. Due to the occurrence of the SPR phenomenon, the light intensity of certain wavelengths will be significantly weakened in the spectrum.

8. Change the refractive index of the liquid to be measured by adding glycerin to the water, and calculate the change in refractive index of the liquid to be measured by observing the change in the spectrum.

Claims (3)

1. a kind of distributed surface plasma resonance optical fiber sensor, it is characterized in that：It is machined with one section of twin-core fiber To the V-groove of distribution, the depth of V-groove exceedes two V-groove mutual dislocations arrangement in fibre core, each pair V-groove, V-groove Sensing layer is coated with inclined-plane；In each pair V-groove, SPR is excited at the first V-groove inclined-plane from the incident wide spectrum optical of the first fibre core And be totally reflected, reflex to and also excite SPR at the second V-groove inclined-plane and reflex to the second fibre core；Light in each pair of V-groove according to Distributed sensing is realized in secondary transmission.

2. distributed surface plasma resonance optical fiber sensor according to claim 1, it is characterized in that：Each pair V-groove In the magnitude of misalignment L of two V-grooves meet L=d*cot Φ, the corner angle that wherein d is two fibre core spacing, Φ is V-groove.

3. distributed surface plasma resonance optical fiber sensor according to claim 1 or 2, it is characterized in that：Described The thickness of sensing layer is 35-65 nanometers, and the material of sensing layer is gold, silver, aluminium or copper.