CN108872157B - A side-polished open-loop PCF-SPR sensor - Google Patents

Abstract

The invention discloses a side-polished open-loop PCF‑SPR sensor, which comprises a fiber core and a cladding covering the outside of the fiber core. The air hole; the air hole includes a first air hole, a plurality of second air holes and a plurality of third air holes, the first air hole is located in the center of the optical fiber cross section, and the second air hole is in layers around the first air hole It is an annular N-angle structure of K, and the third air hole is symmetrically located on both sides of the fiber core, replacing the position of the second air hole; a polished plane is set on the side of the fiber, and an open ring is set on the polished plane; the open ring is coated with a sensor Membrane, open ring as sensing channel. The invention adopts the method of combining side polished optical fiber end face and open loop, the SPR sensing layer is very close to the fiber core, and can detect liquid oxygen, liquid CO ₂ , and fluorine-containing organic substances with a refractive index lower than 1.3 substances, and capable of multi-channel sensing, expanding the application range of existing PCF‑SPR sensors.

Description

A side-polished open-loop PCF-SPR sensor

technical field

The invention relates to the technical fields of biochemical detection and optical fiber sensing, and more particularly relates to a side-polished open-loop PCF-SPR sensor.

Background technique

Surface Plasmon Resonance (SPR) sensing technology is an advanced optical sensing technology. Surface plasmons (Surface Plasmon, SP for short) propagating at the interface between metal and dielectric are extremely sensitive to incident light and changes in the refractive index of the medium to be measured. A large number of SPR sensors have been manufactured based on this principle. Conventional SPR sensors such as the prism type are not suitable for applications based on moving optical and mechanical parts due to their bulky size. This limitation led to the emergence of fiber-optic-based SPR sensors in the 1990s. Usually, the cladding of the ordinary optical fiber is stripped first, and then a gold or silver film is plated on the fiber core. The evanescent field leaked from the fiber core interacts with external substances to achieve sensing. In recent years, the advent of photonic crystal fibers (PCFs) offers great potential for novel SPR sensors. Compared with traditional optical fibers, PCF is small in size, flexible in design, and has a special porous structure and guided mode mechanism, which can accommodate samples in the form of gas or liquid in the air holes near the fiber core for high-sensitivity sensing. PCF-SPR sensor can effectively solve the phase matching problem of SPR sensor based on traditional optical fiber or waveguide, and compared with fluorescence sensor, PCF-SPR sensor has higher sensitivity, real-time fast, no need to mark the measured object, remote monitoring, etc. Due to its many advantages, it is widely used in various fields such as biotechnology, drug screening, environmental monitoring, and food safety. The patent titled "An Optical Fiber Surface Plasmon Resonance Sensing Device" (Patent Application No. 200820212280.2) is a typical representative of the realization of PCF-SPR sensors. Since Canada's Hassani et al. proposed the first PCF-SPR sensor structure in 2006, a variety of novel SPR-PCF sensor structure designs have been proposed so far, with their own structural characteristics and better performance applications. Most existing PCF-SPR sensors have a refractive index measurement range higher than 1.30, which makes it impossible to measure some low-refractive-index substances (films, liquid CO ₂ , low-refractive-index aerosol particles, etc.). In addition, when a multi-channel SPR sensor detects multiple analytes, adjacent channels are likely to interfere with each other, resulting in the broadening of the SPR resonance spectrum curve, and there are multiple resonance peaks at the same time, which reduces the signal-to-noise ratio of the actual system, and there is cross-sensitivity between parameters, etc. question. And most of the PCF-SPR sensors are not outstanding in application, and the practicability is not strong. Nowadays, it is urgent to design a PCF-SPR sensor with high sensitivity, anti-interference, good integration, multi-channel measurement, and meet the requirements of flexibility and practicability.

Contents of the invention

In view of the above defects, the present invention provides a side-polished open-loop PCF-SPR sensor, which aims to solve the technical problem of low sensitivity of the existing PCF-SPR sensor.

In order to solve the above technical problems, the invention provides a side polished open-loop PCF-SPR sensor, comprising:

The fiber core and the cladding covering the outside of the fiber core, the fiber core and the cladding are not concentric, and the cladding is provided with air holes arranged along the direction of the fiber core axis; the air holes include a first air hole, a plurality of second Air holes and a plurality of third air holes, the first air hole is located in the center of the optical fiber cross section, the second air hole is arranged around the first air hole in an annular N-angle structure with layers K, the third air hole replaces the second The position of the air hole is symmetrically located on both sides of the fiber core, replacing the position of the second air hole; a polished plane is formed on the side of the fiber after cutting and polishing, and an open ring is provided on the polished plane; the open ring is coated with a sensor Membrane, open ring as sensing channel.

Preferably, the polishing plane is located on a side close to the fiber core.

Preferably, a fourth air hole is introduced into the center of the fiber core, and the ratio of the diameter of the fourth air hole to the diameter of the second air hole is less than 1.

Preferably, the cross-section of the open ring is rectangular, and the size of the open ring can be determined according to the molecular size of the substance to be measured.

Preferably, all or part of the third air hole is coated with a sensing film for serving as another sensing channel, and the diameter of the third air hole is larger than that of the second air hole.

Preferably, the third air hole is filled with a liquid having a thermo-optic coefficient two orders of magnitude higher than the thermo-optic coefficient of the optical fiber material by means of liquid capillary phenomenon or pressurization.

Preferably, one sensing channel is used to inject the measured substance, and the other sensing channel is used to inject the reference substance, so as to improve the anti-interference ability of the sensor.

Preferably, the two sensing channels are used to inject the measured substance, and the sensing film in the sensing channel is determined according to the measured parameters of the measured substance, so as to realize simultaneous measurement of different parameters of the measured substance.

Preferably, the sensing film is a multilayer film structure.

Preferably, the distance between each air hole is Λ, the radius size range of the first air hole and the second air hole is 0.4Λ-0.6Λ, the radius size range of the third air hole is 0.6Λ-1.2Λ, and the fourth air hole radius size range is 0.6Λ-1.2Λ. The size range of air hole radius is 0.1Λ-0.3Λ, and the size range of open ring depth and width is 0.5Λ-2Λ.

Generally speaking, compared with the prior art, the above technical solutions conceived by the present invention can achieve the following beneficial effects:

1. The present invention adopts the combination of side-polished optical fiber end face and open loop. The SPR sensing layer is only located on the width of the open loop surface in the X and Y directions, which is very close to the fiber core. Compared with the SPR layer The entire sensor is laid flat on the side polished surface, and the measurement sensitivity of the sensor provided by the invention is greatly improved under low refractive index.

2. The polished plane and the open ring are located on the side close to the fiber core. When the light is incident on the fiber, the fundamental mode excited at the fiber core and the plasmon mode excited by the metal/medium layer are more likely to resonate, so that the measured substance can be obtained in a certain A resonant peak in which the loss of the refractive index varies significantly with the wavelength of the incident light.

3. A fourth air hole is introduced at the fiber core to increase the sensitivity of detecting low-refractive-index solutions in the open loop and realize high-sensitivity sensing.

4. The advantage of using a rectangular open ring is that the flat surface can well control the deposition of the metal film, and removing part of the air holes near the bottom of the rectangular open ring exposes the fiber core, which can promote the leakage of the fiber core energy into the metal layer and improve detection. sensitivity. The size of the open-loop entrance can be specifically designed according to the size of the analyte molecules, and the analyte molecules smaller than the entrance size can automatically penetrate the channel through the entrance, so that the open-loop can filter.

5. The introduction of the third air hole on the left and right sides of the fiber core can realize multi-channel sensing and meet the requirements of practicality and flexibility. The ring opening breaks the structural symmetry, causes birefringence and destroys the original degenerate mode, and the X-polarization and Y-polarization of the fundamental mode are separated, thereby realizing dual-parameter measurement and solving the problem of cross-sensitivity of the two parameters.

6. By changing the open-ring surface coating material, air hole arrangement, air hole size and open-ring size, the detection of substances with a refractive index lower than 1.3 can be realized. This sensor breaks through the lower detection limit of the existing similar sensors. Within the limit of 1.3, it can detect substances such as liquid oxygen (refractive index 1.22), liquid carbon dioxide (refractive index 1.20), fluorine-containing organic compounds (refractive index lower than 1.3) or aerosol particles with low refractive index, and can realize Multi-channel sensing is expected to be applied to a variety of practical applications such as the development of new thin films, atmospheric humidity and temperature detection, micro-sample detection, and atmospheric haze detection, expanding the application range of existing PCF-SPR sensors.

Description of drawings

The technical solutions of the present invention will be further specifically described below in conjunction with the accompanying drawings and specific embodiments.

Fig. 1 is the schematic cross-sectional view of the side polishing open-loop PCF-SPR sensor provided by the present invention;

Fig. 2 is the schematic diagram of the experimental detection system device provided by the present invention;

Among them, 1: fiber core, 2: first air hole, 3: metal film, 4: second air hole, 5: third air hole, 6: fourth air hole, 7: open loop, 8: polished end face, 9: Ring hexagonal structure, 10: Broad-spectrum light source or near-infrared laser, 11: Polarizer, 12: Transmission fiber, 13: Coupler, 14: Sensing fiber, 15: Spectrum analyzer, 16: Computer.

Detailed ways

In order to make the object, technical solution and advantages of the present invention more clear, the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described here are only used to explain the present invention, not to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not constitute a conflict with each other.

The purpose of the present invention is to provide a high-sensitivity side-polished open-ring PCF-SPR sensor that can detect low-refractive-index substances and meet the requirements of flexibility and practicability. Due to the shortcomings of being unable to detect low-refractive index analytes and poor practicability, it is expected to be used in practical applications such as the development of new thin films, atmospheric humidity and temperature detection, micro-sample detection, and atmospheric haze detection.

As shown in FIG. 1 , the background material of the optical fiber is quartz, and the optical fiber includes a core 1 and a cladding covering the outside of the core, and the core 1 and the cladding are not concentric. The cladding is provided with air holes arranged axially along the fiber core 1, the air holes include a first air hole 2, a second air hole 4, and a third air hole 5; the first air hole 2 is located at the center of the fiber cross section, The second air holes 4 are arranged around the first air holes 2 in an annular N-angle structure with layers K, wherein K and N are both integers greater than 2, and the third air holes 5 are evenly and symmetrically distributed on the left and right sides of the fiber core 1 , instead of the second air hole 4; on the side of the optical fiber close to the core, a polished plane is formed after cutting and polishing, and an open ring is provided in the center of the polished plane toward the core. In this embodiment, the second air holes 4 are arranged around the first air holes in an annular hexagonal structure 9 with four layers.

In the process of making the optical fiber, the optical fiber side polishing technology is used to polish and polish the end face of the optical fiber into a flat polished end face 8, and then a rectangular open ring 7 is polished at the center of the end face. The polished optical fiber is made of a special optical fiber After the fixture is fixed, a layer of metal film 3 with a thickness of 20-40nm is plated on the plane of the rectangular polishing area by the coating equipment as the SPR sensing film, which is used as a solution channel for SPR detection or other types of sensing channels.

The invention adopts the method of combining the side polished fiber end face and the open loop, adopts the open loop structure, the SPR sensing layer concentrates on the fiber core only in the width of the bottom of the open loop in the transverse x direction, and measures the amplitude sensitivity under low refractive index compared with the SPR layer Overall laying is greatly improved on side polished surfaces.

In another embodiment of the present invention, the open ring is rectangular, and the advantage of using a rectangular open ring is that the flat surface can well control the deposition of the metal film. The size of the open-loop entrance can be specifically designed according to the size of the measured substance molecule. The measured substance molecules smaller than the entrance size can automatically penetrate the channel through the entrance. The open-loop acts as a solution filter, which can detect low refractive index aerosols in the atmosphere. particle.

In another embodiment provided by the present invention, the inner wall of the third air hole is coated with a sensing film with a thickness of 30-60nm, and the sensing film can be coated in all the third air holes, or in some of the third air holes Coated with a sensing film, as another detection channel of the PCF-SPR sensor, due to the open ring breaking the structural symmetry, causing birefringence and destroying the original degenerate mode, the X polarization and Y polarization of the fundamental mode are separated, thereby achieving dual Parameter measurement, which solves the problem of cross-sensitivity of two parameters. The diameter ratio of the third air hole to the second air hole is greater than 1, and the large hole is more conducive to the coating operation and the filling of the sensing medium, which increases the practicality.

In another embodiment of the present invention, a fourth air hole is introduced into the center of the fiber core, and the ratio of the diameter of the fourth air hole to the second air hole is less than 1, so as to increase the sensitivity of detecting the low refractive index solution in the open loop.

As a further application scheme, the open loop and the third air hole can be treated as different types of detection and sensing channels according to different practical requirements.

As the application of this PCF-SPR sensor, the liquid with high thermo-optic coefficient can be injected into the third air hole channel of the detection fiber by using the capillary phenomenon of liquid or pressurization method as the temperature channel, and the thermo-optic coefficient is selected to be higher than that of the fiber material. The liquid with a coefficient of two orders of magnitude, the liquid with a higher thermo-optic coefficient can be chloroform, a mixed liquid of ethanol and chloroform, or isopropanol.

As the application of this PCF-SPR sensor, the sensing film is a multi-layer film structure, and the sensing film includes a metal film and other materials coated _on the metal film, such as graphene, MoS2 and other materials, which can realize biosensing, Atmospheric humidity sensing.

As an application of the PCF-SPR sensor, the present invention adopts the following technical solutions to realize multi-channel and multi-parameter parallel measurement of the sensor. When detecting multiple parameters of the same sample, it is only necessary to fill the same sample in different detection channels, and the sensing material of each detection channel is selected according to different measurement parameters.

As an application of the PCF-SPR sensor, the present invention can realize a self-referencing function to eliminate the influence of various environmental factors, including instrument noise, temperature, interference of other molecules in the sample on target molecules, and the like. Simply select one of the channels as the detection channel to fill the sample and the other as the reference channel. The method of measuring the difference between the resonance wavelengths of the two channels is used to effectively counteract the influence of environmental factors.

In the embodiment provided by the present invention, the distance between the air holes is Λ, the radius size range of the first air hole and the second air hole is 0.4Λ-0.6Λ, and the radius size range of the third air hole is 0.6Λ-1.2Λ, The size range of the radius of the fourth air hole is 0.1Λ-0.3Λ, and the size range of the open-loop depth and width is 0.5Λ-2Λ. The SPR sensing layer is only located on the width of the bottom of the open loop in the transverse X direction, and is very close to the fiber core. By adjusting the size of the open loop, the arrangement and size of each air hole, and selecting a suitable SPR sensing layer material, it can be achieved. The range of measured refractive index moves to the direction of low refractive index, and the detected refractive index value reaches below 1.3.

Take the dual-parameter measurement of the sample as a specific example. As shown in FIG. 2 , the present invention uses an online transmission working method based on wavelength modulation to detect the SPR signal of the sample, and the SPR signal appears on the transmission spectrum in the form of an absorption peak. The detection device includes a wide-spectrum light source 10 , a polarizer 11 , a transmission fiber 12 , a coupler 13 , a sensing fiber 14 , a spectrum analyzer 15 and a computer 16 .

Taking the detection of the two parameters of aerosol particle refractive index and atmospheric temperature in the atmosphere as an example, the open-loop opening size of the sensing fiber is designed according to the molecular diameter of the aerosol solution sample to be measured, and the chloroform The third air hole channel injected into the detection fiber is used as a channel for measuring atmospheric temperature. Pour the aerosol solution sample directly on the side polished surface of the sensing fiber, at this time, the open ring acts as a filter, and the target molecules smaller than the entrance size of the open ring can directly pass through the entrance to automatically penetrate the channel, and the macromolecules will be blocked in the opening. outside the ring. After the sensing fiber sample is filled, adjust its position on the three-dimensional translation stage to keep it horizontal and coaxial with the optical coupling system.

The incident light from a broadband light source or near-infrared laser enters the transmission fiber for transmission, and is adjusted to linearly polarized light by a polarizer so that its polarization direction is parallel to the symmetry axis of the sensing fiber core, and the coupling conditions are controlled so that the broadband light source or near-infrared laser The light emitted by the infrared laser is coupled into the core of the sensing fiber with the highest efficiency, so that the fundamental mode of the detection fiber has the maximum excitation efficiency. The incident light enters the spectrum analyzer through the coupler after being modulated by the sample in the sensing area, and the resonance spectrum is reflected on the spectrum analyzer in the form of a transmission absorption peak. When the parameters of the measured sample change, the transmission absorption peak also changes. When drift occurs, the spectrometer is connected to the computer through the USB port, and the computer records and saves the spectral data. The change of each target parameter is finally reflected in the change of the equivalent refractive index of the sample under test. By measuring the resonance wavelength drift of the X-polarization and Y-polarization directions of the fundamental mode respectively, the dual refraction index and temperature of the sample under test are realized. Real-time online measurement and monitoring of parameters.

The sensor provided by the invention has a rectangular open loop for sampling, and the bottom of the rectangular open loop is flat, and a film can be evenly coated on the bottom, and the operation is simple and safe. If the target parameter is atmospheric humidity, one or more layers of MoS ₂ two-dimensional materials are coated on the surface of the flat metal layer of the open-loop channel by using coating technology. Since the surface of MoS ₂ has no dangling bonds, it has a physical adsorption effect on water molecules, so The change of atmospheric humidity can be obtained by detecting the change of the refractive index of molybdenum disulfide, and a humidity sensor can be made. If graphene coating is used, the high electron density of the hexagonal ring of graphene can prevent oxygen, helium atoms, etc. Oxidation of the surface, in turn, can be used in biosensor applications, greatly improving its sensitivity and performance.

The detection refractive index of the sensor of the invention is lower than 1.3, so it can also be used in the development of new thin film materials. Low refractive index films (such as nanoporous silica films, cryolite films, etc.) are widely used in various fields such as production and life due to their excellent properties such as transparency, low thermal conductivity, and low dielectric properties. As the application of the PCF-SPR sensor, one or more thin films can be deposited at the bottom of the rectangular open-loop channel, and the refractive index parameters or film thickness of the film can be obtained by observing the spectral resonance peak wavelength and its drift on the spectrometer.

Finally, it should be noted that the above specific embodiments are only used to illustrate the technical solutions of the present invention and not limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that the present invention can be Modifications or equivalent replacements of the technical solutions without departing from the spirit and scope of the technical solutions of the present invention shall fall within the scope of the claims of the present invention.

Claims (9)

1. a kind of side polishes open ring type PCF-SPR sensor characterized by comprising fibre core and be coated on outside fibre core Covering, fibre core are equipped with the airport arranged along fibre core axis direction with covering decentraction on covering；Airport includes one first Airport, multiple second airports and multiple third airports, the first airport are located at cross section of optic fibre center, the second air Hole is arranged around the first airport in the annular N corner structure that the number of plies is K, and third airport is by replacing the second air hole site pair Ground is claimed to be located at fibre core two sides；It is provided in optical fiber side and cuts flat with and form surface polishing after polishing treatment, in surface polishing It is equipped with open loop, is coated with sensing membrane in open loop, open loop is as sensing passage；Surface polishing is located at close to the side of fibre core.

2. side as described in claim 1 polishes open ring type PCF-SPR sensor, which is characterized in that in the core centre Introducing is provided with the 4th airport, and the 4th air bore dia and the second air pore diameter size ratio are less than 1.

3. as the described in any item sides of claims 1 or 2 polish open ring type PCF-SPR sensor, which is characterized in that described to open Ring section is rectangle, and open loop size can be determined according to measured matter molecular size.

4. as the described in any item sides of claims 1 or 2 polish open ring type PCF-SPR sensors, which is characterized in that all or Person part third airport is coated with sensing membrane, and for being used as another sensing passage, and the third air bore dia is greater than second Air bore dia.

5. side as claimed in claim 4 polishes open ring type PCF-SPR sensor, which is characterized in that utilize the capillary of liquid Phenomenon or pressuring method fill the liquid that thermo-optical coeffecient is higher than two orders of magnitude of fiber optic materials thermo-optical coeffecient in third airport.

6. side as claimed in claim 4 polishes open ring type PCF-SPR sensor, which is characterized in that on a sensing passage For being injected with measured matter, another sensing passage improves the anti-external interference energy of sensor for being above injected with reference material Power.

7. side as claimed in claim 4 polishes open ring type PCF-SPR sensor, which is characterized in that two sensing passages are used Sensing membrane is determined according to measured matter measured parameter in injection measured matter, sensing passage, is realized while being measured measured matter Different parameters.

8. as claim 1,2,5,6 or 7 described in any item sides polish open ring type PCF-SPR sensor, which is characterized in that Sensing membrane is multi-layer film structure.

9. as claim 1,2,5,6 or 7 described in any item sides polish open ring type PCF-SPR sensor, which is characterized in that Spacing is Λ between each airport, and the first airport and the second airport radius size magnitude range are 0.4 Λ -0.6 Λ, the Three airport radius size magnitude ranges are 0.6 Λ -1.2 Λ, and the 4th airport radius size magnitude range is 0.1 Λ -0.3 Λ, open loop depth and width magnitude range are 0.5 Λ -2 Λ.