Parallel double-cavity optical fiber copper ion sensor and detection method thereof

Abstract

The invention relates to the technical field of optical fiber sensing, and provides a parallel double-cavity optical fiber copper ion sensor, which comprises an optical fiber coupler, a sensing Fabry-Perot interferometer and a reference Fabry-Perot interferometer, the sensing Fabry-Perot interferometer comprises a first single-mode fiber, a first capillary glass tube and hydrogel; one end of the first single-mode optical fiber is connected with the optical fiber coupler, and the other end of the first single-mode optical fiber extends into the first capillary glass tube; hydrogel is arranged on the end surfaces of the first single-mode optical fiber and the first capillary glass tube; the reference Fabry-Perot interferometer comprises a second single-mode fiber, a second capillary glass tube and a third single-mode fiber; one end of the second single-mode optical fiber is connected with the optical fiber coupler, and the other end of the second single-mode optical fiber extends into the second capillary glass tube; the third single-mode optical fiber also extends into the second capillary glass tube; and a gap is reserved between the third single-mode optical fiber and the second single-mode optical fiber. According to the invention, two reflection spectrums with small frequency difference are superposed to generate amplified frequency change, so that the sensitivity of copper ion measurement is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of optical fiber sensing, and in particular to a parallel dual-cavity optical fiber copper ion sensor and a detection method thereof. Background Art

[0002] Copper ion is a common heavy metal ion. Industrial wastewater containing copper ions is often produced in the chemical industry, printing and dyeing, electroplating, non-ferrous metal mining, electronic material cleaning wastewater, and ignition production processes. The discharge of large amounts of copper-containing wastewater has a huge impact on the soil and water resources on which humans depend for survival. Excessive intake of copper ions can also cause kidney damage, liver necrosis, hemolysis, brain tissue lesions and other damages to the human body. Therefore, accurate detection of the concentration of copper ions in industrial wastewater and drinking water is a necessary means to ensure that human health and the ecological environment are free from the impact of copper ion pollution. Commonly used methods for detecting copper ions include fluorescent labeling, atomic absorption spectroscopy, electrochemical method, etc., but these methods generally have problems such as high detection cost, complex sample pretreatment, and long detection time.

[0003] Compared with traditional sensors, fiber optic sensors have the advantages of small size, resistance to electromagnetic interference, high sensitivity, simple process, low cost, high temperature resistance, and corrosion resistance, and have great potential in metal ion detection. Combining fiber optic sensors with specific identification materials can enable sensors to accurately detect metal ions. However, existing fiber optic sensors still have certain deficiencies in sensitivity, repeatability, and selectivity. On the one hand, the detection ability of low-concentration copper ions is limited, and it is difficult to meet certain application scenarios with high requirements for detection accuracy; on the other hand, the sensor probe cannot be reused and is easily interfered by other ions in complex environments, resulting in inaccurate detection results.

[0004] As a unique optical phenomenon, the optical vernier effect has attracted widespread attention in the field of optical measurement in recent years. It can produce amplified frequency changes through the interaction of two optical signals with a small frequency difference, thereby improving the sensitivity and resolution of the measurement. At present, although there have been some studies on sensors based on optical principles, there are relatively few studies on the application of the optical vernier effect to fiber-optic copper ion sensors. Summary of the invention

[0005] The present invention mainly solves the technical problems of low response sensitivity, long detection time, poor repeatability and selectivity in the existing optical fiber sensing technology, and proposes a parallel dual-cavity optical fiber copper ion sensor and a detection method thereof, which generates an amplified frequency change by superimposing two reflection spectra with a small frequency difference to improve the sensitivity of copper ion measurement.

[0006] The present invention provides a parallel dual-cavity optical fiber copper ion sensor, comprising: an optical fiber coupler, a sensing Fabry-Perot interferometer and a reference Fabry-Perot interferometer;

[0007] The sensing Fabry-Perot interferometer comprises: a first single-mode optical fiber, a first capillary glass tube and a hydrogel;

[0008] One end of the first single-mode optical fiber is connected to the optical fiber coupler, and the other end extends into the first capillary glass tube; the end faces of the first single-mode optical fiber and the first capillary glass tube are aligned, and hydrogel is arranged at the end faces of the first single-mode optical fiber and the first capillary glass tube;

[0009] The reference Fabry-Perot interferometer comprises: a second single-mode optical fiber, a second capillary glass tube and a third single-mode optical fiber;

[0010] One end of the second single-mode optical fiber is connected to the optical fiber coupler, and the other end extends into the second capillary glass tube; the third single-mode optical fiber also extends into the second capillary glass tube; the third single-mode optical fiber is arranged opposite to the second single-mode optical fiber, and a gap is left between the third single-mode optical fiber and the second single-mode optical fiber.

[0011] Preferably, the hydrogel is sodium alginate / graphene oxide hydrogel.

[0012] Preferably, the preparation method of the sodium alginate / graphene oxide hydrogel is:

[0013] Add 0.3-0.4 g of graphene oxide to 37-50 mL of deionized water, stir with a magnetic stirrer for more than 1 hour, and ultrasonicate with an ultrasonic cleaner for more than 1 hour to obtain a uniformly dispersed graphene oxide solution;

[0014] Add 0.8-1.0 g of sodium alginate into 35-45 mL of deionized water and stir magnetically for more than 1 h to obtain a sodium alginate sol;

[0015] Then, 80-90 mg of graphene oxide suspension was added to the sodium alginate hydrogel, and stirred for more than 2 h to obtain a sodium alginate / graphene oxide sol;

[0016] Add about 5 mL of 1 g / L Cu(NO3)2 solution to the sodium alginate / graphene oxide sol and stir for more than 20 min to obtain a slightly yellow sol;

[0017] The common end face of the first single-mode optical fiber and the first capillary glass tube is dipped in an appropriate amount of sol and placed in a CaCl2 solution with a mass fraction of 5% for more than 3 hours. The sensing Fabry-Perot interferometer is then placed in deionized water to elute excess copper ions to obtain a sodium alginate / graphene oxide hydrogel that specifically responds to copper ions.

[0018] Preferably, the sensing Fabry-Perot interferometer reflected light intensity I s It is expressed as:

[0019]

[0020] In the formula, I s1 represents the light intensity reflected back to the first single-mode optical fiber from the interface between the first single-mode optical fiber and the hydrogel, I s2 represents the light intensity reflected back to the first single-mode optical fiber from the interface between the hydrogel and the solution to be tested, n s represents the refractive index of the hydrogel, L s represents the thickness of the hydrogel, is the initial phase;

[0021] When the reflected light intensity I in the interference spectrum of the sensing Fabry-Perot interferometer s When the minimum is reached, the wavelength of the reflection spectrum trough is expressed as:

[0022]

[0023] In the formula, λ dip represents the wavelength of the reflection spectrum trough, and m is the interference peak order;

[0024] The sensing Fabry-Perot interferometer free spectral range is:

[0025]

[0026] Among them, FSR s represents the free spectral range of the known sensing Fabry-Perot interferometer;

[0027] When the external copper ion concentration changes, the corresponding trough change of the sensing Fabry-Perot interferometer is expressed as:

[0028]

[0029] Among them, Δλ dip It represents the change of the corresponding trough of the sensing Fabry-Perot interferometer;

[0030] The wavelength of the reflection spectrum trough of the reference Fabry-Perot interferometer is expressed as:

[0031]

[0032] In the formula, λ′ dip represents the wavelength of the reflection spectrum trough of the reference Fabry-Perot interferometer, n is the refractive index of air, L r is the length of the air cavity;

[0033] The reference Fabry-Perot interferometer free spectral range is expressed as:

[0034]

[0035] Among them, FSR r represents the reference Fabry-Perot interferometer free spectral range;

[0036] The relationship between the free spectral range of the sensing Fabry-Perot interferometer and the reference Fabry-Perot interferometer is:

[0037]

[0038] Preferably, the free spectral range of the sensing Fabry-Perot interferometer differs from that of the reference Fabry-Perot interferometer by 5.7-9.1 nm.

[0039] Correspondingly, the present invention also provides a detection method of a parallel dual-cavity optical fiber copper ion sensor provided according to any embodiment of the present invention, comprising the following process:

[0040] Step 1, placing the sensing Fabry-Perot interferometer in the solution to be tested, and placing the reference Fabry-Perot interferometer outside the solution to be tested, without contacting the solution to be tested; connecting the optical fiber coupler to the spectrometer;

[0041] Step 2, standing for a period of time, the sensing Fabry-Perot interferometer and the reference Fabry-Perot interferometer produce an optical cursor effect, the interference spectrum of the sensing Fabry-Perot interferometer and the reference Fabry-Perot interferometer is superimposed through the optical fiber coupler, and the interference spectrum of the sensor is displayed by the spectrometer;

[0042] Step 3, recording the wavelength drift corresponding to the trough in the interference spectrum of the sensor;

[0043] Step 4, bringing the wavelength drift of the trough into the fitting curve of the relationship between the wavelength drift and the copper ion concentration to obtain the copper ion concentration in the solution to be tested.

[0044] Preferably, the fitting curve formula of the relationship between the wavelength drift and the copper ion concentration is:

[0045] y=sC (Cu2+)

[0046] Where y represents the wavelength drift, C (Cu2+) represents the copper ion concentration, and s represents the corresponding sensitivity of the sensor.

[0047] A parallel dual-cavity optical fiber copper ion sensor and a detection method thereof provided by the present invention are based on the optical vernier effect and combined with the Fabry-Perot interference principle, and the reflection spectrum of two small frequency differences is superimposed to generate an amplified frequency change, thereby improving the sensitivity of copper ion measurement. The present invention can effectively make up for the shortcomings of the existing copper ion detection method and optical fiber sensor, realize high-sensitivity detection of copper ions, and improve the performance of the optical fiber copper ion sensor; it has excellent dynamic response characteristics and repeatability; it has good selectivity, can accurately identify copper ions in a complex environment, avoid interference from other ions, and ensure the accuracy of the detection results. The present invention prepares a sodium alginate / graphene oxide hydrogel with a specific spatial structure and binding site for copper ions by an ion imprinting method, has a high degree of selective recognition ability for copper ions, can specifically bind to copper ions, improves the repeatability and stability of the sensor, and shortens the response time of the sensor.

[0048] The sensor of the present invention is small in size, light in weight, easy to install and use, and adaptable to various complex detection environments. The present invention has good application prospects in the fields of environmental detection, water quality analysis, industrial production, etc. It can be used to detect copper ions in water bodies, timely grasp the environmental quality status, and provide strong support for environmental protection; in the chemical, electronic and other industries, it can detect the copper ion concentration in waste liquid. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 It is a structural schematic diagram of the parallel dual-cavity optical fiber copper ion sensor provided by the present invention;

[0050] Figure 2 It is a reflection spectrum diagram of the parallel dual-cavity optical fiber copper ion sensor provided by the present invention when the copper ion concentration is 0 and 0.2 mg / L;

[0051] Figure 3 It is a schematic diagram of the copper ion concentration and wavelength drift of the parallel dual-cavity optical fiber copper ion sensor provided by the present invention;

[0052] Figure 4 It is a dynamic response diagram of the parallel dual-cavity optical fiber copper ion sensor provided by the present invention;

[0053] Figure 5 It is a schematic diagram of the time and wavelength drift of the parallel dual-cavity optical fiber copper ion sensor provided by the present invention;

[0054] Figure 6 This is a result diagram of a repeatability experiment of the parallel dual-cavity optical fiber copper ion sensor provided by the present invention;

[0055] Figure 7 It is a bar graph of the results of the selectivity experiment of the parallel dual-cavity optical fiber copper ion sensor provided by the present invention;

[0056] Figure 8 This is a result diagram of a selectivity experiment of the parallel dual-cavity optical fiber copper ion sensor provided by the present invention. DETAILED DESCRIPTION

[0057] In order to make the technical problems solved by the present invention, the technical solutions adopted and the technical effects achieved clearer, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It is understood that the specific embodiments described herein are only used to explain the present invention, rather than to limit the present invention. It should also be noted that, for the convenience of description, only the parts related to the present invention are shown in the accompanying drawings, rather than all the contents.

[0058] Embodiment 1

[0059] like Figure 1 As shown, a parallel dual-cavity optical fiber copper ion sensor provided by an embodiment of the present invention includes: an optical fiber coupler 1, a sensing Fabry-Perot interferometer 2 and a reference Fabry-Perot interferometer 3.

[0060] The sensing Fabry-Perot interferometer 2 includes: a first single-mode optical fiber 201, a first capillary glass tube 202 and a hydrogel 203. One end of the first single-mode optical fiber 201 is connected to the optical fiber coupler 1, and the other end extends into the first capillary glass tube 202; the end faces of the first single-mode optical fiber 201 and the first capillary glass tube 202 are aligned, and the hydrogel 203 is arranged at the end faces of the first single-mode optical fiber 201 and the first capillary glass tube 202.

[0061] The reference Fabry-Perot interferometer 3 includes: a second single-mode optical fiber 301, a second capillary glass tube 302 and a third single-mode optical fiber 303. One end of the second single-mode optical fiber 301 is connected to the optical fiber coupler 1, and the other end thereof extends into the second capillary glass tube 302; the third single-mode optical fiber 303 also extends into the second capillary glass tube 302; the third single-mode optical fiber 303 is arranged opposite to the second single-mode optical fiber 301, and a gap is left between the third single-mode optical fiber 303 and the second single-mode optical fiber 301, and the gap serves as an interference cavity of the reference Fabry-Perot interferometer 3.

[0062] The hydrogel 203 is sodium alginate / graphene oxide hydrogel.

[0063] The present invention discloses a method for making a parallel dual-cavity optical fiber copper ion sensor: firstly, pre-treat the optical fiber coupler and the single-mode optical fiber, remove the coating layer on the optical fiber surface, cut it flat with an optical fiber cutter, put one optical fiber of the 1×2 50:50 optical fiber coupler 1 on the first capillary glass tube 202, make the end face of the optical fiber flush with the end face of the first capillary glass tube 202 with the aid of a microscope, and fix the first capillary glass tube 202 and the single-mode optical fiber with glue. Dip the sodium alginate / graphene oxide sol, solidify it with a calcium chloride solution with a mass fraction of 5% to form a hydrogel, generate an interference spectrum on the spectrometer, and then immerse it in deionized water to elute the excess copper ions in the hydrogel, as a sensing Fabry-Perot interferometer 2. The other optical fiber of the optical fiber coupler 1 is put into the second capillary glass tube 302, and then a section of the optical fiber that has been cut flat is inserted into the second capillary glass tube 302, and the distance between the two sections of optical fiber (the second single-mode optical fiber 301 and the third single-mode optical fiber 303) is adjusted until a periodic envelope is generated on the spectrometer, which is used as a reference Fabry-Perot interferometer 3.

[0064] The present invention adopts an ion imprinting method to prepare a sodium alginate / graphene oxide hydrogel that specifically responds to copper ions. The preparation method of the sodium alginate / graphene oxide hydrogel is as follows:

[0065] (1) Preparation of graphene oxide suspension: Add 0.3-0.4 g of graphene oxide to 37-50 mL of deionized water, stir with a magnetic stirrer for more than 1 hour, and ultrasonicate with an ultrasonic cleaner for more than 1 hour to obtain a uniformly dispersed graphene oxide solution;

[0066] (2) Preparation of sodium alginate hydrogel: add 0.8-1.0 g of sodium alginate into 35-45 mL of deionized water and stir magnetically for more than 1 h to obtain sodium alginate sol;

[0067] (3) Preparation of sodium alginate / graphene oxide hydrogel: Add 80-90 mg of graphene oxide suspension to the sodium alginate hydrogel and stir for more than 2 h to obtain a sodium alginate / graphene oxide sol;

[0068] (4) adding about 5 mL of 1 g / L Cu(NO3)2 solution to the sodium alginate / graphene oxide sol and stirring for more than 20 min to obtain a slightly yellow sol;

[0069] (5) Dipping the common end face of the first single-mode optical fiber 201 and the first capillary glass tube 202 in an appropriate amount of sol, placing it in a CaCl2 solution with a mass fraction of 5% for more than 3 hours, and then placing the sensing Fabry-Perot interferometer 2 in deionized water to elute excess copper ions, thereby obtaining a sodium alginate / graphene oxide hydrogel that specifically responds to copper ions.

[0070] As an anionic polysaccharide, sodium alginate contains a large number of carboxyl groups on its molecular chain. It dissociates with negative charge in aqueous solution and attracts positively charged copper ions through electrostatic attraction. At the same time, carboxyl groups can react with copper ions to form a stable complex. The surface of graphene oxide is rich in oxygen-containing functional groups, such as hydroxyl, carboxyl and epoxy groups, which can also ionize with negative charge and produce electrostatic effects with copper ions. Its oxygen-containing functional groups can participate in complex reactions and enhance the adsorption of copper ions. In addition, the hydrogel has a three-dimensional porous network structure, which provides adsorption space and channels for copper ions, and traps copper ions on the inner surface of the pores and the surface of graphene oxide through physical adsorption. Furthermore, the hydrogen bonding between sodium alginate and graphene oxide makes the two tightly combined, maintains the stability of the hydrogel structure, and ensures that the adsorption sites are effective, thereby achieving efficient adsorption of copper ions.

[0071] Ion imprinting refers to the formation of a sodium alginate / graphene oxide-copper ion complex with a specific spatial structure and binding sites through the interaction between sodium alginate / graphene oxide hydrogel and copper ions in the presence of copper ions. Calcium ions are then added as a cross-linking agent to initiate a polymerization reaction, so that the complex forms a highly cross-linked polymer network. After the polymerization is completed, the excess copper ions are washed away with deionized water, leaving imprinted holes in the polymer that match the shape, size and binding sites of the copper ions. When a solution containing copper ions comes into contact with the imprinted polymer, the imprinted holes can specifically bind to the copper ions because they have a highly selective recognition ability for copper ions.

[0072] The sensor of the present invention generates an optical cursor effect due to the parallel sensing Fabry-Perot interferometer 2 and the reference Fabry-Perot interferometer 3, and the formed periodic envelope can amplify the change of the interference spectrum of the sensing Fabry-Perot interferometer 2. The principle is as follows:

[0073] The sensing Fabry-Perot interferometer 2 can be regarded as a double-beam interference, and its reflected light intensity I s It can be expressed as:

[0074]

[0075] In the formula, I s1 represents the light intensity reflected back to the first single-mode optical fiber 201 from the interface between the first single-mode optical fiber 201 and the hydrogel 203, I s2 represents the light intensity reflected back to the first single-mode optical fiber 201 from the interface between the hydrogel 203 and the solution to be tested, n s represents the refractive index of the hydrogel 203, L s represents the thickness of the hydrogel 203, is the initial phase.

[0076] When the reflected light intensity I in the interference spectrum of the sensing Fabry-Perot interferometer 2 sWhen the minimum is reached, the wavelength of the reflection spectrum trough is expressed as:

[0077]

[0078] In the formula, λ dip It represents the wavelength of the reflection spectrum trough, and m is the interference peak order.

[0079] According to the above formula, the free spectral range of the sensing Fabry-Perot interferometer 2 is:

[0080]

[0081] Among them, FSR s It is shown that the free spectral range of the sensing Fabry-Perot interferometer 2 can be known.

[0082] When the external copper ion concentration When changes, the corresponding trough change of the sensing Fabry-Perot interferometer 2 is expressed as:

[0083]

[0084] Among them, Δλ dip It represents the change of the corresponding trough of the sensing Fabry-Perot interferometer 2.

[0085] Therefore, the change in copper ion concentration can be obtained by observing the wavelength drift of the trough in the interference spectrum.

[0086] Similarly, the wavelength of the reflection spectrum trough of the reference Fabry-Perot interferometer 3 is expressed as:

[0087]

[0088] In the formula, λ′ dip represents the wavelength of the reflection spectrum trough of the reference Fabry-Perot interferometer 3, n is the refractive index of air, L r is the air cavity length. According to the above formula, the free spectrum range of the reference Fabry-Perot interferometer 3 is expressed as:

[0089]

[0090] Among them, FSR r represents the free spectral range of the reference Fabry-Perot interferometer 3.

[0091] When the free spectral range (FSR) of the sensing Fabry-Perot interferometer 2 differs from that of the reference Fabry-Perot interferometer 3 by about 5.7-9.1 nm, the external copper ion concentration changes, and the interference spectrum of the sensing Fabry-Perot interferometer changes accordingly, while the interference cavity of the reference Fabry-Perot interferometer 3 contains only air and is not in contact with the solution to be measured, so the interference spectrum of the reference Fabry-Perot interferometer 3 remains unchanged. The interference spectra of the sensing Fabry-Perot interferometer 2 and the reference Fabry-Perot interferometer 3 are superimposed by the optical fiber coupler 1 to form an envelope, which is analogous to a vernier caliper. An optical vernier effect is generated in the parallel sensing Fabry-Perot interferometer 2, and the periodic envelope formed amplifies the change of the original interference spectrum of the sensing Fabry-Perot interferometer 2. The interference spectrum can be modulated by the envelope, and the simplified free spectral range (FSR) of the envelope can be described by the relationship between the free spectral ranges of the sensing Fabry-Perot interferometer 2 and the reference Fabry-Perot interferometer 3 as follows:

[0092]

[0093] It can be seen from the above formula that the closer the free spectral range of the sensing Fabry-Perot interferometer 2 is to the reference Fabry-Perot interferometer 3, the larger the FSR of the envelope, the higher the response sensitivity of the sensor, and the improvement of the response sensitivity of the sensor is achieved.

[0094] The following is an experimental description of the effect of the parallel dual-cavity optical fiber copper ion sensor of the present invention:

[0095] Experiment 1: Place the sensing Fabry-Perot interferometer 2 in the solution to be tested, and place the reference Fabry-Perot interferometer 3 outside the solution without contacting the solution to be tested. Set the copper ion concentration of the solution to be tested to 0 (deionized water), 0.2, 0.4, 0.6, 0.8, 1.0, 1.2, and 1.4 mg / L. First, place the sensing Fabry-Perot interferometer 2 in deionized water, observe the movement of the trough of the interference spectrum, and let it stand for a while. After the interference spectrum stabilizes, record and save the data, and then add a certain amount of 100 mg / L copper ion solution to the deionized water to change the copper ion concentration in the beaker to 0.2 mg / L. Repeat the experiment until the copper ion concentration of the solution to be tested becomes 1.4 mg / L. Figure 2 , Figure 3As the copper ion concentration increases from 0 to 0.2 mg / L, the envelope moves toward the long wavelength direction (right). Select a trough and record its corresponding wavelength in deionized water (recorded as the initial wavelength). Then record the wavelength corresponding to the trough when the copper ion concentration changes to 0.2 mg / L. Repeat the recording until the copper ion concentration reaches 1.4 mg / L. Subtract the wavelength corresponding to the trough in copper ion solutions of different concentrations from the initial wavelength to obtain the wavelength drift of the sensor in copper ion solutions of different concentrations. After linear fitting of these data, the response sensitivity of the sensor is about 19.58 nm / (mg / L), and the correlation coefficient R 2 =0.98739, the response sensitivity of the parallel sensor is increased by 9.9 times compared with the sensing Fabry-Perot interferometer. The parallel dual-cavity optical fiber copper ion sensor of the present invention has high sensitivity.

[0096] Experiment 2: Place the sensor Fabry-Perot interferometer 2 in a test solution with a copper ion concentration of 0, collect the interference spectrum data of the sensor at a frequency of 30 Hz (i.e., record the interference spectrum data every 15 seconds), add a certain amount of 100 mg / L copper ion solution to deionized water to change the copper ion concentration in the beaker to 0.2 mg / L, observe the movement of the interference spectrum, let it stand for 10 minutes, and after ensuring that the spectrum image is stable, change the copper ion concentration in the test solution to 0.4 mg / L, and repeat the above operation until the copper ion concentration in the test solution is 1.4 mg / L. Extract the spectral data, select a trough, find the wavelength corresponding to the trough in each piece of data, calculate the wavelength drift of this trough, and make a time-wavelength drift graph based on the wavelength drift, that is, the dynamic response experimental curve of the copper ion concentration of the sensor. Figure 4 , Figure 5 In order to further observe the response time, the copper ion concentration was increased from 0.2 mg / L to 0.4 mg / L, and the sensor response time was 27 seconds under the condition of a change of 0.2 mg / L. The parallel dual-cavity optical fiber copper ion sensor of the present invention can respond quickly.

[0097] Experiment 3: Select test solutions with copper ion concentrations of 0 (deionized water), 0.2, 0.4, 0.6, 0.8, 1.0, 1.2, and 1.4 mg / L, respectively. First, place the sensor Fabry-Perot interferometer 2 in deionized water, observe the movement of the trough of the interference spectrum, let it stand for a while, and after the interference spectrum stabilizes, record and save the data. Then, add a certain amount of 100 mg / L copper ion solution to the deionized water to change the copper ion concentration in the beaker to 0.2 mg / L. Repeat the experiment until the copper ion concentration of the test solution becomes 1.4 mg / L. Record and save the data, calculate the wavelength drift of the selected trough, and perform a linear fit on it, which is recorded as one experiment. After one experiment, place the sensor Fabry-Perot interferometer 2 in deionized water for desorption, observe the movement of the interference spectrum, wait for the interference spectrum to stabilize, move the sensor Fabry-Perot interferometer 2 to deionized water, and repeat the above experimental operations until three experiments are completed. Figure 6 , the response sensitivity of the sensor Fabry-Perot interferometer 2 in the three experiments was analyzed to be 2.00768nm / (mg / L), 2.06946nm / (mg / L), and 2.03536nm / (mg / L), respectively, with a maximum difference of 0.062nm / (mg / L). Taking the measurement of a solution with a copper ion concentration of 1mg / L as an example, the standard deviation of the sensor is about 0.0425mg / L. After repeated experiments, the fitting curve formula of the relationship between the wavelength drift of the sensor and the copper ion concentration is y=sC (Cu2+) , where y represents the wavelength shift, C (Cu2+) represents the copper ion concentration, s represents the corresponding sensitivity of the sensor, and the sensor has good repeatability. The parallel double-cavity optical fiber copper ion sensor of the present invention has good repeatability.

[0098] Experiment 4: Select copper ion solution, copper ion and iron ion mixed solution, copper ion and lead ion mixed solution and copper ion and magnesium ion mixed solution of equal concentration as the test solution. Select their concentrations as 0 (deionized water), 0.2, 0.4, 0.6, 0.8, 1.0, 1.2, 1.4 mg / L respectively. First, place the sensor Fabry-Perot interferometer 2 in deionized water, observe the movement of the trough of the interference spectrum, let it stand for a while, and record and save the data after the interference spectrum stabilizes. Then add a certain amount of 100 mg / L copper ion solution to the deionized water to change the copper ion concentration in the beaker to 0.2 mg / L, and repeat the experiment until the copper ion concentration of the test solution becomes 0.8 mg / L. Record and save the data, calculate the wavelength drift of the selected trough, make a bar graph, and perform linear fitting on it. Then place the sensor Fabry-Perot interferometer 2 in deionized water. After the spectrum stabilizes, change the concentration of copper ions and iron ions in the test solution to 0.2 mg / L. Wait for the spectrum to stabilize, record the data, repeat the experiment until the concentration of copper ions and iron ions in the test solution is 0.8 mg / L. Record and save the data, calculate the wavelength drift of the selected trough, make a bar graph, and perform a linear fit. Repeat the above experimental operations, measure the wavelength drift of the sensor Fabry-Perot interferometer 2 in a mixed solution of copper ions and lead ions and a mixed solution of copper ions and magnesium ions, respectively, make a bar graph, and perform a linear fit. Investigate the response characteristics of the sensor in the presence of interference from other metal ions. Figure 7 , Figure 8 , in the concentration range of 0-0.8mg / L, the wavelength drift of the key interference spectrum of the sensing Fabry-Perot interferometer 2 in the copper ion and iron ion mixed solution, the copper ion and lead ion mixed solution and the copper ion and magnesium ion mixed solution is approximately equal to the wavelength drift of the sensing Fabry-Perot interferometer 2 in the copper ion solution. After linear fitting of these data, the response sensitivity of the sensor in the presence of other ion interference is also approximately equal to the response sensitivity to copper ions only, indicating that even if there are other metal ion interferences in the test solution, the performance of the sensor, that is, the wavelength drift and response sensitivity are similar to those when there are only copper ions in the test solution, indicating that the sensor can accurately identify copper ions, and the detection results are accurate and reliable. The parallel dual-cavity optical fiber copper ion sensor of the present invention has high selectivity.

[0099] Embodiment 2

[0100] The present invention provides a detection method of a parallel dual-cavity optical fiber copper ion sensor according to any embodiment of the present invention, comprising the following process:

[0101] Step 1: Place the sensing Fabry-Perot interferometer 2 in the solution to be tested, and place the reference Fabry-Perot interferometer 3 outside the solution to be tested without contacting the solution to be tested. The optical fiber coupler 1 is connected to the spectrometer.

[0102] Step 2, let it stand for a while, the sensing Fabry-Perot interferometer 2 and the reference Fabry-Perot interferometer 3 produce an optical cursor effect, the interference spectrum of the sensing Fabry-Perot interferometer 2 and the reference Fabry-Perot interferometer 3 is superimposed through the optical fiber coupler 1, and the interference spectrum of the sensor is displayed by the spectrometer. Wait until the interference spectrum is stable and no longer moves.

[0103] Step 3, recording the wavelength drift corresponding to the trough in the interference spectrum of the sensor.

[0104] Step 4, the wavelength drift of the trough is brought into the fitting curve of the relationship between the wavelength drift and the copper ion concentration, so as to obtain the copper ion concentration in the solution to be tested.

[0105] The fitting curve formula of the relationship between the wavelength drift and the copper ion concentration is:

[0106] y=sC (Cu2+)

[0107] Where y represents the wavelength drift, C (Cu2+) represents the copper ion concentration, and s represents the corresponding sensitivity of the sensor.

[0108] Step 5, taking out the sensing Fabry-Perot interferometer 2 from the solution to be tested, placing it in deionized water for desorption, and reusing it after the interference spectrum is stable.

[0109] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that modifying the technical solutions described in the aforementioned embodiments, or replacing some or all of the technical features therein by equivalents, does not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A parallel dual-cavity optical fiber copper ion sensor, characterized in that: include: A fiber coupler (1), a sensing Fabry-Perot interferometer (2), and a reference Fabry-Perot interferometer (3); The sensing Fabry-Perot interferometer (2) comprises: a first single-mode optical fiber (201), a first capillary glass tube (202) and a hydrogel (203); One end of the first single-mode optical fiber (201) is connected to the optical fiber coupler (1), and the other end extends into the first capillary glass tube (202); the end faces of the first single-mode optical fiber (201) and the first capillary glass tube (202) are aligned, and hydrogel (203) is provided at the end faces of the first single-mode optical fiber (201) and the first capillary glass tube (202); The reference Fabry-Perot interferometer (3) comprises: a second single-mode optical fiber (301), a second capillary glass tube (302) and a third single-mode optical fiber (303); One end of the second single-mode optical fiber (301) is connected to the optical fiber coupler (1), and the other end extends into the second capillary glass tube (302); the third single-mode optical fiber (303) also extends into the second capillary glass tube (302); the third single-mode optical fiber (303) and the second single-mode optical fiber (301) are arranged opposite to each other, and a gap is left between the third single-mode optical fiber (303) and the second single-mode optical fiber (301).

2. The parallel dual-cavity optical fiber copper ion sensor according to claim 1, characterized in that: The hydrogel (203) is sodium alginate / graphene oxide hydrogel.

3. The parallel dual-cavity optical fiber copper ion sensor according to claim 2, characterized in that: The preparation method of the sodium alginate / graphene oxide hydrogel: Add 0.3-0.4 g of graphene oxide to 37-50 mL of deionized water, stir with a magnetic stirrer for more than 1 hour, and ultrasonicate with an ultrasonic cleaner for more than 1 hour to obtain a uniformly dispersed graphene oxide solution; Add 0.8-1.0 g of sodium alginate into 35-45 mL of deionized water and stir magnetically for more than 1 h to obtain a sodium alginate sol; Then, 80-90 mg of graphene oxide suspension was added to the sodium alginate hydrogel, and stirred for more than 2 h to obtain a sodium alginate / graphene oxide sol; Add about 5 mL of 1 g / L Cu(NO3)2 solution to the sodium alginate / graphene oxide sol and stir for more than 20 min to obtain a slightly yellow sol; The common end face of the first single-mode optical fiber (201) and the first capillary glass tube (202) is dipped in an appropriate amount of sol and placed in a CaCl2 solution with a mass fraction of 5% for more than 3 hours. The sensing Fabry-Perot interferometer (2) is then placed in deionized water to elute excess copper ions, thereby obtaining a sodium alginate / graphene oxide hydrogel that specifically responds to copper ions.

4. The parallel dual-cavity optical fiber copper ion sensor according to claim 1, characterized in that: The sensing Fabry-Perot interferometer (2) reflects the light intensity I s It is expressed as: In the formula, I s1 represents the light intensity reflected from the interface between the first single-mode optical fiber (201) and the hydrogel (203) back to the first single-mode optical fiber (201), I s2 represents the light intensity reflected from the interface between the hydrogel (203) and the solution to be tested back to the first single-mode optical fiber (201), n s represents the refractive index of the hydrogel (203), L s represents the thickness of the hydrogel (203), is the initial phase; When the reflected light intensity I in the interference spectrum of the sensing Fabry-Perot interferometer (2) s When the minimum is reached, the wavelength of the reflection spectrum trough is expressed as: In the formula, λ dip represents the wavelength of the reflection spectrum trough, and m is the interference peak order; The free spectral range of the sensing Fabry-Perot interferometer (2) is: Among them, FSR s represents the free spectral range of the known sensing Fabry-Perot interferometer (2); When the external copper ion concentration changes, the corresponding trough change of the sensing Fabry-Perot interferometer (2) is expressed as: Among them, Δλ dip represents the change in the corresponding trough of the sensing Fabry-Perot interferometer (2); The wavelength of the reflection spectrum trough of the reference Fabry-Perot interferometer (3) is expressed as: In the formula, λ′ dip represents the wavelength of the reflection spectrum trough of the reference Fabry-Perot interferometer (3), n is the refractive index of air, L r is the length of the air cavity; The free spectral range of the reference Fabry-Perot interferometer (3) is expressed as: Among them, FSR r represents the free spectral range of the reference Fabry-Perot interferometer (3); The relationship between the free spectral ranges of the sensing Fabry-Perot interferometer (2) and the reference Fabry-Perot interferometer (3) is:

5. The parallel dual-cavity optical fiber copper ion sensor according to claim 4, characterized in that: The free spectral range of the sensing Fabry-Perot interferometer (2) and the reference Fabry-Perot interferometer (3) differs by 5.7-9.1 nm.

6. A detection method of a parallel dual-cavity optical fiber copper ion sensor according to any one of claims 1 to 5, characterized in that: The process includes: Step 1, placing the sensing Fabry-Perot interferometer (2) in the solution to be tested, and placing the reference Fabry-Perot interferometer (3) outside the solution to be tested, without contacting the solution to be tested; connecting the optical fiber coupler (1) to the spectrometer; Step 2, standing for a period of time, the sensing Fabry-Perot interferometer (2) and the reference Fabry-Perot interferometer (3) generate an optical cursor effect, and the interference spectrum of the sensing Fabry-Perot interferometer (2) and the reference Fabry-Perot interferometer (3) is superimposed through the optical fiber coupler (1), and the interference spectrum of the sensor is displayed by the spectrometer; Step 3, recording the wavelength drift corresponding to the trough in the interference spectrum of the sensor; Step 4, bringing the wavelength drift of the trough into the fitting curve of the relationship between the wavelength drift and the copper ion concentration to obtain the copper ion concentration in the solution to be tested.

7. The detection method according to claim 6, characterized in that: The fitting curve formula of the relationship between the wavelength drift and the copper ion concentration is: y=sC (Cu2+) Where y represents the wavelength drift, C (Cu2+) represents the copper ion concentration, and s represents the corresponding sensitivity of the sensor.

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