Fabrication And Performance Of Modal Interference Heavy Metal Ion Sensor Based On Optical Fiber Coated Composite Film

With the continuous development of industrialization,the current water quality pollution problem is becoming more and more serious.Among the water quality problems,heavy metal pollution accounts for a large proportion.These heavy metal ions not only cause damage to the ecosystem,but they are taken into the human body through water,which is harmful to human health.It is extremely important for the research and development of heavy metal ion detection sensors.Therefore,this paper has produced three Mach-Zehnder sensing optical fiber sensors to realize the detection of cadmium ions and copper ions.The basic theory used in this research paper is the principle of modal interference,which consists of single-mode fiber,no-core fiber,photonic-crystal fiber,and three-core fiber.The composite sensitive film is coated on the no-core fiber and the three-core fiber to realize the detection of heavy metal ions.The main research work of this paper is as follows:(1)Two sections of No-core fiber(NCF)are respectively fused to the two ends of the Photonic-crystal fiber(PCF)to form a fiber Mach-Zehnder interferometer sensor.The SnO₂-MoS₂,SnO₂/MoS₂,MoS₂,and SnO₂sensitive thin films were respectively coated on the NCF,and the four types of films were observed by scanning electron microscopy and X-ray photoelectron spectroscopy XRD analysis,and then measure the sensor's response to cadmium ions.The experimental results show that the sensor coated with SnO₂-MoS₂two-layer film has the highest sensitivity,and the detection sensitivity for cadmium ion0?100?M concentration range is 30.258 pm/?M.The sensor has good selectivity,short response time,and p H and temperature have little effect on the sensor.(2)It is proposed to fusion splice a single-mode fiber(SMF)between two sections of three-core fiber to form a three-core single-mode three-core sensing structure.Then two sections of three-core optical fibers are coated with optimized copper ion imprinted composite membrane,copper ion imprinted composite membrane(Without NaOH solution treatment)and CS/PVA composite membrane,respectively measure the sensor's response to copper ions.The experimental results show that,it is found that the sensor coated with the optimized copper ion imprinting composite membrane has the best response to copper ions,with a sensitivity of 62.258 pm/?M and a detection limit of about 0.602?M.the sensor has excellent selectivity and stable p H.(3)Splicing a single-mode fiber at one end of a 3 cm three-core fiber,and making a thicker taper on the other end of the three-core fiber with the single-mode fiber to form a fiber Mach-Zehnder interferometer sensor.The three-core optical fiber is coated with polyvinyl alcohol/ethyl orthosilicate/3-aminopropyl triethoxysilane(PVA/TEOS/APTES)composite film.The experimental results of the sensor performance test show that the sensitivity of the sensor is 7 nm/?M in the concentration range of cadmium ion concentration of 0?0.4?M.Through SEM analysis,the thickness of the sensitive film is780 nm,the response time is 40 s,and the selectivity is good.