Research On Optical Fiber Fabry-perot Interferometer Sensors Based On Porous Anodic Alumina Film

Recently,optical fiber sensing technology is regarded as one of the new high-tech industry due to its intrinsic advantages including miniature design,electromagnetic immunity and durability to harsh environments.With the development of nanotechnology,more and more nanomaterials with superior performance are applied in optical fiber sensors.Among them,porous anodic alumina?PAA?with uniform aperture size,parallel channel and hexagonal close packing of cylindrical cell membrane periodic structure has been widely used as humidity sensitive materials because of its highly ordered and controllable nano-pores,large surface area and large numbers of negatively charged impure ions.In this paper,the application of anodic porous alumina in optical fiber sensing is investigated.By attaching thin porous alumina film on the fiber tip,three novel sensors based on PAA material was proposed:refractive index sensor,humidity sensor and hydrogen sensor.All of them exhibited superior performance.The main contents are as follows:?1?Porous alumina film was prepared at 40V by anodic oxidation method.Using porous characteristic of alumina to absorb liquid,the refractive index sensor was prepared based on porous alumina film.Experimental result shows that this refractive index sensor can detect different glycerol concentration?0-80%,refractive index of1.333 to 1.443?with high linearity and repeatability.?2?Using porous alumina adsorption of water vapor characteristics,the humidity sensors was prepared based on porous alumina films which were prepared at 40,35and 30V respectively.PAA film realized at 30V can detect 20%-90%RH with better repeatability.But it takes longer responsing time?18 min?and recovery time?22 min?to achieve stability when the humidity changes.The three kinds of humidity sensor formed at different voltages are expertimentally compared and a hypothetical moisture adsorption and release theory is proposed.It can be concluded that smaller anode voltage and aperture size?high porosity?results in the highest sensitivities and largest wavelength drift,which means best sensing performance among these probes.The aperture size of PAA membrane aperture in sulfuric acid system is smaller than that in acetic acid system.And the sensitivity of the sensor based on PAA prepared in sulfuric acid is 0.556 nm/%RH.?3?WO₃/Pt nanopowder was deposited on porous anodic alumina surface with surface modification techniques.And then the hydrogen sensor based on porous anodic alumina film and WO₃/Pt nanopowder was developed.However,the hydrogen sensor can only detect 1%-4%with poor repeatability.In order to improve sensitivity,the sensor was exposed to UV light when it was exposed to O2.According to photolysis water function of WO₃/Pt nanopowder,water splitting was caused by UV light.After that,the equivalent sensitivity of the sensor can reach 0.64nm/%,and linear correlation can reach 99.896%.The sensing repeatability is significantly improved.To our knowledge,most of electrochemical sensors based on PAA were fabricated,while there is rare investigation and report of PAA with optical fiber.Therefore,the application of PAA in optical fiber sensing is one innovation point in this paper.In addition,using PAA membrane surface modification technology,the nano materials can be deposited on porous anodic alumina surface and applied in the optical fiber sensing,which combines the advantages of anodic porous alumina and of fiber sensors.