Based On Chemical Etching Methods Produced Specialty Optical Fiber Fabry - Perot Sensors

Ever since the appreance of fiber-optic sensors, they have become one of the most important branches of sensors and have been intensively investigated due to its high realibility, immunity to electromagnetic interference, capacity of multiplexing, low attenuation and long distance transmission. Among various fiber sensors, fiber Fabry-Perot (FFP) interferometric sensors are one of the most promising fiber sensors and have been widely used in a large number of applications.Various micromachining techniques, including femtosecond laser micromachining method, 157nm excimer laser micromachining method and chemical etching method, have been developed for fabricating miniature FFP sensors. Chemical etching method has the advantages of low cost, easy fabrication and available for mass production. But this method also has several shortcomings, such as short cavity, poor mechanical strength, low flatness and poor repeatability.In this paper, the concentration and component of the etching solution are optimized to enhance the etching rate of various optical fiber cores. The influence of the discharge intensity, discharge duration and number of discharges is investigated to improve the performance of FFP sensors. We fabricate several kinds of FFP sensors based on chemically etching special optical fibers. The main work is provided as follows:1. Micro extrinsic Fabry-Perot interferometric sensors (MEFPI) are fabricated by chemically etching Er-doped fibers with mixed Hydrochloric (HCl) and Hydrofluoric (HF) acid and fusion splicing. Compared with MEFPI sensors fabricated by etched single mode fibers, the sensor performance is greatly improved by the chemical reaction between HCl acid and doped Er₂O₃. A maximum visibility of ²4dB is obtained, comparable to that of MEFPI sensors fabricated by excimer lasers. Our MEFPI sensor has high mechanical strength as the etching rate difference between fiber core and cladding is enlarged. Preliminary results indicate that this kind of sensor is insensitive to temperature while highly sensitive to strain, with sensitivities of ⁰.65 pm/°C and ³.15 pm/με, respectively.2. An extrinsic optical fiber Fabry-Pérot sensor is fabricated by chemical etching of B-Ge co-doped optical fiber and electrical arc discharge. It is found that the etching rate of the fiber core is more than 30 times faster than that of the standard single-mode fiber when using 40% hydrofluoric acid as etching solution. The probe can be directly used for refractive index sensing without cleaving of the fiber end. Within the RI range of 1.350¹.400, the RI sensor has a sensitivity of ³0dB/RIU and a resolution of ³.33×10^-5, with a linearity of >0.99. This low-cost method is suitable for mass production and has great potential for fabricating fiber-optic Fabry-Pérot sensors with long cavity lengths for use in spatial-frequency-division-multiplexing.3. A fiber optic Fabry-Pérot refractive-index sensor based on multi-mold gradation refractive index optical fiber is proposed. The refractive index of the sample liquid is determined by measuring the visibility of the reflective spectrum of the FP sensor. In the range of 1.3329¹.4670, the RI sensor has a sensitivity of about 45dB/RIU and a resolution of ².18×10^-5, with a linearity factor of 0. 99938. The sensor can be easily fabricated by chemical etching, arc-fusion and cutting, with low cost equipment, and can be producted in groups. This kind of low cost refractive index sensor has great potential for biochemical applications.We can measure refractive index in wide-range with only two accurate value of refractive index by using Fabry-Pérot refractive-index sensor based on multi-mold gradation refractive index optical fiber. According to the relationship between refractive index and visibility, temperature and aging of sensor head does not interfere with measurement accuracy. The sensor is expected to make of the refractive index of practical measuring instrument.