Research On Metal-microfiber Current Sensors

With development of optical sensing technology, the sensor grows with characteristicssuch as high sensitivity, low cost, high integration, fast response, and etc. Opticalmicrofiber sensors, having advantages of large evanescent field, simple structure, easyfabrication, anti-electromagnetic interference, and easy integration with optical fibercommunication systems, have exhibited great application potential in biology,medicine, and chemistry areas.Microfiber current sensors have been intensively studied in recent years. In this thesis,we present the current sensors based on microfiber coil, current sensors based onsingle taper modal interference, and the sensors with combination of microfibergrating and metal, respectively. Our research results should be valuable for futurerealization of the devices.Firstly, this thesis analyzes the characteristics and principles of evanescent field effectof microfiber. The coupled-mode theory and fabrication method of microfiber Bragggrating are reviewed. Based on the resonating effect of microfiber coils and modalinterference principle in a single fiber taper, of the previously-mentioned microfibercurrent sensor configurations are discussed.Secondly, an optical current sensor has been realized by wrapping a microfiber arounda chrome-nickel (CrNi) wire. We measure the sensitivities for the CrNi-wire diameterof50um,60um,80um respectively, with microfiber diameters of2~6um. Themaximum current sensitivity of the current sensor can be measured to be220.65nm/A2. We have also made deep understanding for the work mechanism of the sensorand optimization.Thirdly, an optical current sensor based on fiber taper modal interferometer ispresented. The fiber taper is fabricated by heating and drawing ahigh-germanium-doped fiber so that modal coupling occurs. The sensor is compactlypackaged by alcohol, copper tube, and chrome-nickel metal wire. When the carryingcurrent is changed, the interference spectrum shifts based on the heating effect from the CrNi wire, with a sensitivity of1014.5nm/A2. This structure is featured with highcurrent sensitivity, easy implementation, good repeatability, and stability.Finally, we study the current responsivity of a microfiber grating with a metalconductor placed adjacent to it. When the current flowing over the metal changes, theresonant wavelength varies accordingly. The current sensitivity is as high as56.5nm/A2. Such a structure has the advantage of reconfiguration or reconstruction.This thesis mainly focuses on the studying of metal-dielectric current-sensingstructures. Based on the heating effect induced by the current-carrying metal wire, theresonance wavelengths of the optical devices are modified. Our research provides auseful exploration for future applications of both the current sensing and thewavelength-tunable filtering.