Theories And Applications Of Resonance Structures Based On Micro/Nanofiber

With the improvement of designing theory and fabrication technology, optical devices have tended to be more miniaturized and integrated. Micro/nanofiber has the advantages of small footprint, small optical loss, large evanescent fields, outstanding flexibility and has become hotter and hotter in optical fields. Meanwhile, optical fiber sensing technology with the features of high sensitivity, anti-electromagnetic interference performance and excellent multiplexing ability, has attracted more and more attention. Owing to their unique properties, fiber gratings, fiber interferometers, multiwavelength fiber lasers and many other optical devices have already been widely employed in optical sensing networks.This thesis mainly focuses on the demand of high sensitivity sensors and high performance sensing light sources in the next generation optical sensing network. Two kinds of Fabry-Perot interferometers based on micro/nanofiber have been designed and their optical properties have been investigated in depth. Based on these micro/nano-scale Fabry-Perot interferometers(MFPI), fiber filters, tunable wavelength fiber lasers, refractive index and temperature sensors have been achieved. The main parts of this thesis are listed as follows:(1) The development history of micro/nanofiber has been reviewed. Several typical applications of micro/nanofiber in optical sensing fields as well as fiber laser fields are introduced in detail. Then the waveguide model of micro/nanofiber is built based on optical waveguide theory, after which its optical field distribution and sensing properties are investigated and simulated thoroughly. At last, the fabrication technology of micro/nanofiber is discussed and carried out experimentally.(2) A novel SMFBG-MNF-SMFBG structure combining single mode fiber Bragg grating(SMFBG) and micro/nanofiber(MNF) together is proposed. Mathematical modeling is carried out and the influence of different parameters on its optical properties is discussed through simulation analyses. Aiming at avoiding the complicated fabrication technique and low efficient problems in making MNFBG, simple fabrication technique named “SMFBG written and taper drawn at middle point” is proposed and dense broadband filtering spectrum with high extinction ratio and good flatness is obtained.(3) Refractive index sensing experiment and temperature sensing experiment are carried out separately based on the above MFPI structure. The analysis of its refractive index and temperature sensing principle is elaborated. By tracking the shift of certain resonant wavelength of the MFPI and the nominal wavelength of the FBG, a refractive index sensitivity of 220.1nm/RIU and a temperature sensitivity of 11.9pm/ ? are achieved respectively. Furthermore, with the influence of temperature on certain resonant wavelength of MFPI taken into consideration for higher accuracy, dual-parameter sensing, i.e. simultaneous refractive index and temperature sensing experiment can be achieved since certain resonant wavelength of MFPI and nominal wavelength of FBG have different response to refractive index and temperature.(4) A novel Fabry-Perot structure based on cascaded micro/nanofiber Sagnac loop mirrors is proposed. The whole MFPI structure with compact size is integrated in one microfiber. The equivalent model is built and the influence of different physical parameters on its optical properties is analyzed in detail. The fabrication technique named “twisting and rotating a microfiber” as well as a tuning method of adjusting the cavity length to change the filtering spectrum are proposed and elaborated. Based on the simple fabrication method, a comb filtering with high extinction ratio, broadband flatness and good tunability is obtained.(5) Multiwavelength fiber laser based on this MFPI filter is built and 42 lasing wavelengths within 3dB bandwidth is generated at room temperature, with no obvious wavelength shift and power fluctuation less than 0.602 dB within one hour. Furthermore, the MFPI is applied into a tunable multiwavelength fiber laser. By adjusting the cavity length of MFPI through pulling its free-standing end away from the fixed end, tunable lasing output with lasing wavelength numbers varying from 65 to 21 and channel-spacing varying from 0.065 nm to 0.173 nm is achieved at room temperature. Long time stability test shows that the tunable multiwavelength fiber laser has a good stability with a maximum power fluctuation of only 0.46 dB within one hour.