Investigation Of Micro/Nano Fiber Devices And Its Application In All Optical Signal Processing

As an important research topic of Nano-photonics, microfiber will become an alternative fundamental building block of future miniaturized and integrated photonic devices or circuits thanks to its excellent performance. Microfibers have many particular characteristics such as very low fiber-to-fiber coupling loss, extremely small surface roughness, strongly confined field due to high refractive index difference, high fractional evanescent field, extremely light in mass, and flexible dispersion property. Therefore, there are more and more efforts devoted to the research of microfiber fabrication, photonic devices based on microfiber, and application of microfiber.In this thesis, some novel photonic devices based on microfiber are proposed and demonstrated. Optical format conversion and microwave photonics devices based on microfibers are researched. Several research achievements and contributions are summarized as followings:(1) Theoretical model of microfiber and single mode condition of microfiber are researched. We numerically simulate and analyze the distribution of electric-field and power, as well as the properties of waveguide dispersion and group velocity. FDTD simulation is used to research evanescent coupling between parallel microfibers.(2) We establish the fabrication setup of microfiber and assembling and measurement platform of photonic devices based on microfibers. A variety of microfibers with different diameters and lengths are fabricated successfully, which are utilized to assemble some photonic devices based on microfiber. All of these are substantial groundwork of the following experimental research.(3) Reflected microfiber ring resonator (RMRR) is proposed. The transfer function of RMRR is derived. Several RMRRs with different free spectral range are experimentally demonstrated. Novel microfiber Bragg grating (MFBG)is proposed. Simulation results show that the coupling between the forward-propagating fundamental mode and the backward-propagating fundamental mode produces the long-wavelength reflection, and the coupling between the counter propagating HE11 and HE12 modes generates the short-wavelength reflection. We demonstrate several MFBGs with different diameters using specially Ge doped microfiber through KrF excimer laser irradiation with a uniform phase mask. The diffractive index sensors based on these MFBGs are demonstrated,which have high sensitivity.(4) An all-optical return-to-zero (RZ) to nonreturn-to-zero (NRZ) format converter utilizing microfiber ring resonator is proposed. The operation principle is numerically simulated and analyzed. We analyze the Q factor of converted NRZ signal affected by detuning, extinction ratio, and finesse of MRR. We experimentally demonstrate the format conversion from RZ to NRZ at the different bit rates of 20 Gb/s and 40 Gb/s through adjusting the diameter of MRR. The multi-channel format conversions from RZ to NRZ are also successfully demonstrated(5) A novel tunable microwave photonic filter based on MRR is proposed and experimentally demonstrated. A fiber ring laser based on the microfiber ring resonator is employed to generate two singlelongitudinal-mode carriers, then the dispersive element introduces the delay between two modulated carriers. By adjusting the diameter of the microfiber ring resonator, the proposed microwave photonic notch filter with high free spectral range canbe continuously and widely tuned.(6) The photonic generation of millimeter-wave (MMW) ultra-wideband (UWB) signal using MRR is proposed, The operation principle of generating MMW-UWB with opposite polarities monocycle and doublet waveform is analyzed. We experimentally demonstrated the 24-GHz MMW-UWB signal. Through adjusting the transmission spectrum of MRR, the polarity of monocycle waveform can be switched. The generated 24-GHz MMW-UWB signal has power spectrum density complying with the Federal Communication Committee regulation.