Functionalized Polymer Nanofibers For Nanophotonic Devices And Applications

Optical nanofibers/nanowires, including silica and glass nanofibers, semiconductor nanowires, polymer nanofibers, etc. are indispensible building blocks in nanophotonic theoretical research and device/circuit design. Motivated by the realization of optical nanofibers/nanowires with versatile functionalities, by which researchers can expand the categories and practical applications of optical nanofibers/nanowires, we propose to incorporate functionalized nanomateirals (such as quantum dots, nanoparticles, carbon nanotubes and graphene) into polymer nanofibers to fabricate new kinds of optical nanofibers/nanowires with specific functionalities. By means of direct doping, optical nanofibers/nanowires are endowed with more complicated optical characteristics without sacrificing their low-loss optical waveguiding abilities. Additionally, through micromanipulating functionalized nanofibers/nanowires, we can handle and study nanomaterials (e.g., single quantum dot) with simple manipulations and high accuracies, and investigate high-efficient light-matter interaction in nanofibers/nanowires using a waveguiding scheme. Furthermore, based on above works, we successfully realize a series of waveguiding-type one-dimentional nanophotonic devices such as semiconductor nanowire lasers, optical humidity sensors, optical saturable absorbers and modulators.In the first chapter of this thesis, we summarize the research background and recent advances of optical nanofibers/nanowires, including systhesis and applications of optical nanofibers/nanowires. optical waveguiding properties of optical nanofibers, functionalization of polymer nanofibers and corresponding nanophotonic device design. In addition, we also emphasize on the unique advantages of optical nanofibers/nanowires in one-dimentional waveguide-type nanophotonic devices and applications.In the second chapter, we synthesize optical quality quantum-dot-doped polymer nanofibers by physically drawing solvated polymers doped with CdSe/ZnS quantum dots. Quantum dots are doped into polymer nanofibers with good dispersity while maintaining the excellent structural and mechanical properties of polymer nanofibers. We apply a waveguiding approach to investigate optical properties of quantum-dot-doped polymer nanofibers, including waveguiding loss (0.2dB/mm),absorption coefficient (31cm-1@532nm), self-absorption coefficient (53cm-1), self-absorption induced redshift in waveguiding photoluminescence spectra and the photobleaching characteristics. As an application of the above-mentioned functionalized nanofibers, we first demonstrate a quantum-dot-activated nanofiber optical sensor for humidity detection with extremely low power consumption (100pW), very fast response (90ms). high sensitivity and long-term stability.In the third chapter, we synthesize graphene-doped polymer nanofibers based on liquid-phase exfoliated graphene. We carefully compare the structural properties and Raman spectra of graphene-doped polymer nanofibers with pure polymer nanofibers. Similar to the work mentioned in the second part, we adopt a waveguiding scheme to investigate the optical properties of pure polymer nanofibers and graphene-doped polymer nanofibers, including optical damage thresholds (1550-nm continuous-wave laser), visible-near infrared absorption spectra (600nm-1600nm). linear optical absorption coefficients (@633nm and1550nm) and nonlinear saturable absorption properties (modulation depth～10%). Based on single graphene-doped polymer nanofibers. we demonstrate one dimentional waveguide-type nanophotonic devices such as optical saturable absorbers and modulators.In the fourth chapter, we investigate multi-longitudinal mode lasing properties in semiconductor nanowire lasers. Based on the enhanced exciton-exciton and exciton-phonon coupling strength in semiconductor nanowires, we propose a new optical mechanism to control the nanowire lasing output wavelengths. The Cadmium Selenide (CdSe) nanowire (diameter-402nm) dominant lasing wavelength is continuously tuned from746nm to706nm as the length of CdSe nanowires decrease from289μm to8μm, spanning a wavelength range of about40nm. In addition, we systematically explore the nanowire-length-dependent lasing thresholds, mode numbers, mode spacing and multi-longitidinal mode lasing characteristics under different pumping influences. Our work is applicable in lasing wavelength selection and manipulation of various semiconductor nanowire lasers.Finally in the fifth chapter, the summary and prospect of our work are presented. Based on the research of functionalized polymer nanofibers for nanophotonic devices and applications, as well as the semiconductor nanowire lasers, we successfully demonstrate a series of waveguide-type one-dimentional nanophotonic devices such as single-nanofiber optical humidity sensors, single-nanofiber optical saturable absorbers and optical modulators. These functionalized polymer nanofibers and corresponding nanophotonic devices may find potential applications in future nanophotonic integrated circuits and chips.