Nanowire Based Optical Resonators And Nanolasers

Nanowires are emerging as powerful building blocks for exploring the the potential applications in lasers/Light Emitting Diodes,sensing,imaging,photodetector and photovotaics.As the developing of nanofabrication techniques and synthesis methods,the optical quality of nanowire has been improved significantly,providing the opportunity to acquire devices with smaller footprints.Particularly the optical elements combined with surface plasmon polaritons have bee realized at subwavelength.However,several crucial challenges emerge as the shrink of device size.(1)The distribution of the nanowires in substrate determine the isolation of each devices,making them hard to couple or interconnect with other optical elements such as Complementary Metal Oxide Semiconductor(CMOS),fiber system,and silicon waveguide.(2)Nanowires are typical Fabry-Perot cavities,thus the oscillation modes are determined by the shape of the cavity.In this sense,it's difficult to realize the control of resonant modes.The conventional approaches to control the modes are complex and exhibit low error tolerance.This thesis focuses on the nanowire based optical resonators and lasers,including the mode control,the interconnection and information exchange between different photonic devices,and the performance improvement of single nano-device.The main contents of the thesis are summarized as follows:Firstly,the laser properties of organic/inorganic perovskite(CH3NH3Pb Br3)nanowires are investigated.And the laser emissions of nanowire lasers are collected by the tapered fibers.As the first step,the strong two-photon absorption of the perovskite is confirmed on which the two-photon pumped CH3NH3 Pb Br3 nanowire lasers are realized for the first time.To expand the applications of the nanowire lasers,the approaches of collecting the laser emission by tapered fiber are studied.The experimentally measured collction efficiency of the tapered fiber is one manitude larger than that of objective lens.Secondly,the coupling and energy exchange between surface plasmonic waveguides and other photonic elements are discussed.The light emissions from the end-facet of the waveguide can be efficiently collected by other nanowires.The collection ratio is higher than 50% for a wide range of separation distance,transverse shift,and tilt angles.Moreover,by employing a tapered hybrid plasmonic waveguide,the possibility of coupling light from a silicon waveguide to a hybrid plasmonic waveguide is confirmed.The inverse light conversion is also validated by exciting the photonics mode.Thirdly,the modes of the plasmonic resonator are regulated,giving rise to the amplification and lasing of plasmonic modes in large-scale nanowires.The numerical calculations indicate that the surface scattering of Cd S nanowires plays an essential role in transverse mode selection.The photonic modes are strongly scattered by the nanoparticles and thus suppressed,whereas the plasmonic modes utilize most of the gain and lase.When the sizes of the nanoparticels increase,the slope of the measured threshold curves get larger and the emission polarization rotates from 90 degree to 0 degrees,indicating the transition from photonic laser to plasmonic laser.Lastly,the mode control of the nanowire laser is successfully achieved for the first time by combing the non-Hermitian properties of PT-symmetry with Fabry-Perot cavity.The PT-symmetry is applied when the nanowire is half-pumped,the mode spacing is doubled and the lasing wavelengths shift to the center of every two initial lasing modes.This research provides an excellent platform to exploit the light amplification and absorption.In summary,this thesis provides the experimental and theoretical basis for studying nanowire based devices.This research shall also pave a new route of nanowire on biomedical imaging,sensing,and photonic circuits.