Cadmium Telluride Micro/nanowires For Infrared Optical Waveguides And Nonlinear Optical Applications

With the growing research interest in microphotonics,there is a compelling need for development of miniaturized optical devices and optical microwaveguiudes recently.Showing remarkable optical properties including low propagating loss,tight optical confinement,strong evanescent fields and dispersion tunability,optical micro/nanowires(MW/NWs)have been demonstrated as excellent optical microwaveguides,which is becoming basic building blocks for micro optical devices.The study on MW/NWs with versatile optical features(e.g.,broadband transparency window within infrared(IR)spectral region,high optical nonlinearity)is of great importance for applications such as infrared ultrafast spectroscopic techniques,mid-IR optical sensing,low-power on-chip optical communication.In this work,we demonstrated CdTe MW/NWs as promising IR optical waveguides.Our work showed great potential of these MW/NWs in applications such as mid-IR optical sensing and nonlinear micro optical devices.The main contents of the dissertation are as follows:In Chapter 1 of this work,we reviewed the background of optical MW/NWs and the research advances of their applications in IR spectal range.In Chapter 2,CdTe MW/NWs and nanobelts(NBs)with different crystal structures were synthesised by vapor deposition process.The synthesis mechanisms were discussed.The morphology and structure of these MW/NWs and NBs were characterized.The results revealed these synthesized CdTe structures possess excellent smooth surface,uniform size and monocrystal structure with zinc-blende or wurtize structure.In Chapter 3,we studied the linear waveguiding properties of CdTe MW/NWs including the optical confinement and dispersion properties.The transmission spectra of single CdTe MW/NW over near-IR and mid-IR spectral range were obtained experimentally.The result showed good waveguiding properties within the spectral range used in the experiment.Based on FP resonance in single MW/NW,the optical propagating loss was obtained as low as several dB/cm in mid-IR range.In Chapter 4,we studied the nonlinear waveguiding properties of CdTe MW/NWs.Firstly,we demonstrated second-harmonic generation(SHG)in CdTe NWs both theoretically and experimentally.Compared with other typical II-VI semiconductor NWs such as ZnO NWs and CdS NWs,CdTe NWs offer a much higher SHG efficiency(one to two orders of magnitude higher).Secondly,we studied the spectra broadening induced by self-phase modulation(SPM)in a single CdTe NW.A spectrum broadening of about 15 nm was obtained in experiment.The influence of two-photon absorption and free carriers effect on SPM were discussed.From the experimental data,we estimated the nonlinear refractive index(nm)of CdTe as(9.5 ± 1.4)×10-17 m2/W at wavelength of 1550 nm,and analysized the wavelength dependent property of n2.The discussion on supercontinuum generation in single CdTe NW showed that,spectra broadening can be further increased by optimizing the size of NW.Our work demonstrates that,with a relatively large n2,these NWs are promising in developing ultracompact nonlinear micro optical devices.In Chapter 5,we proposed an optical correlator based on the transversal SHG in a single CdTe NW.Benefitting from the high refractive index and optical nonlinearity of CdTe,the input energy can go down to few fJ per pulse.We studied the transversal SHG in a single CdTe nanowire both theoretically and experimentally.And we discussed the influence of multimode effect on transversal SHG.The work showed that,the input power can be further decreased(e.g.,to 100 aJ/pulse level)by optimizing the size of NW or reducing the width of input pulses through dispersion engineering.In Chapter 6,we summarized the works and innovations presented in the work,and provided several prospects.