Chalcogenide Glass Of The Light-induced Modification And Of Microphotonic Learning Devices,

Chalcogenide glasses, which possess high refractive index, wide transparent window and ultrahigh optical nonlinearity and rich photo-induced effects, such as phase changing, photopolymerization, and photodarkening upon light exposure, are very important optical materials. These glasses are excellent candidates for diverse applications including nonlinear and reconfigurable photonic chip devices, high density optical data storage, and biophotonic devices. In this thesis, we focused our research on how to improve the optical properties of chalcogenide glasses and fabrication of micro/nano structures and devices.Firstly, As2S3 glasses were exposed by femtosecond (fs) laser at 780 nm and continuous wave (CW) laser at 579 nm. The different changes in linear and nonlinear optical properties induced by the two-photon excitation of short pulse laser and sub-bandgap excitation of CW laser were also studied. Secondly, we used different laser-glass interactions (laser ablation, laser induced damaging inside material and laser induced selective etching) induced by fs laser at 800 nm to fabricate varieties of photonic structures in As2S3 bulk glasses. Thirdly, we successfully fabricated chalcogenide micro/nano fibers and transferred them on silicon chips to form buried optical waveguides. Different kinds of functions, such as narrow band filtering and super continuum generation, were demonstrated as well.The main achievements of this thesis are as follows:1. The third order optical nonlinearity of As2S3 glasses was tuned by fs laser and CW laser. The fs laser could enhance the nonlinear refractive index up to 50%, while the CW laser could suppress the nonlinear refractive index down to 60%. Then we discussed the origins of the changes induced by the lasers. We point out that two lasers induce different kinds of defects. The fs laser could induce valence alternation pairs to enhance the third order nonlinearity and the CW sub-bandgap laser could induce homopolar bonds to decrease the third order nonlinearity.2. We used different laser-glass interactions in As2S3 bulk glasses to fabricate varieties of photonic structures. By using laser ablations, nanogratings with a period of 180 nm were realized by multi-pulse irradiation, and nanoholes as small as 200 nm in diameter were fabricated by single pulse irradiation. The theories of generation of nanogratings were verified by series of experiments. We point out that the irregular growth of laser induced plasmas could be the main reason for the generation of nanogratings in chalcogenide glasses. And we studied the selective etching of chalcogenide glasses after laser irradiation and produced 2.5-μm-width micro channels.3. We have fabricated on-chip buried chalcogenide micro/nano photonic devices. Nano fibers in diameters of 200 nm were drawn by fiber tapering method. The fibers were then mounted on silicon chip and protected by polymers (SU8). On-chip low optical loss waveguides and high-Q micro knot resonators were fabricated. The post tuning in a range of about 1.5 nm of micro knot resonators were demonstrated by irradiation of CW laser at 532 nm as well. By pumping with an fs laser at 1560 nm in pulse energy of 2 nJ, supercontinuum generation with bandwidth of 500 nm was achieved in a 1-μm-wide 7-cm-long chalcogenide waveguide.