Study On Microstructure And Optical Properties Of Ge-S Binary Chalocgenide Glasses

Photonics,which uses photons for information and image processing,is labeled as one of the technologies of the 21st century,for which nonlinear optical processes provide the key functions of frequency conversion and optical switching.Chalcogenide glasses are novel materials with very intriguing properties for a variety of photonic applications.Low losses and photoinduced effects make these glasses suitable candidates for the fabrication of devices such as gratings and waveguides.In addition,in favor with the IR transmitting property and random quasi-phase-matching technique, chalcogenide crystallized glasses will open a new way to a cheap and efficient optical converter operating in mid-IR spectral region.Therefore,a fundamental study on defect configuration was conducted in the present work for exploring the correlation between its structure and electric-optical properties.An efficient approach to permanent second-order optical nonlinearity was also achieved in GeS₂ chalcogenide glass ceramics.The simplest Ge-S binary glass system was selected as a start to systematically study the defect configurations of sulfide glasses.In this work, the medium-range order framework of Ge-S glasses is constructed by Raman spectroscopy.Defect configuration information is collected by positron annihilation lifetime measurement.It is established that in the GeS_x chalcogenide glasses,different defect configuration was found in Ge-rich glasses(x＜2),S-rich glasses without(2≤x＜3.6)and containing S₈ rings(x≥3.6). The longer positron trapping lifetime(～0.445 ns)of Ge-rich glasses is attributed to the larger size of Ge₃^--based open volume owing to the longer bond-length of Ge-Ge metal bond compared to that of GeS₂ glass;for the S-rich glasses without S₈ rings,the defect state of GeS₃ glass is similar to that of GeS₂ glass due to their almost identical medium-range structural order;and because of the existence of S₈ rings,S-rich glasses of GeS₄ and GeS₆ have a much shorter positron trapping lifetime originated from the reduced size of Ge₃^- CD based open volume.Such defect information in GeS_x glasses would contribute to understanding the different photosensitivity of the materials.Additionally,GeS₂ glass with a stoichiometric composition corresponding toβ-GeS₂ crystal was chosen to study the crystallization process.And using the Maker fringe method,second-order optical nonlinearity of obtained glass ceramics was also studied.In this study,we succeeded in achieving a strong green light of SHG from the nontoxic IR transmittingβ-GeS₂ crystallized glass, which is predominantly due to the nonlinear optical microcrystalβ-GeS₂ fabricated by using careful heat treatments at T_HT=460℃for various durations. On the basis of Maker fringe method and powder technique,a large second-order optical nonlinearity of～4.29 pm/V was evaluated for the first time in the chalcogenide glass ceramics.Even if these chalcogenide glass ceramics cannot be used to fabricate waveguides because of the scattering losses,in favor of the extreme ease-of-use of the random quasi-phase-matching technique(almost no control is needed),they open a way to a cheap and efficient optical converter operating in mid-IR spectral region.