Investigation Of Glass-clad Selenium Core Optical Fiber And Its Crystallization

Multimaterial fibers have experienced an increasing attention for its potential for a wide range of application such as nonliner optics,sensing,power delivery,optical switch,photodecting devices and biomedicine.It has the vision of integrating sophisticated materials inside fibers,which are not traditionally used in optical fibers.The crystalline semiconductor waveguides in fiber form not only offer exceptional nonlinear optical and optoelectronic properties,but also serve as unifying structure between conventional fiber optics and planar semiconductor photonics.It is well-known that silica fibers have high optical losses at midinfrared wavelengths longer than 2.5 ?m,while fluoride and chalcogenide fibers generally can guide only modest optical powers.Crystalline semiconductor core optical fibers are preferred for the guidance of high optical powers with low optical losses at wavelengths well into the farinfrared.As an important semiconductor element,selenium(Se)has a high photoconductivity and infrared transparency,nonlinear optical response and is extensively used in electronic and optoelectronic application.Therefore,Se semiconductor is a very intriguing core material for multimaterial fibers and fiber-integrated optoelectronic devices.However,the main challenges of adopting this fibers are the relatively high optical losses and some poor properties.In this thesis,multicomponent phosphate glass-clad Se semiconductor core optical fibers have been successfully drawn by taking the advantage of the fabrication technology accumulation of multicomponent fibers in our rearch group.A specific post-processing technique in which a two-step thermal annealing has been used to realize low loss of crystalline Se(c-Se)core fibers.In addition,laser crystallization has been demonstrated to crystallizing armophous selenium(a-Se)core fibers using a continuous wave Diode-pumped solid-state(DPSS)laser.The specific research contents and the corresponding results are rendered as follows:(1)The fabiracation technology of phosphate glass-clad Se core optical fibers are studied.Phosphate glass-clad Se core optical fibers are fabricated by using the reactive molten core method.The fiber has an outer diameter of about 175 ?m and inner diameter of about 25 ?m.2 wt % oxygen in the core fiber is found to dissolve in core when analyzing the elements across the core/clad interface.The structure change of Se core from amorphous to polycrystalline is analyzed comprehensively after a simple postdrawing annealing process by using the X-ray diffraction(XRD)spectra,micro-Raman spectra and Transmission electron microscope(TEM)measurement.Propagation loss of 2.44 d B/cm and 3.10 dB/cm at 1310 nm can be realized respectively in the a-Se core and c-Se core optical fibers with a cut-back method.Obviously,the c-Se core fiber with a post-processed annealing treatment exhbits a three-time change in conductivity between dark and 532 nm illuminated states.(2)A two-step heat annealing treatment is studied to achieve an increase the crystallite length in Se core and a loss decrease in the annealing Se core fibers.The crystallization properties of a-Se core are studied systematically.It is found that the two-step annealing process allows for an increase the crystallite length and decrease in the defects in the Se core.Moreover,the propagation loss decrease from 2.44 dB/cm to 1.5 dB/cm at 1310 nm in the c-Se optical fibers with a cut-back method.Compared to the fiber with a simple annealing at 150 °C for 1 h,the conductivity is improved from 4.1×10-7 ?-1cm-1 to 5.1×10-7 ?-1cm-1 under illuminated state in c-Se core fiber with a two-step annealing treatment.(3)The crystallization law of a-Se core with 532 nm laser annealing treatment are studied.Regarding the absorption and transmission properties of the a-Se core and the cladding,the heating source of the 532 nm laser is chosen and determined.An optimization of laser annealing treatment is successfully performed to achieve a crystalline selenium core by Raman spectra.Furthermore,the 532 nm laser annealing treatment is confirmed effectively on the crystallization of a-Se core with TEM techniques.