Fabrication Of Glass-clad Semiconductor Core Composite Optical Fibers

Semiconductor core optical fibers have been developed unceasingly recent years andgained more and more attention, every semiconductor material owns its features, such as:high Raman gain coefficient, photoelectric effect, extended infrared transparency, largeoptical nonlinearities, they have important application prospect in chemical and biologicalsensing, military, Raman laser.At present, composite optical fibers are mainly prepared using rod-in-tube method andmelt-drawing technique. Several semiconductor core glass cladding optical fibers have beensuccessfully fabricated by this method, such as Si, Ge, InSb, Al2O3, ZnSe. However, there arestill some problems in fiber performance and preparation technology. And commercial opticalglasses were often used as clad of these composite optical fibers, which are easy to access andstable, such as quartz glass, borosilicate glass. The compatibility between fiber core andcladding are not considered sufficiently, resulting in large transmission loss, which restricts itspractical application. Consequently, it has become an urgent matter for composite opticalfibers to research semiconductor-core materials systematically, select and optimize claddingmaterials, and develop corresponding preparation technology.In this paper, semiconductor core and glass cladding materials are investigated. Wedesign compatible cladding glasses in accordance with the physical and chemical propertiesof selected semiconductor. Meanwhile, the fabrication methods of composite optical fibersare also developed. We have fabricated and researched four kinds of semiconductor core glassclad composite optical fibers. Deatiled information is described as follows:(1) The compatibility between phosphate glass and selenium is studied, selenium-corephosphate-glass-cladding composite optical fiber with60cm length is fabricated for the firsttime. The core is found to be amorphous Se. The diameters of fiber core and cladding are48and317μm, respectively. And the propagation loss of the fiber is2.6dB/cm at1310nm.With subsequent heat treatment, non-crystalline Se fiber core crystallize and Se crystal coreoptical fiber is obtained. Optical fiber comprising a crystalline Se core has photoelectricproperties, and its electrical conductivity would increase under the irradiation of light (κdark=1.22×10-7Ω-1·cm-1, κlight=4.12×10-7Ω-1·cm-1). However, for amorphous Se core, itsresistance is large whether illuminated or not. Selenium core can be reversibly convertedbetween crystalline and non-crystalline state by controlling the cooling speed after annealing.(2) Gallium antimonide-and indium antimonide-core germinate glass-claddingcomposite optical fibers are fabricated. Crystalline gallium antimonide-coregerminate-glass-cladding optical fiber and crystalline indium antimonide-coregerminate-glass-cladding optical fiber are investigated. The diameters of these two kinds offiber cores are250μm and26μm, respectively. Highly crystalline phases of fiber cores areconfirmed based on Raman spectra and XRD patterns analyses. These results show thatcrystal core optical fiber can be drawn out directly with a molten core approach. In addition,we take a voltage current characteristic measurement for gallium antimonide optical fiberwith a length of2cm, and a small resistivity (9.817×10-3Ω·cm) is achieved.(3) Germanium core germinate glass cladding composite optical fiber is fabricatedpreliminary. But the mismatch between core and cladding in aspects of physical and chemicalproperties lead to the irregular shape core and other defects.By researching these four kinds of composite optical fibers, it is found that thefabrication of composite optical fibers involves complicated physical and chemical processes.Compared with the preparation of conventional glass optical fibers, which only need toconsider the temperature characteristic, optical property and thermal stability of core/claddingmaterials, more factors should be taken into consideration in the fabrication of compositeoptical fibers, such as oxidation-reduction, wettability, glass softening temperature, crystallinesemiconductor melting temperature, chemical reaction under high temperature, etc. If theseproperties of core/cladding materials are matched very well, and corresponding preparationtechniques are developed appropriately, the composite optical fibers as required can befabricated successfully.