Fabrication Of Semiconductor Germanium Fiber And Its High-speed Photo-detecting Applications

The two major functions of traditional optical fibers include(i)laser sources with high spatial beam quality and high brightness and(ii)transmission media for delivering light energy and signals.Due to the dielectric nature of the glass,which is the host material as the traditional optical fibers,it exhibits no electronic response to optical excitation.Hence,traditional optical fibers lack of the functionality of optoelectronic detection,amongst the three major functionalities of optoelectronic devices,i.e.,emission,transmission and photo-detection.With the rapid development of micro/nano-optoelectronics based on silicon/germanium semiconductor materials,highly integrated multifunctional optoelectronic micro-devices become the dominant components of optoelectronic area.The rapid rise of silicon optoelectronics not only shows big challenges to the traditional fiber photonics but also provides inspiring concepts to the latter for future development.One of the potential developing directions for fiber photonics is to introduce multiple materials other than the conventional glasses into the fiber structure to construct a multifunctional optoelectronic fiber.Semiconductor-based photo-detecting devices are highly demanded in many research areas,such as military,medical,academic,and communications.Introducing semiconductor materials,i.e.,silicon or germanium,into the fiber,can combine the advantages of conventional fibers,such as the flexibility,low cost per unit length,together with the unique optoelectronic performance of semiconductor materials,for having novel fiberized optoelectronic materials.The glass-clad semiconductor fiber can thus be regarded as the effective complement to its polymer based counterpart.This thesis covers the fabrication and characterization of glass-clad germanium core optoelectronic fiber.The glass-clad semiconductor-core multimaterial multifunctional fiber has been made by molten core method.In the fabrication,the semiconductor germanium rod is inserted in the borosilicate glass tube.The preform is then drawn into glass-clad germanium-core fibers with core diameters of 21 ?m and 125 ?m respectively,at the drawing temperature of 1000 ?.The yield of each fiber with continuous uniform germanium core is ~100 meters.In addition,glass-clad germanium,brass dual-core fiber has also been fabricated.The high-speed photo-induced electrical response of germanium core fiber has then been carried out.The current-voltage characteristics of the glass-clad germanium fiber show nonlinear relation due to the non-Ohmic nature of the semiconductor germanium.With a configuration of parallel-wired three Ge fibers,the Ge array can detect 1MHz-level high-speed modulated light at 1.55 ?m.Currently,the observed detection speed is only limited by the noise.It is expected to further push the detection speed to 100MHz-1GHz level in germanium core fibers.