Abstract
Long lengths (250 meters) of a flexible 150 microm diameter glass-clad optical fiber containing a 15 microm diameter crystalline and phase-pure germanium core was fabricated using conventional optical fiber draw techniques. X-ray diffraction and spontaneous Raman scattering measurements showed the core to be very highly crystalline germanium with no observed secondary phases. Elemental analysis confirmed a very well-defined core-clad interface with a step-profile in composition and nominally 4 weight-percent oxygen having diffused into the germanium core from the glass cladding. For this proof-of-concept fiber, polycrystalline n-type germanium of unknown dopant concentration was used. The measured infrared transparency of the starting material was poor and, as a likely outcome, the attenuation of the resultant fiber was too high to be measured. However, the larger Raman cross-section, infrared and terahertz transparency of germanium over silicon should make these fibers of significant value for fiber-based mid- to long-wave infrared and terahertz waveguides and Raman-shifted infrared light sources once high-purity, high-resistivity germanium is employed.
Highlights
Continued rapid advances in silicon-based photonics have generated intense interest in the eventual integration of electronics and photonics [1,2]
Elemental analysis confirmed a very well-defined core-clad interface with a step-profile in composition and nominally 4 weight-percent oxygen having diffused into the germanium core from the glass cladding
The larger Raman cross-section, infrared and terahertz transparency of germanium over silicon should make these fibers of significant value for fiber-based mid- to long-wave infrared and terahertz waveguides and Raman-shifted infrared light sources once high-purity, high-resistivity germanium is employed
Summary
Continued rapid advances in silicon-based photonics have generated intense interest in the eventual integration of electronics and photonics [1,2]. The extension of silicon photonics from a planar waveguide platform to an optical fiber-based technology would be a significant progression in this emerging field. This would definitely enable additional functionalities and capabilities in silicon photonics. Highly crystalline silicon core optical fibers were produced for the first time using commercially-scalable fiber draw techniques [6]. While those fibers exhibited attenuation values in the mid-infrared (~4 dB/m) that are acceptable for selected applications, atomic diffusion arising from the high processing temperatures (~2000 °C) led to detrimental effects on oxygen content that could negate the likelihood of singlemode fibers in the infrared
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