Recent developments in processing of fiber materials have enhanced the actualization of optoelectronic gadgets within fibers giving way to large area versatile devices that can be incorporated in fabrics. In order to actualize these devices, a number of approaches have been developed. One of the ways is based on the prefabrication of hollow fibers which are applied as substrates for subsequent deposition of semiconductor material on their inner surface. Another method is based on fiber drawing where the targeted material is fabricated and thermally drawn and scaled to preferred dimensions.
Incorporation of semiconductor such as silicon into silica fibers bears new possibilities for enhancing the functionality of in-fiber gadgets while tapping the scalability of the fiber drawing process. However, thermal drawing of semiconductor and metallic domains necessitates their melting. Their melting is accompanied by mixing and device structure disruption. Also, diffusion at these high temperatures would lead to doping of the semiconductor, therefore, affecting its properties.
In a recent paper published in Advanced materials researchers led by professor Yoel Fink from Massachusetts Institute of Technology, USA, introduced a fully functional in-silica fiber device implementing high temperature semiconductors in a metal-semiconductor-metal architecture. They developed an approach that entailed two processes.
A silica fiber, which contained three spatially separated domains, a semiconductor flaked with two metallic cylinders, was thermally drawn from a preform. When performing the thermal draw, the authors maintained a wide silica barrier in a bid to prevent various domains from mixing and contacting. After the draw, the team heated the fiber so that the semiconductor domain experienced Rayleigh Plateau instability, and transformed to spheres of larger dimeter that bridged the gap between the conductors thereby establishing an electrical connection.
The authors picked materials with distinct melting points and breakups so that only a single domain experienced fluid instability, while the other was unaffected. The process where the semiconductor core is broken into spheres leads to a direct contact between the semiconducting spheres and the metal filaments (Germanium and platinum). The final structure forms an integrated gadget in a silica fiber exhibiting photosensitive attributes and increases the density of functional components over the fiber length.
At high temperatures, an axial viscosity reduction along the length of the fiber initiated the breakup of the cylindrical core into spheres owing to core cladding interface minimizing its energy. Instabilities occurred at all wavelengths that were shorter than the fiber length, however the breakup of the semiconductor core yielded a periodic structure of spheres. A particular wavelength maximized the instability growth rate and, therefore, dominated all others. The dominant periodicity, and the size of the spheres was dictated by the core diameter as well as its viscosity contrast relative to the cladding. The latter is a function of temperature while the former can be adjusted during the drawing process.
This in-fiber optoelectronic device may be applied in a number of areas such as, imaging and diagnostic fields, national security and geophysical exploration. The interplay between material attributes as well as structure integration into the device structures opens up vast opportunities for semiconductor device applications at fiber optic length scale, cost as well as uniformity, which will lead to the actualization of sophisticated performance of multifunctional fibers.
Lei Wei, Chong Hou, Etgar Levy, Guillaume Lestoquoy, Alexander Gumennik, Ayman F. Abouraddy, John D. Joannopoulos, and Yoel Fink. Optoelectronic Fibers via Selective Amplification of In-Fiber Capillary Instabilities. Advanced Material. 2017, 29, 1603033Go To Advanced Material
Michael Rein, Etgar Levy, Alexander Gumennik, Ayman F. Abouraddy, John Joannopoulos & Yoel Fink. Self-assembled fibre optoelectronics with discrete translational symmetry, Nature Communications 7, 12807 (2016).Go To Nature Communications