A novel fabrication technique by composite material processing: Integrated metal-insulator-semiconductor fibers and fibe
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A novel fabrication technique by composite material processing: Integrated metal-insulator-semiconductor fibers and fiber devices Mehmet Bayindir,1 Ayman F. Abouraddy,1 Ofer Shapira,1 Jeff Viens,2 John D. Joannopoulos1,3 and Yoel Fink1,2 1 Research Laboratory of Electronics, 2Department of Materials Science and Engineering, 3 Department of Physics, Massachusetts Institute of Technology, Cambridge, MA 02139, USA. ABSTRACT Fabrication of functional devices in fibers by thermal drawing requires a material identification scheme and challenging composite material processing. A macroscopic preform rod containing metallic, semiconducting and insulating constituents in a variety of geometries and close contact leads to kilometer-long novel optoelectronic, and thermal mesoscopic fiber devices. The preform-to-fiber approach yields spectrally tunable photodetectors and integrated self-monitoring fibers. INTRODUCTION The combination of insulating, semiconducting, and metallic elements in well-defined geometries and prescribed sizes, while forming intimate interfaces, is essential to the realization of practically all functional electronic, optoelectronic, and thermal devices. These devices are typically produced using a variety of elaborate wafer-based processes, which afford small features, but are restricted to planar geometries and limited coverage area. The use of this fabrication approach has been the cornerstone of the electronic revolution, but has had no impact on the optical fiber industry, which relies on a very different fabrication approach. Our goal here is to produce fibers that deliver electronic, optoelectronic, and thermal functionalities maintained over extended lengths of a fiber. Our strategy in achieving this goal is to use the preform-based fiber-drawing technique, which we call the preform-to-fiber approach, that has proven to be simple, and yet to yield extended lengths of highly uniform fiber with well controlled geometries and excellent optical and thermal properties.[1-4] The preform-to-fiber fabrication approach [1] that we adopt thus relies on first preparing a large-scale macroscopic version of the required device in the form of a preform and then reducing it to the desired size through the process of thermal drawing (Fig. 1a). This process obviously places constraints on the materials that may be utilized. Nevertheless, a set of materials with widely disparate electrical, optical, and thermal properties have been identified and successfully incorporated into fiber-based devices. In this paper we discuss two distinct functional fiber devices in detail. In the first design, illustrated in Fig. 1b, the photodetecting glass core contacted with metallic electrodes is surrounded with a multilayer structure for external reflection. Such an arrangement allows for spectral manipulation of the externally incident light before reaching the photosensitive core. One could arrange for a Fabry-Perot resonant structure to enclose the fiber, thus producing a narrow-band tunable fiber photodetector.
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