Debangshu Mukherjee

May 2013
Structured Semiconductor Fibers For Mid-Infrared Transmission
Committee Members: Advisor: Soumendra Basu, MSE/ME; Siddharth Ramachandran, MSE/ECE

Abstract: The mid-Infrared (mid-IR: 3-12 μm wavelength range) spectral range represents a part of the electromagnetic spectrum that impacts practically every aspect of human society, and is used for biomedical surgery, chemical sensing to technologies that enhance defense capabilities. Semiconductors like silicon and germanium can effectively transmit light in the mid infrared region of the electromagnetic spectrum. In addition to remote transmission of mid-Infrared light, by tailoring the index of refraction of a semiconductor fiber waveguide, one can manipulate the nonlinear properties of light pulses, which leads to temporally and spectrally shaping them, thus using the passive optical fiber itself as a medium to create new color sources, or detection systems. To create low loss waveguides and to be able to manipulate light, there is the necessity to fabricate refractive index structures. Current semiconductor waveguides that have refractive index structures are short in length(~30cm), while long semiconductor waveguides do not possess refractive index structures.

Optical fiber is fabricated by drawing preforms in a fiber draw tower. The most versatile technique for preform fabrication with refractive index structures is the Modified Chemical Vapor Deposition (MCVD) process. In this research, the MCVD and the draw tower in the BU Photonics Center were used to deposit silicon and germanium inside glass tubes. Precursor gases like silane and germane were flown through Duran, Vycor and Fused silica tubes in a tube furnce to deposit silicon and germanium in the inner surface of the tubes. The as-deposited glass tubes were collapsed in the flame on the MCVD lathe to form solid preforms. The preforms were characterized by optical and electron microscopy to understand the MCVD reaction kinetics. In this research, semiconductor core preforms were successfully collapsed for the first time.