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Title: Silicon photonic modulators for the mid-infrared
Author: Nedeljkovic, Milos
Awarding Body: University of Southampton
Current Institution: University of Southampton
Date of Award: 2013
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Mid-infrared group-IV material photonics is an emerging field, which aims to migrate techniques used for near-infrared silicon photonics to longer wavelengths, and to address applications in areas such as environmental and bio-chemical sensing, homeland security, telecommunications, medicine or astronomy. In order to create mid-infrared photonic systems, components such as waveguides, splitters/couplers, filters, interferometers and modulators are required. Silicon-on-insulator (SOI) waveguides, which are used in the near-infrared, have high absorption at wavelengths greater than 4μm, and therefore new material platforms will be required for some parts of the mid-infrared. In this project silicon-on-insulator waveguides operating at 3.8μm have been demonstrated with losses as low as 2.0dB/cm. Poly-Si on SOI waveguides, which can be fabricated in a commercial foundry, and germanium on silicon waveguides, which could be used throughout most of the mid-infrared, were also demonstrated at 3.8μm. The passive components required to make a modulator in the SOI material platform were designed, fabricated and characterised. SOI MMIs were demonstrated at 3.8μm with insertion losses as low as 0.10±0.01dB, which is comparable to the best achieved near-IR silicon photonic MMI performance, and Mach-Zehnder interferometers were measured to have insertion losses of 1.3-2.2dB, and extinction ratios of up to 28dB. These components were used to create thermo-optic modulators in SOI, which are the first group-IV waveguide integrated modulators at wavelengths above 3μm. Switching powers as low as 47mW, and a -3dB bandwidth of 23.8kHz, were achieved. In order to build faster modulators, the free-carrier plasma dispersion effect could be employed. However, accurate equations for prediction of this effect in the mid-infrared have not been available until now. A semi-empirical approach has been used to calculate design equations relating the change in absorption coefficient and change in refractive index to change in charge carrier concentration in silicon for wavelengths in the 1.3-14μm wavelength range.
Supervisor: Mashanovich, Goran Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: QC Physics ; TK Electrical engineering. Electronics Nuclear engineering