Title: Application of Nanophotonic Devices in High Speed Optical Communications
Supervisors
Principal supervisor: Prof. Leif Oxenløwe, DTU Fotonik
Co-supervisor: Prof Jesper Mørk, DTU Fotonik
Co-supervisor: Prof. Christophe Peucheret, University de Rennes, France
Co-supervisor: Assoc. Prof. Jing Xu, University of Science and Technology, China
Evaluation Board
Prof Karsten Rottwitt, DTU Fotonik
Dr. Colja Schubert, Fraunhofer Heinrich-Hertz-Institute, Germany
Prof. Eric Cassan, University of Paris-SUD, France
Master of the Ceremony
Prof. Toshio Morioka
Abstract
All-optical signal processing has attracted a significant research interest in the past decade as it might become competitive with electronics in terms of compactness, energy consumption, and reliability. Furthermore it might solve the current bandwidth mismatch between optical transmission and electronic components in the physical layer and maintain high data rates, transparency and efficiency in optical networks. The remarkable advance, maturity, and cost reduction of optical components has therefore intensified research for the realization and exploitation of all-optical signal processing techniques and their applications.
In this thesis, a number of different all-optical signal processing functionalities have been experimentally investigated taking the advantage of silicon and III-V semiconductor photonic devices.
Wavelength converters may find a variety of applications in future high capacity fiber-optic transmission systems including switching nodes, cross-connectors and add-drop multiplexers. One of the expected key advantages of wavelength converters based on four-wave mixing in nonlinear media exhibiting third-order nonlinearities is the possibility for modulation format and bit-rate independent operation, enabling transparent networking. To confirm this, wavelength conversion of high speed WDM polarization multiplexed QPSK signals has been demonstrated using a polarization diversity circuit fully integrated on a silicon platform.
Data signals in a transmission system are suffering from linear and nonlinear impairments, which accumulate along the link and limit the reach of the system. These impairments need to be compensated. Since four-wave mixing provides phase conjugation of the converted signal, dispersion and nonlinearity distortion accumulated during transmission can be compensated using wavelength converters often placed in the middle of the link. This has been confirmed by demonstrating distortion mitigation using a silicon waveguide as optical phase conjugator.
The availability of a fast, compact and low energy all-optical switch should help the development of on-chip photonic networks. In this thesis, the use of a indium phosphide (InP) photonic crystal nanocavity to perform optical switching that is compatible with telecommunication signals has been demonstrated. Cavity switching induced by free carrier generation was achieved in the GHz range with very low energy consumption.