Plasmonic Switches and Modulators for Optical Communications

With global data traffic growing continuously, a communication infrastructure capable of dealing with the ever-increasing bandwidth demands of the global society is required. A large amount of traffic arises inside the datacenters that house thousands of servers for computing and storing information. These servers are interconnected by communication links that more and more rely on optical rather than electrical technologies mainly due to the high bandwidth offered by optical interconnects. Recently, the field of plasmonics has attracted attention by the scientific community for applications in optical communications. The main feature of plasmonics is the ability to process optical signal at the nanometer scale. Device dimensions even below the wavelength of light are achieved, because plasmonic devices are not limited by diffraction unlike conventional optical approaches. Furthermore, plasmonic waveguides rely on metals and dielectrics only, which allows the metals to function as their own electrical contacts. The low resistances of the electrical contacts and the small capacitances given by the small device dimensions offer high-speed operation, since limiting RC time constants are minimized. The small dimensions further ensure sufficiently large electric fields to manipulate the signals, even at low drive voltages. The low drive voltages and small capacitances permit low-power operation. Additionally, the technology is suitable for cheap mass-production and may be processed together with electronic circuits on the same chip. In this thesis, two kinds of plasmonic devices are investigated: a modulator and a memristive switch. The modulator relies on phase modulation due to the linear electro-optic effect of an organic material that is integrated into a plasmonic waveguide. The plasmonic phase modulator is combined with a silicon photonic Mach-Zehnder interferometer to achieve efficient intensity modulation at highest speed. Furthermore, the modulator was demonstrated to function reliably in an optical interconnect, thus showing that plasmonics is indeed a viable proposition for future interconnect concepts. The plasmonic memristive switch is an electrically controlled plasmonic switch with a memory effect. The operation principle is based on the reversible formation of a conductive path in the dielectric layer. The device may find applications as a latching switch that maintains its state after activation and as a new kind of memory