Architectures for optical millimeter wave generation in radio over fiber applications

Abstract

Over the last few decades, with an enormous rise in the number of wireless gadgets, the rise in bandwidth requirements has been unprecedented. Researchers are inclined towards millimeter wave signal generation, a possible solution to alleviate the spectral crunch existent today. There have been many experimentations on the feasibility of Millimeter waves (MMW) for use in future wireless access networks. Electronic methods of generating millimeter waves are not suitable as the expenses incurred are high and the tunability is restricted. Hence, investigations are widely carried out in optical methods of generation. This thesis being split into three parts, emphasizes on the various techniques of generating optical millimeter wave signals. Every superseding technique, eliminates the short comings associated with the earlier technique. The first part pertains to Stimulated Brillouin Scattering (SBS) based generation of millimeter wave signals. An advantageous trait of SBS, frequency selective amplification, becomes instrumental in millimeter wave signal generation. A pump source introduces SBS gain in the fiber. Proper adjustment of pump source frequency ensures an exact match between the gain due to SBS and the required frequency. The generated 60 GHz RF signal has potential applications in enhancing future wireless communication. However, SBS based MMW generation techniques have their own setbacks. High pump source required to induce SBS gain is a major shortcoming. Further, optical fiber with inherent non-linear effects tends to place SBS based schemes on the lower side. Therefore, external modulation based frequency multiplication techniques emerge as promising solutions to the problems of cost, stability and convolutedness. The other two parts are pivoted on frequency multiplication techniques based on external modulation which eliminate the necessity of optical filters for carrier suppression. The second part of this thesis presents an investigation of 4 cascaded stages of Lithium Niobate Mach-Zehnder Modulato