Generation of THz radiation in two-color fiber laser with frequency selection

We introduce a new type of microresonator for frequency selection in a terahertz (THz) generator. The THz source by itself is based on intracavity difference frequency generation in two-color fiber laser. We show that asymmetrical nanoscale deformation can fully localize whispering gallery modes and filter out two modes for difference frequency generation with high effectiveness. Our theory confirms localization of whispering gallery modes (WGMs) for typical longitudinal dimensions of the microresonator 10-100 mu m. In this case the theory is in excellent agreement with the experimental results obtained previously. A simple condition for the stability of this geodesic corresponding to the appearance of a high Q-factor nanobump microresonator is found.