Enhanced Kelly sidebands of mode-locking fiber lasers for efficient terahertz signal generation

Intensity enhancement of the ±1 order Kelly sidebands of soliton mode-locking fiber laser is investigated to achieve efficient terahertz (THz) signal generation. A model is presented for studying on the ±1 order Kelly sidebands. Two key factors are found and their relationships with the intensity of the ±1 order Kelly sidebands are confirmed and quantified. A technical method which is introducing a highly nonlinear fiber (HNLF) in laser cavity is proposed for enhancing the sideband intensity. Consequently, intensity difference of 10 dB between the ±1 order sidebands and the central soliton in optical spectrum has been achieved. Using the data of the optical spectrum including the strong ±1 order sidebands, frequency spectrum of generated THz signals is calculated. The intensity of the required THz signal is increased significantly at 30 times larger than that without using the HNLF-based method.