Abstract

Application of ultrashort optical pulses has been studied in various research areas. They can be used to high-speed optical communication systems, optical frequency metrology, millimetre/terahertz wave sources for high-speed wireless communication systems and so forth. Conventional ultrashort optical pulse sources are based on mode-locking techniques, and mode-locked semiconductor lasers and Er-doped fibre lasers were developed. However, they have drawbacks in stability and tunability. In addition, the repetition rate of the mode-locked lasers is almost fixed. Optical-modulator-based pulse sources are good candidates for a flexible and stable source [1]. These sources have no cavity configuration: thus, they can operate stably. A Mach-Zehnder modulator (MZM)-based flat comb generator (MZ-FCG) can generate comb signals with high flatness [2]. The benefit of the MZ-FCG is high stability, low jitter, and independent control of the comb spacing and the centre wavelength. In addition, this system can operate with alignment-free and turn-key starting. In this paper, we report on generation of ultrashort optical pulse with a pulsewidth of 80 fs by using the MZ-FCG and a dispersion-flattened dispersion-decreasing fibre (DF-DDF).

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